In spite of years of efforts to control and reduce pollution in the nation's streams and groundwater supplies, a study by the Interior Department's U.S. Geological Survey finds that concentrations of nitrogen and phosphorus have remained the same or increased in many streams and aquifers across the nation since the early 1990s. According to USGS, the finding poses a long-term ecosystem threat from excessive nutrients.
Nutrients, essential for plant growth, can stimulate growth of large amounts of algae and other plants in streams, lakes, and coastal waters. Decay of the algae and other plants then can deplete oxygen in water and create "dead" zones that stress or kill aquatic life.
Because nitrogen and phosphorus are used in so much agricultural and residential fertilizer and are such significant components of manure, the challenge to lawmakers and regulators has been substantial, made more complicated by the diffuse, "nonpoint" nature of much of the nutrient pollution in rainwater runoff. The Environmental Protection Agency in recent years has identified nutrient pollution and nonpoint-source pollutants as priorities for action.
According to the report, "Nutrients in the Nation's Streams and Groundwater, 1992-2004," national-scale progress was not evident, despite major federal, state, and local efforts and expenditures to control sources and movement of nutrients. The assessment was based on thousands of measurements and hundreds of studies across the country from 1992 through 2004, USGS said in announcing its study results.
Upward trends were evident among all land uses, including those only minimally affected by agricultural or urban development, suggesting that additional protection of some of the nation's most pristine streams warrants consideration, the report said.
The agency said its study showed that excessive nutrients were a widespread cause of stream degradation and that nitrate contamination of groundwater used for drinking water remains a human health concern, especially because of the pollutants in shallow water wells in agricultural areas.
Because nitrate can persist in groundwater for years and even decades, nitrate concentrations are likely to increase in aquifers used for drinking water supplies during at least the next several decades, as shallow groundwater with high nutrient concentrations moves downward into deeper aquifers, according to the report.
Nitrate concentrations above the federal maximum contaminant level of 10 milligrams per liter for drinking water are exceeded in more than 20 percent of shallow domestic wells in agricultural areas, the report said, defining "shallow" as less than 100 feet below the water table. The report can be found online at this site.
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