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A clean, abundant supply of water is essential to sustainable development because it is required by all forms of life (humans, other animals, plants, and other organisms) and supports a range of human activities such as agriculture, recreation, mining, and manufacturing. The United States is a water-rich nation with 3.5 million miles of rivers and streams and 41 million acres of lakes. Many of these surface waters, however, are polluted. Over the past 25 years, water quality has improved and the most conspicuous point sources of pollution have been eliminated; but water pollution continues to be a problem. Agriculture is a major source of pollution for streams, rivers, and lakes today. Other important sources of pollution include industrial and municipal point sources, urban runoff, mining, and runoff and siltation associated with the destruction of natural habitat.
Since the passage of the Clean Water Act, the quality of U.S. surface waters has gradually improved even though the population and economy have expanded (Figure 4.16). The most positive trend has been for total phosphorus: concentration levels for total phosphorus have dropped at 22% of the stations analyzed in the U.S. Geological Survey’s National Stream Quality Assessment Network and shown no change in trends at 73% of the stations. In contrast, nitrate levels have decreased at only 8% of the stations and shown no trend at 86% of the stations. Suspended sediments have decreased at 11% of the stations and shown no trend at 87% of the stations; and dissolved solids have decreased at 14% of the stations and shown no trend at 78% of the stations. Concentrations of heavy metals and persistent toxic chemicals in lakes increased until the 1970s but have declined since then due to regulatory controls. However, since lakes tend to flush their contents very slowly, these toxic substances (particularly mercury) continue to limit the use of some lake resources.
Using water quality measurements by Federal and state agencies, a portion of U.S. surface waters are periodically assessed to determine their suitability for designated uses such as supporting aquatic life, recreation, agriculture, and domestic uses. In 1994, roughly 50% of the surface waters fully supported designated uses (Figures 4.17, 4.18, and 4.19). Threatened waters support designated uses at the current time, but they may not support these uses in the future unless actions are taken to control pollution. Partially supporting waters are in fair condition and fail to meet designated uses on some occasions. Waters that do not support designated uses are in poor condition and frequently fail to meet criteria. Siltation, nutrients, pathogens, and pesticides are the most common pollutants in streams and rivers; while metals, nutrients, organic enrichment, and siltation are the most common causes of pollution in lakes.
Reference:
Council on Environmental Quality, Environmental Quality, 24th Annual Report, 1993; and Council on Environmental Quality, Environmental Quality, 25th Annual Report, 1994-1995.
Link(s) to national databases (also see section on Related Internet Links):
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http://www.sdi.gov/indicators/lc_wq.htm Last Modified: May 14, 2002 |