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Altered Hydroperiod and Saltwater Intrusion in the Bald Cypress Swamps of the Loxahatchee River“Not So Deep”
20th Saltwater Intrusion Meeting – Naples, FL – June 23-27, 2008
David A. Kaplan1, Rafael Muñoz-Carpena1, Yuncong Li2, Yongshan Wan3, Marion Hedgepeth3, and Dick Roberts4
1Agricultural and Biological Engineering, University of Florida2Soil and Water Science, University of Florida, Tropical Research and Education Center
3 South Florida Water Management District, Coastal Ecosystems Division4 Florida Department of Environmental Protection, Division of Recreation and Parks
Photo by Paul Lane
Introduction - Loxahatchee River
• 240 square mile (~620 km2) watershed
• Public lands = conserved ecosystems
Ecologically diverse
• National “Wild and Scenic River” (NPS)
• Minimum Flows and Levels
“…the last free-flowing river in southeast Florida…”
Source: SFWMD 2005 Atlantic Ocean
C14
Source: Loxahatchee River District
Introduction - Hydrology
• Construction of the C-18 canal (1958) and minor canals that direct water away from the historic watershed
– Reduces freshwater flow in the NW Fork severely
• Lowering of the regional groundwater table
• Permanent opening of the Jupiter Inlet (1947)
Introduction - Floodplain Vegetation
Introduction - Floodplain Vegetation
Introduction - Minimum Flows and Levels
• Florida requires Water Management Districts to minimum flows and levels (MFLs) (Chapter 40E-8 of the FAC) – protects water resource functions: flood control, water quality, water
supply and storage, fish and wildlife protection, navigation, and recreation
• MFLs linked to valued ecosystem components (VEC) – Intended to prevent “significant harm”– Lox VEC’s: FW floodplain swamp, downstream estuarine resources
• Loxahatchee River MFL adopted in April 2003– Intensive modeling effort, but only in river channel– Flow in NW Fork may not fall below 35 cfs for > 20
consecutive days within any calendar year – Required the development and implementation of a
Recovery Plan
Introduction - Bald Cypress
• Bald cypress (Taxodium distichum) life cycle requirements:
• Require moist soil, but will NOT germinate under water
• Low germination rates, short viability
• Germination reduced by increasing salinity
• Seeds from brackish sources more tolerant
Source: hiltonpond.org
Seeds Seedlings
• Growth and survival dependent on hydroperiod and salinity
• Tolerates shallow flooding, but causes stress
• Moderately salt tolerant (2 ppt) (Li et al. 2006)
• Impacts of combined flooding and high salinity greater than either alone
Source: Dr. Yuncong Li, UF, TREC Copyright Raymond Gehman, 2005
Mature Trees
• Highly flood tolerant• Salinity tolerance less
well-established
Objectives
• Characterize soil moisture and soil porewater salinity dynamics in the floodplain of the Loxahatchee River over several wet and dry seasons
Copyright Clyde Butcher, 1989
• Establish functional relationships between river stage and soil moisture and porewater salinity to better predict the effects of proposed restoration scenarios on the root zone of bald cypress
• Two established vegetation transects chosen for monitoring soil moisture and salinity
Materials and Methods
– Transect 7: Transitional riverine/ upper tidal swamp with mix of freshwater swamp species (bald cypress, red maple, cabbage palm) transitioning to red mangrove ~30 m from river
– Transect 1: “Unimpacted” riverine swamp dominated by mature bald cypress
Materials and Methods
• 24 combined dielectric probes (Stevens Hydra Probe) installed– Determines soil moisture and conductivity by
measuring soil dielectric properties
= K 0 (1)
K = r - i i (2)
– εr (m3
m-3 ) εi
a (S/m)
– Soil-specific calibrations by Mortl (2006) for a
w (S/m) based on
– Soil moisture, porewater electrical conductivity, and temperature measured every 30 minutes
Results – Transect 1
Results – Transect 1
Distance along Transect 1 (m)
Soil Map UnitSoil description by
depth (cm)Vegetation
25Winder fine
sand
0-90: fine sand cabbage palm, slash pine, bald
cypress transition
90-120: sandy clay loam
65 Fluvent
0-30: clay
bald cypress, cabbage palm,
red maple, water hickory
30-50: sandy clay
50-80: fine sand
80-120: loamy sand
Soil Horizon (Transect)
Field - ρb
(g/cm3)† Ks (cm/hr) † θr θs %C
Fine sand (Tr. 1)1.36 ± 0.18
(1.06 - 1.55)37.04 ±7.70
(29.26 - 48.42)0.04 0.40
0.45(0.1-0.48)
Fluvent (Tr. 1)0.69 ± 0.38
(0.30 - 1.22)84.33 ± 83.52 (0.81 - 166.17)
0.20 0.9011.0
(1.0-15.0)
Source: Mortl (2006)
Station T1-60
Station T1-50
Station T1-30 Station T1-1
Soil Moisture – Transect 1
T1-60 T1-50
T1-30 T1-1
Soil Moisture – Transect 1
T1-60 T1-50
T1-30 T1-1
T1-60 T1-50
T1-30 T1-1
Soil Moisture – Transect 1
Soil Moisture – Transect 1
T1-60 T1-50
T1-30 T1-1
e A
1 exp x b
c
Source: www.hydram.epfl.ch
•Conceptual Model – Sigmoidal Curve
e r
s r
River Stage - e Relationship
River Stage (m, NGVD29)
T1-60 T1-50
T1-30 T1-1
River Stage - e Relationship (T-1)
River Stage (m, NGVD29)
T1-60 T1-50
T1-30 T1-1
River Stage - e Relationship (T-1)
River Stage (m, NGVD29)
T1-60 T1-50
T1-30 T1-1
River Stage - e Relationship (T-1)
River Stage (m, NGVD29)
River Stage - e Relationship (T-1)
e (
m3/m
3)
- surface
- middle
- deep
Probe Depth e
(-)
River Stage (m, NGVD29)T1-60 T1-50
T1-30 T1-1
River Stage - e Relationship (T-1)
e A
1 exp x b
c
T1-60 T1-50
T1-30 T1-1
Sensor A b c NS
T1-60 (25 cm) 1 3.913 0.243 0.72
T1-60 (35 cm) 1 3.629 0.153 0.78
T1-60 (55 cm) 1 3.326 0.055 0.66
T1-50 (30 cm) 1 3.633 0.161 0.84
T1-50 (60 cm) 1 3.414 0.067 0.89
T1-50 (95 cm) 1 3.261 0.063 0.63
T1-30 (25 cm) 1 3.014 0.116 0.42
T1-30 (50 cm) 1 2.749 0.121 0.32
T1-30 (80 cm) 1 -- 0.000 1.00
T1-1 (25 cm) 1 3.125 0.086 0.60
T1-1 (50 cm) 1 2.759 0.120 0.42
T1-1 (72 cm) 1 -- 0.000 1.00
NS = Nash Sutcliffe Coefficient of Efficiency(1970)
elevation, distance
River Stage (m, NGVD29)
• Salinity dynamics likely not tied to river salinity
• Rainfall/ET driven
• Concentration of salts in the floodplain
Soil Porewater EC – Transect 1 D
EC
F
Results – Transect 7
Results – Transect 7
Distance along Transect 7 (m)
Soil map unitSoil description by depth (cm)
Vegetation
15Terra Ceia
Variant Muck0-40: muck
young bald cypress, poison
ivy
65Terra Ceia
Variant Muck
0-180: muck pond apple, pop ash, bald
cypress180: sand layer
145Terra Ceia
Variant Muck
0-130: muck red mangrove, cabbage palm, swamp fern, pond apple
130: sand layer
Soil Horizon (Transect)
Field - ρb
(g/cm3)† Ks (cm/hr) † θr θs %C
Muck (Tr. 7)0.25± 0.15
(0.14 - 0.54)3.05 ± 2.29 (0.23 - 7.18)
0.20 0.9020.0
(5-25)
Source: Mortl (2006)
Station T7-145
Station T7-90Station T7-25 Station T7-2
• High tide elevation greater than all probe elevations all but one day (6/10/06) All probes flooded twice daily
Soil Moisture – Transect 7
15-minute tide data from USGS station 265906080093500
River Stage - e Relationship (T-7)
River Salinity at River Mile 9.1 (T-7)
Data from USGS Station 265906080093500
2.0 ppt
11.8 ppt 16.1 ppt
River Salinity (T-7) — Stage (T-1) Relationship
Lainhart Dam stage data from SFWMD’s DBHYDRO browser
Porewater Salinity – Transect 7
T7-145 T7-90 T7-25 T7-2
Porewater Salinity – Transect 7
T7-145 T7-90 T7-25 T7-2
Porewater Salinity – Transect 7
T7-145 T7-90 T7-25 T7-2
Porewater Salinity – Transect 7
T7-145 T7-90 T7-25 T7-2
River and Porewater EC Relationship (T-7)
T7-145 T7-90 T7-25 T7-2Percentage of Peak River EC Value
Reached in Porewater
Sensor 2005 2006 2007
T7-145 (20 cm) 4% 7% 12%
T7-145 (40 cm) 1% 5% 10%
T7-145 (67 cm) 0% 0% 3%
T7-90 (23 cm) 7% 11% 10%
T7-90 (40 cm) 7% 7% 13%
T7-90 (60 cm) 6% 6% 12%
T7-25 (23 cm) 6% 12% 23%
T7-25 (46 cm) 6% 10% 20%
T7-25 (66 cm) 6% 11% 18%
T7-2 (16 cm) 6% 9% 18%
T7-2 (32 cm) 5% 9% 15%
T7-2 (48 cm) 7% 4% 12%
Average 5% 8% 14%
River and Porewater Salinity Lag (T-7)
Time Lag (days):
Sensor 2005 2006 2007
T7-145 (20 cm)
22 50 51
T7-145 (40 cm)
41 64 52
T7-145 (67 cm)
--- --- 50
T7-145 (23 cm)
--- 22 31
T7-145 (46 cm)
--- 27 49
T7-145 (66 cm)
--- 60 49
T7-145 T7-90 T7-25 T7-2
Conclusions – Soil Moisture
• Variation in soil moisture is dominated by distance from river and topographical elevation of the floodplain and can be functionally tied to river stage at Transect 1.
management tool
• The floodplain at Transect 7 is inundated twice daily, though the effects of the daily tidal inundation on soil moisture can be seen over tidal cycle.
seed germination; microtopography
• Increases in porewater salinity in the floodplain are related to the magnitude and duration of river salinity.
• There is a time lag between river and porewater salinity peaks, which increases with elevation and distance from river.
• Groundwater flow towards the river is likely very important to maintaining low EC levels in the floodplain porewater
Next steps! GW data analysis, dynamic factor analysis, hydro-ecological modeling?
Conclusions – Porewater EC
Acknowledgements
• Funding for this project provided by the South Florida Water Management District
• Ph.D. Committee: Rafael Muñoz-Carpena, Gregory Kiker, Thomas Crisman, Yuncong Li, Yongshan Wan
• Previous work by Amanda Mortl (UF Masters Thesis)
• Thanks to the rest of the research team that collaborated in the field and laboratory efforts:
– Paul Lane and Lindsey Nolan (UF/ABE)– Guodong Liu, Qingren Wang, Newton Campbell, Tina Dispenza, and Harry Trafford
(UF TREC)– Marion Hedgepath, Yongshan Wan, Fawen Zheng (SFWMD), Dick Roberts and Jeff
Fisher (JDSP, FDEP), and Kevin Sullivan (NRCS) – Additional field assistance by Zuzanna Zajac, Stuart Muller, Jonathan Schroeder,
Daniel Preston, Karl VanDerlinden, Axel Ritter, Johanna Freeman, Roger Freeman.
• Special thanks to the SWIM Organizing Committee for providing travel funds!!!
Questions?
Photo by Paul Lane
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