Water Quality Results: Slough Creek CREP Wetland

Chris Jones and Chad Drake

IIHR-Hydroscience & Engineering, University of Iowa

March 31, 2017

June 15, 2016 following 2-3” of rain in 24 hours

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Flow

Inlet

Outlet

IIHR Water Quality Sensor Setup

TurbidityWater Temp, pH, SC, DO

Nitrogen (NOx)

Iowa CREP – Conservation Reserve Enhancement Program

• Goal: restore/construct wetlands to intercept tile drainage water and process nutrients

• CREP wetland requirements:• Drain a minimum of 500 acres of predominantly tile-

drained, cropland • Wetland pool area:watershed area ratio of 0.5-2%• At least 75% of the wetland pool area must be less

than 3 feet deep to encourage vegetation establishment

Slough Creek Summary:• Watershed drainage area: 6.10 mi2

• Wetland pool area: 24.6 acres• Wetland:watershed ratio: 0.63%• Row crops: 87% (50% corn and 32% soybeans)• Average annual precipitation (1980-2016): 36”• Water quality data available for 2014-2016

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2016 Precipitation

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2016: 48.3”Long term avg: 36”

May-Nov 2016:38.2” (79%)

May-Nov Long term avg: 26.9” (75%)

2016

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2016 daily averages:In: 12.2 mg/lOut: 9.1 mg/lReduction: 3.1 mg/l23%

2016 NOx Load

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2016 daily averages:In: 190 kg/dayOut: 152 kg/dayReduction: 38 kg/day21%

34% 27% 35% 33% 11% 7% -2%

Precipitation Comparison

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Annual Precipitation2014: 38.9”2015: 36.3”2016: 48.3”Long term average (1980-2016): 36”

~75% of annual precipitation occurs between May and Nov on average

NOx Load

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57% 59% 21% 46%

Implications: Cedar River at Palo Example

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Cedar River at Palo (6,342 mi2)

Slough Creek CREP wetland (6.1 mi2)

Achieving a 45% Load Reduction at Palo

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2014 2015 2016 3 yr avg

Cedar River at Palo Load(kg/day)

170,640 133,645 240,937 181,857

Slough Creek Load Reduction (kg/day)

37 52 38 43

Palo Load Reduction from Slough Creek

0.022% 0.039% 0.016% 0.024%

Slough Creek CREP wetlands required to reduce Palo Load by 45%

2082 1167 2855 1886

Estimated Total Cost(construction & design)

$524M $294M $718M $474M

Estimated Cost ($/acre) $129 $72 $177 $117

Notes:1. Calculated loads for Cedar River at Palo are for corresponding months of available data at Slough Creek2. Estimated cost includes design ($51K) and construction ($201K) costs reported for the Slough Creek CREP site in the Iowa CREP 2015 Annual Performance Report

September 2016: Middle Cedar

11Animation created by Antonio Arenas Amado, IIHR Research Scientist and Engineer

2016 NOx Concentration

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2016 daily averages:In: 12.2 mg/lOut: 9.1 mg/lReduction: 3.1 mg/l23%

35% 27% 38% 36% 14% 8% 0%

NOx Concentration

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Percent Reductions

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Conclusions

• IIHR has been conducting continuous water quality monitoring at Slough Creek over the past 3 years (2014-2016) to quantify the water quality benefits of the CREP wetland

• A hydrologic model was used to estimate the discharge entering/leaving the wetland to calculate nitrogen loading

• Wetland nutrient removal efficiency can be highly variable and depends on a number of factors including precipitation and discharge, incoming NOx concentration, water temperature, and wetland conditions

• Precipitation in 2014 and 2015 was similar to the long term average; 2016 was a wetter than normal year

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Year Total Sampling Days

Precipitation(in)

ConcentrationReduction (mg/l)

ConcentrationReduction (%)

Load Reduction (kg/day)

Load Reduction (%)

2014 141 38.9 5.6 59 37 57

2015 234 36.3 5.8 61 52 59

2016 182 48.3 3.1 23 38 21

All 3 years 557 41.2 4.9 48 43 46

Supply and Transport Controls on Stream Nitrate

9.27017.6

124

11.4102

12.1146

12.6138

10.6113

8.4146

8.481

6.547

9.499

8.7115

5.769

4.849

1.812

10.2158

13.0198

9.2124

16.2137

7.982

6.547

10.594

10.398

11.4

9.280

120

7.3113

6.987

7.474

6.9102

7.988

8.5148

7.682

7.738

6.051

Top: Flow Weighted Average Concentration mg L-1

Bottom: N Yield g Ha-1 day-1

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3

4

5

6

78

910 11

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13

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2016 N Load Estimation

1: 28

2: 81

4: 19

5: 30

6: 19

7: 7.6

8: 1.7

9: 255

10: 44

11: 236

12: 46

13: 35

14: 42

Million pounds

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3

4

5

6

78

910 11

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13

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2016 N Load Estimation

Yields to Missouri:

32.7 lbs/ac

354 Million lbsi

Yields to Mississippi:

28.8 lbs/ac

695 million lbs

Total: 1.05 billion lbs Iowa’s share of

N load:

63% of Missouri @ Hermann49% of UMRB41% MRB to the Gulf