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U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigation Report 99-4018B

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Atmospheric Deposition of Nitrogen in the Mississippi River Basin

By Gregory B. Lawrence, Donald A. Goolsby and William A. Battaglin

This report is available in pdf format: pdfLawrence.pdf

ABSTRACT

Atmospheric deposition of nitrogen has been cited as a major factor in the overfertilization of forests (often termed nitrogen saturation) in the northeastern United States and as a contributor to the eutrophication of coastal waters, including the Gulf of Mexico near the mouth of the Mississippi River. Sources of nitrogen emissions and the spatial patterns of nitrogen deposition within the Mississippi River Basin, however, have not been fully assessed. The objectives of this study were to (1) quantify the spatial distribution of atmospheric nitrogen deposition throughout the Mississippi River Basin, and (2) relate the locations of emission sources to the spatial deposition patterns to infer patterns of atmospheric transport. Data collected through the NADP/NTN (National Atmospheric Deposition Program/National Trends Network) and CASTNet (Clean Air Status and Trends Network) were used for this analysis.

The highest rates of wet deposition of NO3 were in the northeastern part of the basin where electric utility plants are concentrated, whereas the highest rates of wet deposition of NH4 were in Iowa, near the center of intensive agricultural activities in the midwest. The lowest rates of atmospheric nitrogen deposition are on the (windward) side of the basin, which suggests that most of the nitrogen deposited within the western basin is derived from internal sources. Atmospheric transport eastward across the basin boundary is greater for NO3 than NH4, but a significant amount of NH4 is likely to be transported out of the basin through the formation of (NH4)2SO4 and NH4NO3 particles, which greatly increases the atmospheric residence time of NH4. This process may be a factor in the transport of nitrogen from the midwest to upland forest regions in the Northeast, such as the western Adirondack region of New York, where NH4 constitutes 40 percent of total wet nitrogen deposition.

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