Water pollution glossary

Acid rain — Rain with a higher than normal acid range. Caused when polluted air mixes with cloud moisture. The "acid" in acid rain comes from sulfur oxides and nitrogen oxides, products of burning coal and other fuels and from certain industrial processes. Acid rain can make lakes devoid of fish and damage human health and property.

Algal bloom — An unusual, sudden or excessive abundance of algae. Algal blooms can adversely affect water quality.

Ammonia — An inorganic form of nitrogen, is contained in fertilizers, septic system effluent, and animal wastes. It is also a product of bacterial decomposition of organic matter. Ammonia NH3-N (NH3-N) becomes a concern if high levels of the un-ionized form are present. In this form NH3-N can be toxic to aquatic organisms. The presence of un-ionized ammonia is a function of the NH3-N concentration, pH, and temperature. Conversion of NH3-N to nitrite nitrogen by nitrification requires large quantities of oxygen which can kill aquatic organisms due to the lowered dissolved oxygen concentrations in water. NH3-N concentrations are reported in mg/L NH3-N.

Aquifer — An underground layer of sand, gravel or rock that stores or conveys water below the surface of the soil.

Biological Oxygen Demand — The amount of oxygen required by aerobic microorganisms to decompose the organic matter in sample of water. Used as a measure of the degree of water pollution.

Clean Water Act — An act passed by the U.S. Congress to control water pollution (formerly referred to as the Federal Water Pollution Control Act of 1972). Public Law 92-500, as amended. 33 U.S.C. 1251 et seq. Section 303(d) is a report to Congress from EPA that identifies those waters for which existing controls are not sufficiently stringent to achieve applicable water quality standards. Section 305(b) involves biennial reporting requiring description of the quality of the Nation's surface waters, evaluation of progress made in maintaining and restoring water quality, and description of the extent of remaining problems by using biological data to make aquatic life use support decisions.

Clean Water Partnership program — A program created by the Legislature in 1990 to protect and improve ground water and surface water in Minnesota by providing financial and technical assistance to local units of government interested in controlling nonpoint source pollution.

Dissolved oxygen — The concentration of molecular oxygen (O2) dissolved in water, usually expressed in milligrams per liter (mg/L), parts per million, or percent of saturation. The DO level represents one of the most important measurements of water quality and is a critical indicator of a water body's ability to support healthy ecosystems. Levels above 5 mg/L are considered optimal, and most fish cannot survive for prolonged periods at levels below 3 mg/L. Microbial communities in water use oxygen to breakdown organic materials, such as manure, sewage and decomposing algae. Low levels of dissolved oxygen can be a sign that too much organic material is in a water body.

E. coli — Escherichia coli, a subgroup of fecal coliform bacteria that is present in the intestinal tracts and feces of warm-blooded animals. It is used as an indicator of the potential presence of pathogens. There are many different strains of E. coli that are classified into more than 170 serogroups. Although most strains of E. coli are harmless and live in the intestines of healthy humans and animals, the E. coli O157:H7 strain produces a powerful toxin and can cause severe illness.

Effluent — Liquid flowing out of a system, such as a discharge of liquid waste from a factory or water leaving a sewage treatment plant.

Eutrophic lake — A nutrient-rich lake — usually shallow, "green" and with limited oxygen in the bottom layer of water.

Eutrophication — The aging process by which lakes are fertilized with nutrients. Natural eutrophication will very gradually change the character of a lake. Cultural eutrophication is the accelerated aging of a lake as a result of human activities.

Fecal coliform — A group of bacteria found in the intestinal tract of humans and animals, and also found in soil. While harmless in themselves, coliform bacteria are commonly used as indicators of the presence of pathogenic organisms and other disease-causing bacteria, such as those that cause typhoid, dysentery, hepatitis A and cholera. Measured in number of bacteria per 100 milliliters of water. Failing septic systems and runoff from feedlots are common sources of fecal coliform in water samples.

Feedlot — A lot or building or a group of lots or buildings used for the confined feeding, breeding or holding of animals. This definition includes areas specifically designed for confinement in which manure may accumulate or any area where the concentration of animals is such that a vegetative cover cannot be maintained. Lots used to feed and raise poultry are considered to be feedlots. Pastures are not animal feedlots.

Groundwater — Underground water in an aquifer, used for drinking water in 75 percent of Minnesota households. The subsurface water supply in the saturated zone below the level of the water table.

Herbicides — Chemicals used to kill undesirable vegetation.

Impaired water — The Clean Water Act requires states to publish, every two years, an updated list of streams and lakes that are not meeting their designated uses because of excess pollutants. The list, known as the 303(d) list, is based on violations of water quality standards. For a list and maps of impaired waters in MN go to the TMDL Web page.

Maximum contaminant level — The legal threshold limit on the amount of a hazardous substance that is allowed in drinking water under the Safe Drinking Water Act. The limit, set by the U.S. Environmental Protection Agency, is usually expressed as a concentration in milligrams or micrograms per liter of water.

Mercury — Mercury is a highly toxic element that is found both naturally and as an introduced contaminant in the environment. Although concentrations in water are very low, mercury accumulates through the aquatic food chain, resulting in high concentrations in fish that can threaten the health of people and wildlife. It is measured in units of nanograms per liter (ng/L) in water and milligrams per kilogram (mg/Kg) in fish.

Nitrates — In lakes, most nitrate/nitrogen is in NO3 form. It is measured in milligrams per liter. Elevated levels of nitrates/nitrogen are often caused by over application of fertilizers that leach into waterbodies.

Non-point pollution source — Polluted runoff sources not discharged from a single point, such as runoff from agricultural fields or feedlots.

Pesticides — Chemicals used to kill or control pests, such as weeds, insects, fungus, mites, algae, rodents and other undesirable agents.

pH — A measure of acidity, with 7 being neutral. Numbers under 7 are acidic and numbers over 7 are alkaline.

Phosphate — An essential nutrient containing phosphorus and oxygen. Phosphate is often a critical nutrient in lake eutrophication management.

Point pollution source — Pollution arising from a well-defined origin, such as a discharge from an industrial plant.

Runoff — That portion of precipitation or irrigation water that flows off a field or paved area and enters surface water.

Secchi depth — The depth in a lake, measured in meters, to which a Secchi disk can be observed, as a measure of light penetration in water. The Secchi disk is lowered into a section of shaded water until it can no longer be seen and then lifted back up until it can be seen once again. Averaging the two depths gives the clarity of the water.

Sediment — Solid material that is in suspension, is being transported, or has been moved from its original location by air, water, gravity or ice.

Surface water — Aboveground water, such as streams, rivers and lakes.

Suspended solids — Small particles that hang in the water column and create turbid, or cloudy conditions.

Turbidity — Indicates the degree to which light is scattered in water by suspended particulate material and soluble colored compounds. It provides an estimate of the muddiness or cloudiness of the water due to clay, silt, finely divided organic and inorganic matter, soluble colored organic compounds, plankton, and microscopic organisms. In streams, a major cause of elevated turbidity is disturbed and eroding soils carried by storm run-off to streams. Once in the stream system, elevated turbidity reduces the depth of photosynthesis and the feeding ability of aquatic organisms. When soils settle out in downstream reaches with slower flow, bed substrate becomes embedded, removing essential habitat for aquatic insects and other organisms.

Watershed — The surrounding land area that drains into a lake, river or river system.

Credit: Minnesota Pollution Control Agency. For more, go here.

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