Nutrient pollution

Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters, in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth. Sources of nutrient pollution include surface runoff from farm fields and pastures, discharges from septic tanks and feedlots, and emissions from combustion. Excess nutrients have been summarized as potentially leading to:

In a 2011 United States Environmental Protection Agency report, the agency's Science Advisory Board succinctly stated: “Excess reactive nitrogen compounds in the environment are associated with many large-scale environmental concerns, including eutrophication of surface waters, toxic algae blooms, hypoxia, acid rain, nitrogen saturation in forests, and global warming.”

The regulatory mechanism in the United States, a Total Maximum Daily Load (TMDL), prescribes the maximum amount of a pollutant (including nutrients) that a body of water can receive while still meeting U.S. Clean Water Act water quality standards. Specifically, Section 303 of the Clean Water Act requires each state to generate a TMDL report for each body of water impaired by pollutants. TMDL reports identify pollutant levels and strategies to accomplish pollutant reduction goals. EPA has described TMDLs as establishing a pollutant budget then allocating portions of the overall budget to the pollutant's sources. For many coastal water bodies, the main pollutant issue is excess nutrients, also termed nutrient over-enrichment. A TMDL can prescribe the minimum level of Dissolved Oxygen (DO) available in a body of water, which is directly related to nutrient levels. (See Aquatic Hypoxia.) In 2010, 18 percent of TMDLs nationwide were related to nutrient levels including organic enrichment/oxygen depletion, noxious plants, algal growth, and ammonia. In Long Island Sound the TMDL development process enabled the Connecticut Department of Environmental Protection (CTDEP) and the New York State Department of Environmental Conservation (NYSDEC) to incorporate a 58.5 percent nitrogen reduction target into a regulatory and legal framework.

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