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Iowa Nutrient Load Estimations for Point and Non-point Sources

Iowa Nutrient Load Estimations for Point and Non-point Sources. Iowa DNR November 14, 2012. DNR Staff. Jackie Gautsch, Watershed Monitoring Rick Langel, Watershed Monitoring Mary Skopec, Watershed Monitoring Keith Schilling, Geology and Groundwater Steve Williams, Wastewater

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Iowa Nutrient Load Estimations for Point and Non-point Sources

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  1. Iowa Nutrient Load Estimations for Point and Non-point Sources Iowa DNR November 14, 2012

  2. DNR Staff • Jackie Gautsch, Watershed Monitoring • Rick Langel, Watershed Monitoring • Mary Skopec, Watershed Monitoring • Keith Schilling, Geology and Groundwater • Steve Williams, Wastewater • Adam Schnieders, Wastewater • Calvin Wolter, GIS

  3. Iowa’s Ambient Monitoring Network • 98 Sites throughout State • Includes Sites Upstream and Downstream of Urban Centers • Monitored monthly • Mostly paired with USGS Gage locations • Data from 2000-2010

  4. Stream Load Estimation Methods • AutoBeale, Pete Richards, 1998 • Load Estimator (LoadEst), Rob Runkel, USGS, 2004 • Mean Value

  5. AutoBeale Method • Method that uses a ratio of load to flow to estimate missing data • Data for 2003 Nutrient Budget • Data from 2000-2002 • 71 Sites

  6. LoadEst Method • Method that uses a regression model incorporating flow and time to estimate missing data • Data from 2000-2010 • 77 sites estimated

  7. Mean Value • Data from 2000-2010 • Mean value for NO3-N and Total P from all samples • Mean flow rate from USGS gages • 77 sites evaluated

  8. Check for Unreasonable LoadEst Values • More than +/- 15% of Mean Value loads • Residual error more than +/- 2.0 • Error ratio > 10 • NO3-N concentration > 25 ppm • Total P concentration > 10 ppm • Check hydrograph vs. sample date to see if full range of flows sampled

  9. Final Load Estimates • Use acceptable LoadEst models (59 for Nitrate, 51 for Total P), • AutoBeale models (71) • Mean Value models (77) • Average of all models available (77 sites)

  10. Total N and P Loads • Sum up loads for 24 outer basins • Total N = NO3-N/0.82 • Sum area of outer basins (83% of state) • Scale up to State area

  11. Point Source Load Calculation • For 102 Major Municipal and 28 Industrial Facilities • Load = Flow * Concentration • Use Average Annual Flow = 2/3 Wet Weather Design Flow • Use 25 ppm N and 4 ppm P in discharge from “Wastewater Engineering” Metcalf & Eddy

  12. Non-point Source Calculation • Total State Load minus Point Source Load

  13. Point Source Biological Nutrient Removal • For 102 Municipal and 28 Industrial Major facilities • Assume concentration reduction for TN from 25 mg/l to 10 mg/l • Assume concentration reduction for TP from 4 mg/l to 1 mg/l • Use Average Annual Flow = 2/3 Wet Weather Design Flow

  14. Point Source Biological Nutrient Removal • Total N Point source reduction = 11,000 tons/year (4% of Total N stream load) • Total P Point source reduction = 2,170 tons/year (16% of Total P stream load)

  15. Non-point Source Reduction needed to meet 45% goal • Non-point Source TN reduction needed = 45%-4% = 41% or 115,000 tons Total N • Non-point Source TP reduction needed = 45%-16% = 29% or 4,040 tons Total P

  16. Summary • Stream load estimation process could be improved by tailoring the monitoring schedule to better meet the needs of load estimation programs • Point source load estimations could be improved by requiring nutrient sampling and obtaining flow data

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