2010 Rathbun Technical Summary

8/6/2019 2010 Rathbun Technical Summary

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2010 Technical Summa

RATHBUNLAKE2010

WATERSHEDSTUDY

LIMNOLOGY LABORATORY


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2010 RATHBUN LAKE WATERSHED STUDY

Submitted by:

Iowa State University

Department of Ecology, Evolution, and Organismal Biology

John A. Downing, ProfessorMichelle Balmer, Graduate Research Assistant

This study and report executed with support from the Rathbun Land and WaterAlliance, Chariton, Iowa and the Iowa Department of Natural Resources, and the US

Army Corps of Engineers

2010 TECHNICAL SUMMARY


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Rathbun Watershed 2010 Technical Summary 1

2010 Rathbun WatershedTechnical Summary

Iowa State University Limnology LaboratoryJohn Downing, Ph.D.

Michelle B. Balmer, Graduate Research AssistantForThe Rathbun Land and Water Alliance

May 1, 2011

EXECUTIVE SUMMARY

This technical summary presents the results of the 2010 water quality monitoringof the Rathbun lake watershed. Streams within the Rathbun watershed have

poor water quality, with high concentrations of nutrients, suspended solids, andfecal coliform bacteria. Major field-loss rates for nutrients and suspended solidswere estimated across the watershed for 2010. Loss rates are often correlatedwith the timing, intensity, and amount of rainfall a region receives, as well as landuse, slope, and soil characteristics.

Water quality monitoring of the Rathbun watershed was completed on scheduleas outlined in the workplan, with sampling occurring once a month betweenMarch and November of 2010 on 14 pre-determined sites. Three storm eventsampling events were also completed, all in the spring of 2010 (March May).Considerable variation was observed in nutrient and suspended solidsconcentrations both within and between sites, with total phosphorusconcentrations ranging from 34 to 730 g/L, Total suspended solidsconcentrations ranged from 5.2 to 1223 mg/L and total Kjeldahl nitrogenconcentrations ranged from 0 to 8.04 mg/L.

High in stream organic nitrogen and phosphorus concentrations were oftenrelated to runoff associated with the timing and intensity of precipitation eventsbecause these nutrients tend to bind to soil particles transported with runoffwater. It is interesting to note that despite more than a decade of investment inBMPs installed in this watershed, a high water-year yielded unprecedentedlosses of nutrients and sediments from fields throughout the watershed. Such aresult suggests that hydrologic BMPs designed to decrease the flashiness ofwatersheds in high water years and increase the capacity of watersheds toabsorb storm events may be more effective than management practicesdesigned for the average year or average event. Faced with a future ofincreasing storm frequency and severity, BMPs that do not address large waterevents may have insignificant effects.


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1. BACKGROUND AND INTRODUCTION

Rathbun Lake is an important resource for the state of Iowa, serving as a sourcefor drinking water, recreation, and is home to a fish hatchery. It has long been

documented that watershed characteristics often dictate the water quality of alake. This 2010 study of the Rathbun watershed was completed with supportfrom the Rathbun Land and Water Alliance (RLWA) and the US Army Corps ofEngineers (USACE) to document changes in water quality within the watershedover time. Because the lake serves as such an important resource, monitoringthe lakes watershed is important to project stakeholders. This monitoring isuseful for assessing the long-term effectiveness of a variety of best managementpractices introduced to the watershed. In addition to baseline water qualitymonitoring, this project also provides information on nutrient and suspendedsolids loading from the 14 sub-watersheds studied.

Project partners, including the Rathbun Land and Water Alliance (RLWA), theIowa State University Limnology Laboratory (ISULL) and the US Army Corps ofEngineers (USACE) collaborate and have conducted a long term study ofRathbun Lake and its watershed to monitor for pesticides, nutrients, bacteria andsediment. This monitoring program gives project partners necessary informationfor making effective management decisions regarding the lake and watershed.

Sites included in this 2010 study were those previously determined and used inpast monitoring studies. Samples were collected from 14 pre-determined sites inthe Rathbun watershed. These 14 watershed sites (Figure 1) were sampled on aregular basis between March and November 2010 and analyzed for a number ofparameters important for water quality monitoring. Samples were analyzed at aUSACE contracted laboratory for nutrients once monthly March - September andonce monthly March - July for atrazine. Samples were analyzed for nutrientsonce monthly in October and November and for three storm events at the ISULL.The ISULL also analyzed all samples for bacteria, suspended solids, chloride,and dissolved organic carbon.

This technical summary of 2010 watershed monitoring is organized into threesections. First, completed work plan monitoring activities are described. Second,results from 2010 monitoring are presented, as well as export rates calculatedfrom 2010 monitoring activities. Finally, trends in water quality are discussed forthe Rathbun watershed.


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Figure 1. The Rathbun watershed, with sub-basins included in 2010 studyoutlined. RA-34 has been included in previous studies, but was omitted in this2010 watershed study as per workplan specifications.

2. 2010 COMPLETED WORKPLAN ACTIVITIES

Baseline Water Quality Monitoring 14 pre-determined stations wereestablished in previous studies at the base of many sub-watersheds within theRathbun Lake watershed (Figure 1). Stations were sampled once monthly fromMarch to November 2010, plus three storm events (March 6, April 24, May 11). A

storm event was defined as one inch or more of precipitation within 24 hours inthe watershed. Samples were collected as surface grabs from stream stationsites. Field measurements were also collected at the time of sampling, includingflow measurements across the stream. Stage depth and instantaneous flowmeasurements were recorded across the channel to calculate instantaneousdischarges for the sampling stations. Temperature, pH, specific conductivity,turbidity, and dissolved oxygen measurements (using a YSI Sonde) were alsocollected at each sampling station. This sampling approach has been employedin the Rathbun watershed for over 10 years in previous water quality monitoringstudies. Water samples were analyzed using accepted standard methods.

Monitoring of sub-watershed exports Field measurements were collected asdescribed above from all sampling stations between March and November of2010. Instantaneous discharge values calculated from flow measurements (in-field) were used with instantaneous discharge data collected from two USGSsteam gauges (06903400 and 06903700) located within the Rathbun watershedto generate discharge rating curves for estimating continuous water flux rates.Water samples were analyzed for nutrient and sediment concentrations usingaccepted standard methods. Estimated discharges and sub-watershed areas,


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delineated by sampling stations, were then used to calculate exports of nutrientsand sediment from sub-watersheds.

3. RESULTS

BASELINE WATER QUALITY MONITORING

Table 1. Averages of water quality parameters across the Rathbun watershedmonitored in the 2010 sampling period (March - November). Data presented arefrom both the ISULL and the USACE contracted laboratory. Samples below theISULLs practical quantification limits are not included in these statistics.

Average Max Min

Major NutrientsTotal Phosphorus (g/L) 273 730 34

SRP as P (g/L) 93 580 8.8

Total Kjeldahl Nitrogen (mg/L) 0.86 8.04 0NO2+NO3-N (mg/L) 2.28 17.84 0.35

NH3+NH4-N (g/L) 560 3169 160

Total Suspended Solids (mg/L) 173 1223 5.2

Chloride (mg/L) 9.6 41.6 0.6

Atrazine (g/L) 5.3 3.03 0.41

Dissolved Organic Carbon (mg/L) 8.53 16.51 5.61

MicrobiologyTotal Coliforms (most probable number/100mL) >2419.6 >2419.6 1553.1

E. Coli (most probable number/100mL) 650 >2419.6 12

Field Measurements

Temperature (C) 14 27 0Dissolved Oxygen Concentration (mg/L) 9.50 18.73 4.72

Dissolved Oxygen (% Saturation) 91 216 46

pH 7.49 8.09 6.05

Conductivity (mS/cm) 0.328 0.595 0.007

Turbidity (NTU) 123.7 >1000 4.7

MONITORING OF SUB-WATERSHED EXPORTS

Discharge - 11 of the 14 sampling sites were located on small order streamsthroughout the Rathbun Lake watershed, except for RA-15 and RA-32, located

on the Chariton River, and RA-12 and RA-35, and located on the South Fork ofthe Chariton River. Two continuous USGS stage depth and flow monitors arelocated in the watershed, one on the South Fork of the Chariton River (RA-12;USGS gauge 06903700) and one on the Chariton River (USGS 06903700;located near sites RA-15 and RA-41; Figure 1).

High flows were observed several times throughout the year, with peakhydrographs occurring at continuous discharge monitoring sites shortly after


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heavy rainfall events. There was a wide range of instantaneous dischargesobserved throughout the year for each sampling station.

Continuous discharge was monitored at site RA-12 by a USGS gauging station(06903700). While the timing and volume of discharges at the other 13 sampling

stations was unknown and, although there is no continuous record for thesesites, discharge can be estimated using rating curves. These rating curves wereestablished using historical flow and stage measurements throughout thewatershed from sampling events between 2002 and 2009. Discharges calculatedfrom these events were regressed with USGS gauge data from the date andused to generate equations that best represented how a given stationsdischarge related to a corresponding USGS sampling site for a specific date.

Nutrient and Sediment Exports Exports from 14 sub-basins monitored in2010 show high nutrient and suspended solids exports for the sampling period.Table 2 shows the export numbers for several limnological parameters in the

monitored portion of the watershed. For all of the following tables and figures, thesampling period is defined as March 6, 2010 November 20, 2010, the periodwhen monitoring was completed.

The term export, for the purposes of this report, is the nutrient or sediment loadmoving from the land to the water at a specific sampling point. Exports in thisstudy were calculated from the estimates of continuous discharges at eachsampling point (as described above). Discharge was summed between samplingevents and multiplied by the average concentration of nutrients or sedimentbetween sampling events. These values were then summed to obtain a totalamount of a nutrient/sediment per sampling site.

To calculate the actual export rate of kilograms/hectare/sampling period(kg/ha/sp), the total amount of nutrient/sediment per the sampling site at thebottom of each sub-basin was divided by the area of each sub-basin, asdelineated in ArcGIS. Downstream export rates were adjusted to reflect onlywhat was found in that sub-basin by subtracting exports from the next tributaryupstream. Estimates of these exports were then used to understand trends inwater quality between sub-basins within the watershed.


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Table 2. Estimated exports in the sampled area of the Rathbun watershed for2010

Parameter:Average Export

(kg/ha/year)

Total Phosphorus 3.3

Total Kjeldahl Nitrogen 8.8

Total Suspended Solids 2389.3

Nitrate/Nitrite Nitrogen 15.6

Ammonia Nitrogen 0.9

Dissolved Organic Carbon 71

Chloride 91

Table 3. Estimated exports per sub-basin for 2010.

4. TRENDS IN WATER QUALITY

A number of trends were observed when comparing 2010 data with studies fromprevious years in the Rathbun lake watershed. Concentrations of major nutrients,nitrogen and phosphorus, varied considerable between sites. Nutrient exports in

agricultural regions, like the Rathbun lake watershed, have been linked to landuse practices, soil class, slope, and watershed transport capacity, as well asseasonality and the timing and intensity of precipitation.

Peak phosphorus (P) concentrations were generally observed after rainfallevents, usually in the spring and summer throughout the watershed, although Pconcentrations were generally lower than observed in the first half of the decade.

Sub-basin ID

TotalPhosphorus

(kg/ha/yr)

TotalKjeldahlNitrogen(kg/ha/yr)

TotalSuspended

Solids(kg/ha/yr)

NO2+NO3as N

(kg/ha/yr)

NH4+NH3as N

(kg/ha/yr)

DissolvedOrganicCarbon

(kg/ha/yr)Chloride(kg/ha/yr)

RA-12 2 -3 2465 -1 0 21 12

RA-15 6 13 3917 10 0 122 133

RA-32 1 2 279 4 0 17 23

RA-33 4 13 1793 26 2 94 115

RA-35 3 9 1913 22 1 64 95

RA-36 1 4 702 6 0 23 33

RA-37 2 5 145 7 0 37 33

RA-38 3 10 1525 13 1 63 134

RA-39 5 17 4035 14 1 126 143

RA-40 1 3 300 6 1 10 38RA-41 13 29 11968 43 3 276 274

RA-42 2 7 1634 11 1 50 58

RA-43 3 7 1040 51 2 57 141

RA-44 2 6 736 8 1 35 45


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Nitrogen concentrations were more consistent throughout the sampling seasonthan phosphorus or suspended solids. High concentrations were observed in latefall, which usually coincides with fall fertilizer application.

High concentrations of suspended soils were most often observed during high

flow events, as sediment was transported via runoff to the stream channel andstream bank erosion occurred due to high flow within the stream channel. Thesehigh flows usually followed intense rain events.

Figure 2. Average total phosphorus concentrations by sampling location overtime.

2010 and Historical Average Total Phosphorus Concentrations

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

12 15 32 33 35 36 37 38 39 40 41 42 43 44

Sampling Site

TotalPhosphoru

s(mg/L)

2000-2005

average

2009 sampling

season average

2010 sampling

season average

Figure 3. Estimated total phosphorus yields by sampling location.

2009 and 2010 Total Phosphorus Yields

-2

0

2

4

6

8

10

12

14

12 15 32 33 35 36 37 38 39 40 41 42 43 44

Sampling Site

EstimatePhosphorusYield

(lb/ac/yr)

2009 sampling

season average

2010 sampling

season average


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Figure 4. Average total Kjeldahl nitrogen concentrations by sampling location.

2010 and Historical Average Total Kjeldahl Nitrogen

Concentrations

0

0.5

1

1.5

2

2.5

12 15 32 33 35 36 37 38 39 40 41 42 43 44

Sampling Site

TotalKjeldahl

Nitrogen(mg/L

) 2000-2005 annual

average

2009 sampling

season average

2010 sampling

season average

Figure 5. Estimated total Kjeldahl nitrogen yields by sampling station.

2009 and 2010 Total Kjeldahl Nitrogen Yields

-8

-3

2

7

12

17

22

27

12 15 32 33 35 36 37 38 39 40 41 42 43 44

Sampling Site

Total

KjeldahlNitrogen

(lb/ac/yr)

2009 sampling

season average

2010 sampling

season average


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Figure 6. Average total suspended solids concentrations by sampling location.

2010 and Historical Total Suspended Solids Concentrations

0

100

200

300

400

500

12 15 32 33 35 36 37 38 39 40 41 42 43 44

Sampling Site

TotalSuspendedSo

lids

(mg/L)

2000-2005

annual average

2009 sampling

season average

2010 sampling

season average

Figure 7. Estimated total suspended solids yields by sampling location.

2009 and 2010 Total Suspended Solids Yields

-5

0

5

10

15

20

25

30

12 15 32 33 35 36 37 38 39 40 41 42 43 44

Sampling Site

Total

SuspendedSolids

(lb/ac/yr)

2009 sampling

season average

2010 sampling

season average

As seen in many previous years, discharge rates were generally higher withinlarger sub-basins throughout the sampling season. High stream flows wererecorded at many sampling sites throughout the season, usually after aprecipitation event. Flow throughout the watershed was higher in the spring and

summer months, with low flows detected in the fall.

2010 was a very high water year, and a good portion of the watershed wasflooded for several months during the sampling season. According to the IowaEnvironmental Mesonet, Chariton (the northern point of the watershed) received56.32 inches of rain in 2010. The annual precipitation average at this site is 35.61inches. Since the transport of certain nutrients and sediment is linked to runoff


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associated with precipitation events, it is understandable that higher thanaverage loads of nutrients and sediment were estimated in 2010.

Total phosphorus concentrations were consistently lower than the average from2000-2005, although they were generally higher than average concentrations

observed in 2009 (Figure 2). Both 2009 and 2010 showed high total phosphorusyields. Since organic phosphorus is often associated with runoff, it isunderstandable that high yields were observed throughout watershed, since itwas a high water year and highly erodible soils are prevalent throughout thewatershed.

Except for one site (RA-32), total Kjeldahl nitrogen (TKN) concentrations werelower than both the 2000-2005 and 2009 averages. High exports of TKN,however, were observed both in 2009 and 2010. Again, high exports of organicnitrogen are often associated with runoff from precipitation events. Animalmanure is also an important source of organic nitrogen. It should be noted that

high levels of nitrates were also seen in many places within the Rathbunwatershed.

Total suspended solids (TSS) concentrations varied considerably by site andacross the sampling season and were often highly correlated with discharge. Aswith nutrients, high exports of TSS were observed both in 2009 and 2010.

Precipitation was an important driver in 2010, moving nutrients and sedimentfrom the land to the streams. With annual precipitation approximately 20 inchesabove average, it is easy to see the link between the landscape and the streams,as nutrient and suspended solids exports were higher in 2010 than in 2009.

Actual concentrations and instantaneous discharges for all sampling sites andsampling dates were reported to the RLWA and other project partners earlier thisyear from both the ISULL and the USACE contracted laboratory, as outlined inthe workplan. Details regarding specific dates and nutrient and suspended solidconcentrations, fecal coliform estimations, and field data for each sampling sitecan be seen in the reported data file.

It is interesting to note that despite more than a decade of investment in BMPsinstalled in this watershed, a high water-year yielded unprecedented losses ofnutrients and sediments from fields throughout the watershed. Table 1 showshigh concentrations that are greater than most seen in the published literature onnutrient losses through streams in agricultural areas. Figures 3, 5, and 7 showthat both in 2009 and 2010 losses of P, N, and suspended solids were very high.Such a result suggests that hydrologic BMPs designed to decrease theflashiness of watersheds in high water years and increase the capacity ofwatersheds to absorb storm events may be more effective than managementpractices designed for the average year or average event. Faced with a future of


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Documents

2010 Rathbun Technical Summary