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Nonpoint Sources of Pollution

A nonpoint source (NPS) of pollution is defined as any water pollution coming from a diffused source. Whereas point pollution sources such as wastewa-ter from sewage or industries are discharged on a single location, NPSs can spread over a very large area where rain, irrigation, or snowmelt can carry pollutants and discharge them in streams, lakes, reservoirs, or coastal waters. These pollutants can be carried either over the ground through surface runoff or below the ground surface through seepage. Depending on their type, these pollutants can be carried over large distances and have a drastic effect on water quality.

Common NPSs

There can be many different kinds of NPSs, but the most significant are crop and grazing agriculture practices that use large amounts of insecticides and fertilizers. Fertilizers are chemicals usually containing nitrogen and phosphorus that are good plant nutrients. Although their presence in the water is not in itself a threat to human health, they encourage algae blooms and eutrophication of the water causing the death of fish and other life forms of the aquatic ecosystem. Both intensive and extensive domestic livestock produce huge amounts of feces that, when improperly managed, can pollute water and create a health hazard for humans and other animals. Pathogenic diseases such as cholera, dysentery, and hepatitis A are known to be associated with the presence of feces in the water. Fecal coliform bacteria is a good indicator of the presence of fecal material in the water but should not entirely be attributed to feces. Storm runoff water from urban areas can escape the sewage system and carry toxic oils and chemicals to nearby streams. Bad soil conservation practices in agricultural areas can also promote soil erosion and increase the amount of sediment load carried by runoff to water bodies.

Controlling NPSs

Because many human activities are potential contributors, NPSs are inherently difficult to control. Although some of these activities such as burying toxic waste are illegal, others, such as spraying fertilizers and insecticides, are not only legal but are often encouraged and even subsidized by the government. This makes NPS pollution extremely hard to reduce on a large scale, and local policies seldom show sensibility or awareness of the problem. It is considered in many parts of the world as the leading source of water-quality problems. While many actions to reduce NPS pollution necessitate state action, such as the creation and enforcement of more restrictive laws of land management, other measures require local initiatives, such as the implementation of better soil conservation practices or the restoration of riparian vegetation, that can have a strong filtering effect on runoff water.

  • nonpoint source pollution
  • nonpoint sources of pollution
PhilippeMaillard
http://dx.doi.org/10.4135/9781412939591.n822
See also

Further Readings

Hranova, R. (Ed.). (2005).Diffuse pollution of water resources: Principles and case studies in the Southern African Region.London: Taylor & Francis.
Novotny, V.(2003).Water quality: Diffuse pollution and watershed management. New York: Wiley.
Olsson, L., & Pilesjö, P.(2002).Approaches to spatially distributed hydrological modelling in a GIS environment. In A. Skidmore (Ed.), Environmental modelling with GIS

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