Nonpoint source pollution

Muddy river
Runoff of soil and fertilizer during a rain storm
Nonpoint source pollution is caused when precipitation (1) carries pollutants from the ground such as nitrogen (N) and phosphorus (P) pollutants which come from fertilizers used on farm lands (2) or urban areas (3). These nutrients can cause eutrophication (4).
Contour buffer strips used to retain soil and reduce erosion

Nonpoint source (NPS) pollution refers to diffuse contamination (or pollution) of water or air that does not originate from a single discrete source.

- Nonpoint source pollution

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Water pollution

Contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses.

Raw sewage and industrial waste in the New River as it passes from Mexicali (Mexico) to Calexico, California
Poster to teach people in South Asia about human activities leading to the pollution of water sources
Bauxite residue is an industrial waste that is dangerously alkaline and can lead to water pollution if not managed appropriately (photo from Stade, Germany).
Muddy river polluted by sediment.
Solid waste and plastics in the Lachine Canal, Canada.
The Brayton Point Power Station in Massachusetts discharges heated water to Mount Hope Bay.
A polluted river draining an abandoned copper mine on Anglesey
Perfluorooctanesulfonic acid (PFOS) is a global pollutant that has been found in drinking water. It appears not to biodegrade.
Environmental scientists preparing water autosamplers.
Oxygen depletion, resulting from nitrogen pollution and eutrophication is a common cause of fish kills.
Fecal sludge collected from pit latrines is dumped into a river at the Korogocho slum in Nairobi, Kenya.
View of secondary treatment reactors (activated sludge process) at the Blue Plains Advanced Wastewater Treatment Plant, Washington, D.C., United States. Seen in the distance are the sludge digester building and thermal hydrolysis reactors.
Silt fence installed on a construction site.
Share of water bodies with good water quality in 2020 (a water body is classified as "good" quality if at least 80% of monitoring values meet target quality levels, see also SDG 6, Indicator 6.3.2)

Sources of water pollution are either point sources or non-point sources.

Pollution

Introduction of contaminants into the natural environment that cause adverse change.

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Smog in the center of Moscow, Russia in August 2010
The Lachine Canal in Montreal, Quebec, Canada
Blue drain and yellow fish symbol used by the UK Environment Agency to raise awareness of the ecological impacts of contaminating surface drainage
An industrial area, with a power plant, south of Yangzhou's downtown, China
Overview of main health effects on humans from some common types of pollution
Great Pacific garbage patch
A litter trap catches floating waste in the Yarra River, east-central Victoria, Australia
Air pollution control system, known as a thermal oxidizer, decomposes hazard gases from industrial air streams at a factory in the United States.
A dust collector in Pristina, Kosovo
A visual comparison of the free market and socially optimal outcomes
Air pollution in the US, 1973
Smog pollution in Taiwan

Pollution is often classed as point source or nonpoint source pollution.

Urban runoff

Surface runoff of rainwater, landscape irrigation, and car washing created by urbanization.

Urban runoff flowing into a storm drain
A creek filled with urban runoff after a storm
Flooded streets in New Orleans
Relationship between impervious surfaces and surface runoff
Weasel Brook in Passaic, New Jersey has been channelized with concrete walls to control localized flooding.
An open runoff system in Africa
Oil slick created by runoff
A percolation trench infiltrates stormwater through permeable soils into the groundwater aquifer.
An oil-grit separator is designed to capture settleable solids, oil and grease, debris and floatables in runoff from roads and parking lots

Eroding soils or poorly maintained construction sites can often lead to increased sedimentation in runoff.

Eutrophication

Process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus.

1. Excess nutrients are applied to the soil. 2. Some nutrients leach into the soil and later drain into surface water. 3. Some nutrients run off over the ground into the body of water.  4. The excess nutrients cause an algal bloom.  5. The algal bloom reduces light penetration. 6. The plants beneath the algal bloom die because they cannot get sunlight to perform photosynthesis.  7. Eventually, the algal bloom dies and sinks to the bottom of the lake. Bacterial communities begin to decompose the remains, using up oxygen for respiration.  8. The decomposition causes the water to become depleted of oxygen if the water body is not regularly mixed vertically. Larger life forms, such as fish die.
Sodium triphosphate, once a component of many detergents, was a major contributor to eutrophication.
Cultural eutrophication is caused by human additions of nutrients into the water that cause over growth of algae which can block light and air exchange. The algae eventually are broken down by bacteria causing anoxic conditions and "dead zones".
Aerial view of Lake Valencia experiencing a large cultural eutrophication flux due to untreated wastewater discharging into the lake.
Eutrophication is apparent as increased turbidity in the northern part of the Caspian Sea, imaged from orbit.
Map of measured Gulf hypoxia zone, July 25–31, 2021-LUMCON-NOAA
Oxygen minimum zones (OMZs) (blue) and areas with coastal hypoxia (red) in the world’s ocean.
Eutrophication in a canal
The eutrophication of the Mono Lake which is a cyanobacteria-rich Soda lake.
Application of a phosphorus sorbent to a lake - The Netherlands

Approaches for prevention and reversal of eutrophication include: minimizing point source pollution from sewage, and minimizing nutrient pollution from agriculture and other nonpoint pollution sources.

Surface runoff

Flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil.

Runoff flowing into a stormwater drain
Surface runoff from a hillside after soil is saturated
Precipitation washing contaminates into local streams
Urban surface water runoff
Willow hedge strengthened with fascines for the limitation of runoff, north of France.
Soil erosion by water on intensively-tilled farmland.
Farmland runoff
Runoff holding ponds (Uplands neighborhood of North Bend, Washington)

Runoff that occurs on the ground surface before reaching a channel can be a nonpoint source of pollution, as it can carry man-made contaminants or natural forms of pollution (such as rotting leaves).

Stormwater

Water that originates from precipitation , including heavy rain and meltwater from hail and snow.

Urban runoff entering a storm drain
Relationship between impervious surfaces and surface runoff
Stormwater carrying street bound pollutants to a storm drain for coastal discharge.
Urban runoff being discharged to coastal waters
Retention basin for management of stormwater
Volunteers clearing gutters in Ilorin, Nigeria during a volunteer sanitation day. Even when there is adequate infrastructure for sanitation, plastic pollution can interfere with storm water runoff creating space for mosquitos to breed in water, and causing flooding. Some sewage systems in the Global South are frequently overwhelmed by the waste, such as in Bangkok, Thailand.
Stormwater filtration system for urban runoff
Rain barrels can reduce runoff from building's downspouts and replace the use of potable water for activities such as gardening.
Rain garden designed to treat stormwater from adjacent parking lot
Map of municipal separate storm sewer systems
A silt fence, a type of sediment control, installed on a construction site
Public education graphic distributed by EPA

Agricultural runoff (except for concentrated animal feeding operations, or "CAFO") is classified as nonpoint source pollution under the CWA.

Erosion control

Practice of preventing or controlling wind or water erosion in agriculture, land development, coastal areas, river banks and construction.

Terraces, conservation tillage, and conservation buffers save soil and improve water quality on this Iowa farm.
Hydroseeding in the United Kingdom

By the 1970s the models had expanded to complex computer models addressing nonpoint source pollution with thousands of lines of computer code.

Polycyclic aromatic hydrocarbon

Hydrocarbon—a chemical compound containing only carbon and hydrogen—that is composed of multiple aromatic rings.

Smog in Cairo. Particulate air pollution, including smog, is a substantial cause of human exposure to PAHs.
Crude oil on a beach after a 2007 oil spill in Korea.
An 18th-century drawing of chimney sweeps.
An adduct formed between a DNA strand and an epoxide derived from a benzo[a]pyrene molecule (center); such adducts may interfere with normal DNA replication.
Naphthalene
Biphenyl
Fluorene
Anthracene
Phenanthrene
Phenalene
Tetracene
Chrysene
Triphenylene
Pyrene
Pentacene
Perylene
Benzo[a]pyrene
Corannulene
Benzo[ghi]perylene
Coronene
Ovalene
Benzo[c]fluorene
Phenanthrene
Anthracene
Chrysene

PAHs typically disperse from urban and suburban non-point sources through road runoff, sewage, and atmospheric circulation and subsequent deposition of particulate air pollution.

Clean Water Act

Primary federal law in the United States governing water pollution.

Common point source discharges
Nonpoint source pollutants, such as sediments, nutrients, pesticides, fertilizers and animal wastes, account for more than half of the pollution in U.S. waters.
Map of municipal separate storm sewer systems
The construction grants program funded new sewage treatment plants and upgrading existing plants to national secondary treatment standards.
Components of an NPDES permit

Such sources were therefore considered to be nonpoint sources that were not subject to the permit program.

Agriculture

Practice of cultivating plants and livestock.

China has the largest agricultural output of any country.
Centres of origin, as numbered by Nikolai Vavilov in the 1930s. Area 3 (gray) is no longer recognised as a centre of origin, and New Guinea (area P, orange) was identified more recently.
Agricultural scenes of threshing, a grain store, harvesting with sickles, digging, tree-cutting and ploughing from ancient Egypt. Tomb of Nakht, 15th century BC
Agricultural calendar, c. 1470, from a manuscript of Pietro de Crescenzi
Reindeer herds form the basis of pastoral agriculture for several Arctic and Subarctic peoples.
Harvesting wheat with a combine harvester accompanied by a tractor and trailer
Spreading manure by hand in Zambia
On the three-sector theory, the proportion of people working in agriculture (left-hard bar in each group, green) falls as an economy becomes more developed.
Rollover protection bar retrofitted to a mid-20th century Fordson tractor
Value of agricultural production, 2016
Slash and burn shifting cultivation, Thailand
Intercropping of coconut and Mexican marigold
Intensively farmed pigs
Raising chickens intensively for meat in a broiler house
Tilling an arable field
A center pivot irrigation system
Winnowing grain: global warming will probably harm crop yields in low latitude countries like Ethiopia.
Wheat cultivar tolerant of high salinity (left) compared with non-tolerant variety
Seedlings in a green house. This is what it looks like when seedlings are growing from plant breeding.
Genetically modified potato plants (left) resist virus diseases that damage unmodified plants (right).
Water pollution in a rural stream due to runoff from farming activity in New Zealand
Farmyard anaerobic digester converts waste plant material and manure from livestock into biogas fuel.
Circular irrigated crop fields in Kansas. Healthy, growing crops of corn and sorghum are green (sorghum may be slightly paler). Wheat is brilliant gold. Fields of brown have been recently harvested and plowed or have lain in fallow for the year.
Spraying a crop with a pesticide
Terraces, conservation tillage and conservation buffers reduce soil erosion and water pollution on this farm in Iowa.
Mechanised agriculture: from the first models in the 1940s, tools like a cotton picker could replace 50 farm workers, at the price of increased use of fossil fuel.
In 19th century Britain, the protectionist Corn Laws led to high prices and widespread protest, such as this 1846 meeting of the Anti-Corn Law League.
An agronomist mapping a plant genome

These nutrients are major nonpoint pollutants contributing to eutrophication of aquatic ecosystems and pollution of groundwater, with harmful effects on human populations.