Detailed Assessment of Phosphorus Sources to Minnesota Watersheds. Volume 1: Executive Summary and Report

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Barr Engineering Company
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Minnesota Pollution Control Agency
In 2003, concerns about the phosphorus content of automatic dishwashing detergents prompted the passage of legislation requiring a comprehensive study of all of the sources and amounts of phosphorus entering publicly-owned treatment works and, ultimately, Minnesota surface waters. The assessment, funded by the Legislative Commission on Minnesota Resources and conducted for the MPCA by a consulting firm, is the first scientific study of just how much phosphorus enters Minnesota's lakes, wetlands, rivers and streams, and where it comes from in each of the state's 10 major watersheds. Findings. The study found that statewide, automatic dishwashing detergents contribute about three percent of the total phosphorus load to state waters. Under normal water flow conditions, roughly two-thirds of the total load comes from nonpoint sources: runoff from cropland and pasture supplying most of the load, with lesser amounts coming from streambank erosion, urban runoff and atmospheric deposition. Approximately 31 percent of the phosphorus load comes from point sources such as wastewater treatment facilities and industrial treatment facilities.
nutrients, Minnesota Pollution Control Agency, TMDL, phosphorus, watersheds, wetlands, detergent, streams, wastewater