National Water-Quality Assessment Program

Nutrients in the Nation's Waters--Too Much of a Good Thing?

Contamination of water by nutrients has been a national concern for several decades. The earliest public interest was in lake and reservoir eutrophication, which produces unsightly scums of algae on the water surface and can occasionally result in fishkills. Beginning in the 1970's, additional concern focused on nutrients discharged to streams from sewage-treatment plants. Nutrients in treatment-plant effluent adversely affect aquatic life through direct toxicity and by removing oxygen from water during chemical transformations. The Water Pollution Control Act of 1972, later known as the Clean Water Act, mandated improvements in sewage-treatment technology, to be funded jointly by the Federal, State, and local governments. Twenty years later, the EPA reported that nutrients still were among the two leading causes of water-quality degradation in rivers, lakes, and estuaries throughout the Nation. Also, one particular nutrient compound, nitrate, was reported to be the most prevalent contaminant in ground water nationwide. The other nutrients of concern in water pollution are ammonia and phosphorus.

Nitrate

The EPA has established a maximum contaminant level (MCL) of 10 mg/L (as nitrogen) for nitrate in drinking water. Excessive nitrate can result in restriction of oxygen transport in the bloodstream. Infants under the age of 4 months lack the enzyme necessary to correct this condition. Fatalities from methemoglobinemia ("blue baby syndrome") occur infrequently and are most common in rural areas. Illness and death caused by methemoglobinemia are not always recognized; therefore, its occurrence might be underreported. Although one case in Colorado was attributed to infant formula made from public-supply water that had a nitrate concentration of 13.3 mg/L, most cases involve concentrations that are somewhat higher. In parts of Eastern Europe where ground water is contaminated with 50-100 mg/L nitrate, pregnant women and children under 1 year of age are supplied with bottled water.

The EPA has established criteria for maximum ammonia concentrations in surface water based on danger to aquatic organisms such as fish. These criteria vary with acidity and water temperature, which affect both the toxicity of ammonia and the form in which it occurs. In most natural surface waters, total ammonia concentrations greater than about 2 mg/L exceed the chronic exposure criteria for fish. In alkaline water at high temperature, the criteria can be exceeded by total ammonia concentrations less than 0.1 mg/L. The natural conversion of ammonia to nitrate in streams removes oxygen from water and, therefore, can also adversely affect fish.

In 1992, the EPA reported that accelerated eutrophication was one of the leading problems facing the Nation's lakes and reservoirs. Eutrophication caused by the overabundance of nutrients in water can result in a variety of water-quality problems, including fishkills, noxious tastes and odors, clogged pipelines, and restricted recreation. In freshwater, phosphorus is often the nutrient responsible for accelerated eutrophication. No national criteria have been established for concentrations of phosphorus compounds in water; however, to control eutrophication, the EPA makes the following recommendations:

• Total phosphates should not exceed 0.05 mg/L (as phosphorus) in a stream at a point where it enters a lake or reservoir.

• Total phosphorus should not exceed 0.1 mg/L in streams that do not discharge directly into lakes or reservoirs.

U.S. Department of the Interior, U.S. Geological Survey Maintainer: Kerie Hitt (kjhitt@usgs.gov) Last update: 17:47:47 Mon 09 Jul 2001 Privacy Statement || Disclaimer || Accessibility URL: http://water.usgs.gov/nawqa/circ-1136/h6.html