Submitted to: International Union of Geodesy and Geophysics Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 30, 1999
Publication Date: N/A
Technical Abstract: Nitrate of agricultural origin is transported through the Mississippi River basin and contributes to hypoxia in the Gulf of Mexico. Knowledge of the geographic distribution of nitrogen sources and losses are critical to understanding the problem and identifying solutions. Sources include nitrogen imported as inorganic fertilizer, manure, and atmospheric deposition, and in situ sources such as mineralized nitrogen from soil organic matter and nitrogen fixed by legume crops. Losses that can be readily quantified include crop harvests, denitrification in soil, and losses to the atmosphere through volatilization of manure, inorganic fertilizer and plant senescence. The State Soils Geographic Database, 1992 Census of Agriculture, and the National Atmospheric Deposition Program/National Trends Network were used in the analysis. The hydrologic units with the largest residual nitrogen contributions are located in the Upper Mississippi River and parts of the Missouri basins where N-fertilizer, mineralizable N in organic rich soils, and legume fixation constitute the major sources. However, the Midwest regions utilize a greater fraction of the inputs to produce crop nitrogen than do southern hydrologic regions. Residual contributions to the Arkansas/Red and Tennessee River hydrologic regions are greatest where manure inputs are largest. Further reductions of inorganic fertilizer in the upper Mississippi Region may not provide substantial improvements in residual nitrogen because this region already produces the smallest residual of all Regions. Also, solutions to excess nitrogen in southern hydrologic regions may provide some of the best opportunities for successful reduction in nitrogen loads to the Basin.