The National Atmospheric Deposition Program (NADP) Office has published an informational brochure entitled Nitrogen in the Nation's Rain, developed under guidance from NADP's Environmental Effects Subcommittee. The brochure presents a concise summary of the phenomenon of nitrogen in precipitation by addressing three questions: How is nitrogen deposition measured? Which human activities contribute nitrogen? What effects are associated with nitrogen deposition?
The NADP currently operates a nationwide network of ~220 National Trends Network (NTN) stations that collect precipitation for chemical analysis. Two forms of nitrogen--nitrate and ammonium--are measured in NTN samples. Together, these forms of inorganic nitrogen tend to be greatest in Illinois and its Midwestern neighbors, where precipitation annually deposits about 6 to 7 pounds of nitrogen per acre per year.
Precipitation deposits nearly 100 million pounds of nitrogen per year in the Illinois portion of the Illinois River watershed. This is less than 10 percent of the nitrogen needs of corn in Illinois' farm-rich countryside. Dry deposition of gases and particles contributes additional nitrogen. Current estimates for coastal areas such as the Chesapeake Bay are that atmospheric nitrogen accounts for 20-25 percent of the nitrogen entering the Bay. In such an estuarine environment, nitrogen promotes growth of algae, microscopic plants that cloud water and interfere with aquatic plant and animal productivity. Decaying algae remove oxygen from bottom waters leading to hypoxia, a low-oxygen condition that has negative impacts on clams, crabs, oysters, mussels, and other bottom-dwellers. Hypoxia also has been observed in the Gulf of Mexico, where the relative importance of various nitrogen sources is under intensive study. Data from the NTN are being used to investigate the role of atmospheric nitrogen deposition in the onset of summertime hypoxic conditions in these Gulf Coastal waters.
Printed copies of this four-color NADP brochure are available from the NADP Program Office. The brochure is also accessible from the NADP Web site (http://nadp.isws.illinois.edu/lib/brochures/nitrogen.pdf).