Monitoring agricultural subwatersheds containing conservation practices in the Black Hawk Lake watershed

Transcription

1 Agricultural and Biosystems Engineering Monitoring agricultural subwatersheds containing conservation practices in the Black Hawk Lake watershed Leigh Ann Long, M.S. Research Associate Iowa Water Conference March 22, 2018

2 Collaborators Drs. Michelle Soupir, Matthew Helmers, Amy Kaleita Iowa State University, Dept. of Agricultural and Biosystems Engineering Graduate students: Conrad Brendel, Katherine van der Woude, Tim Neher Iowa DNR staff Allen Bonini, Jason Palmer, Charles Ikenberry T.J. Lynn; watershed coordinator, Black Hawk Lake Watershed Project 2

3 Acknowledgments Funding: US EPA Region 7, Section 319; Iowa Water Center Additional support from: Ben Wallace; Iowa DNR Local landowners Technicians: Loulou Dickey, Megan Lukas, Carl Pederson, Kyle Werning, Pamila Vongdeuane, and others Sac County Engineer and Secondary Roads Depts. 3

4 Background: Black Hawk Lake Image: 4

5 Background: Black Hawk Lake watershed Watershed area = 5,324 ha (13,156 acres) Watershed:lake ratio = 14:1 Land use: 74.6% row crops (corn/soybeans) 6.7% grass/hay 5.8% wetlands 1.9% timber 11% other. Active watershed restoration project. 5

6 Background: NWQI Monitoring Project 5-year project ( ) to analyze water quality and quantity trends in three subwatersheds within the Black Hawk Lake watershed. Objective: Determine if strategies to reduce sediment and nutrient loads have been effective. 6

7 Materials and Methods: Monitoring locations NWQI Monitoring sites Map by Katherine van der Woude Source, T.J. Lynn, personal communication; windshield survey

8 Background: Conservation practices (BMPs) Terraces Grass waterways Cover crops No-till, strip-till Perennial native grass plantings (CRP) Nutrient management plans Streambank stabilization CREP wetland 8

9 Materials and Methods: Monitoring locations Subwatershed 8: Size: 1,988 acres Relatively few BMPs (22.5% of area) Grass waterways, nutrient management, terraces, cover crops. 2 Monitoring Locations: 36 tile (site T8) Surface runoff from grass waterway (site S8)

10 Materials and Methods: Monitoring locations Subwatershed 11: Size: 567 acres. Likely tile fed, but access is not possible. Some BMP implementation (30% of area), but not near the stream No-till, nutrient management, cover crops. 1 Monitoring Location: 1 st order stream (site S11). CREP wetland is just downstream.

11 Materials and Methods: Monitoring locations Subwatershed 12: Size: 547 acres Similar to subwatershed 11. BMP implementation over majority of area (87.5%) Terraces, no-till, nutrient monitoring plans, CRP at surface monitoring point. 2 Monitoring Locations: One 15 tile (site T12), One 1 st order stream (site S12).

12 Materials and Methods: Current monitoring Up to 10 storm events and up to 20 base flow (weekly-flow weighted) samples collected each year from March-November. Flow-weighted composite samples collected using ISCO 6712 automated samplers. Water level and velocity, and precipitation data collected at 5 min. intervals. 12

13 Materials and Methods: Analytical Methods Samples analyzed for: Nitrate+nitrite (NO x -N) Ammonia (NH 4 -N) Total nitrogen (TN) Total phosphorus (TP) Dissolved reactive phosphorus (DRP) Total suspended solids (TSS) Volatile suspended solids (VSS) 13

14 Precipitation (inches) Results Precipitation J F M A M J J A S O N D year ( ) average

15 kg NO3-N/ha Results: Annual Nitrate Export % % 92% % Subwatershed 8 51% Subwatershed 11 8% Subwatershed 12 46% 63% 54% 37% 52% Subwatershed 8 Subwatershed 11 48% Subwatershed 12 71% 80% 70% 29% 20% 30% Subwatershed 8 Subwatershed 11 Subwatershed 12 Storm Events Weekly Flow-weighted 15

16 kg P/ha Results: Annual Total Phosphorus Export % % % % 79% Subwatershed 8 Subwatershed 11 17% Subwatershed 12 32% 53% 33% 56% 32% 14% 68% 68% 47% 86% 67% 44% Subwatershed 8 Subwatershed 11 Subwatershed 12 Subwatershed 8 Subwatershed 11 Subwatershed 12 Storm Events Weekly Flow-weighted 18

17 kg sediment ha-1 Results: Annual Sediment Export (Total Suspended Solids) 10, % , % 65% 93% 41% 59% 37% 63% 19% 81% 44% 56% 30% 70% 23% 77% 67% 33% 0 Subwatershed 8 Subwatershed 11 Subwatershed 12 Subwatershed 8 Subwatershed 11 Subwatershed 12 Subwatershed 8 Subwatershed 11 Subwatershed 12 Storm Events Weekly Flow-weighted 17

18 Results: Storm Events Single events early in the season can overwhelm annual TSS and TP loads Subwatershed 11: 61.8% of total 2015 TSS losses from one event (June 22-30, 2015). 77.6% of total 2016 TSS losses from one event (April 26-May 1, 2016). Stream at Subwatershed 12: 68.7% of total 2015 TP losses from April 25-May 1, 2015 event 62.1% of cumulative TP export from this stream from this same one event. 18 Agricultural and Biosystems Engineering

19 High BMPs (87.5%) Nitrate Load (kg N/d) Low BMPs ( %) Nitrate Load (kg N/d) Results Seasonal Nitrate Load Tile Drainage Surface Drainage Nitrate Load (kg N d) Target Nitrate Load (10 mg L) in ( kg N d) Flow exceeded (%) Flow exceeded (%)

20 High BMPs (87.5%) Total Phosphorus (kg/d) Low BMPs ( %) Total Phosphorus (kg/d) Results Seasonal Total Phosphorus (TP) Load Tile Drainage Surface Drainage Target TP Load (0.05 mg/l), in kg/d TP load (kg/d) Flow exceeded (%) Flow exceeded (%)

21 Conclusions: Subwatershed comparisons Subwatershed 11: 30% BMP implementation Subwatershed 12: 87.5% BMP implementation Nitrate loss = 279 kg/ha TP loss = 3.6 kg/ha TSS (Soil loss) = 3,877 kg/ha Nitrate loss = 180 kg/ha (36% less) TP loss = 2.2 kg/ha (39% less) TSS (Soil loss) = 193 kg/ha (95% less) 21

22 Conclusions Precipitation and flow are the driving force of analyte concentrations. NO x carried primarily by base flow; TP and TSS carried by storm flow. Single storm events can overwhelm annual loads for TP and TSS. TP concentrations frequently exceed EPA limit of 0.05 mg P/L in surface waters. BMPs are effective in reducing TP and sediment losses in both surface and drainage waters. BMP siting may make a difference. Unclear if some BMPs are having a greater effect than others. 22

23 Questions? (then lunch) Image: Traveliowa.com 23