The Role of Stormwater BMPs in Mitigating the Effects of Nutrient Overenrichment in the Urban Watershed

Nutrient overenrichment from agricultural and urban nonpoint and diffuse sources, including urban stormwater, is a leading cause of impairment to our nation's rivers, lakes, and coastal waters. For receiving waters that do not meet existing water quality standards, the United States Environmental Protection Agency's (US EPA) Total Maximum Daily Load (TMDL) program tasks authorities with developing and implementing management plans for the control of point and nonpoint pollutant loads in excess of those allocated. To control pollutants from diffuse sources such as urban stormwater runoff, management efforts will rely heavily on the use of Best Management Practices (BMPs). The implementation of BMPs for the control of stormwater-associated pollutants is already an important component of the US EPA's recently promulgated Phase II stormwater regulations, coastal and surface source water protection programs, and state and local watershed protection plans. Load allocations mandated by the TMDL program may result in additional treatment requirements, e.g., numeric effluent limits for specific pollutants exceeding current ambient standards or future nutrient criteria now under development. The TMDL effort, the Phase II stormwater regulations, and the eventual adoption of more protective nutrient criteria and eutrophication-associated endpoints, together serve to increase the importance of obtaining consistent, seasonal, and species-specific BMP removal data and predictive capabilities to ensure that controls implemented to reduce nutrients have the desired effects of reducing eutrophication in impaired receiving waters.