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High Nitrate Concentrations in Midwestern Streams in 2013 Following the 2012
Drought
Was it really the “perfect storm” we thought it was?
MSQA
Soil and Water Conservation SocietyGreensboro, NC 7-28-2015
Midwest Stream- Quality Assessment
• USEPA National Rivers and Streams Assessment • Temperate Plains Ecoregion• Midwest Cornbelt
100 MSQA Sites• Match our sampling to
NRSA’s first 50 random sites• Fill out stressor gradients
with 50 targeted sites:• Reference – 21 sites• Urban – 12 sites• Trend and other
high-priority sites – 17 sites
West
South
East
Blue – randomGreen – refYellow – other agRed -- urban
100 MSQA sites
Des Moines Water WorksNews ReleaseHistoric Nitrate Levels in Des Moines Water Works’ SourceWaterTuesday, May 28, 2013Nitrate concentrations continue to remain exceptionally high in both the Raccoon and Des Moines Rivers. Through extensive and expensive water treatment, Des Moines Water Works’ finished drinking water is currently under the Environmental Protection Agency’s (EPA) maximum contaminant level (MCL) of 10 milligrams per liter (mg/l) and is safe for drinking.
High nitrate concentrations in Iowa caused expensive and unintended consequences
2012 was a drought followed by a wet spring
Iowa
NAWQA Trend and MSQA site
Eastern study area: 2012 was a drought but wetter earlier
Indiana
NAWQA Trend and MSQA site
2013 - Spatially the highest nitrate concentrations were in IA and MN
2013 - Spatially the highest nitrate concentrations were in IA and MN
Long-term data Comparison• Northeast-Midwest Institute• NWIS/STORET - existing• Searched out additional state, local datasets• Included only data from May-July 1990-2012 (~81,000
NO2+NO3 samples)• Need to quality assure data• Removed sites outside MSQA study area (OK)• All high values were checked with appropriate agency and
removed if needed• Removed all data with “tile”, “Lake”, “inlet”, “outlet” in
name• Final number of NO2+NO3 samples (~35,300)
Historically, Median Nitrate Concentrations were similar or lower in 2013 except for western states: IA, MN, SD
Compared to long term sampling in Iowa the May-July concentrations were the highest ever
NAWQA Trend and MSQA site
Compared to long term sampling in Indiana the May-July concentrations were the 6th highest ever
NAWQA Trend and MSQA site
High nitrate related to high spring streamflow and fall drought conditions
MSQA site
Discharge
Nitrate
At the Indiana site antecedent conditions were much lower than in Iowa
MSQA site
Discharge
Nitrate
Theory: Shallow Groundwater Nitrate Concentrations are higher in IA and southern MN
From Schilling and Zhang, 2004
Many of the highest mean stream NO3 concentrations were found in high BFI watersheds but not all
Acres in Continuous corn
Theory: The amount of corn and continuous corn reflects the MSQA sites with the highest NO3 concentrations
Acres in Corn
Nitrate concentrations were much higher in Row Crop Agriculturally dominated watersheds
Ag Grassland : Ag Row Crops <40% and Ag Grasslands >20%Ag Row Crops : Ag Row Crops >50%
Nitrate concentrations increased as the amount of Row Crop Agriculture increased in watersheds
Ag Grassland : Ag Row Crops <40% and Ag Grasslands >20%Ag Row Crops : Ag Row Crops >50%
Predicting nitrate in unmonitored streams using MSQA data
• Final Model• CornCDL12 – explains 64% of the variability• Forest percent – explains 7%• Irrigation2007 – explains 3%• PPTMJJ13 – explains 3%
Summary
• High concentrations of nitrate were found at many sites in a wet year following a drought• There was a regional pattern to the high concentrations:
West to East, IA and southern MN the highest• Residual N probably contributed to the higher than normal
NO3 concentrations• Historical nitrate concentrations show IA and southern MN
are 3-5 mg/L higher then other states• Many of the highest concentrations of nitrate were found
at streams with a higher connectivity to the groundwater• The amount of the corn was the biggest predictor of stream
nitrate – explains 64% of the variability• Thoughts?
Information and Contacts
NAWQA – USGS http://water.usgs.gov/nawqa Jeff Frey(317) 600-2751 [email protected]
Pete Van Metre (512) 927-3506 [email protected]
