DNR Staff
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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
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
Stream Load Estimation Methods
 AutoBeale, Pete Richards, 1998
 Load Estimator (LoadEst), Rob Runkel,
USGS, 2004
 Mean Value (mean flow X mean
concentration)
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
LoadEst Method
 Method that uses a regression model
incorporating flow and time to estimate
missing data
 Data from 2000-2010
 77 sites estimated
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
Check for Unreasonable LoadEst
Values
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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
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)
Total N and P Loads
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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
Stream load
Tons/yr
Nutrient Yield
Lbs/ac
Concentration
(mg/l)
Total N
280,000
16.0
7.9
Total P
13,800
0.77
0.38
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
Non-point Source Calculation
 Total State Load minus Point Source Load
Total stream load
NPDES load
Non-point source load
Tons N/yr
280,000
18,300 (6.5%)
261,700 (93.5%)
Tons P/yr
13,800
2,900 (21%)
10,900 (79%)
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
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)
Non-point Source Reduction needed
to meet 45% goal
 Non-point Source TN reduction needed =
45%-4% = 41% or 115,000 tons Total N
which is 44% of NPS Total N load
 Non-point Source TP reduction needed =
45%-16% = 29% or 4,040 tons Total P
which is 37% of NPS Total P load
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
Questions?
Calvin Wolter
Iowa DNR
109 Trowbridge Hall
Iowa City, IA 52242
319-335-1492
[email protected]