Impact/Purpose:

Initiative to develop nutrient criteria that Pacific NW states and Tribes can use in developing water quality standards.

Description:

Excess nutrients in waters of the northwest are one of the top contributors to water quality impairment. EPA, states and Tribes lack quantifiable targets for nutrients in the water quality standards. Water quality standards for nutrients usually use narrative language, such as "no nuisance aquatic growth." This needs to be translated into a quantitative target for developing TMDLs and discharge permits. Nitrogen and phosphorus are the primary causes of the eutrophication and resulting algal blooms. Nutrient levels that lead to these problems vary from one region of the country to another due to geographical variations in parent geology and soil types. Nutrient criteria are numerical values for both causative (phosphorus and nutrogen) and response (chlorophyll a and turbidity) variables associated with the prevention and assessment of eutrophic conditions. These recommended water quality criteria would be suggested baselines which should be refined by State and Tribes, and can be used to help identify problem areas, serve as a basis for State and Tribal water quality criteria for nutrients, and evaluate relative success in reducing cultural eutrophication. EPA is taking a two-pronged approach to developing nutrient criteria guidance. Because healthy nutrient levels vary across the country, and because the biological processes vary by water body type, EPA headquarters is developing nutrient criteria by ecoregion (generally at Omernik et al.'s Level 3) and water body type. Region 10 is undertaking a similar effort at a finer ecoregion levels (Omernik's levels 4 and 5) due to the heterogeneity in the Pacific Northwest and Alaska. The approach is being developed in the coastal Olympics ecoregion for lakes. These lakes have been inventoried and entered into GIS, data gathered and similarly entered. Relationships will then be investigated. Once a successful approach is developed, the method will be fully shared with states and will be expanded in a joint effort to develop nutrient criteria for the different ecoregions and water bodies within EPA Region 10. Due to limited data and monitoring resources, this is a long-term (4-8 years) project.

Record Details: