Nitrogen Budget for Beargrass Creek Watershed: A Baseline Study for a 45 Percent Nitrogen Reduction Goal

Abstract

Nitrogen contributions to the Gulf of Mexico hypoxic zone from agriculture watersheds are well documented. Beargrass creek watershed is a 5,985 hectare agriculturally dominated watershed in northern Indiana. A nitrogen budget was developed to account for net input and export of nitrogen from the watershed. Inputs consisted of fertilizer application, soil mineralization, and atmospheric deposition. Exports consisted of nitrogen removal in grain and stream exportation. Water quality testing at two gage stations, fourteen access tubes, and nine drainage tiles determined where excess nitrogen was stored. Nitrogen inputs was estimated at 1,004,213 kg/year or 168 kg/ha/year in 2015. Total nitrogen exports accounted for 860,250 kg/ha or 144 kg/ha/year: with 30% of the applied nitrogen removed by Beargrass Creek through baseflow, tile flows, and runoff. Treatment train BMPs implemented to treated nitrogen rich waters provide the best opportunity for measurable nitrogen reduction in the watershed.