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| Nonpoint Source Pollution |
Nonpoint source pollution occurs when rainfall or snowmelt runs over land or through the ground, picks up pollutants, and deposits them into rivers, lakes, wetlands, and coastal waters or introduces them into groundwater. Some of the primary activities that generate nonpoint source pollution include farming and grazing activities, timber harvesting, new development, construction, and recreational boating.
Manure, pesticides, fertilizers, dirt, oil, and gas produced by these activities are examples of nonpoint source pollutants. Even individual households contribute to nonpoint source pollution through improper chemical and pesticide use, landscaping, and other house-hold practices.
After Congress passed the Clean Water Act in 1972, the water-quality community within the United States placed a primary emphasis on addressing and controlling point source pollution (pollution coming from discrete conveyances or locations, such as industrial and municipal waste discharge pipes). Not only were these sources the primary contributors to the degradation of U.S. waters at the time, but the extent and signficance of nonpoint source pollution were also poorly understood and overshadowed by efforts to control pollution from point sources.
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At the beginning of the twenty-first century, nonpoint source pollution stands as the primary cause of water-quality problems within the United States. According to the National Water Quality Inventory (published by the U.S. Environmental Protection Agency), it is the main reason that approximately 40 percent of surveyed rivers, lakes, and estuaries are not clean enough to meet basic uses such as fishing or swimming.
Leading Contributors to Nonpoint Source Pollution
States and other jurisdictions reported in the National Water Quality Inventory that agriculture and urban runoff are among the leading contributors to deteriorating water quality nationwide. The most common nonpoint source pollutants causing water-quality problems include nutrients (nitrogen and phosphorus), siltation (soil particles), metals, and pathogens (bacteria and viruses).
Agriculture is identified as the leading source of degradation of polluted rivers, streams, and lakes surveyed by states, territories, and tribes in the National Water Quality Inventory. Agricultural activities that result in nonpoint source pollution include concentrated animal feeding operations (CAFOs), grazing, plowing, pesticide spraying, irrigation, fertilizing, planting, and harvesting.
A major nonpoint source pollutant from these activities is an excess of nutrients, which can occur through applications of crop fertilizers and manure from animal production facilities. Excessive nutrients may overstimulate the growth of aquatic weeds and algae, depleting the oxygen available for a healthy aquatic community.
Hydromodification that alters the flow of water is the second leading source of damage to U.S. rivers, streams, and lakes, according to the same National Water Quality Inventory report. Examples of hydromodification projects include channelization, dredging, and construction of dams.
Excess sediment due to erosion caused by projects such as building dams can severely alter aquatic communities by clogging fish gills or suffocating eggs. Sediment may also carry other pollutants into water bodies (e.g., PCBs or mercury) which can accumulate in aquatic species, leading to fish consumption advisories.
Habitat modification is identified as the third-largest source of water pollution in surveyed rivers and streams in the National Water Quality Inventory. Habitat modification occurs when the vegetation along stream banks is removed, diminishing buffers that help filter runoff and provide shade for the adjacent water body. These modifications can result in an increase in the water temperature (because of less shade) and an increase in quantity and velocity of runoff, making the river or stream less suitable for the organisms inhabiting it.
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| Urban runoff |
Runoff from urban areas is the fourth-largest source of water pollution in rivers and streams and the third-largest source of water pollution in lakes, according to the National Water Quality Inventory. Increased urban development brings additional roads, bridges, buildings, and parking lots, which can result in large amounts of runoff that quickly and easily drain into rivers and lakes. In contrast, the porous and varied terrain of natural landscapes like forests, wetlands, and grasslands traps rainwater and snowmelt and allows it to filter slowly into the ground.
Urban runoff transports a variety of pollutants, including sediment from new development; oil, grease, and toxic chemicals from vehicles; and nutrients and pesticides from turf management and gardening. It can also carry pathogenic bacteria and viruses released from failing septic systems and inadequately treated sewage, which can result in closed beaches and shellfish beds, contaminated drinking water sources, and even severe human illness.
Programs for Nonpoint Source Control
The United States has made significant progress in addressing nonpoint source pollution since Congress amended the Clean Water Act in 1987 to establish a national program for controlling nonpoint source pollution. Under section 319 of the Clean Water Act, states adopted management programs to control nonpoint source pollution, and since 1990 the EPA has awarded grants to states to assist them in implementing those management programs.
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Other federal agencies also provide technical and financial support through grants and loans to states, local communities, and farmers and other landowners, to implement nonpoint source pollution controls. In addition, many state and local entities are dedicating increasing amounts of funding to control nonpoint source pollution.
State nonpoint source programs provide for the control of nonpoint source pollution primarily through best management practices (BMPs), which are on-the-ground technical controls used to prevent or reduce nonpoint source pollution.
Common practices used to control nutrients from agriculture include altering fertilizer and pesticide application methods and storing and properly managing manure from confined animal facilities. Developing a buffer of vegetation between the land and the stream bank can help filter all types of nonpoint source pollutants from entering a receiving water body, including sediment transported by overland flow.
Stream-bank protection and channel stabilization practices are also very effective in preventing sediment deposition in the water by limiting the bank erosion processes and streambed degradation. Urban runoff can be controlled by establishing trenches, basins, and detention ponds at construction sites to hold, settle, and retain suspended solids and associated pollutants.
Basic pollution-prevention measures introduced around the home can also prevent nonpoint source pollutants from entering storm water. Practices include the proper storage, use, and disposal of household hazardous chemicals; proper operation and maintenance of onsite disposal systems; and even proper disposal of pet waste so that it does not wash into storm drains.
Watershed Approach to Managing Nonpoint Source Pollution
Nonpoint source pollution derives from many different sources over large geographic areas so regulating and controlling it are challenging. The watershed approach to managing nonpoint source pollution, however, is proving to be an effective technique. Everyone lives in a watershed, or an area of land in which all water drains.
According to the U.S. Geological Survey, the nation can be divided into approximately 2,149 medium-sized watersheds, averaging about 1,700 square miles in each area. The watershed approach relies on coordinating all relevant federal, state, and local government agencies, and the stakeholders who live in a particular watershed, to help solve priority problems in that watershed.
Historically, many water-quality problems were addressed piecemeal in individual water bodies by individual entities, usually limited by political, social, and economic boundaries. The watershed approach, however, relies on the coordination of all entities and stakeholders to help solve the watershed’s most serious environmental problems, which in many instances are caused by nonpoint source pollution.
International Implications
Managing nonpoint source pollution is an international challenge. Like the United States, many developed countries initially directed resources toward controlling point source pollution. However, significant nonpoint source problems remain, especially resulting from an excess of nutrients and sediment in water bodies. The United Nations Environment Programme has identified increased nitrogen loadings, resulting mainly from agricultural runoff and wastewater, as one of the most serious water-quality issues affecting all countries.
Sedimentation is a significant concern for other countries, frequently resulting from deforestation or clear cutting for fuelwood, or agricultural practices. One of the largest threats in developing countries relates to problems with sewage control, either through poor maintenance of sewage collection systems or a lack of it, leading to severe waterborne diseases.
The increasing world population promises even more challenges for managing nonpoint source pollution. Some international communities are embracing integrated solutions (like the watershed approach) to reduce it. Agenda 21 adopted at the United Nations Conference on Environment and Development in 1992 is but one example.
