Nonpoint-source pollution is pollution that enters a waterway from diverse sources. Runoff from precipitation and atmospheric deposition are two of the most common forms of nonpoint-source pollution. Some of the more important sources of nonpoint-source pollution are fertilizers, herbicides, insecticides, oil, grease, toxic chemicals, sediment, salt, and infectious agents. Nonpoint-source pollution is extremely difficult to manage and monitor because it is unpredictable and the source is often hard to trace. Several forms of legislation, such as the Clean Water Act and Coastal Zone Act Reauthorization Amendments have, however, attempted to decrease nonpoint-source pollution in waterways in the United States.
Historical Background and Scientific Foundations
Pollution is a substance or form of energy that affects the natural functioning of the environment, be it chemical, biological, or physical. Major types of pollutants that affect water bodies include oil, sediments, sewage, nutrients, heavy metals, salts, and thermal pollution. Many pollutants enter water from a single point of entry, such as a pipe from a factory, sewage treatment plant, or agricultural entity with a specific point of discharge. These forms of pollutants are called point source pollutants because the location of discharge is known and can easily be monitored. In the United States, cities, industries, storm water runoff from cities with over 100,000 people, and animal feedlots are known point source polluters and are required to have a permit to release pollutants called a National Pollutant Discharge Elimination System Permit (NPDES). Pollution that enters the environment through other pathways that are not governed by NPDES is considered nonpoint-source pollution.
Nonpoint-source pollution comes from many diffuse sources. One of the major forms of nonpoint pollution is runoff from precipitation. When rain and other forms of precipitation fall to the ground, they may not soak directly into the soil, especially if the soil has been damaged by erosion. The water gathers and runs along the surface collecting contaminants as it flows along. Eventually this runoff empties into streams, rivers, lakes, or oceans, bringing with it the pollutants it has collected. Atmospheric deposition of contaminants is also a significant nonpoint-source pollutant. Airborne contaminants, such as pesticides and acids, can precipitate directly into water bodies or onto snow or other surfaces, and then enter water bodies through runoff.
The pollutants transported into waterways via runoff have a diverse range of sources. Oil, grease, heavy metals, and other toxic chemicals from agricultural lands, construction sites, roads, and parking lots are incorporated into runoff. Sediment from construction sites, croplands, and logged areas can be suspended into runoff. In northern latitudes, salt used to melt snow and ice in the winter is a major pollutant in runoff. Salt can also contribute to runoff pollution in areas where abandoned mines are common. Pet wastes, livestock wastes, and overloaded sewage treatment systems can contribute to infectious bacteria and nutrients in runoff.
In contrast to point source pollution, the timing and predictability of nonpoint-source pollution is often difficult to assess. The first heavy rainfall of the year can wash heavy loads of pollutants that have collected on impermeable surfaces like roads and parking lots into waterways. Rainstorms following this initial flush, may not be as damaging. In the spring, melting snow can wash high concentrations of atmospheric deposition containing contaminants into lakes and streams. The unpredictability of nonpoint-source runoff makes it difficult to monitor and manage.
WORDS TO KNOW
EUTROPHICATION: The process whereby a body of water becomes rich in dissolved nutrients through natural or man-made processes. This often results in a deficiency of dissolved oxygen, producing an environment that favors plant over animal life.
POINT SOURCE POLLUTANT: A pollutant that enters the environment from a single point of entry.
SEDIMENT: Solid unconsolidated rock and mineral fragments that come from the weathering of rocks and are transported by water, air, or ice and form layers on Earth’s surface. Sediments can also result from chemical precipitation or secretion by organisms.
Impacts and Issues
The U.S. Environmental Protection Agency (EPA) reports that approximately 40% of all natural freshwater sources that have been mapped have been affected by nonpoint-source pollution. The damage caused by non-point-source pollution has affected drinking supplies, recreation, fisheries, and wildlife.
One of the major effects of nonpoint-source pollution is the addition of nutrients, generally nitrogen and phosphorus compounds found in fertilizers, wastes, and garbage that enter waterways through runoff. These nutrients are a source of food for microorganisms that live in the water and can cause giant blooms of phytoplankton. As these phytoplankton die, decomposers break them down and in the process consume large amounts of dissolved oxygen. This lowers the oxygen concentration in the water and stresses, or even kills, fish and other animals that require oxygen. This process of overfertilization is known as eutrophication. In the 1970s, the once-flourishing ecosystem in the Chesapeake Bay deteriorated so significantly from eutrophication that fisheries collapsed and recreation came to a halt. Pollution prevention programs initially established by grassroots efforts eventually decreased the input of phosphorus by at least 40%, significantly improving the health of the bay.
The Clean Water Act of 1972 is an important control on pollution in waterways. Part of the act established the NPDES permit system. This act led to significant improvements in water quality from point sources. In 1987, the act was amended to include section 319, the Nonpoint Source Management Program. Under this section, states and territories receive money to support a range of activities that help monitor and prevent non-point-source projects.
In 1990, Congress passed the Coastal Zone Act Reauthorization Amendments. This legislation was aimed at controlling nonpoint-source pollution in coastal waters. The regulations provide funding to manage and monitor development on land that borders
waterways that empty into the ocean. The goal of this amendment is to create a situation in which the water that enters the ocean is as free of pollution as possible.
One of the most important ways of decreasing non-point-source pollution is for citizens to play an active role in preventing harmful substances from becoming incorporated into runoff. Properly disposing of wastes such as motor oil, antifreeze, and paints, and using minimal fertilizers and pesticides is one way to reduce contaminants. Planting ground cover in gardens and lawns to minimize areas that are prone to erosion decreases sediment runoff. Using detergents that are low in phosphorus decreases the nutrient concentrations that flow into waterways and prevents eutrophication.
See Also Acid Rain; Algal Blooms; Aquatic Ecosystems; Bays and Estuaries; Clean Water Act; Coastal Ecosystems; Environmental Protection Agency (EPA); Groundwater; Groundwater Quality; Industrial Pollution; Industrial Water Use; Insecticide Use; Lakes; Logging; Marine Ecosystems; Marine Water Quality; Oceans and Coastlines; Precipitation; Runoff; Water Pollution
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Garrison, Tom. Oceanography: An Invitation to Marine Science, 5th ed. Stamford, CT: Thompson/Brooks Cole, 2004.
U.S. Environmental Protection Agency(EPA). “Polluted Runoff (Nonpoint Source Pollution).” February 25th, 2008. http://www.epa.gov/owow/nps/ (accessed March 5, 2008).
U.S. Environmental Protection Agency, Hawaii State Department of Health, and the City and County of Honolulu Department of Environmental Services. “Nonpoint Source Pollution.” 2002. http://protectingwater.com/index.html (accessed March 5, 2008).