transportation significantly contributes as well. since most inputs come from land, either via the rivers, sewage or the atmosphere, it means that continental shelves are more vulnerable to pollution. air pollution is also a contributing factor by carrying off iron, carbonic acid, nitrogen, silicon, sulfur, pesticides or dust particles into the ocean. the pollution often comes from nonpoint sources such as agricultural runoff, wind-blown debris, and dust. these nonpoint sources are largely due to runoff that enters the ocean through rivers, but wind-blown debris and dust can also play a role, as these pollutants can settle into waterways and oceans. pathways of pollution include direct discharge, land runoff, ship pollution, bilge pollution, atmospheric pollution and, potentially, deep sea mining. nutrient pollution this section is an excerpt from nutrient pollution. nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. it is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth. sources of nutrient pollution include surface runoff from farm fields and pastures, discharges from septic tanks and feedlots, and emissions from combustion. raw sewage is a large contributor to cultural eutrophication since sewage is high in nutrients. releasing raw sewage into a large water body is referred to as sewage dumping, and still occurs all over the world. excess reactive nitrogen compounds in the environment are associated with many large-scale environmental concerns. these include eutrophication of surface waters, harmful algal blooms, hypoxia, acid rain, nitrogen saturation in forests, and climate change. thermal pollution the brayton point power station in massachusetts discharges heated water to mount hope bay. this section is an excerpt from thermal pollution. thermal pollution, sometimes called "thermal enrichment", is the degradation of water quality by any process that changes ambient water temperature. thermal pollution is the rise or fall in the temperature of a natural body of water caused by human influence. thermal pollution, unlike chemical pollution, results in a change in the physical properties of water. a common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. urban runoff—stormwater discharged to surface waters from rooftops, roads and parking lots—and reservoirs can also be a source of thermal pollution. thermal pollution can also be caused by the release of very cold water from the base of reservoirs into warmer rivers. elevated water temperatures decrease oxygen levels (due to lower levels of dissolved oxygen, as gases are less soluble in warmer liquids), which can kill fish (which may then rot) and alter food chain composition, reduce species biodiversity, and foster invasion by new thermophilic species.: 179 : 375 biological pollution the introduction of aquatic invasive organisms is a form of water pollution as well. it causes biological pollution. groundwater pollution this section is an excerpt from groundwater pollution. groundwater pollution (also called groundwater contamination) occurs when pollutants are released to the ground and make their way into groundwater. this type of water pollution can also occur naturally due to the presence of a minor and unwanted constituent, contaminant, or impurity in the groundwater, in which case it is more likely referred to as contamination rather than pollution. groundwater pollution can occur from on-site sanitation systems, landfill leachate, effluent from wastewater treatment plants, leaking sewers, petrol filling stations, hydraulic fracturing (fracking) or from over application of fertilizers in agriculture. pollution (or contamination) can also occur from naturally occurring contaminants, such as arsenic or fluoride. using polluted groundwater causes hazards to public health through poisoning or the spread of disease (water-borne diseases). in many areas of the world, groundwater pollution poses a hazard to the wellbeing of people and ecosystems. one-quarter of the world's population depends on groundwater for drinking, yet concentrated recharging is known to carry short-lived contaminants into carbonate aquifers and jeopardize the purity of those waters. pollution from point sources point source water pollution refers to contaminants that enter a waterway from a single, identifiable source, such as a pipe or ditch. examples of sources in this category include discharges from a sewage treatment plant, a factory, or a city storm drain. the u.s. clean water act (cwa) defines point source for regulatory enforcement purposes (see united states regulation of point source water pollution). the cwa definition of point source was amended in 1987 to include municipal storm sewer systems, as well as industrial storm water, such as from construction sites. sewage sewage typically consists of 99.9% water and 0.1% solids. sewage contributes many classes of nutrients that lead to eutrophication. it is a major source of phosphate for example. sewage is often contaminated with diverse compounds found in personal hygiene, cosmetics, pharmaceutical drugs (see also drug pollution), and their metabolites water pollution due to environmental persistent pharmaceutical pollutants can have wide-ranging consequences. when sewers overflow during storm events this can lead to water pollution from untreated sewage. such events are called sanitary sewer overflows or combined sewer overflows.a polluted river draining an abandoned copper mine on anglesey industrial wastewater perfluorooctanesulfonic acid (pfos) is a global pollutant that has been found in drinking water. it appears not to biodegrade.further information: industrial wastewater treatment industrial processes that use water also produce wastewater. this is called industrial wastewater. using the us as an example, the main industrial consumers of water (using over 60% of the total consumption) are power plants, petroleum refineries, iron and steel mills, pulp and paper mills, and food processing industries. some industries discharge chemical wastes, including solvents and heavy metals (which are toxic) and other harmful pollutants. industrial wastewater could add the following pollutants to receiving water bodies if the wastewater is not treated and managed properly: heavy metals, including mercury, lead, and chromium organic matter and nutrients such as food waste: certain industries (e.g. food processing, slaughterhouse waste, paper fibers, plant material, etc.) discharge high concentrations of bod, ammonia nitrogen and oil and grease.: 180 inorganic particles such as sand, grit, metal particles, rubber residues from tires, ceramics, etc.; toxins such as pesticides, poisons, herbicides, etc. pharmaceuticals, endocrine disrupting compounds, hormones, perfluorinated compounds, siloxanes, drugs of abuse and other hazardous substances microplastics such as polyethylene and polypropylene beads, polyester and polyamide thermal pollution from power stations and industrial manufacturers radionuclides from uranium mining, processing nuclear fuel, operating nuclear reactors, or disposal of radioactive waste. some industrial discharges include persistent organic pollutants such as per- and polyfluoroalkyl substances (pfas). oil spills this section is an excerpt from oil spill. an oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. the term is usually given to marine oil spills, where oil is released into the ocean or coastal waters, but spills may also occur on land. oil spills may be due to releases of crude oil from tankers, offshore platforms, drilling rigs and wells, as well as spills of refined petroleum products (such as gasoline, diesel) and their by-products, heavier fuels used by large ships such as bunker fuel, or the spill of any oily refuse or waste oil. pollution from nonpoint sources this section is an excerpt from nonpoint source pollution. nonpoint source (nps) pollution refers to diffuse contamination (or pollution) of water or air that does not originate from a single discrete source. this type of pollution is often the cumulative effect of small amounts of contaminants gathered from a large area. it is in contrast to point source pollution which results from a single source. nonpoint source pollution generally results from land runoff, precipitation, atmospheric deposition, drainage, seepage, or hydrological modification (rainfall and snowmelt) where tracing pollution back to a single source is difficult. nonpoint source water pollution affects a water body from sources such as polluted runoff from agricultural areas draining into a river, or wind-borne debris blowing out to sea. nonpoint source air pollution affects air quality, from sources such as smokestacks or car tailpipes. although these pollutants have originated from a point source, the long-range transport ability and multiple sources of the pollutant make it a nonpoint source of pollution; if the discharges were to occur to a body of water or into the atmosphere at a single location, the pollution would be single-point. agriculture agriculture is a major contributor to water pollution from nonpoint sources. the use of fertilizers as well as surface runoff from farm fields, pastures and feedlots leads to nutrient pollution. in addition to plant-focused agriculture, fish-farming is also a source of pollution. additionally, agricultural runoff often contains high levels of pesticides. atmospheric contributions (air pollution) air deposition is a process whereby air pollutants from industrial or natural sources settle into water bodies. the deposition may lead to polluted water near the source, or at distances up to a few thousand miles away. the most frequently observed water pollutants resulting from industrial air deposition are sulfur compounds, nitrogen compounds, mercury compounds, other heavy metals, and some pesticides and industrial by-products. natural sources of air deposition include forest fires and microbial activity. acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids. some governments have made efforts since the 1970s to reduce the release of sulfur dioxide and nitrogen oxide into the atmosphere. the main source of sulfur and nitrogen compounds that result in acid rain are anthropogenic, but nitrogen oxides can also be produced naturally by lightning strikes and sulphur dioxide is produced by volcanic eruptions. acid rain can have harmful effects on plants, aquatic ecosystems and infrastructure. carbon dioxide concentrations in the atmosphere have increased since the 1850s due anthropogenic influences (emissions of greenhouse gases). this leads to ocean acidification and is another form of water pollution from atmospheric contributions. sampling, measurements, analysis environmental scientists preparing water autosamplers further information: water quality § sampling and measurement, environmental monitoring, analysis of water chemistry, water sampling station, and regulation and monitoring of pollution § water pollution water pollution may be analyzed through several broad categories of methods: physical, chemical and biological. some methods may be conducted in situ, without sampling, such as temperature. others involve collection of samples, followed by specialized analytical tests in the laboratory. standardized, validated analytical test methods, for water and wastewater samples have been published. common physical tests of water include temperature, specific conductance or electrical conductance (ec) or conductivity, solids concentrations (e.g., total suspended solids (tss)) and turbidity. water samples may be examined using analytical chemistry methods. many published test methods are available for both organic and inorganic compounds. frequently used parameters that are quantified are ph, bod,: 102 chemical oxygen demand (cod),: 104 dissolved oxygen (do), total hardness, nutrients (nitrogen and phosphorus compounds, e.g. nitrate and orthophosphates), metals (including copper, zinc, cadmium, lead and mercury), oil and grease, total petroleum hydrocarbons (tph), surfactants and pesticides. the use of a biomonitor or bioindicator is described as biological monitoring. this refers to the measurement of specific properties of an organism to obtain information on the surrounding physical and chemical environment. biological testing involves the use of plant, animal or microbial indicators to monitor the health of an aquatic ecosystem. they are any biological species or group of species whose function, population, or status can reveal what degree of ecosystem or environmental integrity is present. one example of a group of bio-indicators are the copepods and other small water crustaceans that are present in many water bodies. such organisms can be monitored for changes (biochemical, physiological, or behavioral) that may indicate a problem within their ecosystem. this section is an excerpt from water quality § sample collection. the complexity of water quality as a subject is reflected in the many types of measurements of water quality indicators. some measurements of water quality are most accurately made on-site, because water exists in equilibrium with its surroundings. measurements commonly made on-site and in direct contact with the water source in question include temperature, ph, dissolved oxygen, conductivity, oxygen reduction potential (orp), turbidity, and secchi disk depth. impacts oxygen depletion, resulting from nitrogen pollution and eutrophication, is a common cause of fish kills. ecosystems water pollution is a major global environmental problem because it can result in the degradation of all aquatic ecosystems –