The U.S. Geological Survey National Water-Quality Assessment Program: Advances in Understanding Sources, Transport, and the Biological Effects of Nutrients From Headwater Streams to Coastal Rivers

information on the status and long-term changes in the physical, chemical, and biological condition of streams and rivers. This information directly supports national, regional, state, and local information needs and decisions related to water-quality management and policy. The NAWQA Program uses a combination of monitoring-based observations and watershed models to assess nutrient and biological conditions in streams, nutrient transport from headwaters to coastal waters, and effects of human activities and natural processes on nutrient conditions. Agricultural and urban land uses are major sources of stream nutrients, with the highest nitrogen concentrations associated with agricultural streams and the highest phosphorus concentrations associated with agricultural and urban streams. NAWQA studies of nitrogen processing in small streams indicate that some nutrient-enriched agricultural streams are ineffective at removing nitrogen from the water column because of high nutrient inputs and reduced retention time, and therefore, export a large fraction of their nitrogen load to downstrea