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Sources and Trends of Nitrogen Loading to New England Estuaries
Citation:
Detenbeck, N., M. You, AND D. Torre. Sources and Trends of Nitrogen Loading to New England Estuaries. New England Association of Environmental Biologists (NEAEB) Annual Conference, Devens, MA, March 13 - 15, 2018.
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:
A database of nitrogen (N) loading components to estuaries of the conterminous United States has been developed through application of regional SPARROW models. The original SPARROW models predict average detrended loads by source based on average flow conditions and 2002 source terms. We have developed time series for nitrogen sources (1987 – 2016) and landscape features affecting land-to-water delivery ratios to enable an evaluation of recent trends in potential loads. Main data sources include: Community Multiscale Air Quality (CMAQ) models, the U.S. EPA Discharge Monitoring Report database, the Nutrient Use Geographic Information System database, and the National Land Cover Dataset (NLCD) and National Wall-to-Wall Anthropogenic Land Use Trends (NWALT) Dataset. For New England estuaries, the predominant source of estimated delivered loads in 2011 is atmospheric deposition (49% of estuaries) followed by municipal wastewater (26%) and urban runoff (21%). Over 2002 to 2012, the median decline in delivered atmospheric loads was 33% for both direct (estuarine deposition) and indirect (watershed deposition) sources. Median estimated delivered loads from municipal point sources approximately doubled between 2007 and 2016, while the median increase in estimated loads from urban runoff was 12 percent between 1982 and 2011.