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Toward an inventory of nitrogen input to the United States
Citation:
Sobota, D., J. E. COMPTON, AND J. Harrison. Toward an inventory of nitrogen input to the United States. Presented at North American Benthological Society Annual Meeting, Providence, RI, May 22 - 26, 2011.
Impact/Purpose:
Accurate accounting of nitrogen inputs is increasingly necessary for policy decisions related to aquatic nutrient pollution.
Description:
Accurate accounting of nitrogen inputs is increasingly necessary for policy decisions related to aquatic nutrient pollution. Here we synthesize available data to provide the first integrated estimates of the amount and uncertainty of nitrogen inputs to the United States. About 30 Tg yr-1 of newly fixed nitrogen currently enters the conterminous United States, although estimates range from 16 to 45 Tg yr-1 depending on what source data are used. Inorganic fertilizer is clearly the largest source of new nitrogen (9 - 13 Tg yr-1). However, divergent estimates, particularly for biological nitrogen fixation (BNF; 2 - 12 Tg yr-1), obscure the importance of other new nitrogen sources. Redistribution of nitrogen through organic waste recycling amounts to one-third of new nitrogen input (6 - 13 Tg yr-1). Livestock manure nitrogen is the largest "recycled" nitrogen source (4 - 9 Tg yr-1). Spatially, nitrogen input aligns with agriculture, although great uncertainty in total input and dominant source exists for several regions. Our synthesis suggests that improving estimates of BNF and livestock manure disposal is critical for nitrogen pollution management in stream networks across the United States.