Monday, May 26, 2008 - 3:00 PM
79

The use of survey data to estimate nutrient export in the Mississippi River basin

Brian H. Hill1, Terri M. Jicha1, Alan T. Herlihy2, David W. Bolgrien1, and Stephen G. Paulsen3. (1) Office of Research and Development Mid-Continent Ecology Division, United States Environmental Protection Agency, 6201 Congdon Blvd, Duluth, MN 55804, (2) Department of Fisheries and Wildlife, Oregon State University, 104 Nash Hall, Corvallis, OR 97331, (3) Western Ecology Division, US EPA, 200 SW 35th St, Corvallis, OR 97333

The US EPA conducted surveys to assess the ecological conditions in streams and rivers in the Mississippi-Atchafalaya River basin (MARB). Within the MARB, the WSA sampled 509 sites; EMAP-GRE sampled 447 sites. We used 1) total N and P concentrations; 2) National Hydrography Data-Plus estimates of watershed area and annual discharge; 3) 2001 National Land Cover Data; and 4) 2001-2006 National Atmospheric Deposition data associated with each site. A greater proportion of the Upper Mississippi River basin was in agriculture (51%) compared to the other basins (25-29%). Nutrient concentration and yield were highest in Upper Mississippi River basin compared to the Missouri, Ohio and Lower Mississippi River basins. Mean annual discharge was strongly dependent upon watershed area (r2=0.85-0.99), resulting in strong regressions of N and P export vs. watershed area (r2=0.71-0.98). The models estimates annual N export from the MARB to the Gulf of Mexico of 1.42 million T, of which 58% flows from the Upper Mississippi River basin and 37% from the Ohio River basin. Total P export was 0.19 million T, with 61% from the Upper Mississippi River basin and 38% from the Ohio River basin. Our results are similar USGS SPARROW model estimates for the MARB.


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