ECOHYDROLOGYEcohydrol 8 838ndash850 (2015)Published online 30 March 2015 in Wiley Online Library(wileyonlinelibrarycom) DOI 101002eco1625

Hydrologic remediation for the Deepwater Horizon incidentdrove ancillary primary production increase in coastal swamps

Beth A Middleton1 Darren Johnson2 and Brian J Roberts31 US Geological Survey National Wetlands Research Center Lafayette 70506 LA USA2 Five Rivers Services National Wetlands Research Center Lafayette 70506 LA USA3 Louisiana Universities Marine Consortium (LUMCON) Chauvin 70344 LA USA

CoNatE-m

copy 2

Thidist

ABSTRACT

As coastal wetlands subside worldwide there is an urgency to understand the hydrologic drivers and dynamics of plantproduction and peat accretion One incidental test of the effects of high rates of discharge on forested wetland productionoccurred in response to the 2010 Deepwater Horizon incident in which all diversions in Louisiana were operated at or near theirmaximum discharge level for an extended period to keep offshore oil from threatened coastal wetlands Davis Pond Diversionwas operated at six times the normal discharge levels for almost 4months so that Taxodium distichum swamps downstream ofthe diversion experienced greater inundation and lower salinity After this remediation event in 2010 above-ground litterproduction increased by 27 times of production levels in 2007ndash2011 Biomass of the leaf and reproductive tissues of severalspecies increased wood litter was minimal and did not change during this period Root production decreased in 2010 butsubsequently returned to pre-remediation values in 2011 Both litter and root production remained high in the second growingseason after hydrologic remediation Annual tree growth (circumference increment) was not significantly altered by theremediation The potential of freshwater pulses for regulating tidal swamp production is further supported by observations ofhigher T distichum growth in lower salinity andor pulsed environments across the US Gulf Coast Usage of freshwater pulsesto manage altered estuaries deserves further consideration particularly because the timing and duration of such pulses couldinfluence both primary production and peat accretion copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

KEY WORDS saltwater intrusion Taxodium distichum tidal freshwater swamp oil spill

Received 17 October 2014 Revised 7 February 2015 Accepted 15 February 2015

INTRODUCTION

Coastal subsidence and sea level rise are inundatingfreshwater wetlands of the worldrsquos coasts with salinewater leading to vegetation shifts and wetland loss(Poff et al 2002) Freshwater tree species have specificadaptations to cope with flooding but saltwater can limitproduction (Kozlowski 1997) Therefore freshwaterremediation might help to rejuvenate these forests by restoringthe biogeochemistry of pulsed systems (ie decreased salinityor anoxia Junk et al 1989 Middleton 1999) TheComprehensive Master Plan for the coast of Louisiana(CPRA 2012) recommends the usage of freshwaterdiversions to deliver sediment and water from theMississippi River and such approaches could be appliedelsewhere A diversion is a restoration structure whichredirects water to a wetland usually from a river or otherwater source Louisiana diversions were mostly constructed

rrespondence to Beth A Middleton US Geological Surveyional Wetlands Research Center Lafayette LA 70506 USAail middletonbusgsgov

015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

s is an open access article under the terms of the Creative Commonsribution in any medium provided the original work is properly cited the

to deliver sediment and water to rebuild coastal wetlandsbarrier islands and ridges although the purpose of DavisPond Diversion was mostly to reduce salinity in the lowerestuary for fisheries (CPRA 2012) Importantly increasesin freshwater flow have the potential to reduce salinity orchange other biogeochemical processes in receivingwetlands so that these diversions have the potential tochange plant production levels Unexpectedly theDeepwater Horizon oil spill of 2010 provided a field testof the idea that the input of river water might improvegrowing conditions for freshwater species in hydrologicallyaltered estuariesOn 20 April 2010 an explosion on the Deepwater

Horizon drilling rig resulted in a massive oil spill about84 km from Venice LA (Lubchenco et al 2012) This spillthreatened coastal and offshore ecosystems of the entireGulf Coast of the United States As a preventative measureto keep oil away from wetlands all of Louisianarsquos coastaldiversions began operating at or near full capacity as earlyas 30 April 2010 with many being kept open for anextended period Davis Pond Freshwater Diversion locateddirectly upstream of our long-term research sites in the

Attribution-NonCommercial-NoDerivs License which permits use anduse is non-commercial and no modifications or adaptations are made

839HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

Barataria Basin was operated at or near full capacity (sixtimes higher than normal) for a period of almost 4months(MayndashAugust Bianchi et al 2011) At the beginning ofthe remediation event on 30 April flow from the DavisPond Freshwater Diversion was 113m3 s1 By 10 Maythe flow was at full capacity at ~300m3 s1 and remainedabove 200m3 s1 on most days through August 2010 withrates after September less than ~25m3 s1 (Bianchi et al2011) Much consideration was given to the effects of oiland its remediation on biota (Lubchenco et al 2012) butthe potential effects of freshwater release on estuariesreceived little attention (Bianchi et al 2011)

Operation of the Davis Pond Diversion during thisremediation event caused a reduction of salinity in thecentre of Barataria Bay of ~5 ppt (Bianchi et al 2011)This diversion delivered freshwater to Jean Lafitte NationalHistorical Park amp Preserve (JLNHP amp P Figure 1a) which

Figure 1 (a) Location of structures and water releases in 2010 ndash Barataria Bfrom May to August 2010 Arrow points away from the diversion outlet towarin Jean Lafitte National Historical Park amp Preserve (NHP amp P) Water and sufrom water gauges [Louisiana Department of Natural Resources CoastwideCenter (EC) and Palmetto Trail (PC) units on either side of Barataria Blvd] iEducation Center Spur (ECS)Education Center Canal (ECC) vs PTPalmettowhich is connected to the Barataria Estuary A water gauge was deployed toto 4 September 2012 (USGS Sonde 0004264 USGS 2012) and was locatedby this Sonde recorder during Hurricane Isaac it was apparent that the EC(Figure 1 in the Supporting Information) (b) Gulf Coast portion of a long-term

Jean Lafitte NHP amp P Big Thicket National Preserve (N

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

is part of our long-term study network [North AmericanBaldcypress Swamp Network (NABCSN) Figure 1andashb]Taxodium distichum swamps mostly occur in freshwatertidal environments of the Southeastern United States withmean salinity below 05 ppt although the boundary oftidal freshwater and oligohaline systems oscillates withdrought and flood periods (Kaplan et al 2010) Tdistichum occurs where flood waters do not exceed 2 pptsalinity more than 50 of the time but the highestdensity of trees is found in salinity nearest 0 ppt (Wickeret al 1981) Trees exposed to salinity levels of~1ndash45 ppt experience 10ndash80 mortality in 5 years(Hoeppner et al 2008)This oil spill remediation may have been damaging from

some perspectives (Martiacutenez et al 2012) because of thepotential of freshwater release to lower salinity in oysterbeds (GNO Inc 2010) At the same time the historical

ay LA Davis Pond Diversion was operated to discharge more freshwaterds long-term research sites (North American Baldcypress Swamp Network)rface water salinity level data are from publically available long-term dataReference Monitoring System (CRMS) 0234 and CRMS 0188 Educationncluding five long-term production sites [Education Center Parking (ECP)Trail Visitors (PTV) respectively] The PC unit is open to the Kenta Canalexamine short-term pulses of water during Hurricane Isaac from 28 Augustless than 100m from the ECP logger Based on a freshwater pulse recordedunit can be connected hydrologically to other parts of the region at timesresearch network (NABCSN) in which tree growth was studied includingP) and St Marks National Wildlife Refuge (NWR)

Ecohydrol 8 838ndash850 (2015)

840 B A MIDDLETON D JOHNSON AND B J ROBERTS

setting of these estuaries is important to recognize Salinityhas increased during recent decades particularly duringdroughts (Visser et al 2001) and because of extensivehuman modification these wetlands became disconnectedfrom the river (Wissel and Fry 2005) In responsediversion structures have been built along the lowerMississippi to reconnect coastal wetlands to their riversource Davis Pond Diversion began operation in 2003 tomimic spring floods and release freshwater into estuaries toimprove fisheries reduce land loss (CPRA 2013) andincrease primary production by altering sediment waterand nutrient levels (ie subsidyndashstress model Mitsch et al2001) After the construction of the diversion increases insecondary production have been documented along theflow path (Wissel and Fry 2005)Tidal forests south of the Davis Pond Diversion in

JLNHP amp P (Figure 1a) have been undergoing increasedsubsidence flooding and salinity (Day 2000) because ofshifting faults sediment and water loading (Dokka 2006)oil and gas exploration canal and levee construction andreduction in sediment input (Day 2000) Subsidence mightbe slowed by projects such as Davis Pond Diversion (USACOE 2000) particularly if hydrologic manipulationcan increase primary production Freshwater remediationmight reinvigorate plant growth because salinity causesinjury to cells metabolic dysfunction and leaf shedding infreshwater tree species (Kozlowski 1997) Few studies todate have evaluated threshold salinity levels for Tdistichum maintenance and growth with the data availablesuggesting these values to be about 20 and 07 ppt (Krausset al 2009 and Kaplan et al 2010 respectively) notingthat photosynthesis can be reduced at even lower levels ofsalinity (Pezeshki et al 1987)The objectives of this project were to determine if

hydrologic remediation efforts during the 2010 Deepwa-ter Horizon incident could have led to reduced salinityand consequently increased production in coastalfreshwater forests We tested the hypothesis that pro-duction of Gulf Coastal T distichum swamps was higherduring hydrologic remediation than at other timesfollowing predictions of the subsidyndashstress model(Mitsch et al 2001)

STUDY SITE

Hydrologic remediation event and study site details

Davis Pond Diversion is located at the northern end ofLake Cataouatche upstream of New Orleans and north ofthe head of the Mississippi River passes (~25 and 199kmrespectively) Davis Pond Diversion from the MississippiRiver was operated to discharge a large amount offreshwater from May to August 2010 (Bianchi et al2011) Water and salinity levels were monitored with two

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

permanent water gauges [Coastwide Reference MonitoringSystem (CRMS) 0234 and CRMS 0188] operated by theLouisiana Department of Natural Resources (LA DNR) inseparate hydrologic units on either side of Barataria Blvd inJLNHP amp P [Education Center (EC) unit and PalmettoTrail (PT) unit respectively Figure 1a Table I]Five research sites within coastal T distichum swamp

were selected in JLNHP amp P (Figure 1a) to evaluate inter-annual variability in production within the EC and PTunits [sites Education Center Parking (ECP)EducationCenter Spur (ECS)Education Center Canal vs PalmettoTrail (PT)Palmetto Trail Visitors (PTV) respectivelyTable I] Two of these sites were selected for T distichumtree growth studies in addition to two sites each in BigThicket National Preserve (Texas) and St Marks NationalWildlife RefugeBig Bend Wildlife Management Area(Florida) which comprise a portion of the NABSCN(Figure 1b and Table I) Most swamps in this network aredeeply flooded for many months of the year so thatmethodology is optimized for access during consistentlyunflooded seasons (AugustndashDecember)

METHODS

Tree production and growth

Annual peak litterfall production was measured usingfloating litterfall collectors (diameter = 03m2 Middleton1995 Middleton and McKee 2005) in plots within fivesites in JLNHP amp P (Table I) Five production plots wereselected along one 125-m-long linear transect within eachof these sites at stratified random positions at 25-mintervals to the right of the transect and marked with awooden stake Traps were set in August and litterremoved after peak litterfall (main season) each Decemberin 2007ndash2011 with off-season quarterly samples collectedin 2007 and 2011 Means of the total biomass captured inthe 20072011 quarterly samples were used to create acorrection factor for the main season of capture notingthat most dominant species were deciduous Litterfall wassorted by species into leaf stem (wood) and reproductivecomponents dried at 70 degC and weighed Note thatany large woody material falling on the litter trap (stemgt05-cm diameter) was not likely to have been producedduring that growing season and was removed from thesample To measure annual root production a soil core(7 cm diameter times 30 cm depth) was filled with an im-planted root bag (root ingrowth core Lund et al 1970)adjacent to each of the five plot markers after the previousyearrsquos core had been removed during seasonal drawdown(August 2007ndash2011) After removal cores were dividedinto three depths (0ndash10 10ndash20 and 20ndash30 cm) andwashed through a sieve to separate soil from rootsCollected roots were dried to a constant mass at 70 degC and

Ecohydrol 8 838ndash850 (2015)

TableILocations

ofstudysiteshydrologicalunitsC

RMSwater

recorders(w

ater

leveland

salin

ityL

ADNR2

013)S

olinstwater

recordersproductio

nsitesin

JLNHPamp

Pand

tree

grow

thsitesin

JLNHPamp

PBTNPandSMNWRBBWMA

Site

andyears

Location

Site

type

Hydrologicalunit

CRMSanddates

Solinstanddates

Sonde

0004264

anddates

Site

coordinates

Educatio

nCenterParking

(ECP)2007ndash2011

JLNHPamp

PLA

Production

andtree

grow

thECunit

CRMS0234-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

28August2012ndash

4September2012

29785N

90113W

Educatio

nCenterSpur

(ECS)2007ndash2011

JLNHPamp

PLA

Production

andtree

grow

thECunit

CRMS0234-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

na29786N

90114W

Educatio

nCenterCanal

(ECC)2007ndash2011

JLNHPamp

PLA

Production

ECunit

CRMS0234-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

na29787N

90115W

Palmetto

Trail

(PT)2007ndash2011

JLNHPamp

PLA

Production

PTunit

CRMS0188-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

na29791N

90122W

Palmetto

TrailVisito

rs(PTV)2007ndash2011

JLNHPamp

PLA

Production

PTunit

CRMS0188-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

na29789N

90121W

LakeBayou

(LB)

2011ndash2

012

BTNPTX

Treegrow

thna

nana

na30150N

94096W

Low

erCypress

Tract

(LCT)2011ndash2012

BTNPTX

Treegrow

thna

nana

na30134N

94081W

BuckhornCreek

(BUC)2012

SMNWR

FL

Treegrow

thna

nana

na30030N

84470W

MandalayRoad

(MR)2012

BBWMA

FL

Treegrow

thna

nana

na30129N

83962W

CRMS0234

andCRMS0188

wereon

theECversus

PTsidesof

BaratariaBlvd(ECvs

PTunitsrespectively)S

edim

entelevatio

ntables

wereinserted

into

ECPandECSin

2007

andPTandPTVin

2011

Day-of-visitsalinity

porewatersalin

itysamples

weremeasuredthroughout

thestudyandmoreintensivelyin

2011ndash2012Surface

watersalin

ityattheCRMSrecordersweremeasuredfrom

thesameheight

below

thesoilor

water

columnas

thewater

sensorDavis

PondDiversion

dischargeandsalin

itydata

wereavailablefrom

1January2008ndash31Decem

ber2011

(USGS295501090190400)Alsosee

Figure1

CRMSCoastwideReference

Monito

ring

SystemJLNHPamp

PJean

Lafitte

NationalHistoricalParkamp

Preserve

BTNPBig

Thicket

NationalPreserve

LA

DNRLouisiana

Departm

entof

Natural

Resources

BBWMABig

BendWild

lifeManagem

entArea

SMNWRStMarks

NationalWild

lifeRefuge

841HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd Ecohydrol 8 838ndash850 (2015)

842 B A MIDDLETON D JOHNSON AND B J ROBERTS

weighed Annual sampling allowed many months for theregrowth of roots into the core (Vogt et al 1998 Herteland Leuschner 2002) Other root production approachescould not be used because of flooded seasons in networkswamps (water depth gt75 cm)Annual growth (incremental circumference increase) of

T distichum trees and knees was measured usingdendrometer bands (Anemaet and Middleton 2013) whichwere placed on the nearest tree and knee (one each) to markproduction plots (plot 1 3 and 5) along each transect in twosites (ECP and ECS) in JLNHP amp P in 2006 (n=3 per site)T distichum trees more than 20m from a large tree andemerged into the canopy were selected for bandingWe useda similar procedure to examine tree growth and salinityacross the US Gulf Coast except that we used five treesadjacent to all five production plots in each site in Texas andFlorida (Lake Bayou and Lower Cypress Tract vs BuckhornCreek and Mandalay Road respectively) (Table I andFigure 1b) in 2011 and 2012 respectively Note that thebands placed on trees in JLNHPampP in 2006were of an olderstyle and could not be measured until 2008 (Anemaet andMiddleton 2013) Tree bands were placed at ~15m heighton the tree above any fluting or buttressing Knee bands wereplaced ~6 cm from the tip of the knee

Water dynamics and salinity

Day-of-site visit measurements Within 1m of each plot asipper was used to extract soil pore water during each sitevisit (five samples per site) Water was transported in aportable freezer to the lab and the salinity measured with aYSI EC 300reg probe Water depth was measured adjacentto each plot marker with a metre stick

Water gauge analyses To study water dynamics over timewe analyzed patterns in daily mean and maximum values ofdischarge (m3 s1) and surface water salinity (ppt) fromthree recording gauges including the Davis Pond Diversion(US Geological Survey DCPBA03 2013) and CRMSrecorders (Table I CRMS 0234 and CRMS 0188 LA DNR2013) Water level and salinity patterns in 2010 (year ofhydrologic remediation) were compared with the average ofvarious groups of years in the available data set (2003ndash2011long-term) the average of comparably wet years (2008ndash2011 wet) and each individual year during 2006ndash2011 Allcomparisons were conducted for three periods within eachyear andor period pre- (days 1ndash119 1 Januaryndash30 April)during (days 120ndash244 1Mayndash1 September) and post- (days245ndash365 2 Septemberndash31 December)Water patterns were compared during the year of

hydrologic remediation (2010) with sets of long-termwet and individual years We used maximum daily valuesof both water level and surface salinity for these analysesbecause maximum values are more likely than mean values

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

to capture short-term changes in photosynthesis Note thatmean versus maximum daily values varied little from eachother [mean vs maximum difference plusmn standard error(SE) = 105plusmn 00018]To determine if short-term water level fluctuation within

plots generally followed those of CRMS gauges weinserted Solinst water level recorders (Levelogger Gold)within the ECP and PT sites in JLNHP amp P on 13 August2012 (~05ndash10 km apart within EC unit and PT unitrespectively Figure 1a and Table I) Daily mean andmaximum adjusted water levels and surface salinity levelsfrom CRMS gauges (publically available data) werecompared with those from Solinst water recorders andday-of-site visit measurements during periods of overlap (13Augustndash27 September 4 December 2012 Table I) Meanday-of-visit pore water salinity from sites were comparedwith those from CRMS gauges during 2011ndash2012Flood water was assumed to be connected by a

contiguous water sheet across units and consistent withinelevations corresponding to CRMS gauges Solinst waterrecorders sediment elevation table (SET) monumentsplots and the Sonde Following this idea hydrographswere constructed for each Solinst water logger SETmonument and plot stake by offsetting elevation of thewater sheet and matching water level fluctuations withthe continuous CRMS gauges within the hydrological unit(ie EC unit and PT unit gauge to SET offset +10 and50 cm respectively) Water levels were not adjusted to acommon datum Water depths were measured on days ofvisits at each plot stake and SET which here were used as asurface water-recording benchmark (Cahoon et al 2002)two SETs were placed within both ECP and ECS in 2006and PT and PTV in 2011 (eight total SETs) Absoluteelevations at SETs near ECPECS in 2007 were about0093m above sea level (Middleton and Jiang 2013)A water gauge was deployed less than 100m from ECP

to examine short-term pulses of water during HurricaneIsaac from 28 Augustndash4 September 2012 (Sonde0004264 USGS 2012 Figure 1b and Table I) All watermeasurement devices in units on both the EC side and PTside of Barataria Blvd detected the pulse signal fromHurricane Isaac (Table I) By comparing water recordsfrom these various sources it was determined that waterlevels measured with CRMS recorders within EC unit vsPT unit were relevant to those of production plots (Figure 1in the Supporting Information)

Climate analysis Monthly total precipitation (mm) andmean temperature (degC) were acquired from a weatherstation about 1 km away from the JLNHPampP study plots[Marrero 9 SSW Station LA 297853degN 901158degW] anddata from 2002 to 2012 were compared with those of 2010during pre-remediation during remediation and post-remediation periods (NOAA 2013)]

Ecohydrol 8 838ndash850 (2015)

843HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

DATA ANALYSIS

Vegetation production

Annual total litterfall (leaf and wood) was calculated frompeak litterfall estimates by determining the percentage ofannual litterfall collected during the main season (mean of20072011 correction factor = 0718plusmn0176 SE) so thatbiomass captured during the main season of each year wasdivided by 07180 to express yearly production Thiscorrection factor better portrayed annual total litterfallbased on peak litterfall while fully recognizing that certainswamp species do not lose their leaves during this period(eg Myrica cerifera) Most deciduous trees shed all oftheir leaves within 30ndash60 days (Dixon 1976) fromSeptember through mid-November (Tdistichum swampNorth Carolina Brinson et al 1980) or into Decemberfarther southward (eg South Carolina mixed bottomlandforest Shure and Gottschalk 1985)

Litterfall totals by year species and tissue type (leafreproductive and wood) from 2007 to 2011 were analyzedusing repeated measures analysis nesting plot within yearin analysis of variance (ANOVA) (one-way or two-wayANOVA JMP SAS 2012) For annual log root produc-tion ANOVA was used by nesting plot (depth year) Rootproduction by year did not interact with depth (year times depthinteraction pgt005) so that total root production wasanalyzed by year The lower two root depths (10ndash20 and20ndash30 cm) did not differ (t=097 p=033) so that a meanof these two depths was calculated (10ndash30 cm) andcompared with the upper depth (0ndash10 cm) In all ANOVAanalyses the highest-order significant interaction or maineffect was tested using one degree-of-freedom contrasts inJMP SAS (2012) Data were appropriately transformed tomeet assumptions of ANOVA and multiple comparisonsadjusted using Bonferroni corrections (two one-degree-of-freedom contrasts or three one degree-of-freedomcontrasts p=0025 or 00167 respectively)

Tree and knee growth were analyzed by comparingmeans of growth (circumference ratios ie yearrsquos circum-ference divided by previous yearrsquos circumference) for2008ndash2011 For the Gulf Coast-wide assessment of treegrowth and salinity regression analysis compared means oftree growth (circumference ratios) in LA TX and FL(2011ndash2012) versus annual mean salinity Annual meansalinity was based on the mean of day-of-visit measure-ments from 2011 to 2012 (7 to 14 measurements with allseasons represented)

Climate

We used ANOVA to compare monthly total precipitationand mean temperature by year and remediation periodusing the main effects and interactions of year andremediation period

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Water environment and remediation

Water and salinity level shifts and remediation Todetermine if the water dynamics differed from expectedconditions we compared mean and maximum values ofdaily levels of water and surface salinity during times ofinterest Because short periods of high salinity or anoxiawere likely to affect tree production and growth we focusedon daily maximum water level for these analyses Watercomparisons were made of three time periods in 2010 (pre-remediation during and post-remediation) with the sameperiods in other years in three ways wet years (mean of2008ndash2011) long-term (mean of 2003ndash2011) and individualyears (2006ndash2011) These comparisons were made usingautoregressive integrated moving average (ARIMA) models(detailed description provided in Table 1 in the SupportingInformation) generated in SAS Institute Inc (2002) whichare appropriate for comparing water and salinity levels shiftsover time because these models can predict the shape of thefunction and account for the autocorrelation of the samplesover time better than other statistical approaches (SASInstitute Inc 2002) A nonparametric sign test comparednumber of times the 2010 series had more water or salinitythan the average of the comparison series and vice versa

Predicted daily threshold values of salinity in productionplots To determine the number of days that productionsites exceeded threshold values of various salinity levelsthe following procedure was followed Using linearregression mean daily surface water salinity from CRMSgauges in the EC and PT units on specific days wereplotted against mean pore water salinity on day-of-visit inproduction plots and SET monuments in 2011ndash2012(Table I) Equations generated from this process were usedto predict daily mean salinity levels in sites from 2008 to2011 (for equations see Figure 2 caption in the SupportingInformation) as well as the percentage of growing seasondays (1 Aprilndash31 October) each year above certain salinitylevels (ie 01 03 07 10 15 and 20 ppt)

RESULTS

Production and vegetation responses to hydrologicremediation

Total litter biomass was 27 times higher after hydrologicremediation in 2010 and 2011 than before remediation in2007ndash2009 (Figure 2a Table IIa one degree-of-freedomcontrast t=838 plt 00001) In litterfall Tdistichum leafbiomass was 31 and 25 times higher in 2010 andor 2011respectively than in 2007ndash2009 (Table IIa) while repro-ductive biomass was 77 times in 2011 but not different in2010 (Table IIa and Table III) In addition leaf andreproductive tissue biomass in litterfall was higher in 2010

Ecohydrol 8 838ndash850 (2015)

Figure 2 Total annual mean production from 2007 to 2011 including (a)total litter biomass (leaf reproductive and wood) [g m2 y1 plusmn standarderror (SE)] and (b) total annual root biomass (total of all depths 0ndash30 cmg m2 y1 plusmn SE) in Jean Lafitte National Historical Park amp Preserve(n = 25) Different letters indicated that means of years differed statistically(one degree-of-freedom contrasts plt 005) (c) Regression analysis ofstem growth expressed as mean salinity (ppt) versus Taxodium distichumcircumference ratio plusmn SE along the Gulf Coast (R2 = 086) Salinity isbased on means of pore water salinity during day-of-visit measurements

844 B A MIDDLETON D JOHNSON AND B J ROBERTS

andor 2011 than in 2007ndash2009 for Acer rubrum (not in2007) Liquidambar styraciflua and M cerifera (Table IIaand Table III) Annual litterfall biomass of wood tissue didnot change from 2007 to 2011 although the mean wassubstantially higher in 2010 (Table IIb plt 005) Annuallog root biomass was higher in shallower than deeper soildepths (Figure 2b and Table IIb 0ndash10 vs 10ndash30 cmt=279 p=00058 N=5) and total root biomass variedby year and was 23ndash53 times lower in 2010 than in 2007ndash2011 (Figure 2b t=489 plt 00001 N=5)Neither tree nor knee growth varied with circumference

increasing by 18 plusmn 01 and 29 plusmn 10 respectively peryear during 2008ndash2011 in JLNHP amp P (pgt005Table IIcndashd) In JLNHP amp P we found no relationship

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

between tree growth and the percentage days per year a siteexceeded published thresholds of salinity (eg 07 or20 ppt pgt005 Table IV) In 2010 both EC and PT unitshad fewer days with salinity gt03 ppt and in 2008 moredays with salinity gt20 ppt (Table IV Figure 1 in theSupporting Information) Across the Gulf Coast Tdistichum growth varied from 011 to 21 increase incircumference per year with average annual salinityexplaining 86 of the variance in growth with the highestgrowth observed in the lowest mean pore water salinity(eg JLNHP amp P Figure 2c)

Climate and environment

Regionally mean annual precipitation was 13209plusmn1065mm per year from 2002 to 2012 (National Oceanicand Atmospheric Administration (NOAA) 2013) but didnot vary by year or remediation period (pgt 0130 Table V)Mean monthly air temperature did not vary by year but didvary by remediation period (mean monthly temperaturesduring pre-remediation remediation and post-remediation157 plusmn 06 degC 269 plusmn03 degC and 187 plusmn 08 degC respectivelyF=817 plt0001 Table V) (NOAA 2013)

Water and salinity responses to hydrologic remediation

Short-term water and salinity comparisons ndash 2010 versuswet years (2008ndash2011) Davis Pond CRMS 0188 andCRMS 0234 had higher dischargewater level and lowersalinity during the remediation period in 2010 than duringwet years As based on ARIMA time series comparisonswater discharged from Davis Pond in 2010 exceeded meanand maximum daily discharge of wet years (mean dailydischarge of 2010 vs wet years 113 out of 119 daysrespectively maximum daily discharge of 2010 vs wetyears 102 out of 119 days respectively sign testsplt 00001 Figure 3a and Table 2 in the SupportingInformation) Discharge rates from the Davis PondFreshwater Diversion and water levels at gauges werelower in 2010 during the post-remediation period than inwet years (Figure 3a and Table 2 in the SupportingInformation) Maximum daily gauge levels were higherduring hydrologic remediation in 2010 than in wet years(CRMS 0234 026 vs 011m respectively Figure 3bCRMS 0188 115 vs 106m respectively Figure 3c andTable 2 in the Supporting Information)Long-term gauging stations can be used to indicate

conditions at sites even though salinity relationships weresomewhat different (ie EC sites had significantly highersalinity than CRMS 0234 and PT sites had significantlylower salinity than CRMS 0188 as based on day-of-visitmeasurements) Salinity environments in the EC and PTsites were relatively similar (Figure 2 in the SupportingInformation) Nevertheless maximum daily water levels atCRMS 0234 were linearly related to day-of-visit water

Ecohydrol 8 838ndash850 (2015)

Table II Analysis of variances of production variables in JLNHP amp P from 2007 to 2011

DF F p Mean plusmn SE

(a) Total annual productionLitterfall (gm2 y1)Year 4 236 lt00001

Root biomass (gm2 y1)Year 4 84 lt00001 Depth 1 78 00225

Year times depth 4 10 04142 ns(b) Tissue typeLeafSpecies 15 155 lt00001 Year 4 1566 lt00001 Species times year 60 41 lt00001

ReproductiveSpecies 5 400 lt00001 Year 4 69 lt00001 Species times year 20 44 lt00001

WoodYear 4 21 00794 ns

(c) Tree growth (annual circumference ratio)Initial tree circumference (covariate) 1 38 00668 nsYear 3 01 09718 ns2008 1019210 plusmn 000552009 1018628 plusmn 000712010 1018855 plusmn 000382011 1015170 plusmn 00022

(d) Knee growth (annual circumference ratio)Initial knee circumference (covariate) 1 05 04945 nsYear 4 09 04628 ns

Mean total annual production of (a) litterfall (g m2 y1 including leaves reproductive material and wood) and log root biomass (g m3 y1) (b) Meanbiomass of tissue types of dominant species including leaf reproductive and wood Dendrometer bands were used to measure incremental increase incircumference growth was estimated as a year-to-year ratio of circumference change of Taxodium distichum from 2008 to 2011 for (c) trees and (d)knees Mean comparisons that differed based on contrasts indicated by lsquorsquo lsquorsquo or ns (plt 00001 plt 005 pgt 005 respectively Figure 2) SeeTable III for tissue type times species interactionsJLNHP amp P Jean Lafitte National Historical Park amp Preserve SE standard error DF degrees of freedom ns not significant

845HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

depths at SETs in the EC unit (ie SETs at ECP and ECSFigure 2 in the Supporting Information r= 06043p=00015) As indicated in the Section on Methods tojustify the selection of salinity variables and analysesoverall maximum daily values were within 105plusmn 00018of mean values Mean daily salinity levels at CRMS 0234and CRMS 0188 were linearly related to day-of-visitsalinity at SETs and plots within the same hydrologicalunits (EC unit r=0600 p=00004 Figure 2b in theSupporting Information PT unit r=0702 p=00005Figure 2c in the Supporting Information)

Long-term water level comparisons ndash 2010 versus long-term (2003ndash2011) Water discharge from Davis Pond in2010 during hydrologic remediation was higher than in thelong-term set of years (2003ndash2011 mean discharge perday =1983 plusmn 49 vs 331 plusmn 16m3 s1 respectively) andmaximum daily water levels at CRMS 0234 and CRMS0188 also were higher (sign tests plt00001 Figure 4 inthe Supporting Information)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Individual year water and salinity level comparisons ndash2010 vs 2006ndash2011 Comparisons of maximum dailywater level and salinity levels during 2010 to individualyears were similar to the comparisons of 2010 to sets ofwet and long-term years (ie 2008ndash2011 and 2003ndash2011respectively) As expected discharge levels for Davis Pondand water levels at CRMS 0234 and CRMS 0188 weresignificantly higher during hydrologic remediation in 2010compared with those in any individual year from 2006 to2011 (plt00001) One exception was that maximumsalinity was higher in 2010 than in 2009 at CRMS 0234(plt 00001)

DISCUSSION

Freshwater flow variability controls ecological processes inestuaries so that alteration of water delivery is a keyconservation challenge (Lester et al 2013) Unfortunatelyinformation on how to manage salinity flux in freshwaterwetlands in altered estuaries is lacking (Kaplan et al 2010

Ecohydrol 8 838ndash850 (2015)

Table III Means plusmn SE listed by species dominance of dry litterfall biomass (gm2) based on species times year interactions for leafreproductive and wood tissue from 2007 to 2011 in JLNHP amp P

Species

Year

2007 2008 2009 2010 2011

Leaf tissueTaxodium distichum 264 plusmn 48 b 150 plusmn 25 c 291 plusmn 48 b 723plusmn 91 a 590plusmn 112 a

Acer rubrum 239 plusmn 53 ab 123 plusmn 26 b 184 plusmn 435 b 249plusmn 45 a 258plusmn 47 a

Fraxinus pennsylvanica 65 plusmn 21 b 28 plusmn 09 c 117 plusmn 29 a 136 plusmn 38 a 34 plusmn 22 c

Liquidambar styraciflua 47 plusmn 14 b 23 plusmn 06 b 45 plusmn 17 b 69plusmn 14 a 49 plusmn 16 b

Nyssa aquatica 80 plusmn 26 a 09 plusmn 08 b 14 plusmn 12 b 19 plusmn 11 b 00 plusmn 00 b

Myrica cerifera 00 plusmn 00 c 18 plusmn 07 b 23 plusmn 07 b 41plusmn 12 a 21 plusmn 07 b

Salix nigra 22 plusmn 11 a 13 plusmn 09 a 02 plusmn 01 a 39 plusmn 35 a 17 plusmn 16 a

Ulmus americana 10 plusmn 06 a 01 plusmn 01 b 04 plusmn 02 b 14 plusmn 08 a 21 plusmn 09 a

Quercus nigra 07 plusmn 02 a 01 plusmnlt01 a 08 plusmn 03 a 16 plusmn 06 a 09 plusmn 05 a

Other leaf 12 plusmn 04 c 18 plusmn 07 c 26 plusmn 07 b 45 plusmn 15 b 144 plusmn 32 a

Cephalanthus occidentalis 23 plusmn 09 a 00 plusmn 00 b 01 plusmn 01 b lt01 plusmnlt01 b 00 plusmn 00 b

Acer spp 22 plusmn 18 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a

Carya aquatica 00 plusmn 00 a 18 plusmn 09 a 02 plusmn 02 a 00 plusmn 00 a 00 plusmn 00 a

Quercus spp (red) 05 plusmn 04 a 03 plusmn 02 a 02 plusmn 01 a 04 plusmn 02 a 00 plusmn 00 a

Triadica sebifera 00 plusmn 00 a 02 plusmn 01 a 01 plusmnlt01 a 09 plusmn 06 a 06 plusmn 03 a

Gleditsia aquatica 14 plusmn 06 a 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b

Reproductive tissueTaxodium distichum 65 plusmn 30 b 06 plusmn 04 c 55 plusmn 31 b 57 plusmn 18 b 325plusmn 139 a

Other reproductive lt01 plusmnlt01 b lt01 plusmnlt01 b 02 plusmn 01 b 02 plusmn 01 b 44plusmn 24 a

Fraxinus pennsylvanica 05 plusmn 01 b 04 plusmn 01 b 03 plusmn 01 b 25plusmn 07 a 01 plusmn 01 b

Liquidambar styraciflua 09 plusmn 09 a 00 plusmn 00 a lt01 plusmnlt01 a 05 plusmn 05 a 00 plusmn 00 a

Nyssa aquatica 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 04 plusmn 04 a 00 plusmn 00 a

Wood tissueWood total all species 22 plusmn 05 a 28 plusmn 12 a 50 plusmn 21 a 129 plusmn 54 a 92 plusmn 43 a

Different letters indicate significant differences of litterfall biomass of species based on one-degree-of-freedom contrasts Dominant species are listedwith biomass gt02 g m2 with the biomass of non-dominant species summed in an lsquootherrsquo group Species with significantly higher litterfall in 2010 andor 2011 after Bonferroni correction are listed in bold lettersSE standard error

846 B A MIDDLETON D JOHNSON AND B J ROBERTS

Kingsford 2011) Out of necessity programmes to manageflood flow are emerging in the United States AustraliaSouth Africa and to a lesser extent Europe (Hughes andRood 2003) As an example the Comprehensive MasterPlan for Louisiana has proposed to use diversions torelease river water and sediment to rebuild coastalwetlands (CPRA 2012) While managed flood releasesare used increasingly in restoration (Middleton 1999Schmidt et al 2001 Souter et al 2014) theseapproaches may become even more important as salinityincreases with changes in climate sea level subsidenceand surfacegroundwater levels (Poff et al 2002 Kaplanet al 2010 Souter et al 2014) Studies such as ours caninform management procedures to explore the utility offreshwater release for coastal conservationVarious studies demonstrate the potential benefits of short

periods of increased freshwater flow to hydrologically alteredcoastal forests While hydrologic remediation lasted only 2 to4months in this study and the Souter et al 2014 study treeresponses were impressive After freshwater remediation inJLNHP amp P high levels of above-ground litter productionpersisted for several species for one or more growing season

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

(this study) Similarly healthy trees of Eucalyptuscamaldulensis Dehnh in the Murray River drainage (Austra-lia) vigorously grew more foliage while highly stressed ordefoliated trees responded positively but less vigorously fortwo growing seasons following ~2months of freshwaterrelease (Souter et al 2014) In the Lake Pontchartrain Basin ofLouisiana coastal Tdistichum trees grew two times fasterwith periodicflowof riverwater (Day et al 2012) In additionreproductive output was higher in 2010 and especially in 2011for certain tree species suggesting that resourcematchingmayhave occurred ie species varied reproductive output tomatchavailable resources (Kelly 1994) In the context of this studythe hydrologic remediation may have allowed these trees tobuild up their physiological resources via higher levels ofphotosynthetic activity prior to mass floweringEnvironmental flow prescriptions might revive moribund

coastal swamps yet no definitive range of flow amount ortiming has been identified to improve environments related tosalinity anoxia nutrients or other factors We linked sharplyhigher production of litter (leaf and reproductive) in 2010 tohydrologic remediation in salinity levels well below 20pptwith maximummeasured values at plots of EC vs PT sites 04

Ecohydrol 8 838ndash850 (2015)

Table V Analysis of variances of climate variables for JLNHP ampP from Marrero 9 SSW weather station data (NOAA 2013) foryears 2002ndash2012 remediation periods relative to the hydrologicremediation period in 2010 (pre-remediation remediation andpost-remediation) including mean monthly (a) total precipitation

and (b) temperature

Variable DF F p

(a) PrecipitationYear 10 12 03339Remediation period 2 21 01297Year times remediation period 20 11 04077

(b) TemperatureYear 10 01 09989Remediation period 2 817 lt00001 Year times remediation period 20 02 09999

DF degrees of freedom

Table IV Percentage of days exceeding predicted values for maximum and mean daily salinity levels (ppt) in the EC and PT unitsin JLNHP amp P (sites ECSECPECC vs PTPTV respectively)

Percent () days per year exceeding the specified maximum or minimum values of salinity (eg gt01 to 20 ppt) were predicted from linear regressionanalysis of surface salinity levels at CRMS 0234 and CRMS 0188 gauges (EC and PT units respectively) versus day-of-visit pore water salinity atproduction sites including ECSECPECC and PTPTV (Figure 4) Total days are the number of days per year during the growing season (1 Aprilndash31October 2008ndash2011) Published threshold salinity levels for forest tree maintenanceflooded seedling photosynthesis and basal area growth (size) arethought to be 20 and 07 ppt (in bold letters Kaplan et al 2010Pezeshki et al 1987 and Krauss et al 2009 respectively) Dark to light grey highlightsindicate percent () days per year exceeding maximum values as 70ndash100 30ndash70 1ndash30 and 0 respectivelyECS Education Center Spur ECP Education Center Parking ECC Education Center Canal PT Palmetto Trail PTV Palmetto Trail Visitors ECEducation Center JLNHP amp P Jean Lafitte National Historical Park amp Preserve

847HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

and 05ppt respectively (also see Figure 2a and Table IV) Incontrast to 2008 predicted levels of salinity were high in boththe EC and PT units (Table IV) and total annual leaf litterbiomass by individual species was low (A rubrum Tdistichum Fraxinuspennsylvanicum Mcerifera and Salixnigra Figure 2a and Table III) Nevertheless rendering asimple statement of an ideal threshold of salinity for theseswamps is impractical Among other problems field environ-ments are difficult to characterize simply (eg salinity levelsvary by depth in the vadose zone)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Trees in JLNHP amp P responded positively to remedia-tion but we recognize that this unplanned study did notpermit us to determine whether changes in salinity or someother unmeasured biogeochemical factors were ultimatelyresponsible for the observed responses Tidal flowreconnection in previously restricted salt marshes decreasessoil anoxia and sulphides and changes pH nutrientavailability and decomposition rates (Anisfeld and Benoit1997) The fact that we detected increased water levels anddecreased salinity with freshwater remediation indicatedthat other important site characteristics and biogeochemicalshifts likely were occurring at JLNHP amp P Unfortunatelywe do not have any other supportive data especially asrelated to any possible causal linkagesPhotosynthetic stressors such as salinity and anoxiamay be

more harmful during the growing season Flooding reducesregeneration seedlings and saplings of Tdistichum surviveovertopping by flooding while dormant but not during thegrowing season and most tree species will not germinateunderwater (Middleton 2000) A better understanding of anyseasonal component of remediation response is critical tohydrologic remediation planning for managementThe immediate mechanisms of increased tree production

with improved environment are not well studied but maybe related to the photosynthetic regulation of trees tochanges in environment As salinity (at some level) entersthe transpiration stream stomata close and photosynthesisdecreases (Stiller 2009) Any short-term increase in

Ecohydrol 8 838ndash850 (2015)

Figure 3 State of Louisiana water recorder information for maximum (a) daily discharge (m3 s1) from Davis Pond Diversion and adjusted water levels(m) at (b) Coastwide Reference Monitoring System (CRMS) 0234 and (c) CRMS 0188 and salinity (ppt) of (d) discharge of diversion and surface waterat (e) CRMS 00234 and (f) CRMS 0188 during hydrologically remediated (2010) versus lsquowetrsquo years (mean of 2008 2009 and 2011) CRMS 0234 andCRMS 0188 are in the same hydrological units as the Education Center and Palmetto Trail plots respectively in JLNHP amp P Pre-remediationremediation and post-remediation days of the year included days 1ndash119 120ndash244 and 245ndash365 respectively Sign tests indicated that 2010 was higherlower or not different from wet years as lsquo+rsquo lsquo-rsquo or lsquonsrsquo respectively (plt 00001) Only significant variables of time were kept p values for the sign testcomparisons were based on normally distributed error with constant variance All tests of fit were performed at p = 005 except that one test wasperformed at p = 001 to obtain a model fit Equations were based on the difference of the two year groups (2010 vs set of years compared) Mean dailydischarge values are not shown but these comparisons were also significant using similarly constructed ARIMA models and sign tests (plt 00001)Note that short periods of missing data were interpolated linearly Longer periods of missing data were omitted eg Davis Pond Diversion had nodischarge data available for 1ndash28 January 2010 Note that the measured water and salinity levels at plots in the EC and PT units were intermediate and

similar to each other (see Supplementary Figure 2)

848 B A MIDDLETON D JOHNSON AND B J ROBERTS

photosynthetic output and leaf production after freshwaterremediation is most likely to occur in healthy trees withrelatively intact leaf architecture such as Tdistichum in

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

JLNHP amp P or E camaldulensis trees along the MurrayRiver in Australia (Souter et al 2014) The positive effectsof remediation may have broad application in freshwater

Ecohydrol 8 838ndash850 (2015)

849HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

forests particularly because several species respondedpositively to freshwater remediation in JLNHP amp P

In our study litter but not root production increased duringthe year of hydrologic remediation If environment conditionsimproved in 2010 trees may have been experiencing a fastspurt of leaf litter production at the expense of roots(Figure 2b) Falling rootshoot ratios are an indicator of fastshoot growth in response to favourable environments (Harris1992 Litton et al 2007) and Tdistichum root and shootallocation patterns shift in response to changing resources(Megonigal and Day 1992) Note that we did not distinguishbetween species of roots in our study Alterations in root andshoot allocations following hydrologic remediationmay haveimportant implications for the elevation of subsiding swampsby influencing peat accumulation The decrease in rootgrowth during remediation is important because root tissuesoften contribute more to the accumulation of peat than leaf orwoody tissue (Middleton and McKee 2002) Whilereinvigorating the production of freshwater coastal vegetationoverall hydrologic remediation may reduce root growth forsome tree species at least temporarily (this study) Thereforea better understanding of the relationship of remediation androot growth is critical (Langley et al 2010 Wigand et al2014) to the development of management techniques relatedto remediation

CONCLUSION

Concerns are growing because of losses of coastal wetlandsalong the Gulf Coast (Kaplan et al 2010 CPRA 2012)Special attention should be given to our findings thatfreshwater release might reinvigorate the production offreshwater coastal vegetation Our study has worldwideimplications in that it demonstrates that sustained releases offreshwater can affect the primary production of many speciesFreshwater coastal species are increasingly affected bysaltwater intrusion so this idea deserves further explorationfor the management of coastal freshwater wetlands

ACKNOWLEDGEMENTS

This work is funded by the US Geological Survey andNational Science Foundation (DEB-1049838) Specialthanks are given to Evelyn Anemaet Mel McCulloughSamantha Primer Justin Stelly Lei Ting and GuodongWang for their field assistance Any use of trade productor firm names is for descriptive purposes only and does notimply endorsement by the US Government

CONFLICT OF INTEREST

The authors declare no conflict of interest with thisresearch

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

REFERENCES

Anemaet E Middleton BA 2013 Dendrometer bands made easy usingmodified cable ties to measure incremental growth of trees Applicationsin Plant Sciences 1 1300044

Anisfeld SC Benoit G 1997 Impacts of flow restriction on salt marshesan instance of acidification Environmental Science and Technology 311650ndash1699

Bianchi TS Cook RL Perdue EM Kolic PE Green N Zhang Y SmithRW Kolker AS Ameen A King G Ojwang LM Schneider CLNormand AE Hetland R 2011 Impacts of diverted freshwater ondissolved organic matter and microbial communities in Barataria BayLA Marine Environmental Research 72 248257

Brinson MM Bradshaw HD Holmes RN Elkins JB Jr 1980 Litterfallstemflow and throughfall nutrient fluxes in an alluvial swamp forestEcology 61 827ndash835

Cahoon DR Lynch JC Hensel P Boumans R Perez BC Segura B DayJW Jr 2002 A device for high precision measurement of wetlandsediment elevation I Recent improvements to the sedimentation-erosion table Journal of Sedimentary Research 72 730ndash733

Coastal Protection and Restoration Authority of Louisiana (CPRA) 2012Louisianarsquos Comprehensive Master Plan for a Sustainable CoastCPRA Baton Rouge LA

Coastal Protection and Restoration (CPRA) 2013 Modifications to theDavis Pond Diversion Louisiana Coastal Protection and RestorationBaton Rouge LA wwwlcagovProjects14Defaultaspx

Day JW 2000 Pattern and process of land loss in the Mississippi Delta aspatial and temporal analysis of wetland habitat change Estuaries 23425438

Day J Hunter R Keim RF DeLaune R Shaffer G Evers E Reed DBrantley C Kemp P Day J Hunter M 2012 Ecological response offorested wetlands with and without large-scale Mississippi River inputimplications for management Ecological Engineering 46 57 67

Dixon KR 1976 Analysis of seasonal leaf fall in north temperaturedeciduous forests Oikos 27 300306

Dokka RK 2006 Modern-day tectonic subsidence in coastal LouisianaGeology 34 281294

Greater NewOrleans Inc Regional Economic Alliance (GNO) 2010 A studyon the economic impact of the Deepwater Horizon oil spill GNORegionalEconomic Alliance New Orleans wwwuflibufledu docs Economic20Impact 20Study 20Part20I20-20Full20Reportpdf

Hertel D Leuschner C 2002 A comparison of four different fine rootproduction estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest Plant and Soil 239 237251

Hoeppner SS Schaffer GP Perkins TE 2008 Through droughts andhurricanes tree mortality forest structure and biomass production in acoastal swamp targeted for restoration in the Mississippi River DeltaicPlain Forest Ecology and Management 256 937948

Hughes FM Rood SB 2003 Allocation of river flows for restorationof floodplain forest ecosystems Environmental Management 321233

Harris RW 1992 Root-shoot ratios Journal of Arboriculture 18 39ndash42JMP SAS 2012 Statistical Analysis System v 1002 SAS Institute IncCary NC

Junk WJ Bayley PB Sparks RE 1989 The flood pulse concept in river-floodplain systems In Proceedings of the International Large RiverSymposium Vol 106 Canadian Special Publications in Fisheries andAquatic Science Ottawa Ontario Canada 110127

Kaplan D Muntildeoz-Carpena R Wan Y Hedgepeth M Zheng F Roberts RRossmanith R 2010 Linking river floodplain and vadose hydrology toimprove restoration of a coastal river affected by saltwater intrusionJournal of Environmental Quality 39 15701584

Kelly D 1994 The evolutionary ecology of mast seeding Trends inEcology and Evolution 9 465ndash470

Kingsford RT 2011 Conservation management of rivers and wetlandsunder climate change a synthesis Marine and Freshwater Research62 217222

Kozlowski TT 1997 Responses of woody plants to flooding and salinityTree Physiology 1 129

KraussKWDuberstein JADoyle TWConnerWHDayRH Inabinette LWWhitbeck JL 2009 Site condition structure and growth of baldcypressalong tidalnon-tidal salinity gradients Wetlands 29 505519

Ecohydrol 8 838ndash850 (2015)

840 B A MIDDLETON D JOHNSON AND B J ROBERTS

setting of these estuaries is important to recognize Salinityhas increased during recent decades particularly duringdroughts (Visser et al 2001) and because of extensivehuman modification these wetlands became disconnectedfrom the river (Wissel and Fry 2005) In responsediversion structures have been built along the lowerMississippi to reconnect coastal wetlands to their riversource Davis Pond Diversion began operation in 2003 tomimic spring floods and release freshwater into estuaries toimprove fisheries reduce land loss (CPRA 2013) andincrease primary production by altering sediment waterand nutrient levels (ie subsidyndashstress model Mitsch et al2001) After the construction of the diversion increases insecondary production have been documented along theflow path (Wissel and Fry 2005)Tidal forests south of the Davis Pond Diversion in

JLNHP amp P (Figure 1a) have been undergoing increasedsubsidence flooding and salinity (Day 2000) because ofshifting faults sediment and water loading (Dokka 2006)oil and gas exploration canal and levee construction andreduction in sediment input (Day 2000) Subsidence mightbe slowed by projects such as Davis Pond Diversion (USACOE 2000) particularly if hydrologic manipulationcan increase primary production Freshwater remediationmight reinvigorate plant growth because salinity causesinjury to cells metabolic dysfunction and leaf shedding infreshwater tree species (Kozlowski 1997) Few studies todate have evaluated threshold salinity levels for Tdistichum maintenance and growth with the data availablesuggesting these values to be about 20 and 07 ppt (Krausset al 2009 and Kaplan et al 2010 respectively) notingthat photosynthesis can be reduced at even lower levels ofsalinity (Pezeshki et al 1987)The objectives of this project were to determine if

hydrologic remediation efforts during the 2010 Deepwa-ter Horizon incident could have led to reduced salinityand consequently increased production in coastalfreshwater forests We tested the hypothesis that pro-duction of Gulf Coastal T distichum swamps was higherduring hydrologic remediation than at other timesfollowing predictions of the subsidyndashstress model(Mitsch et al 2001)

STUDY SITE

Hydrologic remediation event and study site details

Davis Pond Diversion is located at the northern end ofLake Cataouatche upstream of New Orleans and north ofthe head of the Mississippi River passes (~25 and 199kmrespectively) Davis Pond Diversion from the MississippiRiver was operated to discharge a large amount offreshwater from May to August 2010 (Bianchi et al2011) Water and salinity levels were monitored with two

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

permanent water gauges [Coastwide Reference MonitoringSystem (CRMS) 0234 and CRMS 0188] operated by theLouisiana Department of Natural Resources (LA DNR) inseparate hydrologic units on either side of Barataria Blvd inJLNHP amp P [Education Center (EC) unit and PalmettoTrail (PT) unit respectively Figure 1a Table I]Five research sites within coastal T distichum swamp

were selected in JLNHP amp P (Figure 1a) to evaluate inter-annual variability in production within the EC and PTunits [sites Education Center Parking (ECP)EducationCenter Spur (ECS)Education Center Canal vs PalmettoTrail (PT)Palmetto Trail Visitors (PTV) respectivelyTable I] Two of these sites were selected for T distichumtree growth studies in addition to two sites each in BigThicket National Preserve (Texas) and St Marks NationalWildlife RefugeBig Bend Wildlife Management Area(Florida) which comprise a portion of the NABSCN(Figure 1b and Table I) Most swamps in this network aredeeply flooded for many months of the year so thatmethodology is optimized for access during consistentlyunflooded seasons (AugustndashDecember)

METHODS

Tree production and growth

Annual peak litterfall production was measured usingfloating litterfall collectors (diameter = 03m2 Middleton1995 Middleton and McKee 2005) in plots within fivesites in JLNHP amp P (Table I) Five production plots wereselected along one 125-m-long linear transect within eachof these sites at stratified random positions at 25-mintervals to the right of the transect and marked with awooden stake Traps were set in August and litterremoved after peak litterfall (main season) each Decemberin 2007ndash2011 with off-season quarterly samples collectedin 2007 and 2011 Means of the total biomass captured inthe 20072011 quarterly samples were used to create acorrection factor for the main season of capture notingthat most dominant species were deciduous Litterfall wassorted by species into leaf stem (wood) and reproductivecomponents dried at 70 degC and weighed Note thatany large woody material falling on the litter trap (stemgt05-cm diameter) was not likely to have been producedduring that growing season and was removed from thesample To measure annual root production a soil core(7 cm diameter times 30 cm depth) was filled with an im-planted root bag (root ingrowth core Lund et al 1970)adjacent to each of the five plot markers after the previousyearrsquos core had been removed during seasonal drawdown(August 2007ndash2011) After removal cores were dividedinto three depths (0ndash10 10ndash20 and 20ndash30 cm) andwashed through a sieve to separate soil from rootsCollected roots were dried to a constant mass at 70 degC and

Ecohydrol 8 838ndash850 (2015)

TableILocations

ofstudysiteshydrologicalunitsC

RMSwater

recorders(w

ater

leveland

salin

ityL

ADNR2

013)S

olinstwater

recordersproductio

nsitesin

JLNHPamp

Pand

tree

grow

thsitesin

JLNHPamp

PBTNPandSMNWRBBWMA

Site

andyears

Location

Site

type

Hydrologicalunit

CRMSanddates

Solinstanddates

Sonde

0004264

anddates

Site

coordinates

Educatio

nCenterParking

(ECP)2007ndash2011

JLNHPamp

PLA

Production

andtree

grow

thECunit

CRMS0234-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

28August2012ndash

4September2012

29785N

90113W

Educatio

nCenterSpur

(ECS)2007ndash2011

JLNHPamp

PLA

Production

andtree

grow

thECunit

CRMS0234-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

na29786N

90114W

Educatio

nCenterCanal

(ECC)2007ndash2011

JLNHPamp

PLA

Production

ECunit

CRMS0234-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

na29787N

90115W

Palmetto

Trail

(PT)2007ndash2011

JLNHPamp

PLA

Production

PTunit

CRMS0188-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

na29791N

90122W

Palmetto

TrailVisito

rs(PTV)2007ndash2011

JLNHPamp

PLA

Production

PTunit

CRMS0188-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

na29789N

90121W

LakeBayou

(LB)

2011ndash2

012

BTNPTX

Treegrow

thna

nana

na30150N

94096W

Low

erCypress

Tract

(LCT)2011ndash2012

BTNPTX

Treegrow

thna

nana

na30134N

94081W

BuckhornCreek

(BUC)2012

SMNWR

FL

Treegrow

thna

nana

na30030N

84470W

MandalayRoad

(MR)2012

BBWMA

FL

Treegrow

thna

nana

na30129N

83962W

CRMS0234

andCRMS0188

wereon

theECversus

PTsidesof

BaratariaBlvd(ECvs

PTunitsrespectively)S

edim

entelevatio

ntables

wereinserted

into

ECPandECSin

2007

andPTandPTVin

2011

Day-of-visitsalinity

porewatersalin

itysamples

weremeasuredthroughout

thestudyandmoreintensivelyin

2011ndash2012Surface

watersalin

ityattheCRMSrecordersweremeasuredfrom

thesameheight

below

thesoilor

water

columnas

thewater

sensorDavis

PondDiversion

dischargeandsalin

itydata

wereavailablefrom

1January2008ndash31Decem

ber2011

(USGS295501090190400)Alsosee

Figure1

CRMSCoastwideReference

Monito

ring

SystemJLNHPamp

PJean

Lafitte

NationalHistoricalParkamp

Preserve

BTNPBig

Thicket

NationalPreserve

LA

DNRLouisiana

Departm

entof

Natural

Resources

BBWMABig

BendWild

lifeManagem

entArea

SMNWRStMarks

NationalWild

lifeRefuge

841HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd Ecohydrol 8 838ndash850 (2015)

842 B A MIDDLETON D JOHNSON AND B J ROBERTS

weighed Annual sampling allowed many months for theregrowth of roots into the core (Vogt et al 1998 Herteland Leuschner 2002) Other root production approachescould not be used because of flooded seasons in networkswamps (water depth gt75 cm)Annual growth (incremental circumference increase) of

T distichum trees and knees was measured usingdendrometer bands (Anemaet and Middleton 2013) whichwere placed on the nearest tree and knee (one each) to markproduction plots (plot 1 3 and 5) along each transect in twosites (ECP and ECS) in JLNHP amp P in 2006 (n=3 per site)T distichum trees more than 20m from a large tree andemerged into the canopy were selected for bandingWe useda similar procedure to examine tree growth and salinityacross the US Gulf Coast except that we used five treesadjacent to all five production plots in each site in Texas andFlorida (Lake Bayou and Lower Cypress Tract vs BuckhornCreek and Mandalay Road respectively) (Table I andFigure 1b) in 2011 and 2012 respectively Note that thebands placed on trees in JLNHPampP in 2006were of an olderstyle and could not be measured until 2008 (Anemaet andMiddleton 2013) Tree bands were placed at ~15m heighton the tree above any fluting or buttressing Knee bands wereplaced ~6 cm from the tip of the knee

Water dynamics and salinity

Day-of-site visit measurements Within 1m of each plot asipper was used to extract soil pore water during each sitevisit (five samples per site) Water was transported in aportable freezer to the lab and the salinity measured with aYSI EC 300reg probe Water depth was measured adjacentto each plot marker with a metre stick

Water gauge analyses To study water dynamics over timewe analyzed patterns in daily mean and maximum values ofdischarge (m3 s1) and surface water salinity (ppt) fromthree recording gauges including the Davis Pond Diversion(US Geological Survey DCPBA03 2013) and CRMSrecorders (Table I CRMS 0234 and CRMS 0188 LA DNR2013) Water level and salinity patterns in 2010 (year ofhydrologic remediation) were compared with the average ofvarious groups of years in the available data set (2003ndash2011long-term) the average of comparably wet years (2008ndash2011 wet) and each individual year during 2006ndash2011 Allcomparisons were conducted for three periods within eachyear andor period pre- (days 1ndash119 1 Januaryndash30 April)during (days 120ndash244 1Mayndash1 September) and post- (days245ndash365 2 Septemberndash31 December)Water patterns were compared during the year of

hydrologic remediation (2010) with sets of long-termwet and individual years We used maximum daily valuesof both water level and surface salinity for these analysesbecause maximum values are more likely than mean values

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

to capture short-term changes in photosynthesis Note thatmean versus maximum daily values varied little from eachother [mean vs maximum difference plusmn standard error(SE) = 105plusmn 00018]To determine if short-term water level fluctuation within

plots generally followed those of CRMS gauges weinserted Solinst water level recorders (Levelogger Gold)within the ECP and PT sites in JLNHP amp P on 13 August2012 (~05ndash10 km apart within EC unit and PT unitrespectively Figure 1a and Table I) Daily mean andmaximum adjusted water levels and surface salinity levelsfrom CRMS gauges (publically available data) werecompared with those from Solinst water recorders andday-of-site visit measurements during periods of overlap (13Augustndash27 September 4 December 2012 Table I) Meanday-of-visit pore water salinity from sites were comparedwith those from CRMS gauges during 2011ndash2012Flood water was assumed to be connected by a

contiguous water sheet across units and consistent withinelevations corresponding to CRMS gauges Solinst waterrecorders sediment elevation table (SET) monumentsplots and the Sonde Following this idea hydrographswere constructed for each Solinst water logger SETmonument and plot stake by offsetting elevation of thewater sheet and matching water level fluctuations withthe continuous CRMS gauges within the hydrological unit(ie EC unit and PT unit gauge to SET offset +10 and50 cm respectively) Water levels were not adjusted to acommon datum Water depths were measured on days ofvisits at each plot stake and SET which here were used as asurface water-recording benchmark (Cahoon et al 2002)two SETs were placed within both ECP and ECS in 2006and PT and PTV in 2011 (eight total SETs) Absoluteelevations at SETs near ECPECS in 2007 were about0093m above sea level (Middleton and Jiang 2013)A water gauge was deployed less than 100m from ECP

to examine short-term pulses of water during HurricaneIsaac from 28 Augustndash4 September 2012 (Sonde0004264 USGS 2012 Figure 1b and Table I) All watermeasurement devices in units on both the EC side and PTside of Barataria Blvd detected the pulse signal fromHurricane Isaac (Table I) By comparing water recordsfrom these various sources it was determined that waterlevels measured with CRMS recorders within EC unit vsPT unit were relevant to those of production plots (Figure 1in the Supporting Information)

Climate analysis Monthly total precipitation (mm) andmean temperature (degC) were acquired from a weatherstation about 1 km away from the JLNHPampP study plots[Marrero 9 SSW Station LA 297853degN 901158degW] anddata from 2002 to 2012 were compared with those of 2010during pre-remediation during remediation and post-remediation periods (NOAA 2013)]

Ecohydrol 8 838ndash850 (2015)

843HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

DATA ANALYSIS

Vegetation production

Annual total litterfall (leaf and wood) was calculated frompeak litterfall estimates by determining the percentage ofannual litterfall collected during the main season (mean of20072011 correction factor = 0718plusmn0176 SE) so thatbiomass captured during the main season of each year wasdivided by 07180 to express yearly production Thiscorrection factor better portrayed annual total litterfallbased on peak litterfall while fully recognizing that certainswamp species do not lose their leaves during this period(eg Myrica cerifera) Most deciduous trees shed all oftheir leaves within 30ndash60 days (Dixon 1976) fromSeptember through mid-November (Tdistichum swampNorth Carolina Brinson et al 1980) or into Decemberfarther southward (eg South Carolina mixed bottomlandforest Shure and Gottschalk 1985)

Litterfall totals by year species and tissue type (leafreproductive and wood) from 2007 to 2011 were analyzedusing repeated measures analysis nesting plot within yearin analysis of variance (ANOVA) (one-way or two-wayANOVA JMP SAS 2012) For annual log root produc-tion ANOVA was used by nesting plot (depth year) Rootproduction by year did not interact with depth (year times depthinteraction pgt005) so that total root production wasanalyzed by year The lower two root depths (10ndash20 and20ndash30 cm) did not differ (t=097 p=033) so that a meanof these two depths was calculated (10ndash30 cm) andcompared with the upper depth (0ndash10 cm) In all ANOVAanalyses the highest-order significant interaction or maineffect was tested using one degree-of-freedom contrasts inJMP SAS (2012) Data were appropriately transformed tomeet assumptions of ANOVA and multiple comparisonsadjusted using Bonferroni corrections (two one-degree-of-freedom contrasts or three one degree-of-freedomcontrasts p=0025 or 00167 respectively)

Tree and knee growth were analyzed by comparingmeans of growth (circumference ratios ie yearrsquos circum-ference divided by previous yearrsquos circumference) for2008ndash2011 For the Gulf Coast-wide assessment of treegrowth and salinity regression analysis compared means oftree growth (circumference ratios) in LA TX and FL(2011ndash2012) versus annual mean salinity Annual meansalinity was based on the mean of day-of-visit measure-ments from 2011 to 2012 (7 to 14 measurements with allseasons represented)

Climate

We used ANOVA to compare monthly total precipitationand mean temperature by year and remediation periodusing the main effects and interactions of year andremediation period

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Water environment and remediation

Water and salinity level shifts and remediation Todetermine if the water dynamics differed from expectedconditions we compared mean and maximum values ofdaily levels of water and surface salinity during times ofinterest Because short periods of high salinity or anoxiawere likely to affect tree production and growth we focusedon daily maximum water level for these analyses Watercomparisons were made of three time periods in 2010 (pre-remediation during and post-remediation) with the sameperiods in other years in three ways wet years (mean of2008ndash2011) long-term (mean of 2003ndash2011) and individualyears (2006ndash2011) These comparisons were made usingautoregressive integrated moving average (ARIMA) models(detailed description provided in Table 1 in the SupportingInformation) generated in SAS Institute Inc (2002) whichare appropriate for comparing water and salinity levels shiftsover time because these models can predict the shape of thefunction and account for the autocorrelation of the samplesover time better than other statistical approaches (SASInstitute Inc 2002) A nonparametric sign test comparednumber of times the 2010 series had more water or salinitythan the average of the comparison series and vice versa

Predicted daily threshold values of salinity in productionplots To determine the number of days that productionsites exceeded threshold values of various salinity levelsthe following procedure was followed Using linearregression mean daily surface water salinity from CRMSgauges in the EC and PT units on specific days wereplotted against mean pore water salinity on day-of-visit inproduction plots and SET monuments in 2011ndash2012(Table I) Equations generated from this process were usedto predict daily mean salinity levels in sites from 2008 to2011 (for equations see Figure 2 caption in the SupportingInformation) as well as the percentage of growing seasondays (1 Aprilndash31 October) each year above certain salinitylevels (ie 01 03 07 10 15 and 20 ppt)

RESULTS

Production and vegetation responses to hydrologicremediation

Total litter biomass was 27 times higher after hydrologicremediation in 2010 and 2011 than before remediation in2007ndash2009 (Figure 2a Table IIa one degree-of-freedomcontrast t=838 plt 00001) In litterfall Tdistichum leafbiomass was 31 and 25 times higher in 2010 andor 2011respectively than in 2007ndash2009 (Table IIa) while repro-ductive biomass was 77 times in 2011 but not different in2010 (Table IIa and Table III) In addition leaf andreproductive tissue biomass in litterfall was higher in 2010

Ecohydrol 8 838ndash850 (2015)

Figure 2 Total annual mean production from 2007 to 2011 including (a)total litter biomass (leaf reproductive and wood) [g m2 y1 plusmn standarderror (SE)] and (b) total annual root biomass (total of all depths 0ndash30 cmg m2 y1 plusmn SE) in Jean Lafitte National Historical Park amp Preserve(n = 25) Different letters indicated that means of years differed statistically(one degree-of-freedom contrasts plt 005) (c) Regression analysis ofstem growth expressed as mean salinity (ppt) versus Taxodium distichumcircumference ratio plusmn SE along the Gulf Coast (R2 = 086) Salinity isbased on means of pore water salinity during day-of-visit measurements

844 B A MIDDLETON D JOHNSON AND B J ROBERTS

andor 2011 than in 2007ndash2009 for Acer rubrum (not in2007) Liquidambar styraciflua and M cerifera (Table IIaand Table III) Annual litterfall biomass of wood tissue didnot change from 2007 to 2011 although the mean wassubstantially higher in 2010 (Table IIb plt 005) Annuallog root biomass was higher in shallower than deeper soildepths (Figure 2b and Table IIb 0ndash10 vs 10ndash30 cmt=279 p=00058 N=5) and total root biomass variedby year and was 23ndash53 times lower in 2010 than in 2007ndash2011 (Figure 2b t=489 plt 00001 N=5)Neither tree nor knee growth varied with circumference

increasing by 18 plusmn 01 and 29 plusmn 10 respectively peryear during 2008ndash2011 in JLNHP amp P (pgt005Table IIcndashd) In JLNHP amp P we found no relationship

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

between tree growth and the percentage days per year a siteexceeded published thresholds of salinity (eg 07 or20 ppt pgt005 Table IV) In 2010 both EC and PT unitshad fewer days with salinity gt03 ppt and in 2008 moredays with salinity gt20 ppt (Table IV Figure 1 in theSupporting Information) Across the Gulf Coast Tdistichum growth varied from 011 to 21 increase incircumference per year with average annual salinityexplaining 86 of the variance in growth with the highestgrowth observed in the lowest mean pore water salinity(eg JLNHP amp P Figure 2c)

Climate and environment

Regionally mean annual precipitation was 13209plusmn1065mm per year from 2002 to 2012 (National Oceanicand Atmospheric Administration (NOAA) 2013) but didnot vary by year or remediation period (pgt 0130 Table V)Mean monthly air temperature did not vary by year but didvary by remediation period (mean monthly temperaturesduring pre-remediation remediation and post-remediation157 plusmn 06 degC 269 plusmn03 degC and 187 plusmn 08 degC respectivelyF=817 plt0001 Table V) (NOAA 2013)

Water and salinity responses to hydrologic remediation

Short-term water and salinity comparisons ndash 2010 versuswet years (2008ndash2011) Davis Pond CRMS 0188 andCRMS 0234 had higher dischargewater level and lowersalinity during the remediation period in 2010 than duringwet years As based on ARIMA time series comparisonswater discharged from Davis Pond in 2010 exceeded meanand maximum daily discharge of wet years (mean dailydischarge of 2010 vs wet years 113 out of 119 daysrespectively maximum daily discharge of 2010 vs wetyears 102 out of 119 days respectively sign testsplt 00001 Figure 3a and Table 2 in the SupportingInformation) Discharge rates from the Davis PondFreshwater Diversion and water levels at gauges werelower in 2010 during the post-remediation period than inwet years (Figure 3a and Table 2 in the SupportingInformation) Maximum daily gauge levels were higherduring hydrologic remediation in 2010 than in wet years(CRMS 0234 026 vs 011m respectively Figure 3bCRMS 0188 115 vs 106m respectively Figure 3c andTable 2 in the Supporting Information)Long-term gauging stations can be used to indicate

conditions at sites even though salinity relationships weresomewhat different (ie EC sites had significantly highersalinity than CRMS 0234 and PT sites had significantlylower salinity than CRMS 0188 as based on day-of-visitmeasurements) Salinity environments in the EC and PTsites were relatively similar (Figure 2 in the SupportingInformation) Nevertheless maximum daily water levels atCRMS 0234 were linearly related to day-of-visit water

Ecohydrol 8 838ndash850 (2015)

Table II Analysis of variances of production variables in JLNHP amp P from 2007 to 2011

DF F p Mean plusmn SE

(a) Total annual productionLitterfall (gm2 y1)Year 4 236 lt00001

Root biomass (gm2 y1)Year 4 84 lt00001 Depth 1 78 00225

Year times depth 4 10 04142 ns(b) Tissue typeLeafSpecies 15 155 lt00001 Year 4 1566 lt00001 Species times year 60 41 lt00001

ReproductiveSpecies 5 400 lt00001 Year 4 69 lt00001 Species times year 20 44 lt00001

WoodYear 4 21 00794 ns

(c) Tree growth (annual circumference ratio)Initial tree circumference (covariate) 1 38 00668 nsYear 3 01 09718 ns2008 1019210 plusmn 000552009 1018628 plusmn 000712010 1018855 plusmn 000382011 1015170 plusmn 00022

(d) Knee growth (annual circumference ratio)Initial knee circumference (covariate) 1 05 04945 nsYear 4 09 04628 ns

Mean total annual production of (a) litterfall (g m2 y1 including leaves reproductive material and wood) and log root biomass (g m3 y1) (b) Meanbiomass of tissue types of dominant species including leaf reproductive and wood Dendrometer bands were used to measure incremental increase incircumference growth was estimated as a year-to-year ratio of circumference change of Taxodium distichum from 2008 to 2011 for (c) trees and (d)knees Mean comparisons that differed based on contrasts indicated by lsquorsquo lsquorsquo or ns (plt 00001 plt 005 pgt 005 respectively Figure 2) SeeTable III for tissue type times species interactionsJLNHP amp P Jean Lafitte National Historical Park amp Preserve SE standard error DF degrees of freedom ns not significant

845HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

depths at SETs in the EC unit (ie SETs at ECP and ECSFigure 2 in the Supporting Information r= 06043p=00015) As indicated in the Section on Methods tojustify the selection of salinity variables and analysesoverall maximum daily values were within 105plusmn 00018of mean values Mean daily salinity levels at CRMS 0234and CRMS 0188 were linearly related to day-of-visitsalinity at SETs and plots within the same hydrologicalunits (EC unit r=0600 p=00004 Figure 2b in theSupporting Information PT unit r=0702 p=00005Figure 2c in the Supporting Information)

Long-term water level comparisons ndash 2010 versus long-term (2003ndash2011) Water discharge from Davis Pond in2010 during hydrologic remediation was higher than in thelong-term set of years (2003ndash2011 mean discharge perday =1983 plusmn 49 vs 331 plusmn 16m3 s1 respectively) andmaximum daily water levels at CRMS 0234 and CRMS0188 also were higher (sign tests plt00001 Figure 4 inthe Supporting Information)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Individual year water and salinity level comparisons ndash2010 vs 2006ndash2011 Comparisons of maximum dailywater level and salinity levels during 2010 to individualyears were similar to the comparisons of 2010 to sets ofwet and long-term years (ie 2008ndash2011 and 2003ndash2011respectively) As expected discharge levels for Davis Pondand water levels at CRMS 0234 and CRMS 0188 weresignificantly higher during hydrologic remediation in 2010compared with those in any individual year from 2006 to2011 (plt00001) One exception was that maximumsalinity was higher in 2010 than in 2009 at CRMS 0234(plt 00001)

DISCUSSION

Freshwater flow variability controls ecological processes inestuaries so that alteration of water delivery is a keyconservation challenge (Lester et al 2013) Unfortunatelyinformation on how to manage salinity flux in freshwaterwetlands in altered estuaries is lacking (Kaplan et al 2010

Ecohydrol 8 838ndash850 (2015)

Table III Means plusmn SE listed by species dominance of dry litterfall biomass (gm2) based on species times year interactions for leafreproductive and wood tissue from 2007 to 2011 in JLNHP amp P

Species

Year

2007 2008 2009 2010 2011

Leaf tissueTaxodium distichum 264 plusmn 48 b 150 plusmn 25 c 291 plusmn 48 b 723plusmn 91 a 590plusmn 112 a

Acer rubrum 239 plusmn 53 ab 123 plusmn 26 b 184 plusmn 435 b 249plusmn 45 a 258plusmn 47 a

Fraxinus pennsylvanica 65 plusmn 21 b 28 plusmn 09 c 117 plusmn 29 a 136 plusmn 38 a 34 plusmn 22 c

Liquidambar styraciflua 47 plusmn 14 b 23 plusmn 06 b 45 plusmn 17 b 69plusmn 14 a 49 plusmn 16 b

Nyssa aquatica 80 plusmn 26 a 09 plusmn 08 b 14 plusmn 12 b 19 plusmn 11 b 00 plusmn 00 b

Myrica cerifera 00 plusmn 00 c 18 plusmn 07 b 23 plusmn 07 b 41plusmn 12 a 21 plusmn 07 b

Salix nigra 22 plusmn 11 a 13 plusmn 09 a 02 plusmn 01 a 39 plusmn 35 a 17 plusmn 16 a

Ulmus americana 10 plusmn 06 a 01 plusmn 01 b 04 plusmn 02 b 14 plusmn 08 a 21 plusmn 09 a

Quercus nigra 07 plusmn 02 a 01 plusmnlt01 a 08 plusmn 03 a 16 plusmn 06 a 09 plusmn 05 a

Other leaf 12 plusmn 04 c 18 plusmn 07 c 26 plusmn 07 b 45 plusmn 15 b 144 plusmn 32 a

Cephalanthus occidentalis 23 plusmn 09 a 00 plusmn 00 b 01 plusmn 01 b lt01 plusmnlt01 b 00 plusmn 00 b

Acer spp 22 plusmn 18 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a

Carya aquatica 00 plusmn 00 a 18 plusmn 09 a 02 plusmn 02 a 00 plusmn 00 a 00 plusmn 00 a

Quercus spp (red) 05 plusmn 04 a 03 plusmn 02 a 02 plusmn 01 a 04 plusmn 02 a 00 plusmn 00 a

Triadica sebifera 00 plusmn 00 a 02 plusmn 01 a 01 plusmnlt01 a 09 plusmn 06 a 06 plusmn 03 a

Gleditsia aquatica 14 plusmn 06 a 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b

Reproductive tissueTaxodium distichum 65 plusmn 30 b 06 plusmn 04 c 55 plusmn 31 b 57 plusmn 18 b 325plusmn 139 a

Other reproductive lt01 plusmnlt01 b lt01 plusmnlt01 b 02 plusmn 01 b 02 plusmn 01 b 44plusmn 24 a

Fraxinus pennsylvanica 05 plusmn 01 b 04 plusmn 01 b 03 plusmn 01 b 25plusmn 07 a 01 plusmn 01 b

Liquidambar styraciflua 09 plusmn 09 a 00 plusmn 00 a lt01 plusmnlt01 a 05 plusmn 05 a 00 plusmn 00 a

Nyssa aquatica 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 04 plusmn 04 a 00 plusmn 00 a

Wood tissueWood total all species 22 plusmn 05 a 28 plusmn 12 a 50 plusmn 21 a 129 plusmn 54 a 92 plusmn 43 a

Different letters indicate significant differences of litterfall biomass of species based on one-degree-of-freedom contrasts Dominant species are listedwith biomass gt02 g m2 with the biomass of non-dominant species summed in an lsquootherrsquo group Species with significantly higher litterfall in 2010 andor 2011 after Bonferroni correction are listed in bold lettersSE standard error

846 B A MIDDLETON D JOHNSON AND B J ROBERTS

Kingsford 2011) Out of necessity programmes to manageflood flow are emerging in the United States AustraliaSouth Africa and to a lesser extent Europe (Hughes andRood 2003) As an example the Comprehensive MasterPlan for Louisiana has proposed to use diversions torelease river water and sediment to rebuild coastalwetlands (CPRA 2012) While managed flood releasesare used increasingly in restoration (Middleton 1999Schmidt et al 2001 Souter et al 2014) theseapproaches may become even more important as salinityincreases with changes in climate sea level subsidenceand surfacegroundwater levels (Poff et al 2002 Kaplanet al 2010 Souter et al 2014) Studies such as ours caninform management procedures to explore the utility offreshwater release for coastal conservationVarious studies demonstrate the potential benefits of short

periods of increased freshwater flow to hydrologically alteredcoastal forests While hydrologic remediation lasted only 2 to4months in this study and the Souter et al 2014 study treeresponses were impressive After freshwater remediation inJLNHP amp P high levels of above-ground litter productionpersisted for several species for one or more growing season

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

(this study) Similarly healthy trees of Eucalyptuscamaldulensis Dehnh in the Murray River drainage (Austra-lia) vigorously grew more foliage while highly stressed ordefoliated trees responded positively but less vigorously fortwo growing seasons following ~2months of freshwaterrelease (Souter et al 2014) In the Lake Pontchartrain Basin ofLouisiana coastal Tdistichum trees grew two times fasterwith periodicflowof riverwater (Day et al 2012) In additionreproductive output was higher in 2010 and especially in 2011for certain tree species suggesting that resourcematchingmayhave occurred ie species varied reproductive output tomatchavailable resources (Kelly 1994) In the context of this studythe hydrologic remediation may have allowed these trees tobuild up their physiological resources via higher levels ofphotosynthetic activity prior to mass floweringEnvironmental flow prescriptions might revive moribund

coastal swamps yet no definitive range of flow amount ortiming has been identified to improve environments related tosalinity anoxia nutrients or other factors We linked sharplyhigher production of litter (leaf and reproductive) in 2010 tohydrologic remediation in salinity levels well below 20pptwith maximummeasured values at plots of EC vs PT sites 04

Ecohydrol 8 838ndash850 (2015)

Table V Analysis of variances of climate variables for JLNHP ampP from Marrero 9 SSW weather station data (NOAA 2013) foryears 2002ndash2012 remediation periods relative to the hydrologicremediation period in 2010 (pre-remediation remediation andpost-remediation) including mean monthly (a) total precipitation

and (b) temperature

Variable DF F p

(a) PrecipitationYear 10 12 03339Remediation period 2 21 01297Year times remediation period 20 11 04077

(b) TemperatureYear 10 01 09989Remediation period 2 817 lt00001 Year times remediation period 20 02 09999

DF degrees of freedom

Table IV Percentage of days exceeding predicted values for maximum and mean daily salinity levels (ppt) in the EC and PT unitsin JLNHP amp P (sites ECSECPECC vs PTPTV respectively)

Percent () days per year exceeding the specified maximum or minimum values of salinity (eg gt01 to 20 ppt) were predicted from linear regressionanalysis of surface salinity levels at CRMS 0234 and CRMS 0188 gauges (EC and PT units respectively) versus day-of-visit pore water salinity atproduction sites including ECSECPECC and PTPTV (Figure 4) Total days are the number of days per year during the growing season (1 Aprilndash31October 2008ndash2011) Published threshold salinity levels for forest tree maintenanceflooded seedling photosynthesis and basal area growth (size) arethought to be 20 and 07 ppt (in bold letters Kaplan et al 2010Pezeshki et al 1987 and Krauss et al 2009 respectively) Dark to light grey highlightsindicate percent () days per year exceeding maximum values as 70ndash100 30ndash70 1ndash30 and 0 respectivelyECS Education Center Spur ECP Education Center Parking ECC Education Center Canal PT Palmetto Trail PTV Palmetto Trail Visitors ECEducation Center JLNHP amp P Jean Lafitte National Historical Park amp Preserve

847HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

and 05ppt respectively (also see Figure 2a and Table IV) Incontrast to 2008 predicted levels of salinity were high in boththe EC and PT units (Table IV) and total annual leaf litterbiomass by individual species was low (A rubrum Tdistichum Fraxinuspennsylvanicum Mcerifera and Salixnigra Figure 2a and Table III) Nevertheless rendering asimple statement of an ideal threshold of salinity for theseswamps is impractical Among other problems field environ-ments are difficult to characterize simply (eg salinity levelsvary by depth in the vadose zone)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Trees in JLNHP amp P responded positively to remedia-tion but we recognize that this unplanned study did notpermit us to determine whether changes in salinity or someother unmeasured biogeochemical factors were ultimatelyresponsible for the observed responses Tidal flowreconnection in previously restricted salt marshes decreasessoil anoxia and sulphides and changes pH nutrientavailability and decomposition rates (Anisfeld and Benoit1997) The fact that we detected increased water levels anddecreased salinity with freshwater remediation indicatedthat other important site characteristics and biogeochemicalshifts likely were occurring at JLNHP amp P Unfortunatelywe do not have any other supportive data especially asrelated to any possible causal linkagesPhotosynthetic stressors such as salinity and anoxiamay be

more harmful during the growing season Flooding reducesregeneration seedlings and saplings of Tdistichum surviveovertopping by flooding while dormant but not during thegrowing season and most tree species will not germinateunderwater (Middleton 2000) A better understanding of anyseasonal component of remediation response is critical tohydrologic remediation planning for managementThe immediate mechanisms of increased tree production

with improved environment are not well studied but maybe related to the photosynthetic regulation of trees tochanges in environment As salinity (at some level) entersthe transpiration stream stomata close and photosynthesisdecreases (Stiller 2009) Any short-term increase in

Ecohydrol 8 838ndash850 (2015)

Figure 3 State of Louisiana water recorder information for maximum (a) daily discharge (m3 s1) from Davis Pond Diversion and adjusted water levels(m) at (b) Coastwide Reference Monitoring System (CRMS) 0234 and (c) CRMS 0188 and salinity (ppt) of (d) discharge of diversion and surface waterat (e) CRMS 00234 and (f) CRMS 0188 during hydrologically remediated (2010) versus lsquowetrsquo years (mean of 2008 2009 and 2011) CRMS 0234 andCRMS 0188 are in the same hydrological units as the Education Center and Palmetto Trail plots respectively in JLNHP amp P Pre-remediationremediation and post-remediation days of the year included days 1ndash119 120ndash244 and 245ndash365 respectively Sign tests indicated that 2010 was higherlower or not different from wet years as lsquo+rsquo lsquo-rsquo or lsquonsrsquo respectively (plt 00001) Only significant variables of time were kept p values for the sign testcomparisons were based on normally distributed error with constant variance All tests of fit were performed at p = 005 except that one test wasperformed at p = 001 to obtain a model fit Equations were based on the difference of the two year groups (2010 vs set of years compared) Mean dailydischarge values are not shown but these comparisons were also significant using similarly constructed ARIMA models and sign tests (plt 00001)Note that short periods of missing data were interpolated linearly Longer periods of missing data were omitted eg Davis Pond Diversion had nodischarge data available for 1ndash28 January 2010 Note that the measured water and salinity levels at plots in the EC and PT units were intermediate and

similar to each other (see Supplementary Figure 2)

848 B A MIDDLETON D JOHNSON AND B J ROBERTS

photosynthetic output and leaf production after freshwaterremediation is most likely to occur in healthy trees withrelatively intact leaf architecture such as Tdistichum in

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

JLNHP amp P or E camaldulensis trees along the MurrayRiver in Australia (Souter et al 2014) The positive effectsof remediation may have broad application in freshwater

Ecohydrol 8 838ndash850 (2015)

849HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

forests particularly because several species respondedpositively to freshwater remediation in JLNHP amp P

In our study litter but not root production increased duringthe year of hydrologic remediation If environment conditionsimproved in 2010 trees may have been experiencing a fastspurt of leaf litter production at the expense of roots(Figure 2b) Falling rootshoot ratios are an indicator of fastshoot growth in response to favourable environments (Harris1992 Litton et al 2007) and Tdistichum root and shootallocation patterns shift in response to changing resources(Megonigal and Day 1992) Note that we did not distinguishbetween species of roots in our study Alterations in root andshoot allocations following hydrologic remediationmay haveimportant implications for the elevation of subsiding swampsby influencing peat accumulation The decrease in rootgrowth during remediation is important because root tissuesoften contribute more to the accumulation of peat than leaf orwoody tissue (Middleton and McKee 2002) Whilereinvigorating the production of freshwater coastal vegetationoverall hydrologic remediation may reduce root growth forsome tree species at least temporarily (this study) Thereforea better understanding of the relationship of remediation androot growth is critical (Langley et al 2010 Wigand et al2014) to the development of management techniques relatedto remediation

CONCLUSION

Concerns are growing because of losses of coastal wetlandsalong the Gulf Coast (Kaplan et al 2010 CPRA 2012)Special attention should be given to our findings thatfreshwater release might reinvigorate the production offreshwater coastal vegetation Our study has worldwideimplications in that it demonstrates that sustained releases offreshwater can affect the primary production of many speciesFreshwater coastal species are increasingly affected bysaltwater intrusion so this idea deserves further explorationfor the management of coastal freshwater wetlands

ACKNOWLEDGEMENTS

This work is funded by the US Geological Survey andNational Science Foundation (DEB-1049838) Specialthanks are given to Evelyn Anemaet Mel McCulloughSamantha Primer Justin Stelly Lei Ting and GuodongWang for their field assistance Any use of trade productor firm names is for descriptive purposes only and does notimply endorsement by the US Government

CONFLICT OF INTEREST

The authors declare no conflict of interest with thisresearch

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

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Anemaet E Middleton BA 2013 Dendrometer bands made easy usingmodified cable ties to measure incremental growth of trees Applicationsin Plant Sciences 1 1300044

Anisfeld SC Benoit G 1997 Impacts of flow restriction on salt marshesan instance of acidification Environmental Science and Technology 311650ndash1699

Bianchi TS Cook RL Perdue EM Kolic PE Green N Zhang Y SmithRW Kolker AS Ameen A King G Ojwang LM Schneider CLNormand AE Hetland R 2011 Impacts of diverted freshwater ondissolved organic matter and microbial communities in Barataria BayLA Marine Environmental Research 72 248257

Brinson MM Bradshaw HD Holmes RN Elkins JB Jr 1980 Litterfallstemflow and throughfall nutrient fluxes in an alluvial swamp forestEcology 61 827ndash835

Cahoon DR Lynch JC Hensel P Boumans R Perez BC Segura B DayJW Jr 2002 A device for high precision measurement of wetlandsediment elevation I Recent improvements to the sedimentation-erosion table Journal of Sedimentary Research 72 730ndash733

Coastal Protection and Restoration Authority of Louisiana (CPRA) 2012Louisianarsquos Comprehensive Master Plan for a Sustainable CoastCPRA Baton Rouge LA

Coastal Protection and Restoration (CPRA) 2013 Modifications to theDavis Pond Diversion Louisiana Coastal Protection and RestorationBaton Rouge LA wwwlcagovProjects14Defaultaspx

Day JW 2000 Pattern and process of land loss in the Mississippi Delta aspatial and temporal analysis of wetland habitat change Estuaries 23425438

Day J Hunter R Keim RF DeLaune R Shaffer G Evers E Reed DBrantley C Kemp P Day J Hunter M 2012 Ecological response offorested wetlands with and without large-scale Mississippi River inputimplications for management Ecological Engineering 46 57 67

Dixon KR 1976 Analysis of seasonal leaf fall in north temperaturedeciduous forests Oikos 27 300306

Dokka RK 2006 Modern-day tectonic subsidence in coastal LouisianaGeology 34 281294

Greater NewOrleans Inc Regional Economic Alliance (GNO) 2010 A studyon the economic impact of the Deepwater Horizon oil spill GNORegionalEconomic Alliance New Orleans wwwuflibufledu docs Economic20Impact 20Study 20Part20I20-20Full20Reportpdf

Hertel D Leuschner C 2002 A comparison of four different fine rootproduction estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest Plant and Soil 239 237251

Hoeppner SS Schaffer GP Perkins TE 2008 Through droughts andhurricanes tree mortality forest structure and biomass production in acoastal swamp targeted for restoration in the Mississippi River DeltaicPlain Forest Ecology and Management 256 937948

Hughes FM Rood SB 2003 Allocation of river flows for restorationof floodplain forest ecosystems Environmental Management 321233

Harris RW 1992 Root-shoot ratios Journal of Arboriculture 18 39ndash42JMP SAS 2012 Statistical Analysis System v 1002 SAS Institute IncCary NC

Junk WJ Bayley PB Sparks RE 1989 The flood pulse concept in river-floodplain systems In Proceedings of the International Large RiverSymposium Vol 106 Canadian Special Publications in Fisheries andAquatic Science Ottawa Ontario Canada 110127

Kaplan D Muntildeoz-Carpena R Wan Y Hedgepeth M Zheng F Roberts RRossmanith R 2010 Linking river floodplain and vadose hydrology toimprove restoration of a coastal river affected by saltwater intrusionJournal of Environmental Quality 39 15701584

Kelly D 1994 The evolutionary ecology of mast seeding Trends inEcology and Evolution 9 465ndash470

Kingsford RT 2011 Conservation management of rivers and wetlandsunder climate change a synthesis Marine and Freshwater Research62 217222

Kozlowski TT 1997 Responses of woody plants to flooding and salinityTree Physiology 1 129

KraussKWDuberstein JADoyle TWConnerWHDayRH Inabinette LWWhitbeck JL 2009 Site condition structure and growth of baldcypressalong tidalnon-tidal salinity gradients Wetlands 29 505519

Ecohydrol 8 838ndash850 (2015)

TableILocations

ofstudysiteshydrologicalunitsC

RMSwater

recorders(w

ater

leveland

salin

ityL

ADNR2

013)S

olinstwater

recordersproductio

nsitesin

JLNHPamp

Pand

tree

grow

thsitesin

JLNHPamp

PBTNPandSMNWRBBWMA

Site

andyears

Location

Site

type

Hydrologicalunit

CRMSanddates

Solinstanddates

Sonde

0004264

anddates

Site

coordinates

Educatio

nCenterParking

(ECP)2007ndash2011

JLNHPamp

PLA

Production

andtree

grow

thECunit

CRMS0234-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

28August2012ndash

4September2012

29785N

90113W

Educatio

nCenterSpur

(ECS)2007ndash2011

JLNHPamp

PLA

Production

andtree

grow

thECunit

CRMS0234-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

na29786N

90114W

Educatio

nCenterCanal

(ECC)2007ndash2011

JLNHPamp

PLA

Production

ECunit

CRMS0234-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

na29787N

90115W

Palmetto

Trail

(PT)2007ndash2011

JLNHPamp

PLA

Production

PTunit

CRMS0188-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

na29791N

90122W

Palmetto

TrailVisito

rs(PTV)2007ndash2011

JLNHPamp

PLA

Production

PTunit

CRMS0188-H

01

1January2002ndash

31Decem

ber2011

Educatio

nCenter

13August2012ndash

27September2012

na29789N

90121W

LakeBayou

(LB)

2011ndash2

012

BTNPTX

Treegrow

thna

nana

na30150N

94096W

Low

erCypress

Tract

(LCT)2011ndash2012

BTNPTX

Treegrow

thna

nana

na30134N

94081W

BuckhornCreek

(BUC)2012

SMNWR

FL

Treegrow

thna

nana

na30030N

84470W

MandalayRoad

(MR)2012

BBWMA

FL

Treegrow

thna

nana

na30129N

83962W

CRMS0234

andCRMS0188

wereon

theECversus

PTsidesof

BaratariaBlvd(ECvs

PTunitsrespectively)S

edim

entelevatio

ntables

wereinserted

into

ECPandECSin

2007

andPTandPTVin

2011

Day-of-visitsalinity

porewatersalin

itysamples

weremeasuredthroughout

thestudyandmoreintensivelyin

2011ndash2012Surface

watersalin

ityattheCRMSrecordersweremeasuredfrom

thesameheight

below

thesoilor

water

columnas

thewater

sensorDavis

PondDiversion

dischargeandsalin

itydata

wereavailablefrom

1January2008ndash31Decem

ber2011

(USGS295501090190400)Alsosee

Figure1

CRMSCoastwideReference

Monito

ring

SystemJLNHPamp

PJean

Lafitte

NationalHistoricalParkamp

Preserve

BTNPBig

Thicket

NationalPreserve

LA

DNRLouisiana

Departm

entof

Natural

Resources

BBWMABig

BendWild

lifeManagem

entArea

SMNWRStMarks

NationalWild

lifeRefuge

841HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd Ecohydrol 8 838ndash850 (2015)

842 B A MIDDLETON D JOHNSON AND B J ROBERTS

weighed Annual sampling allowed many months for theregrowth of roots into the core (Vogt et al 1998 Herteland Leuschner 2002) Other root production approachescould not be used because of flooded seasons in networkswamps (water depth gt75 cm)Annual growth (incremental circumference increase) of

T distichum trees and knees was measured usingdendrometer bands (Anemaet and Middleton 2013) whichwere placed on the nearest tree and knee (one each) to markproduction plots (plot 1 3 and 5) along each transect in twosites (ECP and ECS) in JLNHP amp P in 2006 (n=3 per site)T distichum trees more than 20m from a large tree andemerged into the canopy were selected for bandingWe useda similar procedure to examine tree growth and salinityacross the US Gulf Coast except that we used five treesadjacent to all five production plots in each site in Texas andFlorida (Lake Bayou and Lower Cypress Tract vs BuckhornCreek and Mandalay Road respectively) (Table I andFigure 1b) in 2011 and 2012 respectively Note that thebands placed on trees in JLNHPampP in 2006were of an olderstyle and could not be measured until 2008 (Anemaet andMiddleton 2013) Tree bands were placed at ~15m heighton the tree above any fluting or buttressing Knee bands wereplaced ~6 cm from the tip of the knee

Water dynamics and salinity

Day-of-site visit measurements Within 1m of each plot asipper was used to extract soil pore water during each sitevisit (five samples per site) Water was transported in aportable freezer to the lab and the salinity measured with aYSI EC 300reg probe Water depth was measured adjacentto each plot marker with a metre stick

Water gauge analyses To study water dynamics over timewe analyzed patterns in daily mean and maximum values ofdischarge (m3 s1) and surface water salinity (ppt) fromthree recording gauges including the Davis Pond Diversion(US Geological Survey DCPBA03 2013) and CRMSrecorders (Table I CRMS 0234 and CRMS 0188 LA DNR2013) Water level and salinity patterns in 2010 (year ofhydrologic remediation) were compared with the average ofvarious groups of years in the available data set (2003ndash2011long-term) the average of comparably wet years (2008ndash2011 wet) and each individual year during 2006ndash2011 Allcomparisons were conducted for three periods within eachyear andor period pre- (days 1ndash119 1 Januaryndash30 April)during (days 120ndash244 1Mayndash1 September) and post- (days245ndash365 2 Septemberndash31 December)Water patterns were compared during the year of

hydrologic remediation (2010) with sets of long-termwet and individual years We used maximum daily valuesof both water level and surface salinity for these analysesbecause maximum values are more likely than mean values

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

to capture short-term changes in photosynthesis Note thatmean versus maximum daily values varied little from eachother [mean vs maximum difference plusmn standard error(SE) = 105plusmn 00018]To determine if short-term water level fluctuation within

plots generally followed those of CRMS gauges weinserted Solinst water level recorders (Levelogger Gold)within the ECP and PT sites in JLNHP amp P on 13 August2012 (~05ndash10 km apart within EC unit and PT unitrespectively Figure 1a and Table I) Daily mean andmaximum adjusted water levels and surface salinity levelsfrom CRMS gauges (publically available data) werecompared with those from Solinst water recorders andday-of-site visit measurements during periods of overlap (13Augustndash27 September 4 December 2012 Table I) Meanday-of-visit pore water salinity from sites were comparedwith those from CRMS gauges during 2011ndash2012Flood water was assumed to be connected by a

contiguous water sheet across units and consistent withinelevations corresponding to CRMS gauges Solinst waterrecorders sediment elevation table (SET) monumentsplots and the Sonde Following this idea hydrographswere constructed for each Solinst water logger SETmonument and plot stake by offsetting elevation of thewater sheet and matching water level fluctuations withthe continuous CRMS gauges within the hydrological unit(ie EC unit and PT unit gauge to SET offset +10 and50 cm respectively) Water levels were not adjusted to acommon datum Water depths were measured on days ofvisits at each plot stake and SET which here were used as asurface water-recording benchmark (Cahoon et al 2002)two SETs were placed within both ECP and ECS in 2006and PT and PTV in 2011 (eight total SETs) Absoluteelevations at SETs near ECPECS in 2007 were about0093m above sea level (Middleton and Jiang 2013)A water gauge was deployed less than 100m from ECP

to examine short-term pulses of water during HurricaneIsaac from 28 Augustndash4 September 2012 (Sonde0004264 USGS 2012 Figure 1b and Table I) All watermeasurement devices in units on both the EC side and PTside of Barataria Blvd detected the pulse signal fromHurricane Isaac (Table I) By comparing water recordsfrom these various sources it was determined that waterlevels measured with CRMS recorders within EC unit vsPT unit were relevant to those of production plots (Figure 1in the Supporting Information)

Climate analysis Monthly total precipitation (mm) andmean temperature (degC) were acquired from a weatherstation about 1 km away from the JLNHPampP study plots[Marrero 9 SSW Station LA 297853degN 901158degW] anddata from 2002 to 2012 were compared with those of 2010during pre-remediation during remediation and post-remediation periods (NOAA 2013)]

Ecohydrol 8 838ndash850 (2015)

843HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

DATA ANALYSIS

Vegetation production

Annual total litterfall (leaf and wood) was calculated frompeak litterfall estimates by determining the percentage ofannual litterfall collected during the main season (mean of20072011 correction factor = 0718plusmn0176 SE) so thatbiomass captured during the main season of each year wasdivided by 07180 to express yearly production Thiscorrection factor better portrayed annual total litterfallbased on peak litterfall while fully recognizing that certainswamp species do not lose their leaves during this period(eg Myrica cerifera) Most deciduous trees shed all oftheir leaves within 30ndash60 days (Dixon 1976) fromSeptember through mid-November (Tdistichum swampNorth Carolina Brinson et al 1980) or into Decemberfarther southward (eg South Carolina mixed bottomlandforest Shure and Gottschalk 1985)

Litterfall totals by year species and tissue type (leafreproductive and wood) from 2007 to 2011 were analyzedusing repeated measures analysis nesting plot within yearin analysis of variance (ANOVA) (one-way or two-wayANOVA JMP SAS 2012) For annual log root produc-tion ANOVA was used by nesting plot (depth year) Rootproduction by year did not interact with depth (year times depthinteraction pgt005) so that total root production wasanalyzed by year The lower two root depths (10ndash20 and20ndash30 cm) did not differ (t=097 p=033) so that a meanof these two depths was calculated (10ndash30 cm) andcompared with the upper depth (0ndash10 cm) In all ANOVAanalyses the highest-order significant interaction or maineffect was tested using one degree-of-freedom contrasts inJMP SAS (2012) Data were appropriately transformed tomeet assumptions of ANOVA and multiple comparisonsadjusted using Bonferroni corrections (two one-degree-of-freedom contrasts or three one degree-of-freedomcontrasts p=0025 or 00167 respectively)

Tree and knee growth were analyzed by comparingmeans of growth (circumference ratios ie yearrsquos circum-ference divided by previous yearrsquos circumference) for2008ndash2011 For the Gulf Coast-wide assessment of treegrowth and salinity regression analysis compared means oftree growth (circumference ratios) in LA TX and FL(2011ndash2012) versus annual mean salinity Annual meansalinity was based on the mean of day-of-visit measure-ments from 2011 to 2012 (7 to 14 measurements with allseasons represented)

Climate

We used ANOVA to compare monthly total precipitationand mean temperature by year and remediation periodusing the main effects and interactions of year andremediation period

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Water environment and remediation

Water and salinity level shifts and remediation Todetermine if the water dynamics differed from expectedconditions we compared mean and maximum values ofdaily levels of water and surface salinity during times ofinterest Because short periods of high salinity or anoxiawere likely to affect tree production and growth we focusedon daily maximum water level for these analyses Watercomparisons were made of three time periods in 2010 (pre-remediation during and post-remediation) with the sameperiods in other years in three ways wet years (mean of2008ndash2011) long-term (mean of 2003ndash2011) and individualyears (2006ndash2011) These comparisons were made usingautoregressive integrated moving average (ARIMA) models(detailed description provided in Table 1 in the SupportingInformation) generated in SAS Institute Inc (2002) whichare appropriate for comparing water and salinity levels shiftsover time because these models can predict the shape of thefunction and account for the autocorrelation of the samplesover time better than other statistical approaches (SASInstitute Inc 2002) A nonparametric sign test comparednumber of times the 2010 series had more water or salinitythan the average of the comparison series and vice versa

Predicted daily threshold values of salinity in productionplots To determine the number of days that productionsites exceeded threshold values of various salinity levelsthe following procedure was followed Using linearregression mean daily surface water salinity from CRMSgauges in the EC and PT units on specific days wereplotted against mean pore water salinity on day-of-visit inproduction plots and SET monuments in 2011ndash2012(Table I) Equations generated from this process were usedto predict daily mean salinity levels in sites from 2008 to2011 (for equations see Figure 2 caption in the SupportingInformation) as well as the percentage of growing seasondays (1 Aprilndash31 October) each year above certain salinitylevels (ie 01 03 07 10 15 and 20 ppt)

RESULTS

Production and vegetation responses to hydrologicremediation

Total litter biomass was 27 times higher after hydrologicremediation in 2010 and 2011 than before remediation in2007ndash2009 (Figure 2a Table IIa one degree-of-freedomcontrast t=838 plt 00001) In litterfall Tdistichum leafbiomass was 31 and 25 times higher in 2010 andor 2011respectively than in 2007ndash2009 (Table IIa) while repro-ductive biomass was 77 times in 2011 but not different in2010 (Table IIa and Table III) In addition leaf andreproductive tissue biomass in litterfall was higher in 2010

Ecohydrol 8 838ndash850 (2015)

Figure 2 Total annual mean production from 2007 to 2011 including (a)total litter biomass (leaf reproductive and wood) [g m2 y1 plusmn standarderror (SE)] and (b) total annual root biomass (total of all depths 0ndash30 cmg m2 y1 plusmn SE) in Jean Lafitte National Historical Park amp Preserve(n = 25) Different letters indicated that means of years differed statistically(one degree-of-freedom contrasts plt 005) (c) Regression analysis ofstem growth expressed as mean salinity (ppt) versus Taxodium distichumcircumference ratio plusmn SE along the Gulf Coast (R2 = 086) Salinity isbased on means of pore water salinity during day-of-visit measurements

844 B A MIDDLETON D JOHNSON AND B J ROBERTS

andor 2011 than in 2007ndash2009 for Acer rubrum (not in2007) Liquidambar styraciflua and M cerifera (Table IIaand Table III) Annual litterfall biomass of wood tissue didnot change from 2007 to 2011 although the mean wassubstantially higher in 2010 (Table IIb plt 005) Annuallog root biomass was higher in shallower than deeper soildepths (Figure 2b and Table IIb 0ndash10 vs 10ndash30 cmt=279 p=00058 N=5) and total root biomass variedby year and was 23ndash53 times lower in 2010 than in 2007ndash2011 (Figure 2b t=489 plt 00001 N=5)Neither tree nor knee growth varied with circumference

increasing by 18 plusmn 01 and 29 plusmn 10 respectively peryear during 2008ndash2011 in JLNHP amp P (pgt005Table IIcndashd) In JLNHP amp P we found no relationship

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

between tree growth and the percentage days per year a siteexceeded published thresholds of salinity (eg 07 or20 ppt pgt005 Table IV) In 2010 both EC and PT unitshad fewer days with salinity gt03 ppt and in 2008 moredays with salinity gt20 ppt (Table IV Figure 1 in theSupporting Information) Across the Gulf Coast Tdistichum growth varied from 011 to 21 increase incircumference per year with average annual salinityexplaining 86 of the variance in growth with the highestgrowth observed in the lowest mean pore water salinity(eg JLNHP amp P Figure 2c)

Climate and environment

Regionally mean annual precipitation was 13209plusmn1065mm per year from 2002 to 2012 (National Oceanicand Atmospheric Administration (NOAA) 2013) but didnot vary by year or remediation period (pgt 0130 Table V)Mean monthly air temperature did not vary by year but didvary by remediation period (mean monthly temperaturesduring pre-remediation remediation and post-remediation157 plusmn 06 degC 269 plusmn03 degC and 187 plusmn 08 degC respectivelyF=817 plt0001 Table V) (NOAA 2013)

Water and salinity responses to hydrologic remediation

Short-term water and salinity comparisons ndash 2010 versuswet years (2008ndash2011) Davis Pond CRMS 0188 andCRMS 0234 had higher dischargewater level and lowersalinity during the remediation period in 2010 than duringwet years As based on ARIMA time series comparisonswater discharged from Davis Pond in 2010 exceeded meanand maximum daily discharge of wet years (mean dailydischarge of 2010 vs wet years 113 out of 119 daysrespectively maximum daily discharge of 2010 vs wetyears 102 out of 119 days respectively sign testsplt 00001 Figure 3a and Table 2 in the SupportingInformation) Discharge rates from the Davis PondFreshwater Diversion and water levels at gauges werelower in 2010 during the post-remediation period than inwet years (Figure 3a and Table 2 in the SupportingInformation) Maximum daily gauge levels were higherduring hydrologic remediation in 2010 than in wet years(CRMS 0234 026 vs 011m respectively Figure 3bCRMS 0188 115 vs 106m respectively Figure 3c andTable 2 in the Supporting Information)Long-term gauging stations can be used to indicate

conditions at sites even though salinity relationships weresomewhat different (ie EC sites had significantly highersalinity than CRMS 0234 and PT sites had significantlylower salinity than CRMS 0188 as based on day-of-visitmeasurements) Salinity environments in the EC and PTsites were relatively similar (Figure 2 in the SupportingInformation) Nevertheless maximum daily water levels atCRMS 0234 were linearly related to day-of-visit water

Ecohydrol 8 838ndash850 (2015)

Table II Analysis of variances of production variables in JLNHP amp P from 2007 to 2011

DF F p Mean plusmn SE

(a) Total annual productionLitterfall (gm2 y1)Year 4 236 lt00001

Root biomass (gm2 y1)Year 4 84 lt00001 Depth 1 78 00225

Year times depth 4 10 04142 ns(b) Tissue typeLeafSpecies 15 155 lt00001 Year 4 1566 lt00001 Species times year 60 41 lt00001

ReproductiveSpecies 5 400 lt00001 Year 4 69 lt00001 Species times year 20 44 lt00001

WoodYear 4 21 00794 ns

(c) Tree growth (annual circumference ratio)Initial tree circumference (covariate) 1 38 00668 nsYear 3 01 09718 ns2008 1019210 plusmn 000552009 1018628 plusmn 000712010 1018855 plusmn 000382011 1015170 plusmn 00022

(d) Knee growth (annual circumference ratio)Initial knee circumference (covariate) 1 05 04945 nsYear 4 09 04628 ns

Mean total annual production of (a) litterfall (g m2 y1 including leaves reproductive material and wood) and log root biomass (g m3 y1) (b) Meanbiomass of tissue types of dominant species including leaf reproductive and wood Dendrometer bands were used to measure incremental increase incircumference growth was estimated as a year-to-year ratio of circumference change of Taxodium distichum from 2008 to 2011 for (c) trees and (d)knees Mean comparisons that differed based on contrasts indicated by lsquorsquo lsquorsquo or ns (plt 00001 plt 005 pgt 005 respectively Figure 2) SeeTable III for tissue type times species interactionsJLNHP amp P Jean Lafitte National Historical Park amp Preserve SE standard error DF degrees of freedom ns not significant

845HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

depths at SETs in the EC unit (ie SETs at ECP and ECSFigure 2 in the Supporting Information r= 06043p=00015) As indicated in the Section on Methods tojustify the selection of salinity variables and analysesoverall maximum daily values were within 105plusmn 00018of mean values Mean daily salinity levels at CRMS 0234and CRMS 0188 were linearly related to day-of-visitsalinity at SETs and plots within the same hydrologicalunits (EC unit r=0600 p=00004 Figure 2b in theSupporting Information PT unit r=0702 p=00005Figure 2c in the Supporting Information)

Long-term water level comparisons ndash 2010 versus long-term (2003ndash2011) Water discharge from Davis Pond in2010 during hydrologic remediation was higher than in thelong-term set of years (2003ndash2011 mean discharge perday =1983 plusmn 49 vs 331 plusmn 16m3 s1 respectively) andmaximum daily water levels at CRMS 0234 and CRMS0188 also were higher (sign tests plt00001 Figure 4 inthe Supporting Information)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Individual year water and salinity level comparisons ndash2010 vs 2006ndash2011 Comparisons of maximum dailywater level and salinity levels during 2010 to individualyears were similar to the comparisons of 2010 to sets ofwet and long-term years (ie 2008ndash2011 and 2003ndash2011respectively) As expected discharge levels for Davis Pondand water levels at CRMS 0234 and CRMS 0188 weresignificantly higher during hydrologic remediation in 2010compared with those in any individual year from 2006 to2011 (plt00001) One exception was that maximumsalinity was higher in 2010 than in 2009 at CRMS 0234(plt 00001)

DISCUSSION

Freshwater flow variability controls ecological processes inestuaries so that alteration of water delivery is a keyconservation challenge (Lester et al 2013) Unfortunatelyinformation on how to manage salinity flux in freshwaterwetlands in altered estuaries is lacking (Kaplan et al 2010

Ecohydrol 8 838ndash850 (2015)

Table III Means plusmn SE listed by species dominance of dry litterfall biomass (gm2) based on species times year interactions for leafreproductive and wood tissue from 2007 to 2011 in JLNHP amp P

Species

Year

2007 2008 2009 2010 2011

Leaf tissueTaxodium distichum 264 plusmn 48 b 150 plusmn 25 c 291 plusmn 48 b 723plusmn 91 a 590plusmn 112 a

Acer rubrum 239 plusmn 53 ab 123 plusmn 26 b 184 plusmn 435 b 249plusmn 45 a 258plusmn 47 a

Fraxinus pennsylvanica 65 plusmn 21 b 28 plusmn 09 c 117 plusmn 29 a 136 plusmn 38 a 34 plusmn 22 c

Liquidambar styraciflua 47 plusmn 14 b 23 plusmn 06 b 45 plusmn 17 b 69plusmn 14 a 49 plusmn 16 b

Nyssa aquatica 80 plusmn 26 a 09 plusmn 08 b 14 plusmn 12 b 19 plusmn 11 b 00 plusmn 00 b

Myrica cerifera 00 plusmn 00 c 18 plusmn 07 b 23 plusmn 07 b 41plusmn 12 a 21 plusmn 07 b

Salix nigra 22 plusmn 11 a 13 plusmn 09 a 02 plusmn 01 a 39 plusmn 35 a 17 plusmn 16 a

Ulmus americana 10 plusmn 06 a 01 plusmn 01 b 04 plusmn 02 b 14 plusmn 08 a 21 plusmn 09 a

Quercus nigra 07 plusmn 02 a 01 plusmnlt01 a 08 plusmn 03 a 16 plusmn 06 a 09 plusmn 05 a

Other leaf 12 plusmn 04 c 18 plusmn 07 c 26 plusmn 07 b 45 plusmn 15 b 144 plusmn 32 a

Cephalanthus occidentalis 23 plusmn 09 a 00 plusmn 00 b 01 plusmn 01 b lt01 plusmnlt01 b 00 plusmn 00 b

Acer spp 22 plusmn 18 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a

Carya aquatica 00 plusmn 00 a 18 plusmn 09 a 02 plusmn 02 a 00 plusmn 00 a 00 plusmn 00 a

Quercus spp (red) 05 plusmn 04 a 03 plusmn 02 a 02 plusmn 01 a 04 plusmn 02 a 00 plusmn 00 a

Triadica sebifera 00 plusmn 00 a 02 plusmn 01 a 01 plusmnlt01 a 09 plusmn 06 a 06 plusmn 03 a

Gleditsia aquatica 14 plusmn 06 a 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b

Reproductive tissueTaxodium distichum 65 plusmn 30 b 06 plusmn 04 c 55 plusmn 31 b 57 plusmn 18 b 325plusmn 139 a

Other reproductive lt01 plusmnlt01 b lt01 plusmnlt01 b 02 plusmn 01 b 02 plusmn 01 b 44plusmn 24 a

Fraxinus pennsylvanica 05 plusmn 01 b 04 plusmn 01 b 03 plusmn 01 b 25plusmn 07 a 01 plusmn 01 b

Liquidambar styraciflua 09 plusmn 09 a 00 plusmn 00 a lt01 plusmnlt01 a 05 plusmn 05 a 00 plusmn 00 a

Nyssa aquatica 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 04 plusmn 04 a 00 plusmn 00 a

Wood tissueWood total all species 22 plusmn 05 a 28 plusmn 12 a 50 plusmn 21 a 129 plusmn 54 a 92 plusmn 43 a

Different letters indicate significant differences of litterfall biomass of species based on one-degree-of-freedom contrasts Dominant species are listedwith biomass gt02 g m2 with the biomass of non-dominant species summed in an lsquootherrsquo group Species with significantly higher litterfall in 2010 andor 2011 after Bonferroni correction are listed in bold lettersSE standard error

846 B A MIDDLETON D JOHNSON AND B J ROBERTS

Kingsford 2011) Out of necessity programmes to manageflood flow are emerging in the United States AustraliaSouth Africa and to a lesser extent Europe (Hughes andRood 2003) As an example the Comprehensive MasterPlan for Louisiana has proposed to use diversions torelease river water and sediment to rebuild coastalwetlands (CPRA 2012) While managed flood releasesare used increasingly in restoration (Middleton 1999Schmidt et al 2001 Souter et al 2014) theseapproaches may become even more important as salinityincreases with changes in climate sea level subsidenceand surfacegroundwater levels (Poff et al 2002 Kaplanet al 2010 Souter et al 2014) Studies such as ours caninform management procedures to explore the utility offreshwater release for coastal conservationVarious studies demonstrate the potential benefits of short

periods of increased freshwater flow to hydrologically alteredcoastal forests While hydrologic remediation lasted only 2 to4months in this study and the Souter et al 2014 study treeresponses were impressive After freshwater remediation inJLNHP amp P high levels of above-ground litter productionpersisted for several species for one or more growing season

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

(this study) Similarly healthy trees of Eucalyptuscamaldulensis Dehnh in the Murray River drainage (Austra-lia) vigorously grew more foliage while highly stressed ordefoliated trees responded positively but less vigorously fortwo growing seasons following ~2months of freshwaterrelease (Souter et al 2014) In the Lake Pontchartrain Basin ofLouisiana coastal Tdistichum trees grew two times fasterwith periodicflowof riverwater (Day et al 2012) In additionreproductive output was higher in 2010 and especially in 2011for certain tree species suggesting that resourcematchingmayhave occurred ie species varied reproductive output tomatchavailable resources (Kelly 1994) In the context of this studythe hydrologic remediation may have allowed these trees tobuild up their physiological resources via higher levels ofphotosynthetic activity prior to mass floweringEnvironmental flow prescriptions might revive moribund

coastal swamps yet no definitive range of flow amount ortiming has been identified to improve environments related tosalinity anoxia nutrients or other factors We linked sharplyhigher production of litter (leaf and reproductive) in 2010 tohydrologic remediation in salinity levels well below 20pptwith maximummeasured values at plots of EC vs PT sites 04

Ecohydrol 8 838ndash850 (2015)

Table V Analysis of variances of climate variables for JLNHP ampP from Marrero 9 SSW weather station data (NOAA 2013) foryears 2002ndash2012 remediation periods relative to the hydrologicremediation period in 2010 (pre-remediation remediation andpost-remediation) including mean monthly (a) total precipitation

and (b) temperature

Variable DF F p

(a) PrecipitationYear 10 12 03339Remediation period 2 21 01297Year times remediation period 20 11 04077

(b) TemperatureYear 10 01 09989Remediation period 2 817 lt00001 Year times remediation period 20 02 09999

DF degrees of freedom

Table IV Percentage of days exceeding predicted values for maximum and mean daily salinity levels (ppt) in the EC and PT unitsin JLNHP amp P (sites ECSECPECC vs PTPTV respectively)

Percent () days per year exceeding the specified maximum or minimum values of salinity (eg gt01 to 20 ppt) were predicted from linear regressionanalysis of surface salinity levels at CRMS 0234 and CRMS 0188 gauges (EC and PT units respectively) versus day-of-visit pore water salinity atproduction sites including ECSECPECC and PTPTV (Figure 4) Total days are the number of days per year during the growing season (1 Aprilndash31October 2008ndash2011) Published threshold salinity levels for forest tree maintenanceflooded seedling photosynthesis and basal area growth (size) arethought to be 20 and 07 ppt (in bold letters Kaplan et al 2010Pezeshki et al 1987 and Krauss et al 2009 respectively) Dark to light grey highlightsindicate percent () days per year exceeding maximum values as 70ndash100 30ndash70 1ndash30 and 0 respectivelyECS Education Center Spur ECP Education Center Parking ECC Education Center Canal PT Palmetto Trail PTV Palmetto Trail Visitors ECEducation Center JLNHP amp P Jean Lafitte National Historical Park amp Preserve

847HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

and 05ppt respectively (also see Figure 2a and Table IV) Incontrast to 2008 predicted levels of salinity were high in boththe EC and PT units (Table IV) and total annual leaf litterbiomass by individual species was low (A rubrum Tdistichum Fraxinuspennsylvanicum Mcerifera and Salixnigra Figure 2a and Table III) Nevertheless rendering asimple statement of an ideal threshold of salinity for theseswamps is impractical Among other problems field environ-ments are difficult to characterize simply (eg salinity levelsvary by depth in the vadose zone)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Trees in JLNHP amp P responded positively to remedia-tion but we recognize that this unplanned study did notpermit us to determine whether changes in salinity or someother unmeasured biogeochemical factors were ultimatelyresponsible for the observed responses Tidal flowreconnection in previously restricted salt marshes decreasessoil anoxia and sulphides and changes pH nutrientavailability and decomposition rates (Anisfeld and Benoit1997) The fact that we detected increased water levels anddecreased salinity with freshwater remediation indicatedthat other important site characteristics and biogeochemicalshifts likely were occurring at JLNHP amp P Unfortunatelywe do not have any other supportive data especially asrelated to any possible causal linkagesPhotosynthetic stressors such as salinity and anoxiamay be

more harmful during the growing season Flooding reducesregeneration seedlings and saplings of Tdistichum surviveovertopping by flooding while dormant but not during thegrowing season and most tree species will not germinateunderwater (Middleton 2000) A better understanding of anyseasonal component of remediation response is critical tohydrologic remediation planning for managementThe immediate mechanisms of increased tree production

with improved environment are not well studied but maybe related to the photosynthetic regulation of trees tochanges in environment As salinity (at some level) entersthe transpiration stream stomata close and photosynthesisdecreases (Stiller 2009) Any short-term increase in

Ecohydrol 8 838ndash850 (2015)

Figure 3 State of Louisiana water recorder information for maximum (a) daily discharge (m3 s1) from Davis Pond Diversion and adjusted water levels(m) at (b) Coastwide Reference Monitoring System (CRMS) 0234 and (c) CRMS 0188 and salinity (ppt) of (d) discharge of diversion and surface waterat (e) CRMS 00234 and (f) CRMS 0188 during hydrologically remediated (2010) versus lsquowetrsquo years (mean of 2008 2009 and 2011) CRMS 0234 andCRMS 0188 are in the same hydrological units as the Education Center and Palmetto Trail plots respectively in JLNHP amp P Pre-remediationremediation and post-remediation days of the year included days 1ndash119 120ndash244 and 245ndash365 respectively Sign tests indicated that 2010 was higherlower or not different from wet years as lsquo+rsquo lsquo-rsquo or lsquonsrsquo respectively (plt 00001) Only significant variables of time were kept p values for the sign testcomparisons were based on normally distributed error with constant variance All tests of fit were performed at p = 005 except that one test wasperformed at p = 001 to obtain a model fit Equations were based on the difference of the two year groups (2010 vs set of years compared) Mean dailydischarge values are not shown but these comparisons were also significant using similarly constructed ARIMA models and sign tests (plt 00001)Note that short periods of missing data were interpolated linearly Longer periods of missing data were omitted eg Davis Pond Diversion had nodischarge data available for 1ndash28 January 2010 Note that the measured water and salinity levels at plots in the EC and PT units were intermediate and

similar to each other (see Supplementary Figure 2)

848 B A MIDDLETON D JOHNSON AND B J ROBERTS

photosynthetic output and leaf production after freshwaterremediation is most likely to occur in healthy trees withrelatively intact leaf architecture such as Tdistichum in

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

JLNHP amp P or E camaldulensis trees along the MurrayRiver in Australia (Souter et al 2014) The positive effectsof remediation may have broad application in freshwater

Ecohydrol 8 838ndash850 (2015)

849HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

forests particularly because several species respondedpositively to freshwater remediation in JLNHP amp P

In our study litter but not root production increased duringthe year of hydrologic remediation If environment conditionsimproved in 2010 trees may have been experiencing a fastspurt of leaf litter production at the expense of roots(Figure 2b) Falling rootshoot ratios are an indicator of fastshoot growth in response to favourable environments (Harris1992 Litton et al 2007) and Tdistichum root and shootallocation patterns shift in response to changing resources(Megonigal and Day 1992) Note that we did not distinguishbetween species of roots in our study Alterations in root andshoot allocations following hydrologic remediationmay haveimportant implications for the elevation of subsiding swampsby influencing peat accumulation The decrease in rootgrowth during remediation is important because root tissuesoften contribute more to the accumulation of peat than leaf orwoody tissue (Middleton and McKee 2002) Whilereinvigorating the production of freshwater coastal vegetationoverall hydrologic remediation may reduce root growth forsome tree species at least temporarily (this study) Thereforea better understanding of the relationship of remediation androot growth is critical (Langley et al 2010 Wigand et al2014) to the development of management techniques relatedto remediation

CONCLUSION

Concerns are growing because of losses of coastal wetlandsalong the Gulf Coast (Kaplan et al 2010 CPRA 2012)Special attention should be given to our findings thatfreshwater release might reinvigorate the production offreshwater coastal vegetation Our study has worldwideimplications in that it demonstrates that sustained releases offreshwater can affect the primary production of many speciesFreshwater coastal species are increasingly affected bysaltwater intrusion so this idea deserves further explorationfor the management of coastal freshwater wetlands

ACKNOWLEDGEMENTS

This work is funded by the US Geological Survey andNational Science Foundation (DEB-1049838) Specialthanks are given to Evelyn Anemaet Mel McCulloughSamantha Primer Justin Stelly Lei Ting and GuodongWang for their field assistance Any use of trade productor firm names is for descriptive purposes only and does notimply endorsement by the US Government

CONFLICT OF INTEREST

The authors declare no conflict of interest with thisresearch

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

REFERENCES

Anemaet E Middleton BA 2013 Dendrometer bands made easy usingmodified cable ties to measure incremental growth of trees Applicationsin Plant Sciences 1 1300044

Anisfeld SC Benoit G 1997 Impacts of flow restriction on salt marshesan instance of acidification Environmental Science and Technology 311650ndash1699

Bianchi TS Cook RL Perdue EM Kolic PE Green N Zhang Y SmithRW Kolker AS Ameen A King G Ojwang LM Schneider CLNormand AE Hetland R 2011 Impacts of diverted freshwater ondissolved organic matter and microbial communities in Barataria BayLA Marine Environmental Research 72 248257

Brinson MM Bradshaw HD Holmes RN Elkins JB Jr 1980 Litterfallstemflow and throughfall nutrient fluxes in an alluvial swamp forestEcology 61 827ndash835

Cahoon DR Lynch JC Hensel P Boumans R Perez BC Segura B DayJW Jr 2002 A device for high precision measurement of wetlandsediment elevation I Recent improvements to the sedimentation-erosion table Journal of Sedimentary Research 72 730ndash733

Coastal Protection and Restoration Authority of Louisiana (CPRA) 2012Louisianarsquos Comprehensive Master Plan for a Sustainable CoastCPRA Baton Rouge LA

Coastal Protection and Restoration (CPRA) 2013 Modifications to theDavis Pond Diversion Louisiana Coastal Protection and RestorationBaton Rouge LA wwwlcagovProjects14Defaultaspx

Day JW 2000 Pattern and process of land loss in the Mississippi Delta aspatial and temporal analysis of wetland habitat change Estuaries 23425438

Day J Hunter R Keim RF DeLaune R Shaffer G Evers E Reed DBrantley C Kemp P Day J Hunter M 2012 Ecological response offorested wetlands with and without large-scale Mississippi River inputimplications for management Ecological Engineering 46 57 67

Dixon KR 1976 Analysis of seasonal leaf fall in north temperaturedeciduous forests Oikos 27 300306

Dokka RK 2006 Modern-day tectonic subsidence in coastal LouisianaGeology 34 281294

Greater NewOrleans Inc Regional Economic Alliance (GNO) 2010 A studyon the economic impact of the Deepwater Horizon oil spill GNORegionalEconomic Alliance New Orleans wwwuflibufledu docs Economic20Impact 20Study 20Part20I20-20Full20Reportpdf

Hertel D Leuschner C 2002 A comparison of four different fine rootproduction estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest Plant and Soil 239 237251

Hoeppner SS Schaffer GP Perkins TE 2008 Through droughts andhurricanes tree mortality forest structure and biomass production in acoastal swamp targeted for restoration in the Mississippi River DeltaicPlain Forest Ecology and Management 256 937948

Hughes FM Rood SB 2003 Allocation of river flows for restorationof floodplain forest ecosystems Environmental Management 321233

Harris RW 1992 Root-shoot ratios Journal of Arboriculture 18 39ndash42JMP SAS 2012 Statistical Analysis System v 1002 SAS Institute IncCary NC

Junk WJ Bayley PB Sparks RE 1989 The flood pulse concept in river-floodplain systems In Proceedings of the International Large RiverSymposium Vol 106 Canadian Special Publications in Fisheries andAquatic Science Ottawa Ontario Canada 110127

Kaplan D Muntildeoz-Carpena R Wan Y Hedgepeth M Zheng F Roberts RRossmanith R 2010 Linking river floodplain and vadose hydrology toimprove restoration of a coastal river affected by saltwater intrusionJournal of Environmental Quality 39 15701584

Kelly D 1994 The evolutionary ecology of mast seeding Trends inEcology and Evolution 9 465ndash470

Kingsford RT 2011 Conservation management of rivers and wetlandsunder climate change a synthesis Marine and Freshwater Research62 217222

Kozlowski TT 1997 Responses of woody plants to flooding and salinityTree Physiology 1 129

KraussKWDuberstein JADoyle TWConnerWHDayRH Inabinette LWWhitbeck JL 2009 Site condition structure and growth of baldcypressalong tidalnon-tidal salinity gradients Wetlands 29 505519

Ecohydrol 8 838ndash850 (2015)

842 B A MIDDLETON D JOHNSON AND B J ROBERTS

weighed Annual sampling allowed many months for theregrowth of roots into the core (Vogt et al 1998 Herteland Leuschner 2002) Other root production approachescould not be used because of flooded seasons in networkswamps (water depth gt75 cm)Annual growth (incremental circumference increase) of

T distichum trees and knees was measured usingdendrometer bands (Anemaet and Middleton 2013) whichwere placed on the nearest tree and knee (one each) to markproduction plots (plot 1 3 and 5) along each transect in twosites (ECP and ECS) in JLNHP amp P in 2006 (n=3 per site)T distichum trees more than 20m from a large tree andemerged into the canopy were selected for bandingWe useda similar procedure to examine tree growth and salinityacross the US Gulf Coast except that we used five treesadjacent to all five production plots in each site in Texas andFlorida (Lake Bayou and Lower Cypress Tract vs BuckhornCreek and Mandalay Road respectively) (Table I andFigure 1b) in 2011 and 2012 respectively Note that thebands placed on trees in JLNHPampP in 2006were of an olderstyle and could not be measured until 2008 (Anemaet andMiddleton 2013) Tree bands were placed at ~15m heighton the tree above any fluting or buttressing Knee bands wereplaced ~6 cm from the tip of the knee

Water dynamics and salinity

Day-of-site visit measurements Within 1m of each plot asipper was used to extract soil pore water during each sitevisit (five samples per site) Water was transported in aportable freezer to the lab and the salinity measured with aYSI EC 300reg probe Water depth was measured adjacentto each plot marker with a metre stick

Water gauge analyses To study water dynamics over timewe analyzed patterns in daily mean and maximum values ofdischarge (m3 s1) and surface water salinity (ppt) fromthree recording gauges including the Davis Pond Diversion(US Geological Survey DCPBA03 2013) and CRMSrecorders (Table I CRMS 0234 and CRMS 0188 LA DNR2013) Water level and salinity patterns in 2010 (year ofhydrologic remediation) were compared with the average ofvarious groups of years in the available data set (2003ndash2011long-term) the average of comparably wet years (2008ndash2011 wet) and each individual year during 2006ndash2011 Allcomparisons were conducted for three periods within eachyear andor period pre- (days 1ndash119 1 Januaryndash30 April)during (days 120ndash244 1Mayndash1 September) and post- (days245ndash365 2 Septemberndash31 December)Water patterns were compared during the year of

hydrologic remediation (2010) with sets of long-termwet and individual years We used maximum daily valuesof both water level and surface salinity for these analysesbecause maximum values are more likely than mean values

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

to capture short-term changes in photosynthesis Note thatmean versus maximum daily values varied little from eachother [mean vs maximum difference plusmn standard error(SE) = 105plusmn 00018]To determine if short-term water level fluctuation within

plots generally followed those of CRMS gauges weinserted Solinst water level recorders (Levelogger Gold)within the ECP and PT sites in JLNHP amp P on 13 August2012 (~05ndash10 km apart within EC unit and PT unitrespectively Figure 1a and Table I) Daily mean andmaximum adjusted water levels and surface salinity levelsfrom CRMS gauges (publically available data) werecompared with those from Solinst water recorders andday-of-site visit measurements during periods of overlap (13Augustndash27 September 4 December 2012 Table I) Meanday-of-visit pore water salinity from sites were comparedwith those from CRMS gauges during 2011ndash2012Flood water was assumed to be connected by a

contiguous water sheet across units and consistent withinelevations corresponding to CRMS gauges Solinst waterrecorders sediment elevation table (SET) monumentsplots and the Sonde Following this idea hydrographswere constructed for each Solinst water logger SETmonument and plot stake by offsetting elevation of thewater sheet and matching water level fluctuations withthe continuous CRMS gauges within the hydrological unit(ie EC unit and PT unit gauge to SET offset +10 and50 cm respectively) Water levels were not adjusted to acommon datum Water depths were measured on days ofvisits at each plot stake and SET which here were used as asurface water-recording benchmark (Cahoon et al 2002)two SETs were placed within both ECP and ECS in 2006and PT and PTV in 2011 (eight total SETs) Absoluteelevations at SETs near ECPECS in 2007 were about0093m above sea level (Middleton and Jiang 2013)A water gauge was deployed less than 100m from ECP

to examine short-term pulses of water during HurricaneIsaac from 28 Augustndash4 September 2012 (Sonde0004264 USGS 2012 Figure 1b and Table I) All watermeasurement devices in units on both the EC side and PTside of Barataria Blvd detected the pulse signal fromHurricane Isaac (Table I) By comparing water recordsfrom these various sources it was determined that waterlevels measured with CRMS recorders within EC unit vsPT unit were relevant to those of production plots (Figure 1in the Supporting Information)

Climate analysis Monthly total precipitation (mm) andmean temperature (degC) were acquired from a weatherstation about 1 km away from the JLNHPampP study plots[Marrero 9 SSW Station LA 297853degN 901158degW] anddata from 2002 to 2012 were compared with those of 2010during pre-remediation during remediation and post-remediation periods (NOAA 2013)]

Ecohydrol 8 838ndash850 (2015)

843HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

DATA ANALYSIS

Vegetation production

Annual total litterfall (leaf and wood) was calculated frompeak litterfall estimates by determining the percentage ofannual litterfall collected during the main season (mean of20072011 correction factor = 0718plusmn0176 SE) so thatbiomass captured during the main season of each year wasdivided by 07180 to express yearly production Thiscorrection factor better portrayed annual total litterfallbased on peak litterfall while fully recognizing that certainswamp species do not lose their leaves during this period(eg Myrica cerifera) Most deciduous trees shed all oftheir leaves within 30ndash60 days (Dixon 1976) fromSeptember through mid-November (Tdistichum swampNorth Carolina Brinson et al 1980) or into Decemberfarther southward (eg South Carolina mixed bottomlandforest Shure and Gottschalk 1985)

Litterfall totals by year species and tissue type (leafreproductive and wood) from 2007 to 2011 were analyzedusing repeated measures analysis nesting plot within yearin analysis of variance (ANOVA) (one-way or two-wayANOVA JMP SAS 2012) For annual log root produc-tion ANOVA was used by nesting plot (depth year) Rootproduction by year did not interact with depth (year times depthinteraction pgt005) so that total root production wasanalyzed by year The lower two root depths (10ndash20 and20ndash30 cm) did not differ (t=097 p=033) so that a meanof these two depths was calculated (10ndash30 cm) andcompared with the upper depth (0ndash10 cm) In all ANOVAanalyses the highest-order significant interaction or maineffect was tested using one degree-of-freedom contrasts inJMP SAS (2012) Data were appropriately transformed tomeet assumptions of ANOVA and multiple comparisonsadjusted using Bonferroni corrections (two one-degree-of-freedom contrasts or three one degree-of-freedomcontrasts p=0025 or 00167 respectively)

Tree and knee growth were analyzed by comparingmeans of growth (circumference ratios ie yearrsquos circum-ference divided by previous yearrsquos circumference) for2008ndash2011 For the Gulf Coast-wide assessment of treegrowth and salinity regression analysis compared means oftree growth (circumference ratios) in LA TX and FL(2011ndash2012) versus annual mean salinity Annual meansalinity was based on the mean of day-of-visit measure-ments from 2011 to 2012 (7 to 14 measurements with allseasons represented)

Climate

We used ANOVA to compare monthly total precipitationand mean temperature by year and remediation periodusing the main effects and interactions of year andremediation period

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Water environment and remediation

Water and salinity level shifts and remediation Todetermine if the water dynamics differed from expectedconditions we compared mean and maximum values ofdaily levels of water and surface salinity during times ofinterest Because short periods of high salinity or anoxiawere likely to affect tree production and growth we focusedon daily maximum water level for these analyses Watercomparisons were made of three time periods in 2010 (pre-remediation during and post-remediation) with the sameperiods in other years in three ways wet years (mean of2008ndash2011) long-term (mean of 2003ndash2011) and individualyears (2006ndash2011) These comparisons were made usingautoregressive integrated moving average (ARIMA) models(detailed description provided in Table 1 in the SupportingInformation) generated in SAS Institute Inc (2002) whichare appropriate for comparing water and salinity levels shiftsover time because these models can predict the shape of thefunction and account for the autocorrelation of the samplesover time better than other statistical approaches (SASInstitute Inc 2002) A nonparametric sign test comparednumber of times the 2010 series had more water or salinitythan the average of the comparison series and vice versa

Predicted daily threshold values of salinity in productionplots To determine the number of days that productionsites exceeded threshold values of various salinity levelsthe following procedure was followed Using linearregression mean daily surface water salinity from CRMSgauges in the EC and PT units on specific days wereplotted against mean pore water salinity on day-of-visit inproduction plots and SET monuments in 2011ndash2012(Table I) Equations generated from this process were usedto predict daily mean salinity levels in sites from 2008 to2011 (for equations see Figure 2 caption in the SupportingInformation) as well as the percentage of growing seasondays (1 Aprilndash31 October) each year above certain salinitylevels (ie 01 03 07 10 15 and 20 ppt)

RESULTS

Production and vegetation responses to hydrologicremediation

Total litter biomass was 27 times higher after hydrologicremediation in 2010 and 2011 than before remediation in2007ndash2009 (Figure 2a Table IIa one degree-of-freedomcontrast t=838 plt 00001) In litterfall Tdistichum leafbiomass was 31 and 25 times higher in 2010 andor 2011respectively than in 2007ndash2009 (Table IIa) while repro-ductive biomass was 77 times in 2011 but not different in2010 (Table IIa and Table III) In addition leaf andreproductive tissue biomass in litterfall was higher in 2010

Ecohydrol 8 838ndash850 (2015)

Figure 2 Total annual mean production from 2007 to 2011 including (a)total litter biomass (leaf reproductive and wood) [g m2 y1 plusmn standarderror (SE)] and (b) total annual root biomass (total of all depths 0ndash30 cmg m2 y1 plusmn SE) in Jean Lafitte National Historical Park amp Preserve(n = 25) Different letters indicated that means of years differed statistically(one degree-of-freedom contrasts plt 005) (c) Regression analysis ofstem growth expressed as mean salinity (ppt) versus Taxodium distichumcircumference ratio plusmn SE along the Gulf Coast (R2 = 086) Salinity isbased on means of pore water salinity during day-of-visit measurements

844 B A MIDDLETON D JOHNSON AND B J ROBERTS

andor 2011 than in 2007ndash2009 for Acer rubrum (not in2007) Liquidambar styraciflua and M cerifera (Table IIaand Table III) Annual litterfall biomass of wood tissue didnot change from 2007 to 2011 although the mean wassubstantially higher in 2010 (Table IIb plt 005) Annuallog root biomass was higher in shallower than deeper soildepths (Figure 2b and Table IIb 0ndash10 vs 10ndash30 cmt=279 p=00058 N=5) and total root biomass variedby year and was 23ndash53 times lower in 2010 than in 2007ndash2011 (Figure 2b t=489 plt 00001 N=5)Neither tree nor knee growth varied with circumference

increasing by 18 plusmn 01 and 29 plusmn 10 respectively peryear during 2008ndash2011 in JLNHP amp P (pgt005Table IIcndashd) In JLNHP amp P we found no relationship

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

between tree growth and the percentage days per year a siteexceeded published thresholds of salinity (eg 07 or20 ppt pgt005 Table IV) In 2010 both EC and PT unitshad fewer days with salinity gt03 ppt and in 2008 moredays with salinity gt20 ppt (Table IV Figure 1 in theSupporting Information) Across the Gulf Coast Tdistichum growth varied from 011 to 21 increase incircumference per year with average annual salinityexplaining 86 of the variance in growth with the highestgrowth observed in the lowest mean pore water salinity(eg JLNHP amp P Figure 2c)

Climate and environment

Regionally mean annual precipitation was 13209plusmn1065mm per year from 2002 to 2012 (National Oceanicand Atmospheric Administration (NOAA) 2013) but didnot vary by year or remediation period (pgt 0130 Table V)Mean monthly air temperature did not vary by year but didvary by remediation period (mean monthly temperaturesduring pre-remediation remediation and post-remediation157 plusmn 06 degC 269 plusmn03 degC and 187 plusmn 08 degC respectivelyF=817 plt0001 Table V) (NOAA 2013)

Water and salinity responses to hydrologic remediation

Short-term water and salinity comparisons ndash 2010 versuswet years (2008ndash2011) Davis Pond CRMS 0188 andCRMS 0234 had higher dischargewater level and lowersalinity during the remediation period in 2010 than duringwet years As based on ARIMA time series comparisonswater discharged from Davis Pond in 2010 exceeded meanand maximum daily discharge of wet years (mean dailydischarge of 2010 vs wet years 113 out of 119 daysrespectively maximum daily discharge of 2010 vs wetyears 102 out of 119 days respectively sign testsplt 00001 Figure 3a and Table 2 in the SupportingInformation) Discharge rates from the Davis PondFreshwater Diversion and water levels at gauges werelower in 2010 during the post-remediation period than inwet years (Figure 3a and Table 2 in the SupportingInformation) Maximum daily gauge levels were higherduring hydrologic remediation in 2010 than in wet years(CRMS 0234 026 vs 011m respectively Figure 3bCRMS 0188 115 vs 106m respectively Figure 3c andTable 2 in the Supporting Information)Long-term gauging stations can be used to indicate

conditions at sites even though salinity relationships weresomewhat different (ie EC sites had significantly highersalinity than CRMS 0234 and PT sites had significantlylower salinity than CRMS 0188 as based on day-of-visitmeasurements) Salinity environments in the EC and PTsites were relatively similar (Figure 2 in the SupportingInformation) Nevertheless maximum daily water levels atCRMS 0234 were linearly related to day-of-visit water

Ecohydrol 8 838ndash850 (2015)

Table II Analysis of variances of production variables in JLNHP amp P from 2007 to 2011

DF F p Mean plusmn SE

(a) Total annual productionLitterfall (gm2 y1)Year 4 236 lt00001

Root biomass (gm2 y1)Year 4 84 lt00001 Depth 1 78 00225

Year times depth 4 10 04142 ns(b) Tissue typeLeafSpecies 15 155 lt00001 Year 4 1566 lt00001 Species times year 60 41 lt00001

ReproductiveSpecies 5 400 lt00001 Year 4 69 lt00001 Species times year 20 44 lt00001

WoodYear 4 21 00794 ns

(c) Tree growth (annual circumference ratio)Initial tree circumference (covariate) 1 38 00668 nsYear 3 01 09718 ns2008 1019210 plusmn 000552009 1018628 plusmn 000712010 1018855 plusmn 000382011 1015170 plusmn 00022

(d) Knee growth (annual circumference ratio)Initial knee circumference (covariate) 1 05 04945 nsYear 4 09 04628 ns

Mean total annual production of (a) litterfall (g m2 y1 including leaves reproductive material and wood) and log root biomass (g m3 y1) (b) Meanbiomass of tissue types of dominant species including leaf reproductive and wood Dendrometer bands were used to measure incremental increase incircumference growth was estimated as a year-to-year ratio of circumference change of Taxodium distichum from 2008 to 2011 for (c) trees and (d)knees Mean comparisons that differed based on contrasts indicated by lsquorsquo lsquorsquo or ns (plt 00001 plt 005 pgt 005 respectively Figure 2) SeeTable III for tissue type times species interactionsJLNHP amp P Jean Lafitte National Historical Park amp Preserve SE standard error DF degrees of freedom ns not significant

845HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

depths at SETs in the EC unit (ie SETs at ECP and ECSFigure 2 in the Supporting Information r= 06043p=00015) As indicated in the Section on Methods tojustify the selection of salinity variables and analysesoverall maximum daily values were within 105plusmn 00018of mean values Mean daily salinity levels at CRMS 0234and CRMS 0188 were linearly related to day-of-visitsalinity at SETs and plots within the same hydrologicalunits (EC unit r=0600 p=00004 Figure 2b in theSupporting Information PT unit r=0702 p=00005Figure 2c in the Supporting Information)

Long-term water level comparisons ndash 2010 versus long-term (2003ndash2011) Water discharge from Davis Pond in2010 during hydrologic remediation was higher than in thelong-term set of years (2003ndash2011 mean discharge perday =1983 plusmn 49 vs 331 plusmn 16m3 s1 respectively) andmaximum daily water levels at CRMS 0234 and CRMS0188 also were higher (sign tests plt00001 Figure 4 inthe Supporting Information)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Individual year water and salinity level comparisons ndash2010 vs 2006ndash2011 Comparisons of maximum dailywater level and salinity levels during 2010 to individualyears were similar to the comparisons of 2010 to sets ofwet and long-term years (ie 2008ndash2011 and 2003ndash2011respectively) As expected discharge levels for Davis Pondand water levels at CRMS 0234 and CRMS 0188 weresignificantly higher during hydrologic remediation in 2010compared with those in any individual year from 2006 to2011 (plt00001) One exception was that maximumsalinity was higher in 2010 than in 2009 at CRMS 0234(plt 00001)

DISCUSSION

Freshwater flow variability controls ecological processes inestuaries so that alteration of water delivery is a keyconservation challenge (Lester et al 2013) Unfortunatelyinformation on how to manage salinity flux in freshwaterwetlands in altered estuaries is lacking (Kaplan et al 2010

Ecohydrol 8 838ndash850 (2015)

Table III Means plusmn SE listed by species dominance of dry litterfall biomass (gm2) based on species times year interactions for leafreproductive and wood tissue from 2007 to 2011 in JLNHP amp P

Species

Year

2007 2008 2009 2010 2011

Leaf tissueTaxodium distichum 264 plusmn 48 b 150 plusmn 25 c 291 plusmn 48 b 723plusmn 91 a 590plusmn 112 a

Acer rubrum 239 plusmn 53 ab 123 plusmn 26 b 184 plusmn 435 b 249plusmn 45 a 258plusmn 47 a

Fraxinus pennsylvanica 65 plusmn 21 b 28 plusmn 09 c 117 plusmn 29 a 136 plusmn 38 a 34 plusmn 22 c

Liquidambar styraciflua 47 plusmn 14 b 23 plusmn 06 b 45 plusmn 17 b 69plusmn 14 a 49 plusmn 16 b

Nyssa aquatica 80 plusmn 26 a 09 plusmn 08 b 14 plusmn 12 b 19 plusmn 11 b 00 plusmn 00 b

Myrica cerifera 00 plusmn 00 c 18 plusmn 07 b 23 plusmn 07 b 41plusmn 12 a 21 plusmn 07 b

Salix nigra 22 plusmn 11 a 13 plusmn 09 a 02 plusmn 01 a 39 plusmn 35 a 17 plusmn 16 a

Ulmus americana 10 plusmn 06 a 01 plusmn 01 b 04 plusmn 02 b 14 plusmn 08 a 21 plusmn 09 a

Quercus nigra 07 plusmn 02 a 01 plusmnlt01 a 08 plusmn 03 a 16 plusmn 06 a 09 plusmn 05 a

Other leaf 12 plusmn 04 c 18 plusmn 07 c 26 plusmn 07 b 45 plusmn 15 b 144 plusmn 32 a

Cephalanthus occidentalis 23 plusmn 09 a 00 plusmn 00 b 01 plusmn 01 b lt01 plusmnlt01 b 00 plusmn 00 b

Acer spp 22 plusmn 18 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a

Carya aquatica 00 plusmn 00 a 18 plusmn 09 a 02 plusmn 02 a 00 plusmn 00 a 00 plusmn 00 a

Quercus spp (red) 05 plusmn 04 a 03 plusmn 02 a 02 plusmn 01 a 04 plusmn 02 a 00 plusmn 00 a

Triadica sebifera 00 plusmn 00 a 02 plusmn 01 a 01 plusmnlt01 a 09 plusmn 06 a 06 plusmn 03 a

Gleditsia aquatica 14 plusmn 06 a 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b

Reproductive tissueTaxodium distichum 65 plusmn 30 b 06 plusmn 04 c 55 plusmn 31 b 57 plusmn 18 b 325plusmn 139 a

Other reproductive lt01 plusmnlt01 b lt01 plusmnlt01 b 02 plusmn 01 b 02 plusmn 01 b 44plusmn 24 a

Fraxinus pennsylvanica 05 plusmn 01 b 04 plusmn 01 b 03 plusmn 01 b 25plusmn 07 a 01 plusmn 01 b

Liquidambar styraciflua 09 plusmn 09 a 00 plusmn 00 a lt01 plusmnlt01 a 05 plusmn 05 a 00 plusmn 00 a

Nyssa aquatica 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 04 plusmn 04 a 00 plusmn 00 a

Wood tissueWood total all species 22 plusmn 05 a 28 plusmn 12 a 50 plusmn 21 a 129 plusmn 54 a 92 plusmn 43 a

Different letters indicate significant differences of litterfall biomass of species based on one-degree-of-freedom contrasts Dominant species are listedwith biomass gt02 g m2 with the biomass of non-dominant species summed in an lsquootherrsquo group Species with significantly higher litterfall in 2010 andor 2011 after Bonferroni correction are listed in bold lettersSE standard error

846 B A MIDDLETON D JOHNSON AND B J ROBERTS

Kingsford 2011) Out of necessity programmes to manageflood flow are emerging in the United States AustraliaSouth Africa and to a lesser extent Europe (Hughes andRood 2003) As an example the Comprehensive MasterPlan for Louisiana has proposed to use diversions torelease river water and sediment to rebuild coastalwetlands (CPRA 2012) While managed flood releasesare used increasingly in restoration (Middleton 1999Schmidt et al 2001 Souter et al 2014) theseapproaches may become even more important as salinityincreases with changes in climate sea level subsidenceand surfacegroundwater levels (Poff et al 2002 Kaplanet al 2010 Souter et al 2014) Studies such as ours caninform management procedures to explore the utility offreshwater release for coastal conservationVarious studies demonstrate the potential benefits of short

periods of increased freshwater flow to hydrologically alteredcoastal forests While hydrologic remediation lasted only 2 to4months in this study and the Souter et al 2014 study treeresponses were impressive After freshwater remediation inJLNHP amp P high levels of above-ground litter productionpersisted for several species for one or more growing season

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

(this study) Similarly healthy trees of Eucalyptuscamaldulensis Dehnh in the Murray River drainage (Austra-lia) vigorously grew more foliage while highly stressed ordefoliated trees responded positively but less vigorously fortwo growing seasons following ~2months of freshwaterrelease (Souter et al 2014) In the Lake Pontchartrain Basin ofLouisiana coastal Tdistichum trees grew two times fasterwith periodicflowof riverwater (Day et al 2012) In additionreproductive output was higher in 2010 and especially in 2011for certain tree species suggesting that resourcematchingmayhave occurred ie species varied reproductive output tomatchavailable resources (Kelly 1994) In the context of this studythe hydrologic remediation may have allowed these trees tobuild up their physiological resources via higher levels ofphotosynthetic activity prior to mass floweringEnvironmental flow prescriptions might revive moribund

coastal swamps yet no definitive range of flow amount ortiming has been identified to improve environments related tosalinity anoxia nutrients or other factors We linked sharplyhigher production of litter (leaf and reproductive) in 2010 tohydrologic remediation in salinity levels well below 20pptwith maximummeasured values at plots of EC vs PT sites 04

Ecohydrol 8 838ndash850 (2015)

Table V Analysis of variances of climate variables for JLNHP ampP from Marrero 9 SSW weather station data (NOAA 2013) foryears 2002ndash2012 remediation periods relative to the hydrologicremediation period in 2010 (pre-remediation remediation andpost-remediation) including mean monthly (a) total precipitation

and (b) temperature

Variable DF F p

(a) PrecipitationYear 10 12 03339Remediation period 2 21 01297Year times remediation period 20 11 04077

(b) TemperatureYear 10 01 09989Remediation period 2 817 lt00001 Year times remediation period 20 02 09999

DF degrees of freedom

Table IV Percentage of days exceeding predicted values for maximum and mean daily salinity levels (ppt) in the EC and PT unitsin JLNHP amp P (sites ECSECPECC vs PTPTV respectively)

Percent () days per year exceeding the specified maximum or minimum values of salinity (eg gt01 to 20 ppt) were predicted from linear regressionanalysis of surface salinity levels at CRMS 0234 and CRMS 0188 gauges (EC and PT units respectively) versus day-of-visit pore water salinity atproduction sites including ECSECPECC and PTPTV (Figure 4) Total days are the number of days per year during the growing season (1 Aprilndash31October 2008ndash2011) Published threshold salinity levels for forest tree maintenanceflooded seedling photosynthesis and basal area growth (size) arethought to be 20 and 07 ppt (in bold letters Kaplan et al 2010Pezeshki et al 1987 and Krauss et al 2009 respectively) Dark to light grey highlightsindicate percent () days per year exceeding maximum values as 70ndash100 30ndash70 1ndash30 and 0 respectivelyECS Education Center Spur ECP Education Center Parking ECC Education Center Canal PT Palmetto Trail PTV Palmetto Trail Visitors ECEducation Center JLNHP amp P Jean Lafitte National Historical Park amp Preserve

847HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

and 05ppt respectively (also see Figure 2a and Table IV) Incontrast to 2008 predicted levels of salinity were high in boththe EC and PT units (Table IV) and total annual leaf litterbiomass by individual species was low (A rubrum Tdistichum Fraxinuspennsylvanicum Mcerifera and Salixnigra Figure 2a and Table III) Nevertheless rendering asimple statement of an ideal threshold of salinity for theseswamps is impractical Among other problems field environ-ments are difficult to characterize simply (eg salinity levelsvary by depth in the vadose zone)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Trees in JLNHP amp P responded positively to remedia-tion but we recognize that this unplanned study did notpermit us to determine whether changes in salinity or someother unmeasured biogeochemical factors were ultimatelyresponsible for the observed responses Tidal flowreconnection in previously restricted salt marshes decreasessoil anoxia and sulphides and changes pH nutrientavailability and decomposition rates (Anisfeld and Benoit1997) The fact that we detected increased water levels anddecreased salinity with freshwater remediation indicatedthat other important site characteristics and biogeochemicalshifts likely were occurring at JLNHP amp P Unfortunatelywe do not have any other supportive data especially asrelated to any possible causal linkagesPhotosynthetic stressors such as salinity and anoxiamay be

more harmful during the growing season Flooding reducesregeneration seedlings and saplings of Tdistichum surviveovertopping by flooding while dormant but not during thegrowing season and most tree species will not germinateunderwater (Middleton 2000) A better understanding of anyseasonal component of remediation response is critical tohydrologic remediation planning for managementThe immediate mechanisms of increased tree production

with improved environment are not well studied but maybe related to the photosynthetic regulation of trees tochanges in environment As salinity (at some level) entersthe transpiration stream stomata close and photosynthesisdecreases (Stiller 2009) Any short-term increase in

Ecohydrol 8 838ndash850 (2015)

Figure 3 State of Louisiana water recorder information for maximum (a) daily discharge (m3 s1) from Davis Pond Diversion and adjusted water levels(m) at (b) Coastwide Reference Monitoring System (CRMS) 0234 and (c) CRMS 0188 and salinity (ppt) of (d) discharge of diversion and surface waterat (e) CRMS 00234 and (f) CRMS 0188 during hydrologically remediated (2010) versus lsquowetrsquo years (mean of 2008 2009 and 2011) CRMS 0234 andCRMS 0188 are in the same hydrological units as the Education Center and Palmetto Trail plots respectively in JLNHP amp P Pre-remediationremediation and post-remediation days of the year included days 1ndash119 120ndash244 and 245ndash365 respectively Sign tests indicated that 2010 was higherlower or not different from wet years as lsquo+rsquo lsquo-rsquo or lsquonsrsquo respectively (plt 00001) Only significant variables of time were kept p values for the sign testcomparisons were based on normally distributed error with constant variance All tests of fit were performed at p = 005 except that one test wasperformed at p = 001 to obtain a model fit Equations were based on the difference of the two year groups (2010 vs set of years compared) Mean dailydischarge values are not shown but these comparisons were also significant using similarly constructed ARIMA models and sign tests (plt 00001)Note that short periods of missing data were interpolated linearly Longer periods of missing data were omitted eg Davis Pond Diversion had nodischarge data available for 1ndash28 January 2010 Note that the measured water and salinity levels at plots in the EC and PT units were intermediate and

similar to each other (see Supplementary Figure 2)

848 B A MIDDLETON D JOHNSON AND B J ROBERTS

photosynthetic output and leaf production after freshwaterremediation is most likely to occur in healthy trees withrelatively intact leaf architecture such as Tdistichum in

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

JLNHP amp P or E camaldulensis trees along the MurrayRiver in Australia (Souter et al 2014) The positive effectsof remediation may have broad application in freshwater

Ecohydrol 8 838ndash850 (2015)

849HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

forests particularly because several species respondedpositively to freshwater remediation in JLNHP amp P

In our study litter but not root production increased duringthe year of hydrologic remediation If environment conditionsimproved in 2010 trees may have been experiencing a fastspurt of leaf litter production at the expense of roots(Figure 2b) Falling rootshoot ratios are an indicator of fastshoot growth in response to favourable environments (Harris1992 Litton et al 2007) and Tdistichum root and shootallocation patterns shift in response to changing resources(Megonigal and Day 1992) Note that we did not distinguishbetween species of roots in our study Alterations in root andshoot allocations following hydrologic remediationmay haveimportant implications for the elevation of subsiding swampsby influencing peat accumulation The decrease in rootgrowth during remediation is important because root tissuesoften contribute more to the accumulation of peat than leaf orwoody tissue (Middleton and McKee 2002) Whilereinvigorating the production of freshwater coastal vegetationoverall hydrologic remediation may reduce root growth forsome tree species at least temporarily (this study) Thereforea better understanding of the relationship of remediation androot growth is critical (Langley et al 2010 Wigand et al2014) to the development of management techniques relatedto remediation

CONCLUSION

Concerns are growing because of losses of coastal wetlandsalong the Gulf Coast (Kaplan et al 2010 CPRA 2012)Special attention should be given to our findings thatfreshwater release might reinvigorate the production offreshwater coastal vegetation Our study has worldwideimplications in that it demonstrates that sustained releases offreshwater can affect the primary production of many speciesFreshwater coastal species are increasingly affected bysaltwater intrusion so this idea deserves further explorationfor the management of coastal freshwater wetlands

ACKNOWLEDGEMENTS

This work is funded by the US Geological Survey andNational Science Foundation (DEB-1049838) Specialthanks are given to Evelyn Anemaet Mel McCulloughSamantha Primer Justin Stelly Lei Ting and GuodongWang for their field assistance Any use of trade productor firm names is for descriptive purposes only and does notimply endorsement by the US Government

CONFLICT OF INTEREST

The authors declare no conflict of interest with thisresearch

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

REFERENCES

Anemaet E Middleton BA 2013 Dendrometer bands made easy usingmodified cable ties to measure incremental growth of trees Applicationsin Plant Sciences 1 1300044

Anisfeld SC Benoit G 1997 Impacts of flow restriction on salt marshesan instance of acidification Environmental Science and Technology 311650ndash1699

Bianchi TS Cook RL Perdue EM Kolic PE Green N Zhang Y SmithRW Kolker AS Ameen A King G Ojwang LM Schneider CLNormand AE Hetland R 2011 Impacts of diverted freshwater ondissolved organic matter and microbial communities in Barataria BayLA Marine Environmental Research 72 248257

Brinson MM Bradshaw HD Holmes RN Elkins JB Jr 1980 Litterfallstemflow and throughfall nutrient fluxes in an alluvial swamp forestEcology 61 827ndash835

Cahoon DR Lynch JC Hensel P Boumans R Perez BC Segura B DayJW Jr 2002 A device for high precision measurement of wetlandsediment elevation I Recent improvements to the sedimentation-erosion table Journal of Sedimentary Research 72 730ndash733

Coastal Protection and Restoration Authority of Louisiana (CPRA) 2012Louisianarsquos Comprehensive Master Plan for a Sustainable CoastCPRA Baton Rouge LA

Coastal Protection and Restoration (CPRA) 2013 Modifications to theDavis Pond Diversion Louisiana Coastal Protection and RestorationBaton Rouge LA wwwlcagovProjects14Defaultaspx

Day JW 2000 Pattern and process of land loss in the Mississippi Delta aspatial and temporal analysis of wetland habitat change Estuaries 23425438

Day J Hunter R Keim RF DeLaune R Shaffer G Evers E Reed DBrantley C Kemp P Day J Hunter M 2012 Ecological response offorested wetlands with and without large-scale Mississippi River inputimplications for management Ecological Engineering 46 57 67

Dixon KR 1976 Analysis of seasonal leaf fall in north temperaturedeciduous forests Oikos 27 300306

Dokka RK 2006 Modern-day tectonic subsidence in coastal LouisianaGeology 34 281294

Greater NewOrleans Inc Regional Economic Alliance (GNO) 2010 A studyon the economic impact of the Deepwater Horizon oil spill GNORegionalEconomic Alliance New Orleans wwwuflibufledu docs Economic20Impact 20Study 20Part20I20-20Full20Reportpdf

Hertel D Leuschner C 2002 A comparison of four different fine rootproduction estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest Plant and Soil 239 237251

Hoeppner SS Schaffer GP Perkins TE 2008 Through droughts andhurricanes tree mortality forest structure and biomass production in acoastal swamp targeted for restoration in the Mississippi River DeltaicPlain Forest Ecology and Management 256 937948

Hughes FM Rood SB 2003 Allocation of river flows for restorationof floodplain forest ecosystems Environmental Management 321233

Harris RW 1992 Root-shoot ratios Journal of Arboriculture 18 39ndash42JMP SAS 2012 Statistical Analysis System v 1002 SAS Institute IncCary NC

Junk WJ Bayley PB Sparks RE 1989 The flood pulse concept in river-floodplain systems In Proceedings of the International Large RiverSymposium Vol 106 Canadian Special Publications in Fisheries andAquatic Science Ottawa Ontario Canada 110127

Kaplan D Muntildeoz-Carpena R Wan Y Hedgepeth M Zheng F Roberts RRossmanith R 2010 Linking river floodplain and vadose hydrology toimprove restoration of a coastal river affected by saltwater intrusionJournal of Environmental Quality 39 15701584

Kelly D 1994 The evolutionary ecology of mast seeding Trends inEcology and Evolution 9 465ndash470

Kingsford RT 2011 Conservation management of rivers and wetlandsunder climate change a synthesis Marine and Freshwater Research62 217222

Kozlowski TT 1997 Responses of woody plants to flooding and salinityTree Physiology 1 129

KraussKWDuberstein JADoyle TWConnerWHDayRH Inabinette LWWhitbeck JL 2009 Site condition structure and growth of baldcypressalong tidalnon-tidal salinity gradients Wetlands 29 505519

Ecohydrol 8 838ndash850 (2015)

843HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

DATA ANALYSIS

Vegetation production

Annual total litterfall (leaf and wood) was calculated frompeak litterfall estimates by determining the percentage ofannual litterfall collected during the main season (mean of20072011 correction factor = 0718plusmn0176 SE) so thatbiomass captured during the main season of each year wasdivided by 07180 to express yearly production Thiscorrection factor better portrayed annual total litterfallbased on peak litterfall while fully recognizing that certainswamp species do not lose their leaves during this period(eg Myrica cerifera) Most deciduous trees shed all oftheir leaves within 30ndash60 days (Dixon 1976) fromSeptember through mid-November (Tdistichum swampNorth Carolina Brinson et al 1980) or into Decemberfarther southward (eg South Carolina mixed bottomlandforest Shure and Gottschalk 1985)

Litterfall totals by year species and tissue type (leafreproductive and wood) from 2007 to 2011 were analyzedusing repeated measures analysis nesting plot within yearin analysis of variance (ANOVA) (one-way or two-wayANOVA JMP SAS 2012) For annual log root produc-tion ANOVA was used by nesting plot (depth year) Rootproduction by year did not interact with depth (year times depthinteraction pgt005) so that total root production wasanalyzed by year The lower two root depths (10ndash20 and20ndash30 cm) did not differ (t=097 p=033) so that a meanof these two depths was calculated (10ndash30 cm) andcompared with the upper depth (0ndash10 cm) In all ANOVAanalyses the highest-order significant interaction or maineffect was tested using one degree-of-freedom contrasts inJMP SAS (2012) Data were appropriately transformed tomeet assumptions of ANOVA and multiple comparisonsadjusted using Bonferroni corrections (two one-degree-of-freedom contrasts or three one degree-of-freedomcontrasts p=0025 or 00167 respectively)

Tree and knee growth were analyzed by comparingmeans of growth (circumference ratios ie yearrsquos circum-ference divided by previous yearrsquos circumference) for2008ndash2011 For the Gulf Coast-wide assessment of treegrowth and salinity regression analysis compared means oftree growth (circumference ratios) in LA TX and FL(2011ndash2012) versus annual mean salinity Annual meansalinity was based on the mean of day-of-visit measure-ments from 2011 to 2012 (7 to 14 measurements with allseasons represented)

Climate

We used ANOVA to compare monthly total precipitationand mean temperature by year and remediation periodusing the main effects and interactions of year andremediation period

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Water environment and remediation

Water and salinity level shifts and remediation Todetermine if the water dynamics differed from expectedconditions we compared mean and maximum values ofdaily levels of water and surface salinity during times ofinterest Because short periods of high salinity or anoxiawere likely to affect tree production and growth we focusedon daily maximum water level for these analyses Watercomparisons were made of three time periods in 2010 (pre-remediation during and post-remediation) with the sameperiods in other years in three ways wet years (mean of2008ndash2011) long-term (mean of 2003ndash2011) and individualyears (2006ndash2011) These comparisons were made usingautoregressive integrated moving average (ARIMA) models(detailed description provided in Table 1 in the SupportingInformation) generated in SAS Institute Inc (2002) whichare appropriate for comparing water and salinity levels shiftsover time because these models can predict the shape of thefunction and account for the autocorrelation of the samplesover time better than other statistical approaches (SASInstitute Inc 2002) A nonparametric sign test comparednumber of times the 2010 series had more water or salinitythan the average of the comparison series and vice versa

Predicted daily threshold values of salinity in productionplots To determine the number of days that productionsites exceeded threshold values of various salinity levelsthe following procedure was followed Using linearregression mean daily surface water salinity from CRMSgauges in the EC and PT units on specific days wereplotted against mean pore water salinity on day-of-visit inproduction plots and SET monuments in 2011ndash2012(Table I) Equations generated from this process were usedto predict daily mean salinity levels in sites from 2008 to2011 (for equations see Figure 2 caption in the SupportingInformation) as well as the percentage of growing seasondays (1 Aprilndash31 October) each year above certain salinitylevels (ie 01 03 07 10 15 and 20 ppt)

RESULTS

Production and vegetation responses to hydrologicremediation

Total litter biomass was 27 times higher after hydrologicremediation in 2010 and 2011 than before remediation in2007ndash2009 (Figure 2a Table IIa one degree-of-freedomcontrast t=838 plt 00001) In litterfall Tdistichum leafbiomass was 31 and 25 times higher in 2010 andor 2011respectively than in 2007ndash2009 (Table IIa) while repro-ductive biomass was 77 times in 2011 but not different in2010 (Table IIa and Table III) In addition leaf andreproductive tissue biomass in litterfall was higher in 2010

Ecohydrol 8 838ndash850 (2015)

Figure 2 Total annual mean production from 2007 to 2011 including (a)total litter biomass (leaf reproductive and wood) [g m2 y1 plusmn standarderror (SE)] and (b) total annual root biomass (total of all depths 0ndash30 cmg m2 y1 plusmn SE) in Jean Lafitte National Historical Park amp Preserve(n = 25) Different letters indicated that means of years differed statistically(one degree-of-freedom contrasts plt 005) (c) Regression analysis ofstem growth expressed as mean salinity (ppt) versus Taxodium distichumcircumference ratio plusmn SE along the Gulf Coast (R2 = 086) Salinity isbased on means of pore water salinity during day-of-visit measurements

844 B A MIDDLETON D JOHNSON AND B J ROBERTS

andor 2011 than in 2007ndash2009 for Acer rubrum (not in2007) Liquidambar styraciflua and M cerifera (Table IIaand Table III) Annual litterfall biomass of wood tissue didnot change from 2007 to 2011 although the mean wassubstantially higher in 2010 (Table IIb plt 005) Annuallog root biomass was higher in shallower than deeper soildepths (Figure 2b and Table IIb 0ndash10 vs 10ndash30 cmt=279 p=00058 N=5) and total root biomass variedby year and was 23ndash53 times lower in 2010 than in 2007ndash2011 (Figure 2b t=489 plt 00001 N=5)Neither tree nor knee growth varied with circumference

increasing by 18 plusmn 01 and 29 plusmn 10 respectively peryear during 2008ndash2011 in JLNHP amp P (pgt005Table IIcndashd) In JLNHP amp P we found no relationship

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

between tree growth and the percentage days per year a siteexceeded published thresholds of salinity (eg 07 or20 ppt pgt005 Table IV) In 2010 both EC and PT unitshad fewer days with salinity gt03 ppt and in 2008 moredays with salinity gt20 ppt (Table IV Figure 1 in theSupporting Information) Across the Gulf Coast Tdistichum growth varied from 011 to 21 increase incircumference per year with average annual salinityexplaining 86 of the variance in growth with the highestgrowth observed in the lowest mean pore water salinity(eg JLNHP amp P Figure 2c)

Climate and environment

Regionally mean annual precipitation was 13209plusmn1065mm per year from 2002 to 2012 (National Oceanicand Atmospheric Administration (NOAA) 2013) but didnot vary by year or remediation period (pgt 0130 Table V)Mean monthly air temperature did not vary by year but didvary by remediation period (mean monthly temperaturesduring pre-remediation remediation and post-remediation157 plusmn 06 degC 269 plusmn03 degC and 187 plusmn 08 degC respectivelyF=817 plt0001 Table V) (NOAA 2013)

Water and salinity responses to hydrologic remediation

Short-term water and salinity comparisons ndash 2010 versuswet years (2008ndash2011) Davis Pond CRMS 0188 andCRMS 0234 had higher dischargewater level and lowersalinity during the remediation period in 2010 than duringwet years As based on ARIMA time series comparisonswater discharged from Davis Pond in 2010 exceeded meanand maximum daily discharge of wet years (mean dailydischarge of 2010 vs wet years 113 out of 119 daysrespectively maximum daily discharge of 2010 vs wetyears 102 out of 119 days respectively sign testsplt 00001 Figure 3a and Table 2 in the SupportingInformation) Discharge rates from the Davis PondFreshwater Diversion and water levels at gauges werelower in 2010 during the post-remediation period than inwet years (Figure 3a and Table 2 in the SupportingInformation) Maximum daily gauge levels were higherduring hydrologic remediation in 2010 than in wet years(CRMS 0234 026 vs 011m respectively Figure 3bCRMS 0188 115 vs 106m respectively Figure 3c andTable 2 in the Supporting Information)Long-term gauging stations can be used to indicate

conditions at sites even though salinity relationships weresomewhat different (ie EC sites had significantly highersalinity than CRMS 0234 and PT sites had significantlylower salinity than CRMS 0188 as based on day-of-visitmeasurements) Salinity environments in the EC and PTsites were relatively similar (Figure 2 in the SupportingInformation) Nevertheless maximum daily water levels atCRMS 0234 were linearly related to day-of-visit water

Ecohydrol 8 838ndash850 (2015)

Table II Analysis of variances of production variables in JLNHP amp P from 2007 to 2011

DF F p Mean plusmn SE

(a) Total annual productionLitterfall (gm2 y1)Year 4 236 lt00001

Root biomass (gm2 y1)Year 4 84 lt00001 Depth 1 78 00225

Year times depth 4 10 04142 ns(b) Tissue typeLeafSpecies 15 155 lt00001 Year 4 1566 lt00001 Species times year 60 41 lt00001

ReproductiveSpecies 5 400 lt00001 Year 4 69 lt00001 Species times year 20 44 lt00001

WoodYear 4 21 00794 ns

(c) Tree growth (annual circumference ratio)Initial tree circumference (covariate) 1 38 00668 nsYear 3 01 09718 ns2008 1019210 plusmn 000552009 1018628 plusmn 000712010 1018855 plusmn 000382011 1015170 plusmn 00022

(d) Knee growth (annual circumference ratio)Initial knee circumference (covariate) 1 05 04945 nsYear 4 09 04628 ns

Mean total annual production of (a) litterfall (g m2 y1 including leaves reproductive material and wood) and log root biomass (g m3 y1) (b) Meanbiomass of tissue types of dominant species including leaf reproductive and wood Dendrometer bands were used to measure incremental increase incircumference growth was estimated as a year-to-year ratio of circumference change of Taxodium distichum from 2008 to 2011 for (c) trees and (d)knees Mean comparisons that differed based on contrasts indicated by lsquorsquo lsquorsquo or ns (plt 00001 plt 005 pgt 005 respectively Figure 2) SeeTable III for tissue type times species interactionsJLNHP amp P Jean Lafitte National Historical Park amp Preserve SE standard error DF degrees of freedom ns not significant

845HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

depths at SETs in the EC unit (ie SETs at ECP and ECSFigure 2 in the Supporting Information r= 06043p=00015) As indicated in the Section on Methods tojustify the selection of salinity variables and analysesoverall maximum daily values were within 105plusmn 00018of mean values Mean daily salinity levels at CRMS 0234and CRMS 0188 were linearly related to day-of-visitsalinity at SETs and plots within the same hydrologicalunits (EC unit r=0600 p=00004 Figure 2b in theSupporting Information PT unit r=0702 p=00005Figure 2c in the Supporting Information)

Long-term water level comparisons ndash 2010 versus long-term (2003ndash2011) Water discharge from Davis Pond in2010 during hydrologic remediation was higher than in thelong-term set of years (2003ndash2011 mean discharge perday =1983 plusmn 49 vs 331 plusmn 16m3 s1 respectively) andmaximum daily water levels at CRMS 0234 and CRMS0188 also were higher (sign tests plt00001 Figure 4 inthe Supporting Information)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Individual year water and salinity level comparisons ndash2010 vs 2006ndash2011 Comparisons of maximum dailywater level and salinity levels during 2010 to individualyears were similar to the comparisons of 2010 to sets ofwet and long-term years (ie 2008ndash2011 and 2003ndash2011respectively) As expected discharge levels for Davis Pondand water levels at CRMS 0234 and CRMS 0188 weresignificantly higher during hydrologic remediation in 2010compared with those in any individual year from 2006 to2011 (plt00001) One exception was that maximumsalinity was higher in 2010 than in 2009 at CRMS 0234(plt 00001)

DISCUSSION

Freshwater flow variability controls ecological processes inestuaries so that alteration of water delivery is a keyconservation challenge (Lester et al 2013) Unfortunatelyinformation on how to manage salinity flux in freshwaterwetlands in altered estuaries is lacking (Kaplan et al 2010

Ecohydrol 8 838ndash850 (2015)

Table III Means plusmn SE listed by species dominance of dry litterfall biomass (gm2) based on species times year interactions for leafreproductive and wood tissue from 2007 to 2011 in JLNHP amp P

Species

Year

2007 2008 2009 2010 2011

Leaf tissueTaxodium distichum 264 plusmn 48 b 150 plusmn 25 c 291 plusmn 48 b 723plusmn 91 a 590plusmn 112 a

Acer rubrum 239 plusmn 53 ab 123 plusmn 26 b 184 plusmn 435 b 249plusmn 45 a 258plusmn 47 a

Fraxinus pennsylvanica 65 plusmn 21 b 28 plusmn 09 c 117 plusmn 29 a 136 plusmn 38 a 34 plusmn 22 c

Liquidambar styraciflua 47 plusmn 14 b 23 plusmn 06 b 45 plusmn 17 b 69plusmn 14 a 49 plusmn 16 b

Nyssa aquatica 80 plusmn 26 a 09 plusmn 08 b 14 plusmn 12 b 19 plusmn 11 b 00 plusmn 00 b

Myrica cerifera 00 plusmn 00 c 18 plusmn 07 b 23 plusmn 07 b 41plusmn 12 a 21 plusmn 07 b

Salix nigra 22 plusmn 11 a 13 plusmn 09 a 02 plusmn 01 a 39 plusmn 35 a 17 plusmn 16 a

Ulmus americana 10 plusmn 06 a 01 plusmn 01 b 04 plusmn 02 b 14 plusmn 08 a 21 plusmn 09 a

Quercus nigra 07 plusmn 02 a 01 plusmnlt01 a 08 plusmn 03 a 16 plusmn 06 a 09 plusmn 05 a

Other leaf 12 plusmn 04 c 18 plusmn 07 c 26 plusmn 07 b 45 plusmn 15 b 144 plusmn 32 a

Cephalanthus occidentalis 23 plusmn 09 a 00 plusmn 00 b 01 plusmn 01 b lt01 plusmnlt01 b 00 plusmn 00 b

Acer spp 22 plusmn 18 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a

Carya aquatica 00 plusmn 00 a 18 plusmn 09 a 02 plusmn 02 a 00 plusmn 00 a 00 plusmn 00 a

Quercus spp (red) 05 plusmn 04 a 03 plusmn 02 a 02 plusmn 01 a 04 plusmn 02 a 00 plusmn 00 a

Triadica sebifera 00 plusmn 00 a 02 plusmn 01 a 01 plusmnlt01 a 09 plusmn 06 a 06 plusmn 03 a

Gleditsia aquatica 14 plusmn 06 a 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b

Reproductive tissueTaxodium distichum 65 plusmn 30 b 06 plusmn 04 c 55 plusmn 31 b 57 plusmn 18 b 325plusmn 139 a

Other reproductive lt01 plusmnlt01 b lt01 plusmnlt01 b 02 plusmn 01 b 02 plusmn 01 b 44plusmn 24 a

Fraxinus pennsylvanica 05 plusmn 01 b 04 plusmn 01 b 03 plusmn 01 b 25plusmn 07 a 01 plusmn 01 b

Liquidambar styraciflua 09 plusmn 09 a 00 plusmn 00 a lt01 plusmnlt01 a 05 plusmn 05 a 00 plusmn 00 a

Nyssa aquatica 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 04 plusmn 04 a 00 plusmn 00 a

Wood tissueWood total all species 22 plusmn 05 a 28 plusmn 12 a 50 plusmn 21 a 129 plusmn 54 a 92 plusmn 43 a

Different letters indicate significant differences of litterfall biomass of species based on one-degree-of-freedom contrasts Dominant species are listedwith biomass gt02 g m2 with the biomass of non-dominant species summed in an lsquootherrsquo group Species with significantly higher litterfall in 2010 andor 2011 after Bonferroni correction are listed in bold lettersSE standard error

846 B A MIDDLETON D JOHNSON AND B J ROBERTS

Kingsford 2011) Out of necessity programmes to manageflood flow are emerging in the United States AustraliaSouth Africa and to a lesser extent Europe (Hughes andRood 2003) As an example the Comprehensive MasterPlan for Louisiana has proposed to use diversions torelease river water and sediment to rebuild coastalwetlands (CPRA 2012) While managed flood releasesare used increasingly in restoration (Middleton 1999Schmidt et al 2001 Souter et al 2014) theseapproaches may become even more important as salinityincreases with changes in climate sea level subsidenceand surfacegroundwater levels (Poff et al 2002 Kaplanet al 2010 Souter et al 2014) Studies such as ours caninform management procedures to explore the utility offreshwater release for coastal conservationVarious studies demonstrate the potential benefits of short

periods of increased freshwater flow to hydrologically alteredcoastal forests While hydrologic remediation lasted only 2 to4months in this study and the Souter et al 2014 study treeresponses were impressive After freshwater remediation inJLNHP amp P high levels of above-ground litter productionpersisted for several species for one or more growing season

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

(this study) Similarly healthy trees of Eucalyptuscamaldulensis Dehnh in the Murray River drainage (Austra-lia) vigorously grew more foliage while highly stressed ordefoliated trees responded positively but less vigorously fortwo growing seasons following ~2months of freshwaterrelease (Souter et al 2014) In the Lake Pontchartrain Basin ofLouisiana coastal Tdistichum trees grew two times fasterwith periodicflowof riverwater (Day et al 2012) In additionreproductive output was higher in 2010 and especially in 2011for certain tree species suggesting that resourcematchingmayhave occurred ie species varied reproductive output tomatchavailable resources (Kelly 1994) In the context of this studythe hydrologic remediation may have allowed these trees tobuild up their physiological resources via higher levels ofphotosynthetic activity prior to mass floweringEnvironmental flow prescriptions might revive moribund

coastal swamps yet no definitive range of flow amount ortiming has been identified to improve environments related tosalinity anoxia nutrients or other factors We linked sharplyhigher production of litter (leaf and reproductive) in 2010 tohydrologic remediation in salinity levels well below 20pptwith maximummeasured values at plots of EC vs PT sites 04

Ecohydrol 8 838ndash850 (2015)

Table V Analysis of variances of climate variables for JLNHP ampP from Marrero 9 SSW weather station data (NOAA 2013) foryears 2002ndash2012 remediation periods relative to the hydrologicremediation period in 2010 (pre-remediation remediation andpost-remediation) including mean monthly (a) total precipitation

and (b) temperature

Variable DF F p

(a) PrecipitationYear 10 12 03339Remediation period 2 21 01297Year times remediation period 20 11 04077

(b) TemperatureYear 10 01 09989Remediation period 2 817 lt00001 Year times remediation period 20 02 09999

DF degrees of freedom

Table IV Percentage of days exceeding predicted values for maximum and mean daily salinity levels (ppt) in the EC and PT unitsin JLNHP amp P (sites ECSECPECC vs PTPTV respectively)

Percent () days per year exceeding the specified maximum or minimum values of salinity (eg gt01 to 20 ppt) were predicted from linear regressionanalysis of surface salinity levels at CRMS 0234 and CRMS 0188 gauges (EC and PT units respectively) versus day-of-visit pore water salinity atproduction sites including ECSECPECC and PTPTV (Figure 4) Total days are the number of days per year during the growing season (1 Aprilndash31October 2008ndash2011) Published threshold salinity levels for forest tree maintenanceflooded seedling photosynthesis and basal area growth (size) arethought to be 20 and 07 ppt (in bold letters Kaplan et al 2010Pezeshki et al 1987 and Krauss et al 2009 respectively) Dark to light grey highlightsindicate percent () days per year exceeding maximum values as 70ndash100 30ndash70 1ndash30 and 0 respectivelyECS Education Center Spur ECP Education Center Parking ECC Education Center Canal PT Palmetto Trail PTV Palmetto Trail Visitors ECEducation Center JLNHP amp P Jean Lafitte National Historical Park amp Preserve

847HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

and 05ppt respectively (also see Figure 2a and Table IV) Incontrast to 2008 predicted levels of salinity were high in boththe EC and PT units (Table IV) and total annual leaf litterbiomass by individual species was low (A rubrum Tdistichum Fraxinuspennsylvanicum Mcerifera and Salixnigra Figure 2a and Table III) Nevertheless rendering asimple statement of an ideal threshold of salinity for theseswamps is impractical Among other problems field environ-ments are difficult to characterize simply (eg salinity levelsvary by depth in the vadose zone)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Trees in JLNHP amp P responded positively to remedia-tion but we recognize that this unplanned study did notpermit us to determine whether changes in salinity or someother unmeasured biogeochemical factors were ultimatelyresponsible for the observed responses Tidal flowreconnection in previously restricted salt marshes decreasessoil anoxia and sulphides and changes pH nutrientavailability and decomposition rates (Anisfeld and Benoit1997) The fact that we detected increased water levels anddecreased salinity with freshwater remediation indicatedthat other important site characteristics and biogeochemicalshifts likely were occurring at JLNHP amp P Unfortunatelywe do not have any other supportive data especially asrelated to any possible causal linkagesPhotosynthetic stressors such as salinity and anoxiamay be

more harmful during the growing season Flooding reducesregeneration seedlings and saplings of Tdistichum surviveovertopping by flooding while dormant but not during thegrowing season and most tree species will not germinateunderwater (Middleton 2000) A better understanding of anyseasonal component of remediation response is critical tohydrologic remediation planning for managementThe immediate mechanisms of increased tree production

with improved environment are not well studied but maybe related to the photosynthetic regulation of trees tochanges in environment As salinity (at some level) entersthe transpiration stream stomata close and photosynthesisdecreases (Stiller 2009) Any short-term increase in

Ecohydrol 8 838ndash850 (2015)

Figure 3 State of Louisiana water recorder information for maximum (a) daily discharge (m3 s1) from Davis Pond Diversion and adjusted water levels(m) at (b) Coastwide Reference Monitoring System (CRMS) 0234 and (c) CRMS 0188 and salinity (ppt) of (d) discharge of diversion and surface waterat (e) CRMS 00234 and (f) CRMS 0188 during hydrologically remediated (2010) versus lsquowetrsquo years (mean of 2008 2009 and 2011) CRMS 0234 andCRMS 0188 are in the same hydrological units as the Education Center and Palmetto Trail plots respectively in JLNHP amp P Pre-remediationremediation and post-remediation days of the year included days 1ndash119 120ndash244 and 245ndash365 respectively Sign tests indicated that 2010 was higherlower or not different from wet years as lsquo+rsquo lsquo-rsquo or lsquonsrsquo respectively (plt 00001) Only significant variables of time were kept p values for the sign testcomparisons were based on normally distributed error with constant variance All tests of fit were performed at p = 005 except that one test wasperformed at p = 001 to obtain a model fit Equations were based on the difference of the two year groups (2010 vs set of years compared) Mean dailydischarge values are not shown but these comparisons were also significant using similarly constructed ARIMA models and sign tests (plt 00001)Note that short periods of missing data were interpolated linearly Longer periods of missing data were omitted eg Davis Pond Diversion had nodischarge data available for 1ndash28 January 2010 Note that the measured water and salinity levels at plots in the EC and PT units were intermediate and

similar to each other (see Supplementary Figure 2)

848 B A MIDDLETON D JOHNSON AND B J ROBERTS

photosynthetic output and leaf production after freshwaterremediation is most likely to occur in healthy trees withrelatively intact leaf architecture such as Tdistichum in

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

JLNHP amp P or E camaldulensis trees along the MurrayRiver in Australia (Souter et al 2014) The positive effectsof remediation may have broad application in freshwater

Ecohydrol 8 838ndash850 (2015)

849HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

forests particularly because several species respondedpositively to freshwater remediation in JLNHP amp P

In our study litter but not root production increased duringthe year of hydrologic remediation If environment conditionsimproved in 2010 trees may have been experiencing a fastspurt of leaf litter production at the expense of roots(Figure 2b) Falling rootshoot ratios are an indicator of fastshoot growth in response to favourable environments (Harris1992 Litton et al 2007) and Tdistichum root and shootallocation patterns shift in response to changing resources(Megonigal and Day 1992) Note that we did not distinguishbetween species of roots in our study Alterations in root andshoot allocations following hydrologic remediationmay haveimportant implications for the elevation of subsiding swampsby influencing peat accumulation The decrease in rootgrowth during remediation is important because root tissuesoften contribute more to the accumulation of peat than leaf orwoody tissue (Middleton and McKee 2002) Whilereinvigorating the production of freshwater coastal vegetationoverall hydrologic remediation may reduce root growth forsome tree species at least temporarily (this study) Thereforea better understanding of the relationship of remediation androot growth is critical (Langley et al 2010 Wigand et al2014) to the development of management techniques relatedto remediation

CONCLUSION

Concerns are growing because of losses of coastal wetlandsalong the Gulf Coast (Kaplan et al 2010 CPRA 2012)Special attention should be given to our findings thatfreshwater release might reinvigorate the production offreshwater coastal vegetation Our study has worldwideimplications in that it demonstrates that sustained releases offreshwater can affect the primary production of many speciesFreshwater coastal species are increasingly affected bysaltwater intrusion so this idea deserves further explorationfor the management of coastal freshwater wetlands

ACKNOWLEDGEMENTS

This work is funded by the US Geological Survey andNational Science Foundation (DEB-1049838) Specialthanks are given to Evelyn Anemaet Mel McCulloughSamantha Primer Justin Stelly Lei Ting and GuodongWang for their field assistance Any use of trade productor firm names is for descriptive purposes only and does notimply endorsement by the US Government

CONFLICT OF INTEREST

The authors declare no conflict of interest with thisresearch

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

REFERENCES

Anemaet E Middleton BA 2013 Dendrometer bands made easy usingmodified cable ties to measure incremental growth of trees Applicationsin Plant Sciences 1 1300044

Anisfeld SC Benoit G 1997 Impacts of flow restriction on salt marshesan instance of acidification Environmental Science and Technology 311650ndash1699

Bianchi TS Cook RL Perdue EM Kolic PE Green N Zhang Y SmithRW Kolker AS Ameen A King G Ojwang LM Schneider CLNormand AE Hetland R 2011 Impacts of diverted freshwater ondissolved organic matter and microbial communities in Barataria BayLA Marine Environmental Research 72 248257

Brinson MM Bradshaw HD Holmes RN Elkins JB Jr 1980 Litterfallstemflow and throughfall nutrient fluxes in an alluvial swamp forestEcology 61 827ndash835

Cahoon DR Lynch JC Hensel P Boumans R Perez BC Segura B DayJW Jr 2002 A device for high precision measurement of wetlandsediment elevation I Recent improvements to the sedimentation-erosion table Journal of Sedimentary Research 72 730ndash733

Coastal Protection and Restoration Authority of Louisiana (CPRA) 2012Louisianarsquos Comprehensive Master Plan for a Sustainable CoastCPRA Baton Rouge LA

Coastal Protection and Restoration (CPRA) 2013 Modifications to theDavis Pond Diversion Louisiana Coastal Protection and RestorationBaton Rouge LA wwwlcagovProjects14Defaultaspx

Day JW 2000 Pattern and process of land loss in the Mississippi Delta aspatial and temporal analysis of wetland habitat change Estuaries 23425438

Day J Hunter R Keim RF DeLaune R Shaffer G Evers E Reed DBrantley C Kemp P Day J Hunter M 2012 Ecological response offorested wetlands with and without large-scale Mississippi River inputimplications for management Ecological Engineering 46 57 67

Dixon KR 1976 Analysis of seasonal leaf fall in north temperaturedeciduous forests Oikos 27 300306

Dokka RK 2006 Modern-day tectonic subsidence in coastal LouisianaGeology 34 281294

Greater NewOrleans Inc Regional Economic Alliance (GNO) 2010 A studyon the economic impact of the Deepwater Horizon oil spill GNORegionalEconomic Alliance New Orleans wwwuflibufledu docs Economic20Impact 20Study 20Part20I20-20Full20Reportpdf

Hertel D Leuschner C 2002 A comparison of four different fine rootproduction estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest Plant and Soil 239 237251

Hoeppner SS Schaffer GP Perkins TE 2008 Through droughts andhurricanes tree mortality forest structure and biomass production in acoastal swamp targeted for restoration in the Mississippi River DeltaicPlain Forest Ecology and Management 256 937948

Hughes FM Rood SB 2003 Allocation of river flows for restorationof floodplain forest ecosystems Environmental Management 321233

Harris RW 1992 Root-shoot ratios Journal of Arboriculture 18 39ndash42JMP SAS 2012 Statistical Analysis System v 1002 SAS Institute IncCary NC

Junk WJ Bayley PB Sparks RE 1989 The flood pulse concept in river-floodplain systems In Proceedings of the International Large RiverSymposium Vol 106 Canadian Special Publications in Fisheries andAquatic Science Ottawa Ontario Canada 110127

Kaplan D Muntildeoz-Carpena R Wan Y Hedgepeth M Zheng F Roberts RRossmanith R 2010 Linking river floodplain and vadose hydrology toimprove restoration of a coastal river affected by saltwater intrusionJournal of Environmental Quality 39 15701584

Kelly D 1994 The evolutionary ecology of mast seeding Trends inEcology and Evolution 9 465ndash470

Kingsford RT 2011 Conservation management of rivers and wetlandsunder climate change a synthesis Marine and Freshwater Research62 217222

Kozlowski TT 1997 Responses of woody plants to flooding and salinityTree Physiology 1 129

KraussKWDuberstein JADoyle TWConnerWHDayRH Inabinette LWWhitbeck JL 2009 Site condition structure and growth of baldcypressalong tidalnon-tidal salinity gradients Wetlands 29 505519

Ecohydrol 8 838ndash850 (2015)

Figure 2 Total annual mean production from 2007 to 2011 including (a)total litter biomass (leaf reproductive and wood) [g m2 y1 plusmn standarderror (SE)] and (b) total annual root biomass (total of all depths 0ndash30 cmg m2 y1 plusmn SE) in Jean Lafitte National Historical Park amp Preserve(n = 25) Different letters indicated that means of years differed statistically(one degree-of-freedom contrasts plt 005) (c) Regression analysis ofstem growth expressed as mean salinity (ppt) versus Taxodium distichumcircumference ratio plusmn SE along the Gulf Coast (R2 = 086) Salinity isbased on means of pore water salinity during day-of-visit measurements

844 B A MIDDLETON D JOHNSON AND B J ROBERTS

andor 2011 than in 2007ndash2009 for Acer rubrum (not in2007) Liquidambar styraciflua and M cerifera (Table IIaand Table III) Annual litterfall biomass of wood tissue didnot change from 2007 to 2011 although the mean wassubstantially higher in 2010 (Table IIb plt 005) Annuallog root biomass was higher in shallower than deeper soildepths (Figure 2b and Table IIb 0ndash10 vs 10ndash30 cmt=279 p=00058 N=5) and total root biomass variedby year and was 23ndash53 times lower in 2010 than in 2007ndash2011 (Figure 2b t=489 plt 00001 N=5)Neither tree nor knee growth varied with circumference

increasing by 18 plusmn 01 and 29 plusmn 10 respectively peryear during 2008ndash2011 in JLNHP amp P (pgt005Table IIcndashd) In JLNHP amp P we found no relationship

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

between tree growth and the percentage days per year a siteexceeded published thresholds of salinity (eg 07 or20 ppt pgt005 Table IV) In 2010 both EC and PT unitshad fewer days with salinity gt03 ppt and in 2008 moredays with salinity gt20 ppt (Table IV Figure 1 in theSupporting Information) Across the Gulf Coast Tdistichum growth varied from 011 to 21 increase incircumference per year with average annual salinityexplaining 86 of the variance in growth with the highestgrowth observed in the lowest mean pore water salinity(eg JLNHP amp P Figure 2c)

Climate and environment

Regionally mean annual precipitation was 13209plusmn1065mm per year from 2002 to 2012 (National Oceanicand Atmospheric Administration (NOAA) 2013) but didnot vary by year or remediation period (pgt 0130 Table V)Mean monthly air temperature did not vary by year but didvary by remediation period (mean monthly temperaturesduring pre-remediation remediation and post-remediation157 plusmn 06 degC 269 plusmn03 degC and 187 plusmn 08 degC respectivelyF=817 plt0001 Table V) (NOAA 2013)

Water and salinity responses to hydrologic remediation

Short-term water and salinity comparisons ndash 2010 versuswet years (2008ndash2011) Davis Pond CRMS 0188 andCRMS 0234 had higher dischargewater level and lowersalinity during the remediation period in 2010 than duringwet years As based on ARIMA time series comparisonswater discharged from Davis Pond in 2010 exceeded meanand maximum daily discharge of wet years (mean dailydischarge of 2010 vs wet years 113 out of 119 daysrespectively maximum daily discharge of 2010 vs wetyears 102 out of 119 days respectively sign testsplt 00001 Figure 3a and Table 2 in the SupportingInformation) Discharge rates from the Davis PondFreshwater Diversion and water levels at gauges werelower in 2010 during the post-remediation period than inwet years (Figure 3a and Table 2 in the SupportingInformation) Maximum daily gauge levels were higherduring hydrologic remediation in 2010 than in wet years(CRMS 0234 026 vs 011m respectively Figure 3bCRMS 0188 115 vs 106m respectively Figure 3c andTable 2 in the Supporting Information)Long-term gauging stations can be used to indicate

conditions at sites even though salinity relationships weresomewhat different (ie EC sites had significantly highersalinity than CRMS 0234 and PT sites had significantlylower salinity than CRMS 0188 as based on day-of-visitmeasurements) Salinity environments in the EC and PTsites were relatively similar (Figure 2 in the SupportingInformation) Nevertheless maximum daily water levels atCRMS 0234 were linearly related to day-of-visit water

Ecohydrol 8 838ndash850 (2015)

Table II Analysis of variances of production variables in JLNHP amp P from 2007 to 2011

DF F p Mean plusmn SE

(a) Total annual productionLitterfall (gm2 y1)Year 4 236 lt00001

Root biomass (gm2 y1)Year 4 84 lt00001 Depth 1 78 00225

Year times depth 4 10 04142 ns(b) Tissue typeLeafSpecies 15 155 lt00001 Year 4 1566 lt00001 Species times year 60 41 lt00001

ReproductiveSpecies 5 400 lt00001 Year 4 69 lt00001 Species times year 20 44 lt00001

WoodYear 4 21 00794 ns

(c) Tree growth (annual circumference ratio)Initial tree circumference (covariate) 1 38 00668 nsYear 3 01 09718 ns2008 1019210 plusmn 000552009 1018628 plusmn 000712010 1018855 plusmn 000382011 1015170 plusmn 00022

(d) Knee growth (annual circumference ratio)Initial knee circumference (covariate) 1 05 04945 nsYear 4 09 04628 ns

Mean total annual production of (a) litterfall (g m2 y1 including leaves reproductive material and wood) and log root biomass (g m3 y1) (b) Meanbiomass of tissue types of dominant species including leaf reproductive and wood Dendrometer bands were used to measure incremental increase incircumference growth was estimated as a year-to-year ratio of circumference change of Taxodium distichum from 2008 to 2011 for (c) trees and (d)knees Mean comparisons that differed based on contrasts indicated by lsquorsquo lsquorsquo or ns (plt 00001 plt 005 pgt 005 respectively Figure 2) SeeTable III for tissue type times species interactionsJLNHP amp P Jean Lafitte National Historical Park amp Preserve SE standard error DF degrees of freedom ns not significant

845HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

depths at SETs in the EC unit (ie SETs at ECP and ECSFigure 2 in the Supporting Information r= 06043p=00015) As indicated in the Section on Methods tojustify the selection of salinity variables and analysesoverall maximum daily values were within 105plusmn 00018of mean values Mean daily salinity levels at CRMS 0234and CRMS 0188 were linearly related to day-of-visitsalinity at SETs and plots within the same hydrologicalunits (EC unit r=0600 p=00004 Figure 2b in theSupporting Information PT unit r=0702 p=00005Figure 2c in the Supporting Information)

Long-term water level comparisons ndash 2010 versus long-term (2003ndash2011) Water discharge from Davis Pond in2010 during hydrologic remediation was higher than in thelong-term set of years (2003ndash2011 mean discharge perday =1983 plusmn 49 vs 331 plusmn 16m3 s1 respectively) andmaximum daily water levels at CRMS 0234 and CRMS0188 also were higher (sign tests plt00001 Figure 4 inthe Supporting Information)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Individual year water and salinity level comparisons ndash2010 vs 2006ndash2011 Comparisons of maximum dailywater level and salinity levels during 2010 to individualyears were similar to the comparisons of 2010 to sets ofwet and long-term years (ie 2008ndash2011 and 2003ndash2011respectively) As expected discharge levels for Davis Pondand water levels at CRMS 0234 and CRMS 0188 weresignificantly higher during hydrologic remediation in 2010compared with those in any individual year from 2006 to2011 (plt00001) One exception was that maximumsalinity was higher in 2010 than in 2009 at CRMS 0234(plt 00001)

DISCUSSION

Freshwater flow variability controls ecological processes inestuaries so that alteration of water delivery is a keyconservation challenge (Lester et al 2013) Unfortunatelyinformation on how to manage salinity flux in freshwaterwetlands in altered estuaries is lacking (Kaplan et al 2010

Ecohydrol 8 838ndash850 (2015)

Table III Means plusmn SE listed by species dominance of dry litterfall biomass (gm2) based on species times year interactions for leafreproductive and wood tissue from 2007 to 2011 in JLNHP amp P

Species

Year

2007 2008 2009 2010 2011

Leaf tissueTaxodium distichum 264 plusmn 48 b 150 plusmn 25 c 291 plusmn 48 b 723plusmn 91 a 590plusmn 112 a

Acer rubrum 239 plusmn 53 ab 123 plusmn 26 b 184 plusmn 435 b 249plusmn 45 a 258plusmn 47 a

Fraxinus pennsylvanica 65 plusmn 21 b 28 plusmn 09 c 117 plusmn 29 a 136 plusmn 38 a 34 plusmn 22 c

Liquidambar styraciflua 47 plusmn 14 b 23 plusmn 06 b 45 plusmn 17 b 69plusmn 14 a 49 plusmn 16 b

Nyssa aquatica 80 plusmn 26 a 09 plusmn 08 b 14 plusmn 12 b 19 plusmn 11 b 00 plusmn 00 b

Myrica cerifera 00 plusmn 00 c 18 plusmn 07 b 23 plusmn 07 b 41plusmn 12 a 21 plusmn 07 b

Salix nigra 22 plusmn 11 a 13 plusmn 09 a 02 plusmn 01 a 39 plusmn 35 a 17 plusmn 16 a

Ulmus americana 10 plusmn 06 a 01 plusmn 01 b 04 plusmn 02 b 14 plusmn 08 a 21 plusmn 09 a

Quercus nigra 07 plusmn 02 a 01 plusmnlt01 a 08 plusmn 03 a 16 plusmn 06 a 09 plusmn 05 a

Other leaf 12 plusmn 04 c 18 plusmn 07 c 26 plusmn 07 b 45 plusmn 15 b 144 plusmn 32 a

Cephalanthus occidentalis 23 plusmn 09 a 00 plusmn 00 b 01 plusmn 01 b lt01 plusmnlt01 b 00 plusmn 00 b

Acer spp 22 plusmn 18 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a

Carya aquatica 00 plusmn 00 a 18 plusmn 09 a 02 plusmn 02 a 00 plusmn 00 a 00 plusmn 00 a

Quercus spp (red) 05 plusmn 04 a 03 plusmn 02 a 02 plusmn 01 a 04 plusmn 02 a 00 plusmn 00 a

Triadica sebifera 00 plusmn 00 a 02 plusmn 01 a 01 plusmnlt01 a 09 plusmn 06 a 06 plusmn 03 a

Gleditsia aquatica 14 plusmn 06 a 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b

Reproductive tissueTaxodium distichum 65 plusmn 30 b 06 plusmn 04 c 55 plusmn 31 b 57 plusmn 18 b 325plusmn 139 a

Other reproductive lt01 plusmnlt01 b lt01 plusmnlt01 b 02 plusmn 01 b 02 plusmn 01 b 44plusmn 24 a

Fraxinus pennsylvanica 05 plusmn 01 b 04 plusmn 01 b 03 plusmn 01 b 25plusmn 07 a 01 plusmn 01 b

Liquidambar styraciflua 09 plusmn 09 a 00 plusmn 00 a lt01 plusmnlt01 a 05 plusmn 05 a 00 plusmn 00 a

Nyssa aquatica 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 04 plusmn 04 a 00 plusmn 00 a

Wood tissueWood total all species 22 plusmn 05 a 28 plusmn 12 a 50 plusmn 21 a 129 plusmn 54 a 92 plusmn 43 a

Different letters indicate significant differences of litterfall biomass of species based on one-degree-of-freedom contrasts Dominant species are listedwith biomass gt02 g m2 with the biomass of non-dominant species summed in an lsquootherrsquo group Species with significantly higher litterfall in 2010 andor 2011 after Bonferroni correction are listed in bold lettersSE standard error

846 B A MIDDLETON D JOHNSON AND B J ROBERTS

Kingsford 2011) Out of necessity programmes to manageflood flow are emerging in the United States AustraliaSouth Africa and to a lesser extent Europe (Hughes andRood 2003) As an example the Comprehensive MasterPlan for Louisiana has proposed to use diversions torelease river water and sediment to rebuild coastalwetlands (CPRA 2012) While managed flood releasesare used increasingly in restoration (Middleton 1999Schmidt et al 2001 Souter et al 2014) theseapproaches may become even more important as salinityincreases with changes in climate sea level subsidenceand surfacegroundwater levels (Poff et al 2002 Kaplanet al 2010 Souter et al 2014) Studies such as ours caninform management procedures to explore the utility offreshwater release for coastal conservationVarious studies demonstrate the potential benefits of short

periods of increased freshwater flow to hydrologically alteredcoastal forests While hydrologic remediation lasted only 2 to4months in this study and the Souter et al 2014 study treeresponses were impressive After freshwater remediation inJLNHP amp P high levels of above-ground litter productionpersisted for several species for one or more growing season

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

(this study) Similarly healthy trees of Eucalyptuscamaldulensis Dehnh in the Murray River drainage (Austra-lia) vigorously grew more foliage while highly stressed ordefoliated trees responded positively but less vigorously fortwo growing seasons following ~2months of freshwaterrelease (Souter et al 2014) In the Lake Pontchartrain Basin ofLouisiana coastal Tdistichum trees grew two times fasterwith periodicflowof riverwater (Day et al 2012) In additionreproductive output was higher in 2010 and especially in 2011for certain tree species suggesting that resourcematchingmayhave occurred ie species varied reproductive output tomatchavailable resources (Kelly 1994) In the context of this studythe hydrologic remediation may have allowed these trees tobuild up their physiological resources via higher levels ofphotosynthetic activity prior to mass floweringEnvironmental flow prescriptions might revive moribund

coastal swamps yet no definitive range of flow amount ortiming has been identified to improve environments related tosalinity anoxia nutrients or other factors We linked sharplyhigher production of litter (leaf and reproductive) in 2010 tohydrologic remediation in salinity levels well below 20pptwith maximummeasured values at plots of EC vs PT sites 04

Ecohydrol 8 838ndash850 (2015)

Table V Analysis of variances of climate variables for JLNHP ampP from Marrero 9 SSW weather station data (NOAA 2013) foryears 2002ndash2012 remediation periods relative to the hydrologicremediation period in 2010 (pre-remediation remediation andpost-remediation) including mean monthly (a) total precipitation

and (b) temperature

Variable DF F p

(a) PrecipitationYear 10 12 03339Remediation period 2 21 01297Year times remediation period 20 11 04077

(b) TemperatureYear 10 01 09989Remediation period 2 817 lt00001 Year times remediation period 20 02 09999

DF degrees of freedom

Table IV Percentage of days exceeding predicted values for maximum and mean daily salinity levels (ppt) in the EC and PT unitsin JLNHP amp P (sites ECSECPECC vs PTPTV respectively)

Percent () days per year exceeding the specified maximum or minimum values of salinity (eg gt01 to 20 ppt) were predicted from linear regressionanalysis of surface salinity levels at CRMS 0234 and CRMS 0188 gauges (EC and PT units respectively) versus day-of-visit pore water salinity atproduction sites including ECSECPECC and PTPTV (Figure 4) Total days are the number of days per year during the growing season (1 Aprilndash31October 2008ndash2011) Published threshold salinity levels for forest tree maintenanceflooded seedling photosynthesis and basal area growth (size) arethought to be 20 and 07 ppt (in bold letters Kaplan et al 2010Pezeshki et al 1987 and Krauss et al 2009 respectively) Dark to light grey highlightsindicate percent () days per year exceeding maximum values as 70ndash100 30ndash70 1ndash30 and 0 respectivelyECS Education Center Spur ECP Education Center Parking ECC Education Center Canal PT Palmetto Trail PTV Palmetto Trail Visitors ECEducation Center JLNHP amp P Jean Lafitte National Historical Park amp Preserve

847HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

and 05ppt respectively (also see Figure 2a and Table IV) Incontrast to 2008 predicted levels of salinity were high in boththe EC and PT units (Table IV) and total annual leaf litterbiomass by individual species was low (A rubrum Tdistichum Fraxinuspennsylvanicum Mcerifera and Salixnigra Figure 2a and Table III) Nevertheless rendering asimple statement of an ideal threshold of salinity for theseswamps is impractical Among other problems field environ-ments are difficult to characterize simply (eg salinity levelsvary by depth in the vadose zone)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Trees in JLNHP amp P responded positively to remedia-tion but we recognize that this unplanned study did notpermit us to determine whether changes in salinity or someother unmeasured biogeochemical factors were ultimatelyresponsible for the observed responses Tidal flowreconnection in previously restricted salt marshes decreasessoil anoxia and sulphides and changes pH nutrientavailability and decomposition rates (Anisfeld and Benoit1997) The fact that we detected increased water levels anddecreased salinity with freshwater remediation indicatedthat other important site characteristics and biogeochemicalshifts likely were occurring at JLNHP amp P Unfortunatelywe do not have any other supportive data especially asrelated to any possible causal linkagesPhotosynthetic stressors such as salinity and anoxiamay be

more harmful during the growing season Flooding reducesregeneration seedlings and saplings of Tdistichum surviveovertopping by flooding while dormant but not during thegrowing season and most tree species will not germinateunderwater (Middleton 2000) A better understanding of anyseasonal component of remediation response is critical tohydrologic remediation planning for managementThe immediate mechanisms of increased tree production

with improved environment are not well studied but maybe related to the photosynthetic regulation of trees tochanges in environment As salinity (at some level) entersthe transpiration stream stomata close and photosynthesisdecreases (Stiller 2009) Any short-term increase in

Ecohydrol 8 838ndash850 (2015)

Figure 3 State of Louisiana water recorder information for maximum (a) daily discharge (m3 s1) from Davis Pond Diversion and adjusted water levels(m) at (b) Coastwide Reference Monitoring System (CRMS) 0234 and (c) CRMS 0188 and salinity (ppt) of (d) discharge of diversion and surface waterat (e) CRMS 00234 and (f) CRMS 0188 during hydrologically remediated (2010) versus lsquowetrsquo years (mean of 2008 2009 and 2011) CRMS 0234 andCRMS 0188 are in the same hydrological units as the Education Center and Palmetto Trail plots respectively in JLNHP amp P Pre-remediationremediation and post-remediation days of the year included days 1ndash119 120ndash244 and 245ndash365 respectively Sign tests indicated that 2010 was higherlower or not different from wet years as lsquo+rsquo lsquo-rsquo or lsquonsrsquo respectively (plt 00001) Only significant variables of time were kept p values for the sign testcomparisons were based on normally distributed error with constant variance All tests of fit were performed at p = 005 except that one test wasperformed at p = 001 to obtain a model fit Equations were based on the difference of the two year groups (2010 vs set of years compared) Mean dailydischarge values are not shown but these comparisons were also significant using similarly constructed ARIMA models and sign tests (plt 00001)Note that short periods of missing data were interpolated linearly Longer periods of missing data were omitted eg Davis Pond Diversion had nodischarge data available for 1ndash28 January 2010 Note that the measured water and salinity levels at plots in the EC and PT units were intermediate and

similar to each other (see Supplementary Figure 2)

848 B A MIDDLETON D JOHNSON AND B J ROBERTS

photosynthetic output and leaf production after freshwaterremediation is most likely to occur in healthy trees withrelatively intact leaf architecture such as Tdistichum in

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

JLNHP amp P or E camaldulensis trees along the MurrayRiver in Australia (Souter et al 2014) The positive effectsof remediation may have broad application in freshwater

Ecohydrol 8 838ndash850 (2015)

849HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

forests particularly because several species respondedpositively to freshwater remediation in JLNHP amp P

In our study litter but not root production increased duringthe year of hydrologic remediation If environment conditionsimproved in 2010 trees may have been experiencing a fastspurt of leaf litter production at the expense of roots(Figure 2b) Falling rootshoot ratios are an indicator of fastshoot growth in response to favourable environments (Harris1992 Litton et al 2007) and Tdistichum root and shootallocation patterns shift in response to changing resources(Megonigal and Day 1992) Note that we did not distinguishbetween species of roots in our study Alterations in root andshoot allocations following hydrologic remediationmay haveimportant implications for the elevation of subsiding swampsby influencing peat accumulation The decrease in rootgrowth during remediation is important because root tissuesoften contribute more to the accumulation of peat than leaf orwoody tissue (Middleton and McKee 2002) Whilereinvigorating the production of freshwater coastal vegetationoverall hydrologic remediation may reduce root growth forsome tree species at least temporarily (this study) Thereforea better understanding of the relationship of remediation androot growth is critical (Langley et al 2010 Wigand et al2014) to the development of management techniques relatedto remediation

CONCLUSION

Concerns are growing because of losses of coastal wetlandsalong the Gulf Coast (Kaplan et al 2010 CPRA 2012)Special attention should be given to our findings thatfreshwater release might reinvigorate the production offreshwater coastal vegetation Our study has worldwideimplications in that it demonstrates that sustained releases offreshwater can affect the primary production of many speciesFreshwater coastal species are increasingly affected bysaltwater intrusion so this idea deserves further explorationfor the management of coastal freshwater wetlands

ACKNOWLEDGEMENTS

This work is funded by the US Geological Survey andNational Science Foundation (DEB-1049838) Specialthanks are given to Evelyn Anemaet Mel McCulloughSamantha Primer Justin Stelly Lei Ting and GuodongWang for their field assistance Any use of trade productor firm names is for descriptive purposes only and does notimply endorsement by the US Government

CONFLICT OF INTEREST

The authors declare no conflict of interest with thisresearch

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

REFERENCES

Anemaet E Middleton BA 2013 Dendrometer bands made easy usingmodified cable ties to measure incremental growth of trees Applicationsin Plant Sciences 1 1300044

Anisfeld SC Benoit G 1997 Impacts of flow restriction on salt marshesan instance of acidification Environmental Science and Technology 311650ndash1699

Bianchi TS Cook RL Perdue EM Kolic PE Green N Zhang Y SmithRW Kolker AS Ameen A King G Ojwang LM Schneider CLNormand AE Hetland R 2011 Impacts of diverted freshwater ondissolved organic matter and microbial communities in Barataria BayLA Marine Environmental Research 72 248257

Brinson MM Bradshaw HD Holmes RN Elkins JB Jr 1980 Litterfallstemflow and throughfall nutrient fluxes in an alluvial swamp forestEcology 61 827ndash835

Cahoon DR Lynch JC Hensel P Boumans R Perez BC Segura B DayJW Jr 2002 A device for high precision measurement of wetlandsediment elevation I Recent improvements to the sedimentation-erosion table Journal of Sedimentary Research 72 730ndash733

Coastal Protection and Restoration Authority of Louisiana (CPRA) 2012Louisianarsquos Comprehensive Master Plan for a Sustainable CoastCPRA Baton Rouge LA

Coastal Protection and Restoration (CPRA) 2013 Modifications to theDavis Pond Diversion Louisiana Coastal Protection and RestorationBaton Rouge LA wwwlcagovProjects14Defaultaspx

Day JW 2000 Pattern and process of land loss in the Mississippi Delta aspatial and temporal analysis of wetland habitat change Estuaries 23425438

Day J Hunter R Keim RF DeLaune R Shaffer G Evers E Reed DBrantley C Kemp P Day J Hunter M 2012 Ecological response offorested wetlands with and without large-scale Mississippi River inputimplications for management Ecological Engineering 46 57 67

Dixon KR 1976 Analysis of seasonal leaf fall in north temperaturedeciduous forests Oikos 27 300306

Dokka RK 2006 Modern-day tectonic subsidence in coastal LouisianaGeology 34 281294

Greater NewOrleans Inc Regional Economic Alliance (GNO) 2010 A studyon the economic impact of the Deepwater Horizon oil spill GNORegionalEconomic Alliance New Orleans wwwuflibufledu docs Economic20Impact 20Study 20Part20I20-20Full20Reportpdf

Hertel D Leuschner C 2002 A comparison of four different fine rootproduction estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest Plant and Soil 239 237251

Hoeppner SS Schaffer GP Perkins TE 2008 Through droughts andhurricanes tree mortality forest structure and biomass production in acoastal swamp targeted for restoration in the Mississippi River DeltaicPlain Forest Ecology and Management 256 937948

Hughes FM Rood SB 2003 Allocation of river flows for restorationof floodplain forest ecosystems Environmental Management 321233

Harris RW 1992 Root-shoot ratios Journal of Arboriculture 18 39ndash42JMP SAS 2012 Statistical Analysis System v 1002 SAS Institute IncCary NC

Junk WJ Bayley PB Sparks RE 1989 The flood pulse concept in river-floodplain systems In Proceedings of the International Large RiverSymposium Vol 106 Canadian Special Publications in Fisheries andAquatic Science Ottawa Ontario Canada 110127

Kaplan D Muntildeoz-Carpena R Wan Y Hedgepeth M Zheng F Roberts RRossmanith R 2010 Linking river floodplain and vadose hydrology toimprove restoration of a coastal river affected by saltwater intrusionJournal of Environmental Quality 39 15701584

Kelly D 1994 The evolutionary ecology of mast seeding Trends inEcology and Evolution 9 465ndash470

Kingsford RT 2011 Conservation management of rivers and wetlandsunder climate change a synthesis Marine and Freshwater Research62 217222

Kozlowski TT 1997 Responses of woody plants to flooding and salinityTree Physiology 1 129

KraussKWDuberstein JADoyle TWConnerWHDayRH Inabinette LWWhitbeck JL 2009 Site condition structure and growth of baldcypressalong tidalnon-tidal salinity gradients Wetlands 29 505519

Ecohydrol 8 838ndash850 (2015)

Table II Analysis of variances of production variables in JLNHP amp P from 2007 to 2011

DF F p Mean plusmn SE

(a) Total annual productionLitterfall (gm2 y1)Year 4 236 lt00001

Root biomass (gm2 y1)Year 4 84 lt00001 Depth 1 78 00225

Year times depth 4 10 04142 ns(b) Tissue typeLeafSpecies 15 155 lt00001 Year 4 1566 lt00001 Species times year 60 41 lt00001

ReproductiveSpecies 5 400 lt00001 Year 4 69 lt00001 Species times year 20 44 lt00001

WoodYear 4 21 00794 ns

(c) Tree growth (annual circumference ratio)Initial tree circumference (covariate) 1 38 00668 nsYear 3 01 09718 ns2008 1019210 plusmn 000552009 1018628 plusmn 000712010 1018855 plusmn 000382011 1015170 plusmn 00022

(d) Knee growth (annual circumference ratio)Initial knee circumference (covariate) 1 05 04945 nsYear 4 09 04628 ns

Mean total annual production of (a) litterfall (g m2 y1 including leaves reproductive material and wood) and log root biomass (g m3 y1) (b) Meanbiomass of tissue types of dominant species including leaf reproductive and wood Dendrometer bands were used to measure incremental increase incircumference growth was estimated as a year-to-year ratio of circumference change of Taxodium distichum from 2008 to 2011 for (c) trees and (d)knees Mean comparisons that differed based on contrasts indicated by lsquorsquo lsquorsquo or ns (plt 00001 plt 005 pgt 005 respectively Figure 2) SeeTable III for tissue type times species interactionsJLNHP amp P Jean Lafitte National Historical Park amp Preserve SE standard error DF degrees of freedom ns not significant

845HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

depths at SETs in the EC unit (ie SETs at ECP and ECSFigure 2 in the Supporting Information r= 06043p=00015) As indicated in the Section on Methods tojustify the selection of salinity variables and analysesoverall maximum daily values were within 105plusmn 00018of mean values Mean daily salinity levels at CRMS 0234and CRMS 0188 were linearly related to day-of-visitsalinity at SETs and plots within the same hydrologicalunits (EC unit r=0600 p=00004 Figure 2b in theSupporting Information PT unit r=0702 p=00005Figure 2c in the Supporting Information)

Long-term water level comparisons ndash 2010 versus long-term (2003ndash2011) Water discharge from Davis Pond in2010 during hydrologic remediation was higher than in thelong-term set of years (2003ndash2011 mean discharge perday =1983 plusmn 49 vs 331 plusmn 16m3 s1 respectively) andmaximum daily water levels at CRMS 0234 and CRMS0188 also were higher (sign tests plt00001 Figure 4 inthe Supporting Information)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Individual year water and salinity level comparisons ndash2010 vs 2006ndash2011 Comparisons of maximum dailywater level and salinity levels during 2010 to individualyears were similar to the comparisons of 2010 to sets ofwet and long-term years (ie 2008ndash2011 and 2003ndash2011respectively) As expected discharge levels for Davis Pondand water levels at CRMS 0234 and CRMS 0188 weresignificantly higher during hydrologic remediation in 2010compared with those in any individual year from 2006 to2011 (plt00001) One exception was that maximumsalinity was higher in 2010 than in 2009 at CRMS 0234(plt 00001)

DISCUSSION

Freshwater flow variability controls ecological processes inestuaries so that alteration of water delivery is a keyconservation challenge (Lester et al 2013) Unfortunatelyinformation on how to manage salinity flux in freshwaterwetlands in altered estuaries is lacking (Kaplan et al 2010

Ecohydrol 8 838ndash850 (2015)

Table III Means plusmn SE listed by species dominance of dry litterfall biomass (gm2) based on species times year interactions for leafreproductive and wood tissue from 2007 to 2011 in JLNHP amp P

Species

Year

2007 2008 2009 2010 2011

Leaf tissueTaxodium distichum 264 plusmn 48 b 150 plusmn 25 c 291 plusmn 48 b 723plusmn 91 a 590plusmn 112 a

Acer rubrum 239 plusmn 53 ab 123 plusmn 26 b 184 plusmn 435 b 249plusmn 45 a 258plusmn 47 a

Fraxinus pennsylvanica 65 plusmn 21 b 28 plusmn 09 c 117 plusmn 29 a 136 plusmn 38 a 34 plusmn 22 c

Liquidambar styraciflua 47 plusmn 14 b 23 plusmn 06 b 45 plusmn 17 b 69plusmn 14 a 49 plusmn 16 b

Nyssa aquatica 80 plusmn 26 a 09 plusmn 08 b 14 plusmn 12 b 19 plusmn 11 b 00 plusmn 00 b

Myrica cerifera 00 plusmn 00 c 18 plusmn 07 b 23 plusmn 07 b 41plusmn 12 a 21 plusmn 07 b

Salix nigra 22 plusmn 11 a 13 plusmn 09 a 02 plusmn 01 a 39 plusmn 35 a 17 plusmn 16 a

Ulmus americana 10 plusmn 06 a 01 plusmn 01 b 04 plusmn 02 b 14 plusmn 08 a 21 plusmn 09 a

Quercus nigra 07 plusmn 02 a 01 plusmnlt01 a 08 plusmn 03 a 16 plusmn 06 a 09 plusmn 05 a

Other leaf 12 plusmn 04 c 18 plusmn 07 c 26 plusmn 07 b 45 plusmn 15 b 144 plusmn 32 a

Cephalanthus occidentalis 23 plusmn 09 a 00 plusmn 00 b 01 plusmn 01 b lt01 plusmnlt01 b 00 plusmn 00 b

Acer spp 22 plusmn 18 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a

Carya aquatica 00 plusmn 00 a 18 plusmn 09 a 02 plusmn 02 a 00 plusmn 00 a 00 plusmn 00 a

Quercus spp (red) 05 plusmn 04 a 03 plusmn 02 a 02 plusmn 01 a 04 plusmn 02 a 00 plusmn 00 a

Triadica sebifera 00 plusmn 00 a 02 plusmn 01 a 01 plusmnlt01 a 09 plusmn 06 a 06 plusmn 03 a

Gleditsia aquatica 14 plusmn 06 a 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b

Reproductive tissueTaxodium distichum 65 plusmn 30 b 06 plusmn 04 c 55 plusmn 31 b 57 plusmn 18 b 325plusmn 139 a

Other reproductive lt01 plusmnlt01 b lt01 plusmnlt01 b 02 plusmn 01 b 02 plusmn 01 b 44plusmn 24 a

Fraxinus pennsylvanica 05 plusmn 01 b 04 plusmn 01 b 03 plusmn 01 b 25plusmn 07 a 01 plusmn 01 b

Liquidambar styraciflua 09 plusmn 09 a 00 plusmn 00 a lt01 plusmnlt01 a 05 plusmn 05 a 00 plusmn 00 a

Nyssa aquatica 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 04 plusmn 04 a 00 plusmn 00 a

Wood tissueWood total all species 22 plusmn 05 a 28 plusmn 12 a 50 plusmn 21 a 129 plusmn 54 a 92 plusmn 43 a

Different letters indicate significant differences of litterfall biomass of species based on one-degree-of-freedom contrasts Dominant species are listedwith biomass gt02 g m2 with the biomass of non-dominant species summed in an lsquootherrsquo group Species with significantly higher litterfall in 2010 andor 2011 after Bonferroni correction are listed in bold lettersSE standard error

846 B A MIDDLETON D JOHNSON AND B J ROBERTS

Kingsford 2011) Out of necessity programmes to manageflood flow are emerging in the United States AustraliaSouth Africa and to a lesser extent Europe (Hughes andRood 2003) As an example the Comprehensive MasterPlan for Louisiana has proposed to use diversions torelease river water and sediment to rebuild coastalwetlands (CPRA 2012) While managed flood releasesare used increasingly in restoration (Middleton 1999Schmidt et al 2001 Souter et al 2014) theseapproaches may become even more important as salinityincreases with changes in climate sea level subsidenceand surfacegroundwater levels (Poff et al 2002 Kaplanet al 2010 Souter et al 2014) Studies such as ours caninform management procedures to explore the utility offreshwater release for coastal conservationVarious studies demonstrate the potential benefits of short

periods of increased freshwater flow to hydrologically alteredcoastal forests While hydrologic remediation lasted only 2 to4months in this study and the Souter et al 2014 study treeresponses were impressive After freshwater remediation inJLNHP amp P high levels of above-ground litter productionpersisted for several species for one or more growing season

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

(this study) Similarly healthy trees of Eucalyptuscamaldulensis Dehnh in the Murray River drainage (Austra-lia) vigorously grew more foliage while highly stressed ordefoliated trees responded positively but less vigorously fortwo growing seasons following ~2months of freshwaterrelease (Souter et al 2014) In the Lake Pontchartrain Basin ofLouisiana coastal Tdistichum trees grew two times fasterwith periodicflowof riverwater (Day et al 2012) In additionreproductive output was higher in 2010 and especially in 2011for certain tree species suggesting that resourcematchingmayhave occurred ie species varied reproductive output tomatchavailable resources (Kelly 1994) In the context of this studythe hydrologic remediation may have allowed these trees tobuild up their physiological resources via higher levels ofphotosynthetic activity prior to mass floweringEnvironmental flow prescriptions might revive moribund

coastal swamps yet no definitive range of flow amount ortiming has been identified to improve environments related tosalinity anoxia nutrients or other factors We linked sharplyhigher production of litter (leaf and reproductive) in 2010 tohydrologic remediation in salinity levels well below 20pptwith maximummeasured values at plots of EC vs PT sites 04

Ecohydrol 8 838ndash850 (2015)

Table V Analysis of variances of climate variables for JLNHP ampP from Marrero 9 SSW weather station data (NOAA 2013) foryears 2002ndash2012 remediation periods relative to the hydrologicremediation period in 2010 (pre-remediation remediation andpost-remediation) including mean monthly (a) total precipitation

and (b) temperature

Variable DF F p

(a) PrecipitationYear 10 12 03339Remediation period 2 21 01297Year times remediation period 20 11 04077

(b) TemperatureYear 10 01 09989Remediation period 2 817 lt00001 Year times remediation period 20 02 09999

DF degrees of freedom

Table IV Percentage of days exceeding predicted values for maximum and mean daily salinity levels (ppt) in the EC and PT unitsin JLNHP amp P (sites ECSECPECC vs PTPTV respectively)

Percent () days per year exceeding the specified maximum or minimum values of salinity (eg gt01 to 20 ppt) were predicted from linear regressionanalysis of surface salinity levels at CRMS 0234 and CRMS 0188 gauges (EC and PT units respectively) versus day-of-visit pore water salinity atproduction sites including ECSECPECC and PTPTV (Figure 4) Total days are the number of days per year during the growing season (1 Aprilndash31October 2008ndash2011) Published threshold salinity levels for forest tree maintenanceflooded seedling photosynthesis and basal area growth (size) arethought to be 20 and 07 ppt (in bold letters Kaplan et al 2010Pezeshki et al 1987 and Krauss et al 2009 respectively) Dark to light grey highlightsindicate percent () days per year exceeding maximum values as 70ndash100 30ndash70 1ndash30 and 0 respectivelyECS Education Center Spur ECP Education Center Parking ECC Education Center Canal PT Palmetto Trail PTV Palmetto Trail Visitors ECEducation Center JLNHP amp P Jean Lafitte National Historical Park amp Preserve

847HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

and 05ppt respectively (also see Figure 2a and Table IV) Incontrast to 2008 predicted levels of salinity were high in boththe EC and PT units (Table IV) and total annual leaf litterbiomass by individual species was low (A rubrum Tdistichum Fraxinuspennsylvanicum Mcerifera and Salixnigra Figure 2a and Table III) Nevertheless rendering asimple statement of an ideal threshold of salinity for theseswamps is impractical Among other problems field environ-ments are difficult to characterize simply (eg salinity levelsvary by depth in the vadose zone)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Trees in JLNHP amp P responded positively to remedia-tion but we recognize that this unplanned study did notpermit us to determine whether changes in salinity or someother unmeasured biogeochemical factors were ultimatelyresponsible for the observed responses Tidal flowreconnection in previously restricted salt marshes decreasessoil anoxia and sulphides and changes pH nutrientavailability and decomposition rates (Anisfeld and Benoit1997) The fact that we detected increased water levels anddecreased salinity with freshwater remediation indicatedthat other important site characteristics and biogeochemicalshifts likely were occurring at JLNHP amp P Unfortunatelywe do not have any other supportive data especially asrelated to any possible causal linkagesPhotosynthetic stressors such as salinity and anoxiamay be

more harmful during the growing season Flooding reducesregeneration seedlings and saplings of Tdistichum surviveovertopping by flooding while dormant but not during thegrowing season and most tree species will not germinateunderwater (Middleton 2000) A better understanding of anyseasonal component of remediation response is critical tohydrologic remediation planning for managementThe immediate mechanisms of increased tree production

with improved environment are not well studied but maybe related to the photosynthetic regulation of trees tochanges in environment As salinity (at some level) entersthe transpiration stream stomata close and photosynthesisdecreases (Stiller 2009) Any short-term increase in

Ecohydrol 8 838ndash850 (2015)

Figure 3 State of Louisiana water recorder information for maximum (a) daily discharge (m3 s1) from Davis Pond Diversion and adjusted water levels(m) at (b) Coastwide Reference Monitoring System (CRMS) 0234 and (c) CRMS 0188 and salinity (ppt) of (d) discharge of diversion and surface waterat (e) CRMS 00234 and (f) CRMS 0188 during hydrologically remediated (2010) versus lsquowetrsquo years (mean of 2008 2009 and 2011) CRMS 0234 andCRMS 0188 are in the same hydrological units as the Education Center and Palmetto Trail plots respectively in JLNHP amp P Pre-remediationremediation and post-remediation days of the year included days 1ndash119 120ndash244 and 245ndash365 respectively Sign tests indicated that 2010 was higherlower or not different from wet years as lsquo+rsquo lsquo-rsquo or lsquonsrsquo respectively (plt 00001) Only significant variables of time were kept p values for the sign testcomparisons were based on normally distributed error with constant variance All tests of fit were performed at p = 005 except that one test wasperformed at p = 001 to obtain a model fit Equations were based on the difference of the two year groups (2010 vs set of years compared) Mean dailydischarge values are not shown but these comparisons were also significant using similarly constructed ARIMA models and sign tests (plt 00001)Note that short periods of missing data were interpolated linearly Longer periods of missing data were omitted eg Davis Pond Diversion had nodischarge data available for 1ndash28 January 2010 Note that the measured water and salinity levels at plots in the EC and PT units were intermediate and

similar to each other (see Supplementary Figure 2)

848 B A MIDDLETON D JOHNSON AND B J ROBERTS

photosynthetic output and leaf production after freshwaterremediation is most likely to occur in healthy trees withrelatively intact leaf architecture such as Tdistichum in

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

JLNHP amp P or E camaldulensis trees along the MurrayRiver in Australia (Souter et al 2014) The positive effectsof remediation may have broad application in freshwater

Ecohydrol 8 838ndash850 (2015)

849HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

forests particularly because several species respondedpositively to freshwater remediation in JLNHP amp P

In our study litter but not root production increased duringthe year of hydrologic remediation If environment conditionsimproved in 2010 trees may have been experiencing a fastspurt of leaf litter production at the expense of roots(Figure 2b) Falling rootshoot ratios are an indicator of fastshoot growth in response to favourable environments (Harris1992 Litton et al 2007) and Tdistichum root and shootallocation patterns shift in response to changing resources(Megonigal and Day 1992) Note that we did not distinguishbetween species of roots in our study Alterations in root andshoot allocations following hydrologic remediationmay haveimportant implications for the elevation of subsiding swampsby influencing peat accumulation The decrease in rootgrowth during remediation is important because root tissuesoften contribute more to the accumulation of peat than leaf orwoody tissue (Middleton and McKee 2002) Whilereinvigorating the production of freshwater coastal vegetationoverall hydrologic remediation may reduce root growth forsome tree species at least temporarily (this study) Thereforea better understanding of the relationship of remediation androot growth is critical (Langley et al 2010 Wigand et al2014) to the development of management techniques relatedto remediation

CONCLUSION

Concerns are growing because of losses of coastal wetlandsalong the Gulf Coast (Kaplan et al 2010 CPRA 2012)Special attention should be given to our findings thatfreshwater release might reinvigorate the production offreshwater coastal vegetation Our study has worldwideimplications in that it demonstrates that sustained releases offreshwater can affect the primary production of many speciesFreshwater coastal species are increasingly affected bysaltwater intrusion so this idea deserves further explorationfor the management of coastal freshwater wetlands

ACKNOWLEDGEMENTS

This work is funded by the US Geological Survey andNational Science Foundation (DEB-1049838) Specialthanks are given to Evelyn Anemaet Mel McCulloughSamantha Primer Justin Stelly Lei Ting and GuodongWang for their field assistance Any use of trade productor firm names is for descriptive purposes only and does notimply endorsement by the US Government

CONFLICT OF INTEREST

The authors declare no conflict of interest with thisresearch

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

REFERENCES

Anemaet E Middleton BA 2013 Dendrometer bands made easy usingmodified cable ties to measure incremental growth of trees Applicationsin Plant Sciences 1 1300044

Anisfeld SC Benoit G 1997 Impacts of flow restriction on salt marshesan instance of acidification Environmental Science and Technology 311650ndash1699

Bianchi TS Cook RL Perdue EM Kolic PE Green N Zhang Y SmithRW Kolker AS Ameen A King G Ojwang LM Schneider CLNormand AE Hetland R 2011 Impacts of diverted freshwater ondissolved organic matter and microbial communities in Barataria BayLA Marine Environmental Research 72 248257

Brinson MM Bradshaw HD Holmes RN Elkins JB Jr 1980 Litterfallstemflow and throughfall nutrient fluxes in an alluvial swamp forestEcology 61 827ndash835

Cahoon DR Lynch JC Hensel P Boumans R Perez BC Segura B DayJW Jr 2002 A device for high precision measurement of wetlandsediment elevation I Recent improvements to the sedimentation-erosion table Journal of Sedimentary Research 72 730ndash733

Coastal Protection and Restoration Authority of Louisiana (CPRA) 2012Louisianarsquos Comprehensive Master Plan for a Sustainable CoastCPRA Baton Rouge LA

Coastal Protection and Restoration (CPRA) 2013 Modifications to theDavis Pond Diversion Louisiana Coastal Protection and RestorationBaton Rouge LA wwwlcagovProjects14Defaultaspx

Day JW 2000 Pattern and process of land loss in the Mississippi Delta aspatial and temporal analysis of wetland habitat change Estuaries 23425438

Day J Hunter R Keim RF DeLaune R Shaffer G Evers E Reed DBrantley C Kemp P Day J Hunter M 2012 Ecological response offorested wetlands with and without large-scale Mississippi River inputimplications for management Ecological Engineering 46 57 67

Dixon KR 1976 Analysis of seasonal leaf fall in north temperaturedeciduous forests Oikos 27 300306

Dokka RK 2006 Modern-day tectonic subsidence in coastal LouisianaGeology 34 281294

Greater NewOrleans Inc Regional Economic Alliance (GNO) 2010 A studyon the economic impact of the Deepwater Horizon oil spill GNORegionalEconomic Alliance New Orleans wwwuflibufledu docs Economic20Impact 20Study 20Part20I20-20Full20Reportpdf

Hertel D Leuschner C 2002 A comparison of four different fine rootproduction estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest Plant and Soil 239 237251

Hoeppner SS Schaffer GP Perkins TE 2008 Through droughts andhurricanes tree mortality forest structure and biomass production in acoastal swamp targeted for restoration in the Mississippi River DeltaicPlain Forest Ecology and Management 256 937948

Hughes FM Rood SB 2003 Allocation of river flows for restorationof floodplain forest ecosystems Environmental Management 321233

Harris RW 1992 Root-shoot ratios Journal of Arboriculture 18 39ndash42JMP SAS 2012 Statistical Analysis System v 1002 SAS Institute IncCary NC

Junk WJ Bayley PB Sparks RE 1989 The flood pulse concept in river-floodplain systems In Proceedings of the International Large RiverSymposium Vol 106 Canadian Special Publications in Fisheries andAquatic Science Ottawa Ontario Canada 110127

Kaplan D Muntildeoz-Carpena R Wan Y Hedgepeth M Zheng F Roberts RRossmanith R 2010 Linking river floodplain and vadose hydrology toimprove restoration of a coastal river affected by saltwater intrusionJournal of Environmental Quality 39 15701584

Kelly D 1994 The evolutionary ecology of mast seeding Trends inEcology and Evolution 9 465ndash470

Kingsford RT 2011 Conservation management of rivers and wetlandsunder climate change a synthesis Marine and Freshwater Research62 217222

Kozlowski TT 1997 Responses of woody plants to flooding and salinityTree Physiology 1 129

KraussKWDuberstein JADoyle TWConnerWHDayRH Inabinette LWWhitbeck JL 2009 Site condition structure and growth of baldcypressalong tidalnon-tidal salinity gradients Wetlands 29 505519

Ecohydrol 8 838ndash850 (2015)

Table III Means plusmn SE listed by species dominance of dry litterfall biomass (gm2) based on species times year interactions for leafreproductive and wood tissue from 2007 to 2011 in JLNHP amp P

Species

Year

2007 2008 2009 2010 2011

Leaf tissueTaxodium distichum 264 plusmn 48 b 150 plusmn 25 c 291 plusmn 48 b 723plusmn 91 a 590plusmn 112 a

Acer rubrum 239 plusmn 53 ab 123 plusmn 26 b 184 plusmn 435 b 249plusmn 45 a 258plusmn 47 a

Fraxinus pennsylvanica 65 plusmn 21 b 28 plusmn 09 c 117 plusmn 29 a 136 plusmn 38 a 34 plusmn 22 c

Liquidambar styraciflua 47 plusmn 14 b 23 plusmn 06 b 45 plusmn 17 b 69plusmn 14 a 49 plusmn 16 b

Nyssa aquatica 80 plusmn 26 a 09 plusmn 08 b 14 plusmn 12 b 19 plusmn 11 b 00 plusmn 00 b

Myrica cerifera 00 plusmn 00 c 18 plusmn 07 b 23 plusmn 07 b 41plusmn 12 a 21 plusmn 07 b

Salix nigra 22 plusmn 11 a 13 plusmn 09 a 02 plusmn 01 a 39 plusmn 35 a 17 plusmn 16 a

Ulmus americana 10 plusmn 06 a 01 plusmn 01 b 04 plusmn 02 b 14 plusmn 08 a 21 plusmn 09 a

Quercus nigra 07 plusmn 02 a 01 plusmnlt01 a 08 plusmn 03 a 16 plusmn 06 a 09 plusmn 05 a

Other leaf 12 plusmn 04 c 18 plusmn 07 c 26 plusmn 07 b 45 plusmn 15 b 144 plusmn 32 a

Cephalanthus occidentalis 23 plusmn 09 a 00 plusmn 00 b 01 plusmn 01 b lt01 plusmnlt01 b 00 plusmn 00 b

Acer spp 22 plusmn 18 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a

Carya aquatica 00 plusmn 00 a 18 plusmn 09 a 02 plusmn 02 a 00 plusmn 00 a 00 plusmn 00 a

Quercus spp (red) 05 plusmn 04 a 03 plusmn 02 a 02 plusmn 01 a 04 plusmn 02 a 00 plusmn 00 a

Triadica sebifera 00 plusmn 00 a 02 plusmn 01 a 01 plusmnlt01 a 09 plusmn 06 a 06 plusmn 03 a

Gleditsia aquatica 14 plusmn 06 a 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b 00 plusmn 00 b

Reproductive tissueTaxodium distichum 65 plusmn 30 b 06 plusmn 04 c 55 plusmn 31 b 57 plusmn 18 b 325plusmn 139 a

Other reproductive lt01 plusmnlt01 b lt01 plusmnlt01 b 02 plusmn 01 b 02 plusmn 01 b 44plusmn 24 a

Fraxinus pennsylvanica 05 plusmn 01 b 04 plusmn 01 b 03 plusmn 01 b 25plusmn 07 a 01 plusmn 01 b

Liquidambar styraciflua 09 plusmn 09 a 00 plusmn 00 a lt01 plusmnlt01 a 05 plusmn 05 a 00 plusmn 00 a

Nyssa aquatica 00 plusmn 00 a 00 plusmn 00 a 00 plusmn 00 a 04 plusmn 04 a 00 plusmn 00 a

Wood tissueWood total all species 22 plusmn 05 a 28 plusmn 12 a 50 plusmn 21 a 129 plusmn 54 a 92 plusmn 43 a

Different letters indicate significant differences of litterfall biomass of species based on one-degree-of-freedom contrasts Dominant species are listedwith biomass gt02 g m2 with the biomass of non-dominant species summed in an lsquootherrsquo group Species with significantly higher litterfall in 2010 andor 2011 after Bonferroni correction are listed in bold lettersSE standard error

846 B A MIDDLETON D JOHNSON AND B J ROBERTS

Kingsford 2011) Out of necessity programmes to manageflood flow are emerging in the United States AustraliaSouth Africa and to a lesser extent Europe (Hughes andRood 2003) As an example the Comprehensive MasterPlan for Louisiana has proposed to use diversions torelease river water and sediment to rebuild coastalwetlands (CPRA 2012) While managed flood releasesare used increasingly in restoration (Middleton 1999Schmidt et al 2001 Souter et al 2014) theseapproaches may become even more important as salinityincreases with changes in climate sea level subsidenceand surfacegroundwater levels (Poff et al 2002 Kaplanet al 2010 Souter et al 2014) Studies such as ours caninform management procedures to explore the utility offreshwater release for coastal conservationVarious studies demonstrate the potential benefits of short

periods of increased freshwater flow to hydrologically alteredcoastal forests While hydrologic remediation lasted only 2 to4months in this study and the Souter et al 2014 study treeresponses were impressive After freshwater remediation inJLNHP amp P high levels of above-ground litter productionpersisted for several species for one or more growing season

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

(this study) Similarly healthy trees of Eucalyptuscamaldulensis Dehnh in the Murray River drainage (Austra-lia) vigorously grew more foliage while highly stressed ordefoliated trees responded positively but less vigorously fortwo growing seasons following ~2months of freshwaterrelease (Souter et al 2014) In the Lake Pontchartrain Basin ofLouisiana coastal Tdistichum trees grew two times fasterwith periodicflowof riverwater (Day et al 2012) In additionreproductive output was higher in 2010 and especially in 2011for certain tree species suggesting that resourcematchingmayhave occurred ie species varied reproductive output tomatchavailable resources (Kelly 1994) In the context of this studythe hydrologic remediation may have allowed these trees tobuild up their physiological resources via higher levels ofphotosynthetic activity prior to mass floweringEnvironmental flow prescriptions might revive moribund

coastal swamps yet no definitive range of flow amount ortiming has been identified to improve environments related tosalinity anoxia nutrients or other factors We linked sharplyhigher production of litter (leaf and reproductive) in 2010 tohydrologic remediation in salinity levels well below 20pptwith maximummeasured values at plots of EC vs PT sites 04

Ecohydrol 8 838ndash850 (2015)

Table V Analysis of variances of climate variables for JLNHP ampP from Marrero 9 SSW weather station data (NOAA 2013) foryears 2002ndash2012 remediation periods relative to the hydrologicremediation period in 2010 (pre-remediation remediation andpost-remediation) including mean monthly (a) total precipitation

and (b) temperature

Variable DF F p

(a) PrecipitationYear 10 12 03339Remediation period 2 21 01297Year times remediation period 20 11 04077

(b) TemperatureYear 10 01 09989Remediation period 2 817 lt00001 Year times remediation period 20 02 09999

DF degrees of freedom

Table IV Percentage of days exceeding predicted values for maximum and mean daily salinity levels (ppt) in the EC and PT unitsin JLNHP amp P (sites ECSECPECC vs PTPTV respectively)

Percent () days per year exceeding the specified maximum or minimum values of salinity (eg gt01 to 20 ppt) were predicted from linear regressionanalysis of surface salinity levels at CRMS 0234 and CRMS 0188 gauges (EC and PT units respectively) versus day-of-visit pore water salinity atproduction sites including ECSECPECC and PTPTV (Figure 4) Total days are the number of days per year during the growing season (1 Aprilndash31October 2008ndash2011) Published threshold salinity levels for forest tree maintenanceflooded seedling photosynthesis and basal area growth (size) arethought to be 20 and 07 ppt (in bold letters Kaplan et al 2010Pezeshki et al 1987 and Krauss et al 2009 respectively) Dark to light grey highlightsindicate percent () days per year exceeding maximum values as 70ndash100 30ndash70 1ndash30 and 0 respectivelyECS Education Center Spur ECP Education Center Parking ECC Education Center Canal PT Palmetto Trail PTV Palmetto Trail Visitors ECEducation Center JLNHP amp P Jean Lafitte National Historical Park amp Preserve

847HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

and 05ppt respectively (also see Figure 2a and Table IV) Incontrast to 2008 predicted levels of salinity were high in boththe EC and PT units (Table IV) and total annual leaf litterbiomass by individual species was low (A rubrum Tdistichum Fraxinuspennsylvanicum Mcerifera and Salixnigra Figure 2a and Table III) Nevertheless rendering asimple statement of an ideal threshold of salinity for theseswamps is impractical Among other problems field environ-ments are difficult to characterize simply (eg salinity levelsvary by depth in the vadose zone)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Trees in JLNHP amp P responded positively to remedia-tion but we recognize that this unplanned study did notpermit us to determine whether changes in salinity or someother unmeasured biogeochemical factors were ultimatelyresponsible for the observed responses Tidal flowreconnection in previously restricted salt marshes decreasessoil anoxia and sulphides and changes pH nutrientavailability and decomposition rates (Anisfeld and Benoit1997) The fact that we detected increased water levels anddecreased salinity with freshwater remediation indicatedthat other important site characteristics and biogeochemicalshifts likely were occurring at JLNHP amp P Unfortunatelywe do not have any other supportive data especially asrelated to any possible causal linkagesPhotosynthetic stressors such as salinity and anoxiamay be

more harmful during the growing season Flooding reducesregeneration seedlings and saplings of Tdistichum surviveovertopping by flooding while dormant but not during thegrowing season and most tree species will not germinateunderwater (Middleton 2000) A better understanding of anyseasonal component of remediation response is critical tohydrologic remediation planning for managementThe immediate mechanisms of increased tree production

with improved environment are not well studied but maybe related to the photosynthetic regulation of trees tochanges in environment As salinity (at some level) entersthe transpiration stream stomata close and photosynthesisdecreases (Stiller 2009) Any short-term increase in

Ecohydrol 8 838ndash850 (2015)

Figure 3 State of Louisiana water recorder information for maximum (a) daily discharge (m3 s1) from Davis Pond Diversion and adjusted water levels(m) at (b) Coastwide Reference Monitoring System (CRMS) 0234 and (c) CRMS 0188 and salinity (ppt) of (d) discharge of diversion and surface waterat (e) CRMS 00234 and (f) CRMS 0188 during hydrologically remediated (2010) versus lsquowetrsquo years (mean of 2008 2009 and 2011) CRMS 0234 andCRMS 0188 are in the same hydrological units as the Education Center and Palmetto Trail plots respectively in JLNHP amp P Pre-remediationremediation and post-remediation days of the year included days 1ndash119 120ndash244 and 245ndash365 respectively Sign tests indicated that 2010 was higherlower or not different from wet years as lsquo+rsquo lsquo-rsquo or lsquonsrsquo respectively (plt 00001) Only significant variables of time were kept p values for the sign testcomparisons were based on normally distributed error with constant variance All tests of fit were performed at p = 005 except that one test wasperformed at p = 001 to obtain a model fit Equations were based on the difference of the two year groups (2010 vs set of years compared) Mean dailydischarge values are not shown but these comparisons were also significant using similarly constructed ARIMA models and sign tests (plt 00001)Note that short periods of missing data were interpolated linearly Longer periods of missing data were omitted eg Davis Pond Diversion had nodischarge data available for 1ndash28 January 2010 Note that the measured water and salinity levels at plots in the EC and PT units were intermediate and

similar to each other (see Supplementary Figure 2)

848 B A MIDDLETON D JOHNSON AND B J ROBERTS

photosynthetic output and leaf production after freshwaterremediation is most likely to occur in healthy trees withrelatively intact leaf architecture such as Tdistichum in

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

JLNHP amp P or E camaldulensis trees along the MurrayRiver in Australia (Souter et al 2014) The positive effectsof remediation may have broad application in freshwater

Ecohydrol 8 838ndash850 (2015)

849HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

forests particularly because several species respondedpositively to freshwater remediation in JLNHP amp P

In our study litter but not root production increased duringthe year of hydrologic remediation If environment conditionsimproved in 2010 trees may have been experiencing a fastspurt of leaf litter production at the expense of roots(Figure 2b) Falling rootshoot ratios are an indicator of fastshoot growth in response to favourable environments (Harris1992 Litton et al 2007) and Tdistichum root and shootallocation patterns shift in response to changing resources(Megonigal and Day 1992) Note that we did not distinguishbetween species of roots in our study Alterations in root andshoot allocations following hydrologic remediationmay haveimportant implications for the elevation of subsiding swampsby influencing peat accumulation The decrease in rootgrowth during remediation is important because root tissuesoften contribute more to the accumulation of peat than leaf orwoody tissue (Middleton and McKee 2002) Whilereinvigorating the production of freshwater coastal vegetationoverall hydrologic remediation may reduce root growth forsome tree species at least temporarily (this study) Thereforea better understanding of the relationship of remediation androot growth is critical (Langley et al 2010 Wigand et al2014) to the development of management techniques relatedto remediation

CONCLUSION

Concerns are growing because of losses of coastal wetlandsalong the Gulf Coast (Kaplan et al 2010 CPRA 2012)Special attention should be given to our findings thatfreshwater release might reinvigorate the production offreshwater coastal vegetation Our study has worldwideimplications in that it demonstrates that sustained releases offreshwater can affect the primary production of many speciesFreshwater coastal species are increasingly affected bysaltwater intrusion so this idea deserves further explorationfor the management of coastal freshwater wetlands

ACKNOWLEDGEMENTS

This work is funded by the US Geological Survey andNational Science Foundation (DEB-1049838) Specialthanks are given to Evelyn Anemaet Mel McCulloughSamantha Primer Justin Stelly Lei Ting and GuodongWang for their field assistance Any use of trade productor firm names is for descriptive purposes only and does notimply endorsement by the US Government

CONFLICT OF INTEREST

The authors declare no conflict of interest with thisresearch

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

REFERENCES

Anemaet E Middleton BA 2013 Dendrometer bands made easy usingmodified cable ties to measure incremental growth of trees Applicationsin Plant Sciences 1 1300044

Anisfeld SC Benoit G 1997 Impacts of flow restriction on salt marshesan instance of acidification Environmental Science and Technology 311650ndash1699

Bianchi TS Cook RL Perdue EM Kolic PE Green N Zhang Y SmithRW Kolker AS Ameen A King G Ojwang LM Schneider CLNormand AE Hetland R 2011 Impacts of diverted freshwater ondissolved organic matter and microbial communities in Barataria BayLA Marine Environmental Research 72 248257

Brinson MM Bradshaw HD Holmes RN Elkins JB Jr 1980 Litterfallstemflow and throughfall nutrient fluxes in an alluvial swamp forestEcology 61 827ndash835

Cahoon DR Lynch JC Hensel P Boumans R Perez BC Segura B DayJW Jr 2002 A device for high precision measurement of wetlandsediment elevation I Recent improvements to the sedimentation-erosion table Journal of Sedimentary Research 72 730ndash733

Coastal Protection and Restoration Authority of Louisiana (CPRA) 2012Louisianarsquos Comprehensive Master Plan for a Sustainable CoastCPRA Baton Rouge LA

Coastal Protection and Restoration (CPRA) 2013 Modifications to theDavis Pond Diversion Louisiana Coastal Protection and RestorationBaton Rouge LA wwwlcagovProjects14Defaultaspx

Day JW 2000 Pattern and process of land loss in the Mississippi Delta aspatial and temporal analysis of wetland habitat change Estuaries 23425438

Day J Hunter R Keim RF DeLaune R Shaffer G Evers E Reed DBrantley C Kemp P Day J Hunter M 2012 Ecological response offorested wetlands with and without large-scale Mississippi River inputimplications for management Ecological Engineering 46 57 67

Dixon KR 1976 Analysis of seasonal leaf fall in north temperaturedeciduous forests Oikos 27 300306

Dokka RK 2006 Modern-day tectonic subsidence in coastal LouisianaGeology 34 281294

Greater NewOrleans Inc Regional Economic Alliance (GNO) 2010 A studyon the economic impact of the Deepwater Horizon oil spill GNORegionalEconomic Alliance New Orleans wwwuflibufledu docs Economic20Impact 20Study 20Part20I20-20Full20Reportpdf

Hertel D Leuschner C 2002 A comparison of four different fine rootproduction estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest Plant and Soil 239 237251

Hoeppner SS Schaffer GP Perkins TE 2008 Through droughts andhurricanes tree mortality forest structure and biomass production in acoastal swamp targeted for restoration in the Mississippi River DeltaicPlain Forest Ecology and Management 256 937948

Hughes FM Rood SB 2003 Allocation of river flows for restorationof floodplain forest ecosystems Environmental Management 321233

Harris RW 1992 Root-shoot ratios Journal of Arboriculture 18 39ndash42JMP SAS 2012 Statistical Analysis System v 1002 SAS Institute IncCary NC

Junk WJ Bayley PB Sparks RE 1989 The flood pulse concept in river-floodplain systems In Proceedings of the International Large RiverSymposium Vol 106 Canadian Special Publications in Fisheries andAquatic Science Ottawa Ontario Canada 110127

Kaplan D Muntildeoz-Carpena R Wan Y Hedgepeth M Zheng F Roberts RRossmanith R 2010 Linking river floodplain and vadose hydrology toimprove restoration of a coastal river affected by saltwater intrusionJournal of Environmental Quality 39 15701584

Kelly D 1994 The evolutionary ecology of mast seeding Trends inEcology and Evolution 9 465ndash470

Kingsford RT 2011 Conservation management of rivers and wetlandsunder climate change a synthesis Marine and Freshwater Research62 217222

Kozlowski TT 1997 Responses of woody plants to flooding and salinityTree Physiology 1 129

KraussKWDuberstein JADoyle TWConnerWHDayRH Inabinette LWWhitbeck JL 2009 Site condition structure and growth of baldcypressalong tidalnon-tidal salinity gradients Wetlands 29 505519

Ecohydrol 8 838ndash850 (2015)

Table V Analysis of variances of climate variables for JLNHP ampP from Marrero 9 SSW weather station data (NOAA 2013) foryears 2002ndash2012 remediation periods relative to the hydrologicremediation period in 2010 (pre-remediation remediation andpost-remediation) including mean monthly (a) total precipitation

and (b) temperature

Variable DF F p

(a) PrecipitationYear 10 12 03339Remediation period 2 21 01297Year times remediation period 20 11 04077

(b) TemperatureYear 10 01 09989Remediation period 2 817 lt00001 Year times remediation period 20 02 09999

DF degrees of freedom

Table IV Percentage of days exceeding predicted values for maximum and mean daily salinity levels (ppt) in the EC and PT unitsin JLNHP amp P (sites ECSECPECC vs PTPTV respectively)

Percent () days per year exceeding the specified maximum or minimum values of salinity (eg gt01 to 20 ppt) were predicted from linear regressionanalysis of surface salinity levels at CRMS 0234 and CRMS 0188 gauges (EC and PT units respectively) versus day-of-visit pore water salinity atproduction sites including ECSECPECC and PTPTV (Figure 4) Total days are the number of days per year during the growing season (1 Aprilndash31October 2008ndash2011) Published threshold salinity levels for forest tree maintenanceflooded seedling photosynthesis and basal area growth (size) arethought to be 20 and 07 ppt (in bold letters Kaplan et al 2010Pezeshki et al 1987 and Krauss et al 2009 respectively) Dark to light grey highlightsindicate percent () days per year exceeding maximum values as 70ndash100 30ndash70 1ndash30 and 0 respectivelyECS Education Center Spur ECP Education Center Parking ECC Education Center Canal PT Palmetto Trail PTV Palmetto Trail Visitors ECEducation Center JLNHP amp P Jean Lafitte National Historical Park amp Preserve

847HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

and 05ppt respectively (also see Figure 2a and Table IV) Incontrast to 2008 predicted levels of salinity were high in boththe EC and PT units (Table IV) and total annual leaf litterbiomass by individual species was low (A rubrum Tdistichum Fraxinuspennsylvanicum Mcerifera and Salixnigra Figure 2a and Table III) Nevertheless rendering asimple statement of an ideal threshold of salinity for theseswamps is impractical Among other problems field environ-ments are difficult to characterize simply (eg salinity levelsvary by depth in the vadose zone)

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Trees in JLNHP amp P responded positively to remedia-tion but we recognize that this unplanned study did notpermit us to determine whether changes in salinity or someother unmeasured biogeochemical factors were ultimatelyresponsible for the observed responses Tidal flowreconnection in previously restricted salt marshes decreasessoil anoxia and sulphides and changes pH nutrientavailability and decomposition rates (Anisfeld and Benoit1997) The fact that we detected increased water levels anddecreased salinity with freshwater remediation indicatedthat other important site characteristics and biogeochemicalshifts likely were occurring at JLNHP amp P Unfortunatelywe do not have any other supportive data especially asrelated to any possible causal linkagesPhotosynthetic stressors such as salinity and anoxiamay be

more harmful during the growing season Flooding reducesregeneration seedlings and saplings of Tdistichum surviveovertopping by flooding while dormant but not during thegrowing season and most tree species will not germinateunderwater (Middleton 2000) A better understanding of anyseasonal component of remediation response is critical tohydrologic remediation planning for managementThe immediate mechanisms of increased tree production

with improved environment are not well studied but maybe related to the photosynthetic regulation of trees tochanges in environment As salinity (at some level) entersthe transpiration stream stomata close and photosynthesisdecreases (Stiller 2009) Any short-term increase in

Ecohydrol 8 838ndash850 (2015)

Figure 3 State of Louisiana water recorder information for maximum (a) daily discharge (m3 s1) from Davis Pond Diversion and adjusted water levels(m) at (b) Coastwide Reference Monitoring System (CRMS) 0234 and (c) CRMS 0188 and salinity (ppt) of (d) discharge of diversion and surface waterat (e) CRMS 00234 and (f) CRMS 0188 during hydrologically remediated (2010) versus lsquowetrsquo years (mean of 2008 2009 and 2011) CRMS 0234 andCRMS 0188 are in the same hydrological units as the Education Center and Palmetto Trail plots respectively in JLNHP amp P Pre-remediationremediation and post-remediation days of the year included days 1ndash119 120ndash244 and 245ndash365 respectively Sign tests indicated that 2010 was higherlower or not different from wet years as lsquo+rsquo lsquo-rsquo or lsquonsrsquo respectively (plt 00001) Only significant variables of time were kept p values for the sign testcomparisons were based on normally distributed error with constant variance All tests of fit were performed at p = 005 except that one test wasperformed at p = 001 to obtain a model fit Equations were based on the difference of the two year groups (2010 vs set of years compared) Mean dailydischarge values are not shown but these comparisons were also significant using similarly constructed ARIMA models and sign tests (plt 00001)Note that short periods of missing data were interpolated linearly Longer periods of missing data were omitted eg Davis Pond Diversion had nodischarge data available for 1ndash28 January 2010 Note that the measured water and salinity levels at plots in the EC and PT units were intermediate and

similar to each other (see Supplementary Figure 2)

848 B A MIDDLETON D JOHNSON AND B J ROBERTS

photosynthetic output and leaf production after freshwaterremediation is most likely to occur in healthy trees withrelatively intact leaf architecture such as Tdistichum in

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

JLNHP amp P or E camaldulensis trees along the MurrayRiver in Australia (Souter et al 2014) The positive effectsof remediation may have broad application in freshwater

Ecohydrol 8 838ndash850 (2015)

849HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

forests particularly because several species respondedpositively to freshwater remediation in JLNHP amp P

In our study litter but not root production increased duringthe year of hydrologic remediation If environment conditionsimproved in 2010 trees may have been experiencing a fastspurt of leaf litter production at the expense of roots(Figure 2b) Falling rootshoot ratios are an indicator of fastshoot growth in response to favourable environments (Harris1992 Litton et al 2007) and Tdistichum root and shootallocation patterns shift in response to changing resources(Megonigal and Day 1992) Note that we did not distinguishbetween species of roots in our study Alterations in root andshoot allocations following hydrologic remediationmay haveimportant implications for the elevation of subsiding swampsby influencing peat accumulation The decrease in rootgrowth during remediation is important because root tissuesoften contribute more to the accumulation of peat than leaf orwoody tissue (Middleton and McKee 2002) Whilereinvigorating the production of freshwater coastal vegetationoverall hydrologic remediation may reduce root growth forsome tree species at least temporarily (this study) Thereforea better understanding of the relationship of remediation androot growth is critical (Langley et al 2010 Wigand et al2014) to the development of management techniques relatedto remediation

CONCLUSION

Concerns are growing because of losses of coastal wetlandsalong the Gulf Coast (Kaplan et al 2010 CPRA 2012)Special attention should be given to our findings thatfreshwater release might reinvigorate the production offreshwater coastal vegetation Our study has worldwideimplications in that it demonstrates that sustained releases offreshwater can affect the primary production of many speciesFreshwater coastal species are increasingly affected bysaltwater intrusion so this idea deserves further explorationfor the management of coastal freshwater wetlands

ACKNOWLEDGEMENTS

This work is funded by the US Geological Survey andNational Science Foundation (DEB-1049838) Specialthanks are given to Evelyn Anemaet Mel McCulloughSamantha Primer Justin Stelly Lei Ting and GuodongWang for their field assistance Any use of trade productor firm names is for descriptive purposes only and does notimply endorsement by the US Government

CONFLICT OF INTEREST

The authors declare no conflict of interest with thisresearch

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

REFERENCES

Anemaet E Middleton BA 2013 Dendrometer bands made easy usingmodified cable ties to measure incremental growth of trees Applicationsin Plant Sciences 1 1300044

Anisfeld SC Benoit G 1997 Impacts of flow restriction on salt marshesan instance of acidification Environmental Science and Technology 311650ndash1699

Bianchi TS Cook RL Perdue EM Kolic PE Green N Zhang Y SmithRW Kolker AS Ameen A King G Ojwang LM Schneider CLNormand AE Hetland R 2011 Impacts of diverted freshwater ondissolved organic matter and microbial communities in Barataria BayLA Marine Environmental Research 72 248257

Brinson MM Bradshaw HD Holmes RN Elkins JB Jr 1980 Litterfallstemflow and throughfall nutrient fluxes in an alluvial swamp forestEcology 61 827ndash835

Cahoon DR Lynch JC Hensel P Boumans R Perez BC Segura B DayJW Jr 2002 A device for high precision measurement of wetlandsediment elevation I Recent improvements to the sedimentation-erosion table Journal of Sedimentary Research 72 730ndash733

Coastal Protection and Restoration Authority of Louisiana (CPRA) 2012Louisianarsquos Comprehensive Master Plan for a Sustainable CoastCPRA Baton Rouge LA

Coastal Protection and Restoration (CPRA) 2013 Modifications to theDavis Pond Diversion Louisiana Coastal Protection and RestorationBaton Rouge LA wwwlcagovProjects14Defaultaspx

Day JW 2000 Pattern and process of land loss in the Mississippi Delta aspatial and temporal analysis of wetland habitat change Estuaries 23425438

Day J Hunter R Keim RF DeLaune R Shaffer G Evers E Reed DBrantley C Kemp P Day J Hunter M 2012 Ecological response offorested wetlands with and without large-scale Mississippi River inputimplications for management Ecological Engineering 46 57 67

Dixon KR 1976 Analysis of seasonal leaf fall in north temperaturedeciduous forests Oikos 27 300306

Dokka RK 2006 Modern-day tectonic subsidence in coastal LouisianaGeology 34 281294

Greater NewOrleans Inc Regional Economic Alliance (GNO) 2010 A studyon the economic impact of the Deepwater Horizon oil spill GNORegionalEconomic Alliance New Orleans wwwuflibufledu docs Economic20Impact 20Study 20Part20I20-20Full20Reportpdf

Hertel D Leuschner C 2002 A comparison of four different fine rootproduction estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest Plant and Soil 239 237251

Hoeppner SS Schaffer GP Perkins TE 2008 Through droughts andhurricanes tree mortality forest structure and biomass production in acoastal swamp targeted for restoration in the Mississippi River DeltaicPlain Forest Ecology and Management 256 937948

Hughes FM Rood SB 2003 Allocation of river flows for restorationof floodplain forest ecosystems Environmental Management 321233

Harris RW 1992 Root-shoot ratios Journal of Arboriculture 18 39ndash42JMP SAS 2012 Statistical Analysis System v 1002 SAS Institute IncCary NC

Junk WJ Bayley PB Sparks RE 1989 The flood pulse concept in river-floodplain systems In Proceedings of the International Large RiverSymposium Vol 106 Canadian Special Publications in Fisheries andAquatic Science Ottawa Ontario Canada 110127

Kaplan D Muntildeoz-Carpena R Wan Y Hedgepeth M Zheng F Roberts RRossmanith R 2010 Linking river floodplain and vadose hydrology toimprove restoration of a coastal river affected by saltwater intrusionJournal of Environmental Quality 39 15701584

Kelly D 1994 The evolutionary ecology of mast seeding Trends inEcology and Evolution 9 465ndash470

Kingsford RT 2011 Conservation management of rivers and wetlandsunder climate change a synthesis Marine and Freshwater Research62 217222

Kozlowski TT 1997 Responses of woody plants to flooding and salinityTree Physiology 1 129

KraussKWDuberstein JADoyle TWConnerWHDayRH Inabinette LWWhitbeck JL 2009 Site condition structure and growth of baldcypressalong tidalnon-tidal salinity gradients Wetlands 29 505519

Ecohydrol 8 838ndash850 (2015)

Figure 3 State of Louisiana water recorder information for maximum (a) daily discharge (m3 s1) from Davis Pond Diversion and adjusted water levels(m) at (b) Coastwide Reference Monitoring System (CRMS) 0234 and (c) CRMS 0188 and salinity (ppt) of (d) discharge of diversion and surface waterat (e) CRMS 00234 and (f) CRMS 0188 during hydrologically remediated (2010) versus lsquowetrsquo years (mean of 2008 2009 and 2011) CRMS 0234 andCRMS 0188 are in the same hydrological units as the Education Center and Palmetto Trail plots respectively in JLNHP amp P Pre-remediationremediation and post-remediation days of the year included days 1ndash119 120ndash244 and 245ndash365 respectively Sign tests indicated that 2010 was higherlower or not different from wet years as lsquo+rsquo lsquo-rsquo or lsquonsrsquo respectively (plt 00001) Only significant variables of time were kept p values for the sign testcomparisons were based on normally distributed error with constant variance All tests of fit were performed at p = 005 except that one test wasperformed at p = 001 to obtain a model fit Equations were based on the difference of the two year groups (2010 vs set of years compared) Mean dailydischarge values are not shown but these comparisons were also significant using similarly constructed ARIMA models and sign tests (plt 00001)Note that short periods of missing data were interpolated linearly Longer periods of missing data were omitted eg Davis Pond Diversion had nodischarge data available for 1ndash28 January 2010 Note that the measured water and salinity levels at plots in the EC and PT units were intermediate and

similar to each other (see Supplementary Figure 2)

848 B A MIDDLETON D JOHNSON AND B J ROBERTS

photosynthetic output and leaf production after freshwaterremediation is most likely to occur in healthy trees withrelatively intact leaf architecture such as Tdistichum in

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

JLNHP amp P or E camaldulensis trees along the MurrayRiver in Australia (Souter et al 2014) The positive effectsof remediation may have broad application in freshwater

Ecohydrol 8 838ndash850 (2015)

849HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

forests particularly because several species respondedpositively to freshwater remediation in JLNHP amp P

In our study litter but not root production increased duringthe year of hydrologic remediation If environment conditionsimproved in 2010 trees may have been experiencing a fastspurt of leaf litter production at the expense of roots(Figure 2b) Falling rootshoot ratios are an indicator of fastshoot growth in response to favourable environments (Harris1992 Litton et al 2007) and Tdistichum root and shootallocation patterns shift in response to changing resources(Megonigal and Day 1992) Note that we did not distinguishbetween species of roots in our study Alterations in root andshoot allocations following hydrologic remediationmay haveimportant implications for the elevation of subsiding swampsby influencing peat accumulation The decrease in rootgrowth during remediation is important because root tissuesoften contribute more to the accumulation of peat than leaf orwoody tissue (Middleton and McKee 2002) Whilereinvigorating the production of freshwater coastal vegetationoverall hydrologic remediation may reduce root growth forsome tree species at least temporarily (this study) Thereforea better understanding of the relationship of remediation androot growth is critical (Langley et al 2010 Wigand et al2014) to the development of management techniques relatedto remediation

CONCLUSION

Concerns are growing because of losses of coastal wetlandsalong the Gulf Coast (Kaplan et al 2010 CPRA 2012)Special attention should be given to our findings thatfreshwater release might reinvigorate the production offreshwater coastal vegetation Our study has worldwideimplications in that it demonstrates that sustained releases offreshwater can affect the primary production of many speciesFreshwater coastal species are increasingly affected bysaltwater intrusion so this idea deserves further explorationfor the management of coastal freshwater wetlands

ACKNOWLEDGEMENTS

This work is funded by the US Geological Survey andNational Science Foundation (DEB-1049838) Specialthanks are given to Evelyn Anemaet Mel McCulloughSamantha Primer Justin Stelly Lei Ting and GuodongWang for their field assistance Any use of trade productor firm names is for descriptive purposes only and does notimply endorsement by the US Government

CONFLICT OF INTEREST

The authors declare no conflict of interest with thisresearch

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

REFERENCES

Anemaet E Middleton BA 2013 Dendrometer bands made easy usingmodified cable ties to measure incremental growth of trees Applicationsin Plant Sciences 1 1300044

Anisfeld SC Benoit G 1997 Impacts of flow restriction on salt marshesan instance of acidification Environmental Science and Technology 311650ndash1699

Bianchi TS Cook RL Perdue EM Kolic PE Green N Zhang Y SmithRW Kolker AS Ameen A King G Ojwang LM Schneider CLNormand AE Hetland R 2011 Impacts of diverted freshwater ondissolved organic matter and microbial communities in Barataria BayLA Marine Environmental Research 72 248257

Brinson MM Bradshaw HD Holmes RN Elkins JB Jr 1980 Litterfallstemflow and throughfall nutrient fluxes in an alluvial swamp forestEcology 61 827ndash835

Cahoon DR Lynch JC Hensel P Boumans R Perez BC Segura B DayJW Jr 2002 A device for high precision measurement of wetlandsediment elevation I Recent improvements to the sedimentation-erosion table Journal of Sedimentary Research 72 730ndash733

Coastal Protection and Restoration Authority of Louisiana (CPRA) 2012Louisianarsquos Comprehensive Master Plan for a Sustainable CoastCPRA Baton Rouge LA

Coastal Protection and Restoration (CPRA) 2013 Modifications to theDavis Pond Diversion Louisiana Coastal Protection and RestorationBaton Rouge LA wwwlcagovProjects14Defaultaspx

Day JW 2000 Pattern and process of land loss in the Mississippi Delta aspatial and temporal analysis of wetland habitat change Estuaries 23425438

Day J Hunter R Keim RF DeLaune R Shaffer G Evers E Reed DBrantley C Kemp P Day J Hunter M 2012 Ecological response offorested wetlands with and without large-scale Mississippi River inputimplications for management Ecological Engineering 46 57 67

Dixon KR 1976 Analysis of seasonal leaf fall in north temperaturedeciduous forests Oikos 27 300306

Dokka RK 2006 Modern-day tectonic subsidence in coastal LouisianaGeology 34 281294

Greater NewOrleans Inc Regional Economic Alliance (GNO) 2010 A studyon the economic impact of the Deepwater Horizon oil spill GNORegionalEconomic Alliance New Orleans wwwuflibufledu docs Economic20Impact 20Study 20Part20I20-20Full20Reportpdf

Hertel D Leuschner C 2002 A comparison of four different fine rootproduction estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest Plant and Soil 239 237251

Hoeppner SS Schaffer GP Perkins TE 2008 Through droughts andhurricanes tree mortality forest structure and biomass production in acoastal swamp targeted for restoration in the Mississippi River DeltaicPlain Forest Ecology and Management 256 937948

Hughes FM Rood SB 2003 Allocation of river flows for restorationof floodplain forest ecosystems Environmental Management 321233

Harris RW 1992 Root-shoot ratios Journal of Arboriculture 18 39ndash42JMP SAS 2012 Statistical Analysis System v 1002 SAS Institute IncCary NC

Junk WJ Bayley PB Sparks RE 1989 The flood pulse concept in river-floodplain systems In Proceedings of the International Large RiverSymposium Vol 106 Canadian Special Publications in Fisheries andAquatic Science Ottawa Ontario Canada 110127

Kaplan D Muntildeoz-Carpena R Wan Y Hedgepeth M Zheng F Roberts RRossmanith R 2010 Linking river floodplain and vadose hydrology toimprove restoration of a coastal river affected by saltwater intrusionJournal of Environmental Quality 39 15701584

Kelly D 1994 The evolutionary ecology of mast seeding Trends inEcology and Evolution 9 465ndash470

Kingsford RT 2011 Conservation management of rivers and wetlandsunder climate change a synthesis Marine and Freshwater Research62 217222

Kozlowski TT 1997 Responses of woody plants to flooding and salinityTree Physiology 1 129

KraussKWDuberstein JADoyle TWConnerWHDayRH Inabinette LWWhitbeck JL 2009 Site condition structure and growth of baldcypressalong tidalnon-tidal salinity gradients Wetlands 29 505519

Ecohydrol 8 838ndash850 (2015)

849HYDROLOGIC REMEDIATION OF COASTAL SWAMPS

forests particularly because several species respondedpositively to freshwater remediation in JLNHP amp P

In our study litter but not root production increased duringthe year of hydrologic remediation If environment conditionsimproved in 2010 trees may have been experiencing a fastspurt of leaf litter production at the expense of roots(Figure 2b) Falling rootshoot ratios are an indicator of fastshoot growth in response to favourable environments (Harris1992 Litton et al 2007) and Tdistichum root and shootallocation patterns shift in response to changing resources(Megonigal and Day 1992) Note that we did not distinguishbetween species of roots in our study Alterations in root andshoot allocations following hydrologic remediationmay haveimportant implications for the elevation of subsiding swampsby influencing peat accumulation The decrease in rootgrowth during remediation is important because root tissuesoften contribute more to the accumulation of peat than leaf orwoody tissue (Middleton and McKee 2002) Whilereinvigorating the production of freshwater coastal vegetationoverall hydrologic remediation may reduce root growth forsome tree species at least temporarily (this study) Thereforea better understanding of the relationship of remediation androot growth is critical (Langley et al 2010 Wigand et al2014) to the development of management techniques relatedto remediation

CONCLUSION

Concerns are growing because of losses of coastal wetlandsalong the Gulf Coast (Kaplan et al 2010 CPRA 2012)Special attention should be given to our findings thatfreshwater release might reinvigorate the production offreshwater coastal vegetation Our study has worldwideimplications in that it demonstrates that sustained releases offreshwater can affect the primary production of many speciesFreshwater coastal species are increasingly affected bysaltwater intrusion so this idea deserves further explorationfor the management of coastal freshwater wetlands

ACKNOWLEDGEMENTS

This work is funded by the US Geological Survey andNational Science Foundation (DEB-1049838) Specialthanks are given to Evelyn Anemaet Mel McCulloughSamantha Primer Justin Stelly Lei Ting and GuodongWang for their field assistance Any use of trade productor firm names is for descriptive purposes only and does notimply endorsement by the US Government

CONFLICT OF INTEREST

The authors declare no conflict of interest with thisresearch

copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

REFERENCES

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Kaplan D Muntildeoz-Carpena R Wan Y Hedgepeth M Zheng F Roberts RRossmanith R 2010 Linking river floodplain and vadose hydrology toimprove restoration of a coastal river affected by saltwater intrusionJournal of Environmental Quality 39 15701584

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KraussKWDuberstein JADoyle TWConnerWHDayRH Inabinette LWWhitbeck JL 2009 Site condition structure and growth of baldcypressalong tidalnon-tidal salinity gradients Wetlands 29 505519

Ecohydrol 8 838ndash850 (2015)

Additional supporting information may be found in theonline version of this article at the publisherrsquos web site

850 B A MIDDLETON D JOHNSON AND B J ROBERTS

Langley JA McKee KL Cahoon D Cherry JA Megonigal JP 2010Elevated CO2 stimulates marsh elevation gain counterbalancing sea-levelrise Proceedings of the National Academy of Science 106 61826186

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copy 2015 The Authors Ecohydrology published by John Wiley amp Sons Ltd

Pezeshki SR DeLaune RD Patrick WJ 1987 Physiological response ofbaldcypress to increases in flooding salinity in Louisianarsquos MississippiRiver Deltaic Plain Wetlands 7 110

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Visser JM Sasser CE Chabreck RJ Linscombe RG 2001 The impact ofa severe drought on the vegetation of a subtropical estuary Estuaries24 11841195

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SUPPORTING INFORMATION

Ecohydrol 8 838ndash850 (2015)