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Nitrogen (N) and phosphorus (P) are naturally occurring elements that are required in both water and air to sustain life. In the air we breathe, nitrogen is by far the largest constituent gas, at just over 78 percent of our total atmosphere. In the water, P and N support aquatic algae and plants necessary for sustaining healthy fish, shellfish, and other organisms. But too much N or P in either air or water cause problems that are growing nationwide such as ammonia and ozone air pollution and water pollution events like dangerous, toxic algal blooms, drinking water contamination, and related health and economic impacts.
One of the most vivid examples of nutrient pollution is in the Gulf of Mexico, where for years, such pollution has resulted in hypoxic or “dead zones” by reducing available dissolved oxygen to levels that cannot sustain life. In this case, the pollutants come from the Mississippi River, which along its entire length, accumulates N and P from fertilizers, soil erosion, and sewage treatment plant discharges, from both point and nonpoint sources, and atmospheric N deposition. When these nutrients reach the Gulf, the warmer freshwater stays on top of the denser, cooler saline water causing water body stratification that inhibits the mixing of critical oxygen supplies.
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Too much N or P can also cause eutrophication, the excessive growth of water plants and algae that also depletes oxygen supplies and can render lakes, streams, and estuaries unusable for recreational activities, and interfere with pipes and other mechanical structures causing additional economic harm. Such is the case in Lake Erie where, since the 1960s, a battle has been waged to minimize P runoff that has caused repeated algal blooms, including toxic Microcystis blooms from 2003 through 2006.
According to a nutrient pollution study by the U.S. Department of Interior (DOI), in a sampling of 190 streams that drain both agricultural and urban watersheds, 90 percent exceeded background (naturally occurring) levels for five nutrients: nitrate, ammonia, total nitrogen, orthophosphate, and total phosphorus. Overall, the DOI’s analysis showed “total nitrogen concentrations were higher in agricultural streams than in streams draining urban, mixed land use, or undeveloped areas” however, urban streams still showed concentrations that were about three times greater than background concentrations at undeveloped areas. Phosphorus was also high in both agricultural and urban streams with concentrations “about 6 times greater than the average concentration of total phosphorus for undeveloped watersheds that were sampled.”
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Despite the ongoing, even escalating need to reign in nonpoint source nutrient pollution, there is no single regulation or law to control the problem. Instead, the Environmental Protection Agency (EPA) is coordinating with states to develop numeric criteria for both P and N based on the designated use of a water body, which is determined by states and authorized tribes under the Clean Water Act. According to the EPA, currently the only state with N and P criteria in place for all water types is Hawaii, although American Samoa, Guam, and the Commonwealth of Northern Marianas also have complete criteria in place. Three states, Wisconsin, Florida, and New Jersey have N and/or P criteria for two or more water types; West Virginia, and Rhode Island have the criteria for one water type, 17 more states have some water with criteria, and the remaining states have no criteria in place.