Non-point sources
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Non-point_sources".

Muddy river polluted by sediment. Photo courtesy of United States Geological Survey.

Nonpoint source (NPS) pollution is water pollution affecting a water body from diffuse sources, rather than a point source which discharges to a water body at a single location. rather than from a single point. Examples are polluted runoff from agricultural areas draining into a river and wind borne debris blowing out to sea.

NPS may derive from many different sources with no specific solution to rectify the problem, making it difficult to regulate. According to the U.S. Environmental Protection Agency (EPA), nonpoint source pollution is the leading cause of water pollution in the United States today, with polluted runoff from agriculture the primary cause.1 2

Other significant sources of runoff include hydrological and habitat modification, stormwater runoff, and silviculture (forestry).3 4 Another important cause of NPS pollution is urban runoff of items like oil, fertilizers, and lawn chemicals. As rainfall or snowmelt moves over and through the ground, it picks up and carries away natural and human-made pollutants. These pollutants are eventually deposited into bodies of water, such as lakes, rivers, wetlands, coastal waters, and underground sources of drinking water.

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Examples of Nonpoint source pollution

Sediment

Sediment includes silt and suspended solids. The sediment can come from improperly managed construction sites, eroding stream banks, and improper plant cover on urban and rural land.5

Phosphorus

Phosphorus is a nutrient that occurs in many forms that are bioavailable. It is a pollutant in freshwater systems where phosphorus is normally a limiting nutrient. Excess amounts of phosphorus in these systems lead to algae blooms and consequently hypoxia. This is also known as eutrophication. Phosphorus is most often transported to water bodies via soil erosion since the various forms of phosphorus tend to be adsorbed to soil particles.

Nitrogen

Nitrogen is also a nutrient. It becomes a pollutant in saltwater systems where nitrogen is a limiting nutrient. Excess amounts of bioavailable nitrogen in these systems lead to a boom of algae and diatoms. When the excessively large population of autotrophs reach the end of their life cycles, the process of decomposition consumes oxygen. The result is very surpressed levels of dissolved oxygen in the water, otherwise know as hypoxia.

Nitrogen is most often transported by water as nitrate (NO3). The nitrogen is usually added to a watershed as organic-N or ammonia (NH3), so nitrogen stays attached to the soil until oxidation converts it into nitrate. Since the nitrate is generally already incorporated into the soil, the water traveling through the soil is the most likely to transport it. Instead of surface runoff being the primary transporter, interflow and tile drainage.

Bacteria

Bacteria from livestock operations, faulty septic systems, and pet waste can be sources of pollution.5

See also

References

  1. ^ U.S. Environmental Protection Agency. Washington, D.C. "National Water Quality Inventory: Report to Congress; 2002 Reporting Cycle." October 2007. Document No. EPA-841-R-07-001.
  2. ^ U.S. EPA. Washington, D.C. "National Management Measures to Control Nonpoint Source Pollution from Agriculture." July 2003. Document No. EPA 841-B-03-004.
  3. ^ U.S. EPA. Washington, D.C. National Management Measures to Control Nonpoint Source Pollution from Hydromodification." July 2007. Document No. EPA 841-B-07-002
  4. ^ U.S. EPA. Washington, D.C."National Management Measures to Control Nonpoint Source Pollution from Forestry." May 2005. Document No. EPA 841-B-05-001.
  5. ^ a b Iowa State University. University Extension. Ames, IA. "Iowa Fact Sheet: Agriculture and Water Quality." October 2001. Document No. EDC232a.

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