Submitted to: Water Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/1998
Publication Date: N/A
Interpretive Summary: Surplus nitrogen from agriculture is responsible for reduced oxygen (hypoxia) in the Gulf of Mexico. The major sources and losses of nitrogen in agricultural systems in the Mississippi River basin were mapped by applying a geographic information system (GIS) to several national data bases. Nitrogen from soil organic matter was estimated to be the largest contributor of nitrogen related to agriculture followed by inorganic fertilizer and atmospheric deposition of ammonia from crops and animal waste. 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 load in the Gulf of Mexico. This paper defines the distribution of agricultural sources and losses of N in the Mississippi River basin. Nitrogen from soil organic matter was estimated to be the largest contributor of nitrogen related to agriculture followed by inorganic fertilizer and atmospheric deposition of ammonia from crops and animal waste. Major losses of nitrogen are crop harvests followed by plant senescence and volatilization of manure. The largest 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 nitrogen 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.