Natural Resources Conservation

Summary:

Water pollution remains one of the most visible and persistent signs of our impact on the natural world. Cleanup of some older pollutants has been offset by new contaminants that threaten freshwater ecosystems and foul our drinking water.

The sight and smell of grossly polluted waterways provided some of the original impetus to the environmental movement in the 1970s. Nearly a century before that, the dangers of polluted water to human health drove what became known as the "sanitary revolution" in Europe and the United States, emphasizing clean water supplies and sewer systems in cities. Today, despite progress in cleaning up waterways in some areas, water pollution remains a serious global problem, with impacts on the health of freshwater ecosystems and the human communities that rely on them for water supply.

The Changing Pollution Profile

Water pollution spans a wide range of chemical, physical, and microbial factors, but over the years the balance of major pollutants has shifted markedly in most industrialized countries. (See Figure 1 for a summary of major pollution sources and their effects.) One hundred years ago, the main water contamination problems were fecal and organic pollution from untreated human waste and the byproducts of early industries. Through improved treatment and disposal, most industrialized countries have greatly reduced the effects of these pollutants, with consequent improvements in water quality. Pollution laws and pollution control technologies have succeeded especially well in cutting emissions from concentrated "point sources" like factories and sewage treatment plants. For example, from 1972 to 1992 the amount of sewage treated at wastewater treatment plants in the United States increased by 30 percent, yet the organic pollution (measured as the Biological Oxygen Demand) from these plants dropped 36 percent (CEQ 1995:229).

Unfortunately, a new suite of contaminants from intensive agriculture and development activities in watersheds has kept the cleanup from being complete. In general, national water clean-up programs have not been effective in reducing "nonpoint" pollutants such as nutrients, sediments, and toxics that come in runoff from agriculture, urban and suburban stormwater, mining, and oil and gas operations (NRC 1992:47; EEA 1999:178).

Meanwhile, in most developing countries, the problems of traditional pollution sources like sewage and new pollutants like pesticides have combined to heavily degrade water quality, particularly near urban industrial centers and intensive agricultural areas. (Shiklomanov 1997:28; UNEP/GEMS 1995:6). An estimated 90 percent of wastewater in developing countries is still discharged directly to rivers and streams without any waste processing treatment (WMO 1997:11). (See Figure 1.)

Nutrient Pollution: The New Danger

The level of nutrients such as nitrates and phosphorous in freshwater ecosystems is a problem worldwide (Shiklomanov 1997:34-36). In most cases, the major cause of these contaminants is the increased use of manure and manufactured fertilizer in global agriculture. In the United States, for example, agriculture is the single greatest source of pollution degrading the quality of surface waters like rivers and lakes, with croplands alone accounting for nearly 40 percent of the nitrogen pollution and 30 percent of the phosphorous (Faeth 2000:6-7). (See Figure 2.)

Natural waters have very low concentrations of nitrates (a soluble from of nitrogen) and phosphorous, but nutrient levels increase with runoff from farm lands as well as from urban and industrial wastewater. Dissolved nutrients act as fertilizers, stimulating algal blooms and the eutrophication of many inland waters. This can rob the water column of dissolved oxygen, kill aquatic organisms, and degrade water quality. Dissolved nitrates in drinking water can also harm human health.

Data on nutrient trends in global waters are spotty and only give the most generalized picture of current conditions. The relevant water data from the UN's Global Environment Monitoring System (GEMS), for example, only cover 1976-1990. Of these globally monitored watersheds, the highest nutrient concentrations come from sampling stations in Europe. Nitrate concentrations are higher in watersheds that have been intensively used and modified by human activity, such as the Weser, Seine, Rhine, Elbe, and Senegal. High levels are also found in such watersheds in China, South Africa, and the Nile and Mississippi basins (UNEP/GEMS 1995:33-35).

In South America, nitrate concentrations in the monitored watersheds are relatively low and follow human land use. The highest nitrate concentrations are found in the Uruguay watershed, where some of the most intensive agriculture on the continent is found. Nitrate concentrations are also greater in the Magdalena watershed of Colombia than in the less densely populated watersheds of the Amazon basin (UNEP/GEMS 1995:33-35). The nitrate concentrations in South America correspond to lower fertilizer application rates, compared to Europe.

More detailed and recent data available in Europe show distinct regional trends in the concentrations of nitrates and phosphorous in rivers. Nitrate loadings are highest in areas with intensive livestock and crop production, especially in the northern parts of western Europe. Nitrate concentrations are lowest in Finland, Norway, and Sweden. Overall nitrate concentrations in monitored European rivers have not changed significantly since 1980, despite lower nitrogen fertilizer application rates since the 1990s (EEA 1998:194-197; EEA 1999:176-177).

Similar regional patterns are also evident in phosphorous trends. Rivers in Finland, Norway, and Sweden have the lowest phosphorous concentrations, whereas areas from southern England across central and western Europe show the highest levels (EEA 1999:174). In general, phosphorous concentrations have decreased significantly since 1985, mostly due to improvements in wastewater treatment and the reduced use of phosphorous in detergents. However, phosphorus levels remain a problem in most regions of Europe (EEA 1999:174). Despite some positive trends, the overall state of many European rivers with respect to nutrient concentrations remains poor (EEA 1998:194-196).

Figure 3 shows water quality data for the United States for the 1980s. For the 1980-89 period, nitrate concentrations remained relatively stable, with most monitoring stations showing