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
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
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
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
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
Total N
280,000
16.0
Total P
13,800
0.77
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
Non-point Source TP reduction needed =
45%-16% = 29% or 4,040 tons Total P
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