Comprehensive trends assessment of nitrogen sources and loads to estuaries of the coterminous United States
Citation:
Detenbeck, N., D. Torre, T. Plessel, AND D. Schwede. Comprehensive trends assessment of nitrogen sources and loads to estuaries of the coterminous United States. Coastal and Estuarine Research Federation (CERF) 24th Biennial Conference, Providence, RI, November 05 - 09, 2017.
Impact/Purpose:
Nitrogen and phosphorus have beneficial uses as fertilizer but excess applications of nutrients in fertilizer (beyond crop needs) and manure can lead to eutrophication in downstream estuaries. Eutrophication can lead to excess algal growth and declines in dissolved oxygen when algae die and decay, contributing to fish kills. Other sources of nutrients include point source pollution from wastewater treatment plants and industries, as well as atmospheric pollutants emitted from industrial sources and vehicles, then deposited in dry or wet forms. Once eutrophication problems have been identified, coastal managers need to understand the type and magnitude of different sources in order to reduce loadings and to restore estuaries to a healthy condition. We have compiled data on nutrient sources to estuaries around the United States and applied existing SPARROW models with updated inputs to describe long-term trends in nutrient loads and sources to specific estuaries. Data are made publically available for coastal managers to use through EPA’s Estuary Data Mapper application, a virtual data portal.
Description:
Sources of nitrogen and phosphorus to estuaries and estuarine watersheds of the coterminous United States have been compiled from a variety of publically available data sources (1985 – 2015). Atmospheric loading was obtained from two sources. Modelled and interpolated measurements of atmospheric nitrogen deposition to watersheds was obtained from the National Atmospheric Deposition Program (NADP). Nitrogen deposition to both watersheds and estuaries was also obtained from recently updated Community Multiscale Atmospheric Quality (CMAQ) models, which now incorporate bi-directional ammonia fluxes. Measured and modelled watershed nutrient point sources have been compiled from the Environmental Protection Agency’s Discharge Monitoring Report (DMR) Pollutant Loading Tool and Enforcement and Compliance History Online (ECHO) database. Nonpoint sources from urban and agricultural sources have been estimated based on trends in developed lands from the National Land Cover Dataset (NLCD) and fertilizer, and manure applications, the latter derived from the Nutrient Use GIS (NuGIS) database and National Agricultural Statistics Service (NASS) crop layers. These sources were translated to cumulative estimated estuarine loads using updated land-to-water delivery ratios and the fraction delivered to river mouth obtained from regional and national US Geological Survey Spatially Referenced Regressions On Watershed Attributes (SPARROW) models. The SPARROW models were used to estimate both historic and potential future trends in annual loading (2002-2012/2014, 2025). Nutrient source and loading estimates are made available through EPA’s Estuary Data Mapper application (EDM; www.epa.gov/edm). Spatial and temporal trends in loading and source apportionment will be discussed.