Glossary
The terms in this glossary were compiled and modified from numerous sources. Definitions given here may not be the only valid ones for these terms.
- Aquatic-life criteria
- Water-quality guidelines for protection of aquatic life. Often refers to U.S. Environmental Protection Agency water-quality criteria for protection of aquatic organisms. See also Water-quality guidelines, Water-quality criteria, and Freshwater chronic criteria.
- Aquifer
- A water-bearing layer of soil, sand, gravel, or rock that will yield usable quantities of water to a well.
- Base flow
- Sustained, low flow in a stream; ground-water discharge is the source of base flow in most places.
- Basic Fixed Sites
- Sites on streams at which streamflow is measured and samples are collected for temperature, salinity, suspended sediment, major ions and metals, nutrients, and organic carbon to assess the broad-scale spatial and temporal character and transport of inorganic constituents of streamwater in relation to hydrologic conditions and environmental settings.
- Basin
- See Drainage basin.
- Bed sediment
- The material that temporarily is stationary in the bottom of a stream or other watercourse.
- Bioavailability
- The capacity of a chemical constituent to be taken up by living organisms either through physical contact or by ingestion.
- Carbonate rocks
- Rocks (such as limestone or dolostone) that are composed primarily of minerals (such as calcite and dolomite) containing the carbonate ion (CO32-).
- Chlordane
- Octachloro-4,7-methanotetrahydroindane. An organochlorine insecticide no longer registered for use in the U.S. Technical chlordane is a mixture in which the primary components are cis- and trans-chlordane, cis- and trans-nonachlor, and heptachlor.
- Community
- In ecology, the species that interact in a common area.
- Concentration
- The amount or mass of a substance present in a given volume or mass of sample. Usually expressed as microgram per liter (water sample) or micrograms per kilogram (sediment or tissue sample).
- Confined aquifer (artesian aquifer)
- An aquifer that is completely filled with water under pressure and that is overlain by material that restricts the movement of water.
- Contamination
- Degradation of water quality compared to original or natural conditions due to human activity.
- Cubic foot per second (ft3/s, or cfs)
- Rate of water discharge representing a volume of 1 cubic foot passing a given point during 1 second, equivalent to approximately 7.48 gallons per second or 448.8 gallons per minute or 0.02832 cubic meter per second.
- Degradation products
- Compounds resulting from transformation of an organic substance through chemical, photochemical, and/or biochemical reactions.
- Denitrification
- A process by which oxidized forms of nitrogen such as nitrate (NO3-) are reduced to form nitrites, nitrogen oxides, ammonia, or free nitrogen: commonly brought about by the action of denitrifying bacteria and usually resulting in the escape of nitrogen to the air.
- DDT
- Dichloro-diphenyl-trichloroethane. An organochlorine insecticide no longer registered for use in the United States.
- Discharge
- Rate of fluid flow passing a given point at a given moment in time, expressed as volume per unit of time.
- Dissolved constituent
- Operationally defined as a constituent that passes through a 0.45-micrometer filter.
- Dissolved solids
- Amount of minerals, such as salt, that are dissolved in water; amount of dissolved solids is an indicator of salinity or hardness.
- Drainage basin
- The portion of the surface of the Earth that contributes water to a stream through overland run-off, including tributaries and impoundments.
- Drinking-water standard or guideline
- A threshold concentration in a public drinking-water supply, designed to protect human health. As defined here, standards are U.S. Environmental Protection Agency regulations that specify the maximum contamination levels for public water systems required to protect the public welfare; guidelines have no regulatory status and are issued in an advisory capacity.
- Fertilizer
- Any of a large number of natural or synthetic materials, including manure and nitrogen, phosphorus, and potassium compounds, spread on or worked into soil to increase its fertility.
- Fish community
- See Community.
- Fixed Sites
- NAWQA's most comprehensive monitoring sites. See also Basic Fixed Sites and Intensive Fixed Sites.
- Freshwater chronic criteria
- The highest concentration of a contaminant that freshwater aquatic organisms can be exposed to for an extended period of time (4 days) without adverse effects. See also Water-quality criteria.
- Gaging station
- A particular site on a stream, canal, lake, or reservoir where systematic observations of hydrologic data are obtained.
- Ground water
- In general, any water that exists beneath the land surface, but more commonly applied to water in fully saturated soils and geologic formations.
- Habitat
- The part of the physical environment where plants and animals live.
- Health advisory
- Nonregulatory levels of contaminants in drinking water that may be used as guidance in the absence of regulatory limits. Advisories consist of estimates of concentrations that would result in no known or anticipated health effects (for carcinogens, a specified cancer risk) determined for a child or for an adult for various exposure periods.
- Herbicide
- A chemical or other agent applied for the purpose of killing undesirable plants. See also Pesticide.
- Hydrograph
- Graph showing variation of water elevation, velocity, streamflow, or other property of water with respect to time.
- Indicator sites
- Stream sampling sites located at outlets of drainage basins with relatively homogeneous land use and physiographic conditions; most indicator-site basins have drainage areas ranging from 20 to 200 square miles.
- Insecticide
- A substance or mixture of substances intended to destroy or repel insects.
- Instantaneous discharge
- The volume of water that passes a point at a particular instant of time.
- Integrator or Mixed-use site
- Stream sampling site located at an outlet of a drainage basin that contains multiple environmental settings. Most integrator sites are on major streams with relatively large drainage areas.
- Intensive Fixed Sites
- Basic Fixed Sites with increased sampling frequency during selected seasonal periods and analysis of dissolved pesticides for 1 year. Most NAWQA Study Units have one to two integrator Intensive Fixed Sites and one to four indicator Intensive Fixed Sites.
- Karst
- A type of topography that results from dissolution and collapse of carbonate rocks such as limestone and dolomite, and characterized by closed depressions or sinkholes, caves, and underground drainage.
- Load
- General term that refers to a material or constituent in solution, in suspension, or in transport; usually expressed in terms of mass or volume.
- Maximum contaminant level (MCL)
- Maximum permissible level of a contaminant in water that is delivered to any user of a public water system. MCL's are enforceable standards established by the U.S. Environmental Protection Agency.
- Median
- The middle or central value in a distribution of data ranked in order of magnitude. The median is also known as the 50th percentile.
- Milligrams per liter (mg/L)
- A unit expressing the concentration of chemical constituents in solution as weight (milligrams) of solute per unit volume (liter) of water; equivalent to one part per million in most streamwater and ground water. One thousand micrograms per liter equals 1 mg/L.
- Nitrate
- An ion consisting of nitrogen and oxygen (NO3-). Nitrate is a plant nutrient and is very mobile in soils.
- Nutrient
- Element or compound essential for animal and plant growth. Common nutrients in fertilizer include nitrogen, phosphorus, and potassium.
- Organochlorine insecticide
- A class of organic insecticides containing a high percentage of chlorine. Includes dichlorodiphenylethanes (such as DDT), chlorinated cyclodienes (such as chlordane), and chlorinated benzenes (such as lindane). Most organochlorine insecticides were banned because of their carcinogenicity, tendency to bioaccumulate, and toxicity to wildlife.
- Organochlorine pesticide
- See Organochlorine insecticide.
- Pesticide
- A chemical applied to crops, rights of way, lawns, or residences to control weeds, insects, fungi, nematodes, rodents or other "pests".
- Phosphorus
- A nutrient essential for growth that can play a key role in stimulating aquatic growth in lakes and streams.
- Picocurie (pCi)
- One trillionth (10-12) of the amount of radioactivity represented by a curie (Ci). A curie is the amount of radioactivity that yields 3.7 x 1010 radioactive disintegrations per second (dps). A picocurie yields 2.22 disintegrations per minute (dpm) or 0.037 dps.
- Polychlorinated biphenyls (PCBs)
- A mixture of chlorinated derivatives of biphenyl, marketed under the trade name Aroclor with a number designating the chlorine content (such as Aroclor 1260). PCBs were used in transformers and capacitors for insulating purposes and in gas pipeline systems as a lubricant. Further sale for new use was banned by law in 1979.
- Radon
- A naturally occurring, colorless, odorless, radioactive gas formed by the disintegration of the element radium; damaging to human lungs when inhaled.
- Semivolatile organic compound (SVOC)
- Operationally defined as a group of synthetic organic compounds that are solvent-extractable and can be determined by gas chromatography/mass spectrometry. SVOCs include phenols, phthalates, and Polycyclic aromatic hydrocarbons (PAHs).
- Stream reach
- A continuous part of a stream between two specified points.
- Study Unit
- A major hydrologic system of the United States in which NAWQA studies are focused. Study Units are geographically defined by a combination of ground- and surface-water features and generally encompass more than 4,000 square miles of land area.
- Synoptic sites
- Sites sampled during a short-term investigation of specific water-quality conditions during selected seasonal or hydrologic conditions to provide improved spatial resolution for critical water-quality conditions.
- Total concentration
- Refers to the concentration of a constituent regardless of its form (dissolved or bound) in a sample.
- Total DDT
- The sum of DDT and its metabolites (breakdown products), including DDD and DDE.
- Trace element
- An element found in only minor amounts (concentrations less than 1.0 milligram per liter) in water or sediment; includes arsenic, cadmium, chromium, copper, lead, mercury, nickel, and zinc.
- Uranium
- A heavy silvery-white metallic element, highly radioactive and easily oxidized. Of the 14 known isotopes of uranium, U238 is the most abundant in nature.
- Volatile organic compounds (VOCs)
- Organic chemicals that have a high vapor pressure relative to their water solubility. VOCs include components of gasoline, fuel oils, and lubricants, as well as organic solvents, fumigants, some inert ingredients in pesticides, and some by-products of chlorine disinfection.
- Water-quality criteria
- Specific levels of water quality which, if reached, are expected to render a body of water unsuitable for its designated use. Commonly refers to water-quality criteria established by the U.S. Environmental Protection Agency. Water-quality criteria are based on specific levels of pollutants that would make the water harmful if used for drinking, swimming, farming, fish production, or industrial processes.
- Water-quality guidelines
- Specific levels of water quality which, if reached, may adversely affect human health or aquatic life. These are nonenforceable guidelines issued by a governmental agency or other institution.
- Water-quality standards
- State-adopted and U.S. Environmental Protection Agency-approved ambient standards for water bodies. Standards include the use of the water body and the water-quality criteria that must be met to protect the designated use or uses.
- Water table
- The point below the land surface where ground water is first encountered and below which the earth is saturated. Depth to the water table varies widely across the country.
