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

Non-point source (NPS) pollution is water pollution affecting a water body from diffuse sources, such as polluted runoff from agricultural areas draining into a river, or wind-borne debris blowing out to sea. Nonpoint source pollution can be contrasted with point source pollution, where discharges occur to a body of water at a single location, such as discharges from a chemical factory, urban runoff from a roadway storm drain, or from ships at sea.

NPS may derive from many different sources with no specific solution to rectify the problem, making it difficult to regulate. It is the leading cause of water pollution in the Estados Unidos today, with polluted runoff from agriculture the primary cause.[1]​[2]​

Other significant sources of runoff include hydrological and habitat modification, and silviculture (forestry).[3]​[4]​

Contaminated stormwater washed off of parking lots, roads and highways, and lawns (often containing fertilizers and pesticides) is called urban runoff. This runoff is often classified as a type of NPS pollution. Some people may also consider it a point source because many times it is channeled into municipal storm drain systems and discharged through pipes to nearby surface waters. However, not all urban runoff flows through storm drain systems before entering waterbodies. Some may flow directly into waterbodies, especially in developing and suburban areas. Also, unlike other types of point sources, such as industrial discharge, wastewater plants and other operations, pollution in urban runoff cannot be attributed to one activity or even group of activities. Therefore, because it is not caused by an easily identified and regulated activity, urban runoff pollution sources are also often treated as true nonpoint sources as municipalities work to abate them.

Principal types of nonpoint source pollution

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Runoff of soil and fertilizer during a rain storm.

Sediment

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Sediment (loose soil) includes silt (fine particles) and suspended solids (larger particles). Sediment may enter surface waters from eroding stream banks, and from surface runoff due to improper plant cover on urban and rural land[5]​ Sediment creates turbidity (cloudiness) in water bodies, reducing the amount of light reaching lower depths, which can inhibit growth of submerged aquatic plants and consequently affect species which are dependent on them, such as fish and shellfish.[6]​ High turbidity levels also inhibit drinking water purification systems. (Sediment can also be discharged from improperly managed construction sites, although these are point sources, which can be managed with erosion controls and sediment controls.)

Nutrients

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Nutrients mainly refers to organic matter from runoffs, landfill, livestock operation and corp lands, etc. It mainly include Phosphorus and Nitrogen.[7]​

Phosphorus is a nutrient that occurs in many forms that are bioavailable. It is a main ingredient in many fertilizers used for agriculture as well as on residential and commercial properties, and may become a limiting nutrient in freshwater systems. 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 forms of phosphorus tend to be adsorbed to soil particles.

Nitrogen is the other key ingredient in fertilizers, and it becomes a pollutant in saltwater systems where nitrogen is a limiting nutrient. Excess amounts of bioavailable nitrogen in these systems lead to a bloom 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 suppressed levels of dissolved oxygen in the water, otherwise known 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 (i.e., interflow and tile drainage) is the most likely to transport it, rather than surface runoff.

Heavy Metals

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Heavy metals like lead, Mercury, zinc, ect mainly come from mining operations, vehicle emissions, urban runoff, industrial operations and andfills.[8]​

Toxic Chemicals

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Toxic chemicals mainly include organic and inorganic compounds, like pestisides that have severe effects to the ecosystem and waterbody. These toxic chemicals could come from croplands, nurseries, orchards, building sites, gardens, lawns and landfills.[9]​

Acids and salts

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Acids and salts mainly refers to inorganic pollutants from irrigated lands, mining operations, urban runoffs, industrial sites and landfills.[10]​

Pathogens

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Pathogens may be present in nonpoint source runoff, and can be a source of disease if they enter drinking water supplies. Pathogens found in contaminated runoff may include:

Coliform bacteria may also be detected in runoff. These bacteria are a commonly used indicator of water pollution, but not an actual cause of disease.[11]​

Pathogens may contaminate runoff due to poorly managed livestock operations, faulty septic systems, and improper handling of pet waste.[5]​

Control of nonpoint source pollution

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Contour buffer strips used to retain soil and reduce erosion.
Artículos principales: Agricultural wastewater treatment y Erosion control.

Sediment
To control sediment, farmers may utilize erosion controls to reduce runoff flows and retain soil on their fields. Common techniques include contour plowing, crop mulching, crop rotation, planting perennial crops and installing riparian buffers.[12]​[13]​[2]​: pp. 4-95–4-96 

Nutrients
Nutrients (nitrogen and phosphorus) are typically applied to farmland as commercial fertilizer; animal manure; or spraying of municipal or industrial wastewater (effluent) or sludge. Nutrients may also enter runoff from crop residues, irrigation water, wildlife, and atmospheric deposition.[2]​: p. 2-9  Farmers can develop and implement nutrient management plans to reduce excess application of nutrients.[14]​[2]​: pp. 4-37–4-38 

Pesticides
To minimize pesticide impacts, farmers may use Integrated Pest Management (IPM) techniques (which can include biological pest control) to maintain control over pests, reduce reliance on chemical pesticides, and protect water quality.[15]​[16]​

Restoration Methords
Use artificial marsh to treat agricultural wastewater.


See also

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References

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  1. ↑ U.S. Environmental Protection Agency (EPA). Washington, D.C. "National Water Quality Inventory: Report to Congress; 2002 Reporting Cycle." October 2007. Document No. EPA-841-R-07-001.
  2. ↑ a b c d EPA. "National Management Measures to Control Nonpoint Source Pollution from Agriculture." July 2003. Document No. EPA 841-B-03-004.
  3. ↑ EPA. National Management Measures to Control Nonpoint Source Pollution from Hydromodification." July 2007. Document No. EPA 841-B-07-002
  4. ↑ EPA. "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.
  6. ↑ J. Court Stevenson, Catherine B. Piper and Nedra Confer (1979). "Decline of Submerged Plants in Chesapeake Bay." U.S. Fish and Wildlife Service. Annapolis, MD.
  7. ↑ Rob Leeds, Larry C. Brown, Nathan L. Watermeier. "Food, Agricultural and Biological Engineering." Ohio State University Extension Fact Sheet.
  8. ↑ Rob Leeds, Larry C. Brown, Nathan L. Watermeier. "Food, Agricultural and Biological Engineering." Ohio State University Extension Fact Sheet.
  9. ↑ Rob Leeds, Larry C. Brown, Nathan L. Watermeier. "Food, Agricultural and Biological Engineering." Ohio State University Extension Fact Sheet
  10. ↑ Rob Leeds, Larry C. Brown, Nathan L. Watermeier. "Food, Agricultural and Biological Engineering." Ohio State University Extension Fact Sheet
  11. ↑ U.S. Geological Survey. Reston, VA. "A Primer on Water Quality." FS-027-01. March 2001.
  12. ↑ U.S. Natural Resources Conservation Service (NRCS). Fort Worth, TX. National Conservation Practice Standard: Contour Farming." Code 330. June 2007.
  13. ↑ NRCS. National Conservation Practice Standard: Mulching." Code 484. September 2008.
  14. ↑ NRCS. "National Conservation Practice Standard: Nutrient Management." Code 590. August 2006.
  15. ↑ NRCS. National Conservation Practice Standard: Pest Management." Code 595. July 2008.
  16. ↑ EPA. "Integrated Pest Management Principles." March 13, 2008.
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