Chapter 8. The Importance and Role of Watersheds in the Transport of Nitrogen

A recent report to Congress concerning water quality in the United States indicated that 35%, 45%,and 44\u27% of the assessed rivers and streams, lakes, and estuaries, respectively, were impaired by one or more pollutants (US Environmental Protection Agency, 1999). Nutrients, primarily nitrogen (N) and phosphorus (P), contributed to the impairment of 30% or 135,000 km of the nation\u27s impaired rivers and streams. 44% of the impaired lakes, and 23% of the impaired estuaries. Excessive nutrient loads are implicated in the eutrophication of lakes and reservoirs in the United States and coastal ecosystems where N is most limiting to primary productivity (Vitousek et al., 1997; Carpenter et al., 1998). Efforts arc currently underway to establish Total Maximum Daily Load (TMDL) values for pollutants, including nutrients, of impaired water bodies as described under Section 303(d) of the Clean Water Act of 1972