Bronte Wells
Nonpoint source pollution is a type of pollution that comes from a wide range of sources and is challenging to identify and address. It is caused by rainfall or snowmelt, which picks up and carries pollutants from various human activities, such as lawn fertilization, pesticide use, road construction, and industrial emissions, and deposits them into water bodies. This type of pollution has a significant impact on aquatic ecosystems, drinking water supplies, and recreational activities, and it is crucial to implement effective management practices in urban, suburban, and agricultural areas to mitigate its effects. Nonpoint source pollution is a pressing environmental issue that requires collective efforts to reduce and control.
| Characteristics | Values |
|---|---|
| Definition | Any source of water pollution that does not meet the legal definition of "point source" in section 502(14) of the Clean Water Act |
| Difficulty in Identification | Harder to identify and address than point-source pollution |
| Sources | Urban and suburban areas, agricultural operations, atmospheric inputs, highway runoff, forestry and mining operations, marinas and boating activities |
| Examples of Pollutants | Oil, pet waste, pesticides, herbicides, fertilizer, road salt, bacteria, sediment, nutrients, toxic contaminants, chemicals, and pathogens |
| Effects | Harm to aquatic habitats and life, reduction in capacity of water resources for drinking and recreation, negative impact on coastal communities and economies |
| Prevention | Improving management of urban and suburban areas, agricultural operations, forestry operations, and marinas |
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What You'll Learn
Urban and suburban areas
Urban runoff is often classified as a type of NPS pollution. However, some people consider it a point source because it is sometimes channelled into municipal storm drain systems and discharged through pipes into nearby surface waters. Nonetheless, not all urban runoff flows through these systems, especially in developing and suburban areas. Unlike other types of point sources, such as industrial discharges, the pollution in urban runoff cannot be attributed to one activity or 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.
The pollutants in urban runoff can include oils, heavy metals, trash, fertilizers, pesticides, and sediments. These pollutants can have harmful effects on drinking water supplies, recreation, fisheries, and wildlife. For example, nutrients from fertilizers can cause rampant algae growth in water, lowering oxygen levels and inducing algal blooms and eutrophication.
To control nonpoint source pollution in urban and suburban areas, several approaches can be undertaken. Buffer strips can be used to create a barrier of grass between impervious paving materials like parking lots and roads, and the closest body of water. Retention ponds can be built in drainage areas to trap contaminants before they reach the aquatic environment. Porous pavement can be used to allow rainwater to drain into the ground, reducing the amount of runoff. Restoration methods such as constructing wetlands can also help slow runoff and absorb contamination.
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Atmospheric deposition
Agricultural practices also influence atmospheric deposition. The application of commercial fertilizers, animal manure, and pesticides to agricultural land can result in the release of pollutants into the atmosphere. Additionally, forestry operations, including habitat modification and silviculture, can contribute to atmospheric deposition by reducing tree coverage and disrupting soil stability.
The impact of atmospheric deposition on water quality is significant. Pollutants deposited on surfaces can eventually be washed into nearby water bodies through runoff, affecting lakes, rivers, and oceans. This process contributes to nonpoint source pollution in these water bodies, as the pollutants enter the water through multiple dispersed locations rather than a single discharge point. The effects of atmospheric deposition on water quality can be particularly pronounced in coastal areas, where tourism, fishing, and other economic activities rely on pristine aquatic environments.
Furthermore, atmospheric deposition of nitrogen is a specific concern. Nitrogen emissions from point sources, such as coal- and oil-burning electric utilities, can lead to atmospheric deposition, which is then washed into watersheds through precipitation. This deposition contributes to nitrogen pollution in streams, with higher levels observed in areas with greater precipitation and runoff. While regulatory efforts have targeted nitrogen oxide emissions, the complex nature of atmospheric deposition and the involvement of various sources continue to pose challenges in effectively managing this type of nonpoint source pollution.
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Highway runoff
The sources of these pollutants are diverse, ranging from soil erosion caused by road construction to the deposition of contaminants from vehicle emissions and traffic activities. For instance, the removal of vegetation during road building increases soil erosion, leaving the soil exposed and vulnerable to being washed away by rainfall or snowmelt. This eroded soil, or sediment, then becomes a carrier for other pollutants, including heavy metals and pesticides, which adhere to the sediment particles.
Vehicle emissions and traffic activities also play a significant role in highway runoff pollution. Polycyclic aromatic hydrocarbons (PAHs), for example, are a priority pollutant found in highway runoff. PAHs are released from vehicle emissions and can have toxic effects on aquatic life, as evidenced by studies showing the negative impact of highway runoff on salmon and mussel populations. Other pollutants, such as nutrients, can cause excessive algae growth in water bodies, leading to ecological imbalances.
To mitigate the effects of highway runoff, various management practices and legislative actions have been implemented. The Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991, for instance, includes provisions for controlling water pollution from highway runoff. This act allows states to allocate federal funding towards runoff pollution control devices and best management practices (BMPs) to prevent polluted runoff from reaching water bodies. Additionally, the National Estuary Program (NEP) and the pesticides program under the Federal Insecticide, Fungicide and Rodenticide Act aim to regulate pesticides and protect water quality in targeted estuaries.
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Forestry and mining operations
Non-point source pollution is a type of pollution that comes from many places at once, as opposed to point-source pollution, which comes from a single, identifiable place. Non-point source pollution is harder to identify and address.
Forestry Operations
Forestry activities can result in non-point source pollution through various practices:
- Removal of streamside vegetation: Clearing vegetation along streams can impact water quality. It reduces the shading that regulates water temperature and removes vegetation that stabilizes streambanks. These changes can harm aquatic life by limiting their sources of food, shade, and shelter, as well as reducing suitable areas for species intolerant of warmer temperatures.
- Road construction and use: Building and using roads in forested areas can be a major source of sediment, contributing up to 90% of the total sediment from forestry operations. The excess sediment in water bodies can negatively affect aquatic organisms' ability to live, forage, and spawn.
- Timber harvesting: Harvesting trees near streams can have similar effects to removing streamside vegetation, impacting water quality and harming aquatic life.
- Mechanical preparation for tree planting: The use of machinery to prepare sites for tree planting can disturb the land and contribute to sediment runoff and other forms of pollution.
To mitigate these impacts, forest owners can implement best management practices (BMPs) and follow scientifically sound techniques to protect water bodies from polluted runoff. This includes using environmentally sensitive maintenance practices for roads, such as reducing erosion, sediment, and dust pollution. Forest management certification has also emerged as an incentive for landowners to commit to sustainable forest management practices.
Mining Operations
Mining activities, particularly abandoned subsurface mines, can also contribute to non-point source pollution:
- Acidic water seepage: Water that seeps out of abandoned mines can become highly acidic and contaminated with metals. For example, in Colorado, copper, zinc, and arsenic contamination from abandoned mines have affected several streams.
- Acid mine drainage: In some regions of the United States, acid mine drainage and associated contamination from abandoned mines have impacted water bodies. This has resulted in water bodies devoid of life due to high levels of toxic metals like copper.
To address these issues, individuals can get involved in local mining issues, voice concerns about acid mine drainage, and support reclamation projects. Additionally, proper logging and erosion control practices on forest lands, including the construction, maintenance, and closure of logging roads, can help mitigate the impacts of mining operations on non-point source pollution.
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Marinas and boating activities
Marinas are located at the water's edge, so there is a strong potential for marina waters to become contaminated with pollutants from various activities. These include boat cleaning and fueling operations, as well as stormwater runoff from parking lots and hull maintenance and repair areas. Boat cleaners often contain chlorine, ammonia, and phosphates, which can harm plankton and fish. Small oil spills from motors and refueling activities can also contaminate waters around the marina.
To reduce nonpoint source pollution, proper marina planning and an informed boating public are essential. Strategies such as implementing pollution prevention measures, properly containing hull maintenance areas, and designing fueling and sewage collection stations to facilitate spill cleanup can help minimize environmental impacts. Marinas should be located and designed to allow for natural flushing to renew marina waters regularly.
Boaters can also take actions to prevent nonpoint source pollution, such as achieving zero discharge of sewage into recreational waters by using approved marine sanitation devices and emptying waste into approved shoreside handling facilities. Additionally, boat operation and maintenance practices should be carefully managed to prevent the release of solvents, paints, oils, and other pollutants into the groundwater or surface water.
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Frequently asked questions
Yes, oil leaked from car engines is a form of nonpoint source pollution.
Yes, nutrient runoff from agricultural fields is a form of nonpoint source pollution.
No, discharge from a sewage treatment plant is an example of point-source pollution.
Yes, particles of tire rubber washed away during a storm are considered nonpoint source pollution.
Yes, sediment washed off from construction sites is a form of nonpoint source pollution.
