NAWQA Circular 1136

National Water-Quality Assessment Program

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

U.S. Geological Survey Circular 1136

(120K GIF)
Nitrate concentrations in streams and ground water generally are higher in agricultural areas than in areas of other land uses. The highest concentrations were found in ground water from areas intensively cultivated for row crops (farm near Martinsville, Indiana; photograph by Jeffrey Martin).

Nutrients in water are necessary for productive aquatic ecosystems, but in high concentrations, nutrients can adversely affect aquatic life and human health.

MAJOR FINDINGS

Nutrient concentrations in water generally are related to land use in the upstream watershed or the area overlying a ground-water aquifer.

Nitrate concentrations in ground water were highest in samples from wells in agricultural areas. Concentrations in about 12 percent of domestic-supply wells in agricultural areas exceeded the U.S. Environmental Protection Agency's drinking-water standard (10 milligrams per liter).

Nitrate concentrations in ground water generally are highest in parts of the Northeast, Midwest, and West Coast. Concentrations generally are lowest in parts of the Southeast. Regional differences are related to differences in soil-drainage properties and agricultural practices.

Nitrate in ground water is highest in areas of well-drained soils and intensive cultivation of row crops, such as corn, cotton, or vegetables. Low concentrations are found in areas of poorly drained soils and where pasture or woodland is intermixed with cropland in agricultural areas.

Nitrate concentrations in surface water are highest downstream from agricultural or urban areas; however, concentrations are not as high as in ground water and rarely exceed the drinking-water standard.

Elevated concentrations of nitrate in streams of the northeastern States might be related to atmospheric deposition (acid rain). High concentrations in parts of the Midwest might be accentuated by tile drainage of agricultural fields.

Ammonia and phosphorus concentrations in surface water are highest downstream from urban areas. Where these concentrations are high, they warrant concerns about decreased oxygen in the water, toxicity to fish, and accelerated eutrophication.

Recent improvements in sewage treatment have decreased ammonia concentrations downstream from many urban areas by converting the ammonia to nitrate. The result has been an increase in nitrate concentrations.

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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
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