Jordan, T. E.. Smithsonian Environmental Research Center,
Weller, D. E.. Smithsonian Environmental Research Center,
Correll, D. L.. Smithsonian Environmental Research Center,

We used regional data on atmospheric deposition and county-level data on agriculture and population to quantify anthropogenic inputs of nitrogen to watersheds in the United States. Anthropogenic inputs included fertilizer applications, nitrogen-fixation associated with crops, net trade of agricultural products, and atmospheric deposition of nitrate. The relative importance of different inputs differs greatly among watersheds. Total net anthropogenic inputs correlate with watershed discharges of nitrogen at many spatial scales, including major U.S. basins of >150,000 km2, East Coast and Gulf Coast basins of 1,100-160,000 km2, and subbasins of the Chesapeake Bay watershed of 1,200-70,000 km2. For watersheds smaller than a county, we estimated anthropogenic inputs from land-use composition and from nitrogen inputs to particular land types within the county. For watersheds of <1,000 km2, the best predictors of annual nitrogen discharge were the percentage of cropland and the proportion of base-flow. At regional scales, the net anthropogenic input was a better predictor of nitrogen discharge than was the percentage of cropland. For most watersheds analyzed, anthropogenic inputs are about three times watershed discharges of nitrogen.
Day: Tuesday, Feb. 2
Time: 10:45 - 11:00am
Location: Sweeney Center
Code: SS07TU1045S