Submitted to: International Union of Geodesy and Geophysics Meeting
Publication Type: Proceedings
Publication Acceptance Date: July 30, 1999
Publication Date: N/A
Interpretive Summary: Agricultural systems contribute most of the nitrogen transported by the Mississippi River to the Gulf of Mexico where it is responsible for hypoxia, or reduced oxygen content. We mapped the geographic distribution of sources and losses of nitrogen in agricultural systems in the Mississippi River basin by applying a geographic information system to several national data bases. The largest differences between sources and losses (residual) were found in the Upper Mississippi and Ohio River basins, in the heart of the corn belt. However, these basins also were most efficient in using nitrogen inputs for the production of crops. The Tennessee, Arkansas, Red, and Lower Mississippi River basins were the least efficient in utilizing nitrogen inputs in crop production. Knowing the geographic distribution of sources and losses of nitrogen will help scientists and policy planners to isolate areas where research and policy changes may be implemented to reduce the residual nitrogen available to streams.
Technical Abstract: Agriculture is a major contributor to the nitrogen (N) load in the Gulf of Mexico. This paper defines the distribution of agricultural sources and losses of N in the Mississippi River basin. Sources include inorganic fertilizer, manure, atmospheric deposition, mineralized N from soil organic matter, N fixed by legumes, and redeposition of locally derived ammonia and ammonium. N losses include crop harvests, volatilization of manure and fertilizer, plant senescence, and denitrification. The largest residual contributions available to streams are located in the Upper Mississippi River and the Ohio River basins. These northern hydrologic regions utilize a greater fraction of the sources to produce crop N than do the southern hydrologic regions. Residual contributions to the Tennessee, Arkansas/Red and Lower Mississippi hydrologic regions are greatest when analyzed as a percent of the total sources.