Washington Water Science Center Glossary
A
Absorption
Absorption
The process by which substances in gaseous, liquid, or solid form are assimilated or taken up by other substances.
Acid
Acid
Has a pH of water less than 5.5; pH modifier used in the U.S. Fish and Wildlife Service wetland classification system; in common usage, acidic water has a pH less than 7.
Acidic deposition
Acidic deposition
The transfer of acidic or acidifying substances from the atmosphere to the surface of the Earth or to objects on its surface. Transfer can be either by wet-deposition processes (rain, snow, dew, fog, frost, hail) or by dry deposition (gases, aerosols, or fine to coarse particles).
Acre-foot
Acre-foot
The volume of water needed to cover an acre of land to a depth of one foot; equivalent to 43,560 cubic feet or 325,851 gallons.
Adsorption
Adsorption
The adherence of gas molecules, ions, or molecules in solution to the surface of solids.
Aerate
Aerate
To supply air to water, soil, or other media.
Aerobic
Aerobic
Pertaining to, taking place in, or caused by the presence of oxygen.
Algae
Algae
Chlorophyll-bearing nonvascular, primarily aquatic species that have no true roots, stems, or leaves; most algae are microscopic, but some species can be as large as vascular plants.
Algal bloom
Algal bloom
The rapid proliferation of passively floating, simple plant life, such as blue-green algae, in and on a body of water.
Alkaline
Alkaline
Has a pH greater than 7; pH modifier in the U.S. Fish and Wildlife Service wetland classification system; in common usage, a pH of water greater than 7.4.
Alluvial aquifer
Alluvial aquifer
A water-bearing deposit of unconsolidated material (sand and gravel) left behind by a river or other flowing water.
Alluvium
Alluvium
General term for sediments of gravel, sand, silt, clay, or other particulate rock material deposited by flowing water, usually in the beds of rivers and streams, on a flood plain, on a delta, or at the base of a mountain.
Alpine snow glade
Alpine snow glade
A marshy clearing between slopes above the timberline in mountains.
Amalgamation
Amalgamation
The dissolving or blending of a metal (commonly gold and silver) in mercury to separate it from its parent material.
Ammonia
Ammonia
A compound of nitrogen and hydrogen (NH3) that is a common by-product of animal waste. Ammonia readily converts to nitrate in soils and streams.
Anadromous fish
Anadromous fish
Migratory species that are born in freshwater, live mostly in estuaries and ocean water, and return to freshwater to spawn.
Anaerobic
Anaerobic
Pertaining to, taking place in, or caused by the absence of oxygen.
Anomalies
Anomalies
As related to fish, externally visible skin or subcutaneous disorders, including deformities, eroded fins, lesions, and tumors.
Anthropogenic
Anthropogenic
Having to do with or caused by humans.
Anticline
Anticline
A fold in the Earth's crust, convex upward, whose core contains stratigraphically older rocks.
Aquaculture
Aquaculture
The science of farming organisms that live in water, such as fish, shellfish, and algae.
Aquatic
Aquatic
Living or growing in or on water.
Aquatic guidelines
Aquatic guidelines
Specific levels of water quality which, if reached, may adversely affect aquatic life. These are nonenforceable guidelines issued by a governmental agency or other institution.
Aquatic-life criteria
Aquatic-life criteria
Water-quality guidelines for protection of aquatic life. Commonly refers to criteria established by the U.S. Environmental Protection Agency. See also Water-quality guidelines, Water-quality criteria, and Freshwater chronic criteria.
Aquifer
Aquifer
A geologic formation, group of formations, or part of a formation that contains sufficient saturated permeable material to yield significant quantities of water to springs and wells.
Arroyo
Arroyo
A small, deep, flat-floored channel or gully of an ephemeral or intermittent stream, usually with nearly vertical banks cut, into unconsolidated material. A term commonly used in the arid and semiarid regions of the Southwestern United States.
Artificial recharge
Artificial recharge
Augmentation of natural replenishment of ground-water storage by some method of construction, spreading of water, or by pumping water directly into an aquifer.
Atmospheric deposition
Atmospheric deposition
The transfer of substances from the air to the surface of the Earth, either in wet form (rain, fog, snow, dew, frost, hail) or in dry form (gases, aerosols, particles).
Atmospheric pressure
Atmospheric pressure
The pressure exerted by the atmosphere on any surface beneath or within it; equal to 14.7 pounds per square inch at sea level.
Average discharge
Average discharge
As used by the U.S. Geological Survey, the arithmetic average of all complete water years of record of surface water discharge whether consecutive or not. The term "average" generally is reserved for average of record and "mean" is used for averages of shorter periods, namely, daily, monthly, or annual mean discharges.
B
Background concentration
Background concentration
A concentration of a substance in a particular environment that is indicative of minimal influence by human (anthropogenic) sources.
Backwater
Backwater
A body of water in which the flow is slowed or turned back by an obstruction such as a bridge or dam, an opposing current, or the movement of the tide.
Bacteria
Bacteria
Single-celled microscopic organisms.
Bank
Bank
The sloping ground that borders a stream and confines the water in the natural channel when the water level, or flow, is normal.
Bank storage
Bank storage
The change in the amount of water stored in an aquifer adjacent to a surface-water body resulting from a change in stage of the surface-water body.
Barrier bar
Barrier bar
An elongate offshore ridge, submerged at least at high tide, built up by the action of waves or currents.
Barrier beach
Barrier beach
A narrow, elongate sandy ridge rising slightly above the high-tide level and extending generally parallel with the mainland shore, but separated from it by a lagoon.
Base flow
Base flow
The sustained low flow of a stream, usually ground-water inflow to the stream channel.
Basic
Basic
The opposite of acidic; water that has a pH of greater than 7.
Basic Fixed Sites
Basic Fixed Sites
Sites on streams in NAWQA Study Units at which streamflow is measured and samples are collected for analysis of 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 and Range physiography
Basin and Range physiography
A region characterized by a series of generally north-trending mountain ranges separated by alluvial valleys.
Bed material
Bed material
Sediment composing the streambed.
Bed sediment
Bed sediment
The material that temporarily is stationary in the bottom of a stream or other watercourse.
Bed sediment and tissue studies
Bed sediment and tissue studies
Assessment of concentrations and distributions of trace elements and hydrophobic organic contaminants in streambed sediment and tissues of aquatic organisms to identify potential sources and to assess spatial distribution of those constituents.
Bedload
Bedload
Sediment that moves on or near the streambed and is in almost continuous contact with the bed.
Bedrock
Bedrock
A general term used for solid rock that underlies soils or other unconsolidated material.
Benthic invertebrates
Benthic invertebrates
Insects, mollusks, crustaceans, worms, and other organisms without a backbone that live in, on, or near the bottom of lakes, streams, or oceans.
Benthic organism
Benthic organism
A form of aquatic life that lives on or near the bottom of streams, lakes, or oceans.
Best management practice
Best management practice
An agricultural practice that has been determined to be an effective, practical means of preventing or reducing nonpoint-source pollution.
Bind
Bind
To exert a strong chemical attraction.
Bioaccumulation
Bioaccumulation
The biological sequestering of a substance at a higher concentration than that at which it occurs in the surrounding environment or medium. Also, the process whereby a substance enters organisms through the gills, epithelial tissues, dietary, or other sources.
Bioavailability
Bioavailability
The capacity of a chemical constituent to be taken up by living organisms either through physical contact or by ingestion.
Biochemical
Biochemical
Refers to chemical processes that occur inside or are mediated by living organisms.
Biochemical process
Biochemical process
A process characterized by, produced by, or involving chemical reactions in living organisms.
Biochemical-oxygen demand
Biochemical-oxygen demand
The amount of oxygen, expressed in milligrams per liter, that is removed from aquatic environments by the life processes of micro-organisms.
Biodegradation
Biodegradation
Transformation of a substance into new compounds through biochemical reactions or the actions of microorganisms such as bacteria.
Biomass
Biomass
The amount of living matter, in the form of organisms, present in a particular habitat, usually expressed as weight-per-unit area.
Biota
Biota
All living organisms of an area.
Blowout
Blowout
A small saucer- or trough-shaped hollow or depression formed by wind erosion on a pre-existing dune or other sand deposit.
Blue-baby syndrome
Blue-baby syndrome
A condition most common in young infants and certain elderly people that can be caused by ingestion of high amounts of nitrate, which results in the blood losing its ability to effectively carry oxygen.
Bog
Bog
A nutrient-poor, acidic wetland dominated by a waterlogged, spongy mat of sphagum moss that ultimately forms a thick layer of acidic peat; generally has no inflow or outflow; fed primarily by rain water.
Bolson
Bolson
An extensive, flat, saucer-shaped, alluvium-floored basin or depression, almost or completely surrounded by mountains and from which drainage has no surface outlet; a term used in the desert regions of the Southwestern United States.
Boreal
Boreal
A climatic zone having a definite winter with snow and a short summer that is generally hot, and which is characterized by a large annual range of temperature.
Bosque
Bosque
A dense growth of trees and underbrush.
Bottom-land forest
Bottom-land forest
Low-lying forested wetland found along streams and rivers, usually on alluvial flood plains.
Brackish water
Brackish water
Water with a salinity intermediate between seawater and freshwater (containing from 1,000 to 10,000 milligrams per liter of dissolved solids).
Braided stream
Braided stream
A stream characterized by an interlacing or tangled network of several small branching and reuniting shallow channels.
Breakdown product
Breakdown product
A compound derived by chemical, biological, or physical action upon a pesticide. The breakdown is a natural process that may result in a more toxic or a less toxic compound and a more persistent or less persistent compound.
Brine
Brine
Water that contains more than 35,000 milligrams per liter of dissolved solids.
C
Calcareous
Calcareous
A rock or substance formed of calcium carbonate or magnesium carbonate by biological deposition or inorganic precipitation, or containing those minerals in sufficient quantities to effervesce when treated with cold hydrochloric acid.
Caldera
Caldera
A large, more or less circular, basin-shaped volcanic depression whose diameter is many times greater than the volcanic vent.
Canopy angle
Canopy angle
Generally, a measure of the openness of a stream to sunlight. Specifically, the angle formed by an imaginary line from the highest structure (for example, tree, shrub, or bluff) on one bank to eye level at midchannel to the highest structure on the other bank.
Capillary fringe
Capillary fringe
The zone above the water table in which water is held by surface tension. Water in the capillary fringe is under a pressure less than atmospheric.
Carbonate rocks
Carbonate rocks
Rocks (such as limestone or dolostone) that are composed primarily of minerals (such as calcite and dolomite) containing the carbonate ion (CO32-).
Center pivot irrigation
Center pivot irrigation
An automated sprinkler system involving a rotating pipe or boom that supplies water to a circular area of an agricultural field through sprinkler heads or nozzles.
Channel scour
Channel scour
Erosion by flowing water and sediment on a stream channel; results in removal of mud, silt, and sand on the outside curve of a stream bend and the bed material of a stream channel.
Channelization
Channelization
The straightening and deepening of a stream channel to permit the water to move faster or to drain a wet area for farming.
Chlordane
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.
Chlorinated solvent
Chlorinated solvent
A volatile organic compound containing chlorine. Some common solvents are trichloroethylene, tetrachloroethylene, and carbon tetrachloride.
Chlorofluorocarbons
Chlorofluorocarbons
A class of volatile compounds consisting of carbon, chlorine, and fluorine. Commonly called freons, which have been in refrigeration mechanisms, as blowing agents in the fabrication of flexible and rigid foams, and, until banned from use several years ago, as propellants in spray cans.
Cienaga
Cienaga
A marshy area where the ground is wet due to the presence of seepage or springs.
Circumneutral
Circumneutral
Said of water with a pH between 5.5 and 7.4; pH modifier used in the U.S. Fish and Wildlife Service wetland classification system.
Cirque
Cirque
A deep, steep-walled, half-bowllike recess or hollow situated high on the side of a mountain and commonly at the head of a glacial valley; and produced by the erosive activity of mountain glaciers.
Clastic
Clastic
Rock, such as sandstone, or sediment composed principally of broken fragments that are derived from preexisting rocks which have been transported from their place of origin.
Climate
Climate
The sum total of the meteorological elements that characterize the average and extreme conditions of the atmosphere over a long period of time at any one place or region of the Earth's surface.
Combined sewer overflow
Combined sewer overflow
A discharge of untreated sewage and stormwater to a stream when the capacity of a combined storm/sanitary sewer system is exceeded by storm runoff.
Commercial withdrawals
Commercial withdrawals
Water for use by motels, hotels, restaurants, office buildings, commercial facilities, and civilian and military institutions. The water may be obtained from a public supplier or it may be self-supplied.
Community
Community
In ecology, the species that interact in a common area.
Concentration
Concentration
The ratio of the quantity of any substance present in a sample of a given volume or a given weight compared to the volume or weight of the sample.
Cone of depression
Cone of depression
The depression of heads around a pumping well caused by withdrawal of water.
Confined aquifer
Confined aquifer
An aquifer that is completely filled with water under pressure and that is overlain by material that restricts the movement of water.
Confining layer
Confining layer
A body of impermeable or distinctly less permeable (see permeability) material stratigraphically adjacent to one or more aquifers that restricts the movement of water into and out of the aquifers.
Confluence
Confluence
The flowing together of two or more streams; the place where a tributary joins the main stream.
Conglomerate
Conglomerate
A coarse-grained sedimentary rock composed of fragments larger than 2 millimeters in diameter.
Constituent
Constituent
A chemical or biological substance in water, sediment, or biota that can be measured by an analytical method.
Consumptive use
Consumptive use
The quantity of water that is not available for immediate reuse because it has been evaporated, transpired, or incorporated into products, plant tissue, or animal tissue. Also referred to as "water consumption".
Contact recreation
Contact recreation
Recreational activities, such as swimming and kayaking, in which contact with water is prolonged or intimate, and in which there is a likelihood of ingesting water.
Contamination
Contamination
Degradation of water quality compared to original or natural conditions due to human activity.
Contributing area
Contributing area
The area in a drainage basin that contributes water to streamflow or recharge to an aquifer.
Coral reef
Coral reef
A ridge of limestone, composed chiefly of coral, coral sands, and solid limestone resulting from organic secretion of calcium carbonate; occur along continents and islands where the temperature is generally above 18° C.
Core sample
Core sample
A sample of rock, soil, or other material obtained by driving a hollow tube into the undisturbed medium and withdrawing it with its contained sample.
Criterion
Criterion
A standard rule or test on which a judgment or decision can be based.
Crystalline rocks
Crystalline rocks
Rocks (igneous or metamorphic) consisting wholly of crystals or fragments of crystals.
Cubic foot per second
Cubic foot per second
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. In a stream channel, a discharge of 1 cubic foot per second is equal to the discharge at a rectangular cross section, 1 foot wide and 1 foot deep, flowing at an average velocity of 1 foot per second.
Cyclone
Cyclone
An area of low pressure around which winds rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. See also Tropical cyclone.
Cypress dome
Cypress dome
Small, isolated, circular, depressional, forested wetlands, in which cypress predominates, that have convex silhouettes when viewed from a distance.
D
Datum plane
Datum plane
A horizontal plane to which ground elevations or water surface elevations are referenced.
DDT
DDT
Dichloro-diphenyl-trichloroethane. An organochlorine insecticide no longer registered for use in the United States.
Deciduous
Deciduous
Refers to plants that shed foliage at the end of the growing season.
Deepwater habitat
Deepwater habitat
Permanently flooded lands lying below the deepwater boundary of wetlands.
Degradation products
Degradation products
Compounds resulting from transformation of an organic substance through chemical, photochemical, and/or biochemical reactions.
Degraded
Degraded
Condition of the quality of water that has been made unfit for some specified purpose.
Delta
Delta
The low, nearly flat tract of land at or near the mouth of a river, resulting from the accumulation of sediment supplied by the river in such quantities that it is not removed by tides, waves, or currents. Commonly a triangular or fan-shaped plain.
Denitrification
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.
Detect
Detect
To determine the presence of a compound.
Detection limit
Detection limit
The concentration of a constituent or analyte below which a particular analytical method cannot determine, with a high degree of certainty, the concentration.
Diatoms
Diatoms
Single-celled, colonial, or filamentous algae with siliceous cell walls constructed of two overlapping parts.
Dieldrin
Dieldrin
An organochlorine insecticide no longer registered for use in the United States. Also a degradation product of the insecticide aldrin.
Direct runoff
Direct runoff
The runoff entering stream channels promptly after rainfall or snowmelt.
Discharge
Discharge
The volume of fluid passing a point per unit of time, commonly expressed in cubic feet per second, million gallons per day, gallons per minute, or seconds per minute per day.
Discharge area
Discharge area
(Groundwater) Area where subsurface water is discharged to the land surface, to surface water, or to the atmosphere.
Dispersion
Dispersion
The extent to which a liquid substance introduced into a ground-water system spreads as it moves through the system.
Dissected
Dissected
Cut by erosion into valleys, hills, and upland plains.
Dissolved constituent
Dissolved constituent
Operationally defined as a constituent that passes through a 0.45-micrometer filter.
Dissolved oxygen
Dissolved oxygen
Oxygen dissolved in water; one of the most important indicators of the condition of a water body. Dissolved oxygen is necessary for the life of fish and most other aquatic organisms.
Dissolved solids
Dissolved solids
Minerals and organic matter dissolved in water.
Diversion
Diversion
A turning aside or alteration of the natural course of a flow of water, normally considered physically to leave the natural channel. In some States, this can be a consumptive use direct from another stream, such as by livestock watering. In other States, a diversion must consist of such actions as taking water through a canal, pipe, or conduit.
Dolomite
Dolomite
A sedimentary rock consisting chiefly of magnesium carbonate.
Domestic withdrawals
Domestic withdrawals
Water used for normal household purposes, such as drinking, food preparation, bathing, washing clothes and dishes, flushing toilets, and watering lawns and gardens. The water may be obtained from a public supplier or may be self-supplied. Also called residential water use.
Dominant plant
Dominant plant
The plant species controlling the environment.
Drainage area
Drainage area
The drainage area of a stream at a specified location is that area, measured in a horizontal plane, which is enclosed by a drainage divide.
Drainage basin
Drainage basin
The land area drained by a river or stream.
Drainage divide
Drainage divide
Boundary between adjoining drainage basins.
Drawdown
Drawdown
The difference between the water level in a well before pumping and the water level in the well during pumping. Also, for flowing wells, the reduction of the pressure head as a result of the discharge of water.
Drinking-water standard or guideline
Drinking-water standard or guideline
A threshold concentration for a constituent or compound 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.
Drip irrigation
Drip irrigation
An irrigation system in which water is applied directly to the root zone of plants by means of applicators (orifices, emitters, porous tubing, or perforated pipe) operated under low pressure. The applicators can be placed on or below the surface of the ground or can be suspended from supports.
Drought
Drought
A prolonged period of less-than-normal precipitation such that the lack of water causes a serious hydrologic imbalance.
E
Ecological studies
Ecological studies
Studies of biological communities and habitat characteristics in NAWQA Study Units to evaluate the effects of physical and chemical characteristics of water and hydrologic conditions on aquatic biota and to determine how biological and habitat characteristics differ among environmental settings.
Ecoregion
Ecoregion
An area of similar climate, landform, soil, potential natural vegetation, hydrology, or other ecologically relevant variables.
Ecosystem
Ecosystem
A community of organisms considered together with the nonliving factors of its environment.
Effluent
Effluent
Outflow from a particular source, such as a stream that flows from a lake or liquid waste that flows from a factory or sewage-treatment plant.
Emergent plants
Emergent plants
Erect, rooted, herbaceous plants that may be temporarily or permanently flooded at the base but do not tolerate prolonged inundation of the entire plant.
Endangered species
Endangered species
A species that is in imminent danger of becoming extinct.
Endocrine system
Endocrine system
The collection of ductless glands in animals that secrete hormones, which influence growth, gender and sexual maturity.
Environment
Environment
The sum of all conditions and influences affecting the life of organisms.
Environmental framework
Environmental framework
Natural and human-related features of the land and hydrologic system, such as geology, land use, and habitat, that provide a unifying framework for making comparative assessments of the factors that govern water-quality conditions within and among NAWQA Study Units.
Environmental sample
Environmental sample
A water sample collected from an aquifer or stream for the purpose of chemical, physical, or biological characterization of the sampled resource.
Environmental setting
Environmental setting
Land area characterized by a unique combination of natural and human-related factors, such as row-crop cultivation or glacial-till soils.
Ephemeral stream
Ephemeral stream
A stream or part of a stream that flows only in direct response to precipitation; it receives little or no water from springs, melting snow, or other sources; its channel is at all times above the water table.
EPT richness index
EPT richness index
An index based on the sum of the number of taxa in three insect orders, Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies), that are composed primarily of species considered to be relatively intolerant to environmental alterations.
Equal-width increment sample
Equal-width increment sample
A composite sample of water collected across a section of stream with equal spacing between verticals and equal transit rates within each vertical that yields a representative sample of stream conditions.
Erosion
Erosion
The process whereby materials of the Earth's crust are loosened, dissolved, or worn away and simultaneously moved from one place to another.
Estuarine wetlands
Estuarine wetlands
Tidal wetlands in low-wave-energy environments where the salinity of the water is greater than 0.5 part per thousand and is variable owing to evaporation and the mixing of seawater and freshwater; tidal wetlands of coastal rivers and embayments, salty tidal marshes, mangrove swamps, and tidal flats.
Estuary
Estuary
Area where the current of a stream meets the ocean and where tidal effects are evident; an arm of the ocean at the lower end of a river.
Eutrophication
Eutrophication
The process by which water becomes enriched with plant nutrients, most commonly phosphorus and nitrogen.
Evaporation
Evaporation
he process by which water is changed to gas or vapor; occurs directly from water surfaces and from the soil.
Evaporite minerals
Evaporite minerals
Minerals or deposits of minerals formed by evaporation of water containing salts. These deposits are common in arid climates.
Evaporites
Evaporites
A class of sedimentary rocks composed primarily of minerals precipitated from a saline solution as a result of extensive or total evaporation of water.
Evapotranspiration
Evapotranspiration
The process by which water is discharged to the atmosphere as a result of evaporation from the soil and surface-water bodies, and transpiration by plants.
Exotic species
Exotic species
Plants or animals not native to the area.
F
Fall line
Fall line
Imaginary line marking the boundary between the ancient, resistant crystalline rocks of the Piedmont province of the Appalachian Mountains, and the younger, softer sediments of the Atlantic Coastal Plain province in the Eastern United States. Along rivers, this line commonly is reflected by waterfalls.
Fallow
Fallow
Cropland, tilled or untilled, allowed to lie idle during the whole or greater part of the growing season.
FDA action level
FDA action level
A regulatory level recommended by the U.S. Environmental Protection Agency for enforcement by the Food and Drug Administration (FDA) when pesticide residues occur in food commodities for reasons other than the direct application of the pesticide. Action levels are set for inadvertent pesticide residues resulting from previous legal use or accidental contamination. Applies to edible portions of fish and shellfish in interstate commerce.
Fecal bacteria
Fecal bacteria
Microscopic single-celled organisms (primarily fecal coliforms and fecal streptococci) found in the wastes of warm-blooded animals. Their presence in water is used to assess the sanitary quality of water for body-contact recreation or for consumption. Their presence indicates contamination by the wastes of warm-blooded animals and the possible presence of pathogenic (disease producing) organisms.
Fecal coliform
Fecal coliform
Microscopic single-celled organisms (primarily fecal coliforms and fecal streptococci) found in the wastes of warm-blooded animals. Their presence in water is used to assess the sanitary quality of water for body-contact recreation or for consumption. Their presence indicates contamination by the wastes of warm-blooded animals and the possible presence of pathogenic (disease producing) organisms.
Fen
Fen
Peat-accumulating wetland that generally receives water from surface runoff and (or) seepage from mineral soils in addition to direct precipitation; generally alkaline; or slightly acid.
Fertilizer
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.
Filtrate
Filtrate
Liquid that has been passed through a filter.
Fixed Sites
Fixed Sites
Monitoring sites in NAWQA Study Units at which the most comprehensive suites of data are collected. See also Basic Fixed Sites and Intensive Fixed Sites.
Flood
Flood
Any relatively high streamflow that overflows the natural or artificial banks of a stream.
Flood attenuation
Flood attenuation
a weakening or reduction in the force or intensity of a flood.
Flood irrigation
Flood irrigation
The application of irrigation water whereby the entire surface of the soil is covered by ponded water.
Flood plain
Flood plain
A strip of relatively flat land bordering a stream channel that is inundated at times of high water.
Flow line
Flow line
The idealized path followed by particles of water.
Flowpath
Flowpath
An underground route for ground-water movement, extending from a recharge (intake) zone to a discharge (output) zone such as a shallow stream.
Fluvial
Fluvial
Pertaining to a river or stream.
Fluvial deposit
Fluvial deposit
A sedimentary deposit consisting of material transported by suspension or laid down by a river or stream.
Flyway
Flyway
A specific air route taken by birds during migration.
Freshwater
Freshwater
Water that contains less than 1,000 milligrams per liter of dissolved solids.
Freshwater chronic criteria
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.
Friable
Friable
Descriptive of a rock or mineral that crumbles naturally or is easily broken, pulverized, or reduced to powder.
Fumigant
Fumigant
A substance or mixture of substances that produces gas, vapor, fume, or smoke intended to destroy insects, bacteria, or rodents.
Furrow irrigation
Furrow irrigation
A type of surface irrigation whereby water is applied at the upper (higher) end of a field and flows in furrows to the lower end.
G
Gage height
Gage height
Height of the water surface above an established datum plane, such as in a river above a predetermined point that may (or may not) be at the channel floor.
Gaging station
Gaging station
A particular site on a stream, canal, lake, or reservoir where systematic observations of hydrologic data are obtained.
Geomorphic
Geomorphic
Pertaining to the form or general configuration of the Earth or of its surface features.
Geomorphology
Geomorphology
The science that treats the general configuration of the Earth's surface; the description of landforms.
Geothermal
Geothermal
Relating to the Earth's internal heat; commonly applied to springs or vents discharging hot water or steam.
Glacial
Glacial
Of or relating to the presence and activities of ice or glaciers.
Glacial drift
Glacial drift
A general term for rock material transported by glaciers or icebergs and deposited directly on land or in the sea.
Glacial lake
Glacial lake
A lake that derives its water, or much of its water, from the melting of glacial ice; also a lake that occupies a basin produced by glacial erosion.
Glacial outwash
Glacial outwash
Stratified detritus (chiefly sand and gravel) "washed out" from a glacier by meltwater streams and deposited in front of or beyond the end moraine or the margin of an active glacier.
Granite rock
Granite rock
A coarse-grained igneous rock.
Ground water
Ground water
In the broadest sense, all subsurface water; more commonly that part of the subsurface water in the saturated zone.
Ground-water flow system
Ground-water flow system
The underground pathway by which ground water moves from areas of recharge to areas of discharge.
Growing season
Growing season
The frost-free period of the year.
H
Habitat
Habitat
The part of the physical environment in which a plant or animal lives.
Hardness
Hardness
A property of water that causes the formation of an insoluble residue when the water is used with soap and a scale in vessels in which water has been allowed to evaporate. It is due primarily to the presence of ions of calcium and magnesium. Generally expressed as milligrams per liter as calcium carbonate (CaCO3).
Headwaters
Headwaters
The source and upper part of a stream.
Health advisory
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.
Herbaceous
Herbaceous
With characteristics of an herb; a plant with no persistent woody stem above ground.
Herbicide
Herbicide
A type of pesticide designed to kill plants.
Human health advisory
Human health advisory
Guidance provided by U.S. Environmental Protection Agency, State agencies or scientific organizations, in the absence of regulatory limits, to describe acceptable contaminant levels in drinking water or edible fish.
Hydraulic conductivity
Hydraulic conductivity
The capacity of a rock to transmit water. It is expressed as the volume of water at the existing kinematic viscosity that will move in unit time under a unit hydraulic gradient through a unit area measured at right angles to the direction of flow.
Hydraulic gradient
Hydraulic gradient
The change of hydraulic head per unit of distance in a given direction.
Hydraulic head
Hydraulic head
The height of the free surface of a body of water above a given point beneath the surface.
Hydric soil
Hydric soil
Soil that is wet long enough to periodically produce anaerobic conditions, thereby influencing the growth of plants.
Hydrograph
Hydrograph
Graph showing variation of water elevation, velocity, streamflow, or other property of water with respect to time.
Hydrologic cycle
Hydrologic cycle
The circulation of water from the sea, through the atmosphere, to the land, and thence back to the sea by overland and subterranean routes.
Hydrologic regime
Hydrologic regime
The characteristic behavior and total quantity of water involved in a drainage basin.
Hydrologic unit
Hydrologic unit
A geographic area representing part or all of a surface drainage basin or distinct hydrologic feature as delineated by the U. S. Geological Survey on State Hydrologic Unit Maps. Each hydrologic unit is assigned a hierarchical hydrologic unit code consisting of 2 digits for each successively smaller drainage basin unit.
Hydrology
Hydrology
The science that deals with water as it occurs in the atmosphere, on the surface of the ground, and underground.
Hydrophobic
Hydrophobic
Not capable of uniting with or absorbing water.
Hydrophyte
Hydrophyte
Any plant growing in water or on a substrate that is at least periodically deficient in oxygen as a result of excessive water content.
Hydrostatic pressure
Hydrostatic pressure
The pressure exerted by the water at any given point in a body of water at rest.
I
Igneous rocks
Igneous rocks
Rocks that have solidified from molten or partly molten material.
Immobilize
Immobilize
To hold by a strong chemical attraction.
Impaired
Impaired
Condition of the quality of water that has been adversely affected for a specific use by contamination or pollution.
Impermeability
Impermeability
The incapacity of a rock to transmit a fluid.
Impervious
Impervious
Impermeable. The incapacity of a rock to transmit a fluid.
Index of Biotic Integrity
Index of Biotic Integrity
An aggregated number, or index, based on several attributes or metrics of a fish community that provides an assessment of biological conditions.
Indicator sites
Indicator sites
Stream sampling sites (in NAWQA Study Units) 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.
Indurated
Indurated
Cemented, hardened, or a rocklike condition.
Industrial withdrawals
Industrial withdrawals
Water withdrawn for or used for thermoelectric power (electric utility generation) and other industrial and manufacturing uses such as steel, chemical and allied products, paper and allied products, mining, and petroleum refining. The water may be obtained from a public supplier or may be self-supplied.
Infiltration
Infiltration
The downward movement of water from the atmosphere into soil or porous rock.
Inorganic
Inorganic
Containing no carbon; matter other than plant or animal.
Inorganic soil
Inorganic soil
Soil with less than 20 percent organic matter in the upper 16 inches.
Insecticide
Insecticide
A substance or mixture of substances intended to destroy or repel insects.
Instantaneous discharge
Instantaneous discharge
The volume of water that passes a point at a particular instant of time.
Instream use
Instream use
Water use taking place within the stream channel for such purposes as hydroelectric power generation, navigation, water-quality improvement, fish propagation, and recreation. Sometimes called nonwithdrawal use or in-channel use.
Integrated drainage
Integrated drainage
Drainage developed during geomorphic maturity in an arid region, characterized by coalescence of drainage basins as a result of headward erosion in the lower basins or spilling over from the upper basins.
Integrator or Mixed-use site
Integrator or Mixed-use site
Stream sampling site (in a NAWQA Study Unit) 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
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
Interface
Interface
In hydrology, the contact zone between two fluids of different chemical or physical makeup.
Intermittent stream
Intermittent stream
A stream that flows only when it receives water from rainfall runoff or springs, or from some surface source such as melting snow.
Intermontane
Intermontane
Situated between or surrounded by mountains, mountain ranges, or mountainous regions.
Internal drainage
Internal drainage
Surface drainage whereby the water does not reach the ocean, such as drainage toward the lowermost or central part of an interior basin or closed depression.
Intertidal
Intertidal
Alternately flooded and exposed by tides.
Intolerant organisms
Intolerant organisms
Organisms that are not adaptable to human alterations to the environment and thus decline in numbers where alterations occur. See also Tolerant species.
Invertebrate
Invertebrate
An animal having no backbone or spinal column.
Ion
Ion
A positively or negatively charged atom or group of atoms.
Irrigation district
Irrigation district
In the United States, a cooperative, self-governing public corporation set up as a subdivision of the state, with definite geographic boundaries, organized to obtain and distribute water for irrigation of lands within the district; created under authority of the State legislature with the consent of a designated fraction of the land owners or citizens and the taxing power.
Irrigation return flow
Irrigation return flow
The part of irrigation applied to the surface that is not consumed by evapotranspiration or uptake by plants and that migrates to an aquifer or surface-water body.
Irrigation withdrawals
Irrigation withdrawals
Withdrawals of water for application on land to assist in the growing of crops and pastures or to maintain recreational lands.
K
Karst
Karst
A type of topography that results from dissolution and collapse of carbonate rocks such as limestone, dolomite, and gypsum, and that is characterized by closed depressions or sinkholes, caves, and underground drainage.
Kettle
Kettle
A steep-sided hole or depression, commonly without surface drainage, formed by the melting of a large detached block of stagnant ice that had been buried in the glacial drift.
Kettle lake
Kettle lake
A body of water occupying a kettle, as in a pitted outwash plain or in a kettle moraine.
Kill
Kill
Dutch term for stream or creek.
L
Lacustrine
Lacustrine
Pertaining to, produced by, or formed in a lake.
Lacustrine wetlands
Lacustrine wetlands
Wetlands within a lake or reservoir greater than 20 acres or within a lake or reservoir less than 20 acres if the water is greater than 2 meters deep in the deepest part of the basin; ocean-derived salinity is less than 0.5 part per thousand.
Lagoon
Lagoon
A shallow stretch of seawater (or lakewater) near or communicating with the sea (or lake) and partly or completely separated from it by a low, narrow, elongate strip of land.
Land-use study
Land-use study
A network of existing shallow wells in an area having a relatively uniform land use. These studies are a subset of a NAWQA Study-Unit Survey and have the goal of relating the quality of shallow ground water to land use.
Latent heat
Latent heat
The amount of heat given up or absorbed when a substance changes from one state to another, such as from a liquid to a solid.
Lateral moraine
Lateral moraine
A low ridgelike moraine carried on, or deposited near, the side margin of a mountain glacier.
Leachate
Leachate
A liquid that has percolated through soil containing soluble substances and that contains certain amounts of these substances in solution.
Leaching
Leaching
The removal of materials in solution from soil or rock; also refers to movement of pesticides or nutrients from land surface to ground water.
Life zone
Life zone
Major area of plant and animal life; region characterized by particular plants and animals and distinguished by temperature differences.
Limestone
Limestone
A sedimentary rock consisting chiefly of calcium carbonate, primarily in the form of the mineral calcite.
Limnetic
Limnetic
The deepwater zone (greater than 2 meters deep); a subsystem of the Lacustrine System of the U.S. Fish and Wildlife Service wetland classification system.
Littoral
Littoral
The shallow-water zone (less than 2 meters deep); a subsystem of the Lacustrine System of the U.S. Fish and Wildlife Service wetland classification system.
Load
Load
Material that is moved or carried by streams, reported as weight of material transported during a specified time period, such as tons per year.
Loess
Loess
A widespread, homogeneous, commonly nonstratified, porous, friable, slightly coherent, fine-grained blanket deposit of wind-blown and wind-deposited silt and fine sand.
Long-term monitoring
Long-term monitoring
The collection of data over a period of years or decades to assess changes in selected hydrologic conditions.
M
Main stem
Main stem
The principal trunk of a river or a stream.
Major ions
Major ions
Constituents commonly present in water in concentrations exceeding 1.0 milligram per liter. Major cations are calcium, magnesium, sodium, and potassium; the major anions are sulfate, chloride, fluoride, nitrate, and those contributing to alkalinity (see alkaline), most generally assumed to be bicarbonate and carbonate.
Marine wetland
Marine wetland
Wetlands that are exposed to waves and currents of the open ocean and to water having a salinity greater than 30 parts per thousand; present along the coastlines of the open ocean.
Marsh
Marsh
A water-saturated, poorly drained area, intermittently or permanently water covered, having aquatic and grasslike vegetation.
Maturity
Maturity
A stage in the evolutionary erosion of land areas in which the flat uplands have been widely dissected by deep river valleys.
Maturity (stream)
Maturity (stream)
The stage in the development of a stream at which it has reached its maximum efficiency, when velocity is just sufficient to carry the sediment delivered to it by tributaries; characterized by a broad, open, flat-floored valley having a moderate gradient and gentle slope.
Maximum contaminant level
Maximum contaminant level
Maximum permissible level of a contaminant in water that is delivered to any user of a public water system. MCLs are enforceable standards established by the U.S. Environmental Protection Agency.
Mean
Mean
The arithmatic average of a set of observations, unless otherwise specified.
Mean discharge
Mean discharge
The arithmetic mean of individual daily mean discharges of a stream during a specific period, usually daily, monthly, or annually.
Mean high tide
Mean high tide
The average altitude of all high tides recorded at a given place over a 19-year period.
Mean low tide
Mean low tide
The average altitude of all low tides recorded at a given place over a 19-year period.
Median
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.
Mesophyte
Mesophyte
Any plant growing where moisture and aeration conditions lie between the extremes of "wet" and "dry."
Metabolite
Metabolite
A substance produced in or by biological processes.
Metamorphic rocks
Metamorphic rocks
Rocks derived from preexisting rocks by mineralogical, chemical, or structural changes (essentially in a solid state) in response to marked changes in temperature, pressure, shearing stress, and chemical environment at depth in the Earth's crust.
Method detection limit
Method detection limit
The minimum concentration of a substance that can be accurately identified and measured with current laboratory technologies.
Micrograms per liter
Micrograms per liter
A unit expressing the concentration of constituents in solution as weight (micrograms) of solute per unit volume (liter) of water; equivalent to one part per billion in most streamwater and ground water. One thousand micrograms per liter equals one milligram per liter.
Midge
Midge
A small fly in the family Chironomidae. The larval (juvenile) life stages are aquatic.
Milligram
Milligram
A mass equal to 10-3 grams.
Milligrams per liter
Milligrams per liter
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.
Mineral soil
Mineral soil
Soil composed predominantly of mineral rather than organic materials; less than 20 percent organic material.
Minimum reporting level
Minimum reporting level
The smallest measured concentration of a constituent that may be reliably reported using a given analytical method. In many cases, the MRL is used when documentation for the method detection limit is not available.
Mitigation
Mitigation
Actions taken to avoid, reduce, or compensate for the effects of human-induced environmental damage.
Monitoring
Monitoring
Repeated observation, measurement, or sampling at a site, on a scheduled or event basis, for a particular purpose.
Monitoring well
Monitoring well
A well designed for measuring water levels and testing ground-water quality.
Monocyclic aromatic hydrocarbons
Monocyclic aromatic hydrocarbons
Single-ring aromatic compounds. Constituents of lead-free gasoline; also used in the manufacture of monomers and plasticizers in polymers.
Montane
Montane
Of, pertaining to, or inhabiting cool upland slopes below the timber line; characterized by the dominance of evergreen trees.
Moraine
Moraine
A mound, ridge, or other distinct accumulation of unsorted, unstratified glacial drift, predominantly till, deposited chiefly by direct action of glacier ice.
Mouth
Mouth
The place where a stream discharges to a larger stream, a lake, or the sea.
Muck
Muck
Dark, finely divided, well-decomposed, organic matter forming a surface deposit in some poorly drained areas.
Muskeg
Muskeg
Large expanses of peatlands or bogs in subarctic zones.
N
National Academy of Sciences/National Academy of Engineering (NAS/NAE) recommended maximum concentration in water
National Academy of Sciences/National Academy of Engineering (NAS/NAE) recommended maximum concentration in water
Numerical guidelines recommended by two joint NAS/NAE committees for the protection of freshwater and marine aquatic life, respectively. These guidelines were based on results of aquatic toxicity studies, available in 1972, and were considered preliminary even at the time.
National Geodetic Vertical Datum of 1929
National Geodetic Vertical Datum of 1929
Geodetic datum derived from a general adjustment of first - order level nets of the United States and Canada; formerly called "Sea Level Datum of 1929."
Natural levee
Natural levee
A long, broad, low ridge built by a stream on its flood plain along one or both banks of its channel in time of flood.
Navigable water
Navigable water
In the context of the Clean Water Act, all surface water.
NAWQA
NAWQA
National Water-Quality Assessment Program - The long term USGS program, begun in 1991, to assess the occurrence and distribution of water-quality conditions Nationwide.
Nitrate
Nitrate
An ion consisting of nitrogen and oxygen (NO3-). Nitrate is a plant nutrient and is very mobile in soils.
Noncontact water recreation
Noncontact water recreation
Recreational activities, such as fishing or boating, that do not include direct contact with the water.
Nonpersistent emergent plants
Nonpersistent emergent plants
Emergent plants whose leaves and stems break down at the end of the growing season from decay or by the physical forces of waves and ice; at certain seasons, there are no visible traces of the plants above the surface of the water.
Nonpoint source
Nonpoint source
A source (of any water-carried material) from a broad area, rather than from discrete points.
Nonpoint-source contaminant
Nonpoint-source contaminant
A substance that pollutes or degrades water that comes from lawn or cropland runoff, the atmosphere, roadways, and other diffuse sources.
Nonpoint-source water pollution
Nonpoint-source water pollution
Water contamination that originates from a broad area (such as leaching of agricultural chemicals from crop land) and enters the water resource diffusely over a large area.
Nonselective herbicide
Nonselective herbicide
Kills or significantly retards growth of most higher plant species.
Nuisance species
Nuisance species
Undesirable plants and animals, commonly exotic species.
Nutrient
Nutrient
Any inorganic or organic compound needed to sustain plant life.
O
Occurrence and distribution assessment
Occurrence and distribution assessment
A component of the USGS National Water Quality Assessment (NAWQA) Program that entails characterization of broad-scale spatial and temporal distributions of water-quality conditions in relation to major contaminant sources and background conditions for surface water and ground water.
Offstream use
Offstream use
Water withdrawn or diverted from a ground- or surface-water source for use.
Organic
Organic
Containing carbon, but possibly also containing hydrogen, oxygen, chlorine, nitrogen, and other elements.
Organic detritus
Organic detritus
Any loose organic material in streams - such as leaves, bark, or twigs - removed and transported by mechanical means, such as disintegration or abrasion.
Organic soil
Organic soil
Soil that contains more than 20 percent organic matter in the upper 16 inches.
Organochlorine compound
Organochlorine compound
Synthetic organic compounds containing chlorine. As generally used, term refers to compounds containing mostly or exclusively carbon, hydrogen, and chlorine. Examples include organochlorine insecticides, polychlorinated biphenyls, and some solvents containing chlorine.
Organochlorine insecticide
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 from use in the United States because of their carcinogenicity, tendency to bioaccumulate, and toxicity to wildlife.
Organonitrogen herbicides
Organonitrogen herbicides
A group of herbicides consisting of a nitrogen ring with associated functional groups and including such classes as triazines and acetanilides. Examples include atrazine, cyanazine, alachlor, and metolachlor.
Organophosphate insecticides
Organophosphate insecticides
A class of insecticides derived from phosphoric acid. They tend to have high acute toxicity to vertebrates. Although readily metabolized by vertebrates, some metabolic products are more toxic than the parent compound.
Organophosphorus insecticides
Organophosphorus insecticides
Insecticides derived from phosphoric acid and generally the most toxic of all pesticides to vertebrate animals.
Orographic
Orographic
Pertaining to mountains, in regard to their location and distribution; said of the precipitation caused by the lifting of moisture-laden air over mountains.
Outwash
Outwash
Soil material washed down a hillside by rainwater and deposited upon more gently sloping land.
Overland flow
Overland flow
The flow of rainwater or snowmelt over the land surface toward stream channels.
Oxbow
Oxbow
A bow-shaped lake formed in an abandoned meander of a river.
P
Paleohydrology
Paleohydrology
Study of hydrologic processes and events, using geological, botanical, and cultural evidence, that occurred before the beginning of the systematic collection of hydrologic data and observations.
Palustrine wetlands
Palustrine wetlands
Freshwater wetlands including open water bodies of less than 20 acres in which water is less than 2 meters deep; includes marshes, wet meadows, fens, playas, potholes, pocosins, bogs, swamps, and shallow ponds; most wetlands are in the Palustrine system.
Part per million
Part per million
Unit of concentration equal to one milligram per kilogram or one milligram per liter.
Pathogen
Pathogen
Any living organism that causes disease.
Peak stage
Peak stage
Maximum height of a water surface above an established datum plane.
Peat
Peat
A highly organic soil, composed of partially decomposed vegetable matter.
Perched ground water
Perched ground water
Unconfined ground water separated from an underlying main body of ground water by an unsaturated zone.
Percolation
Percolation
The movement, under hydrostatic pressure, of water through interstices of a rock or soil (except the movement through large openings such as caves).
Perennial stream
Perennial stream
A stream that normally has water in its channel at all times.
Periphyton
Periphyton
Micro-organisms that coat rocks, plants, and other surfaces on lake bottoms.
Permafrost
Permafrost
Any frozen soil, subsoil, surficial deposit, or bedrock in arctic or subarctic regions where below-freezing temperatures have existed continuously from two to tens of thousands of years.
Permeability
Permeability
The capacity of a rock for transmitting a fluid; a measure of the relative ease with which a porous medium can transmit a liquid.
Pesticide
Pesticide
Any substance used to kill plant or animal pests; major categories of pesticides include herbicides and insecticides.
PH
PH
A measure of the acidity (less than 7) or alkalinity (greater than 7) of a solution; a pH of 7 is considered neutral.
Phenols
Phenols
A class of organic compounds containing phenol (C6H5OH) and its derivatives. Used to make resins, weed killers, and as a solvent, disinfectant, and chemical intermediate. Some phenols occur naturally in the environment.
Phosphorus
Phosphorus
A nutrient essential for growth that can play a key role in stimulating aquatic growth in lakes and streams.
Photosynthesis
Photosynthesis
The synthesis of compounds with the aid of light.
Phthalates
Phthalates
A class of organic compounds containing phthalic acid esters [C6H4(COOR)2] and derivatives. Used as plasticizers in plastics. Also used in many other products (such as detergents, cosmetics) and industrial processes (such as defoaming agents in paper and paperboard manufacture, and dielectrics in capacitors).
Physiographic province
Physiographic province
A region in which the landforms are distinctive and differ significantly from those of adjacent regions.
Physiography
Physiography
A description of the surface features of the Earth, with an emphasis on the origin of landforms.
Picocurie
Picocurie
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.
Pioneer plant
Pioneer plant
Herbaceous annual and perennial seedling plants that colonize bare areas as a first stage in secondary succession.
Piping
Piping
Erosion by percolating water in a layer of subsoil, resulting in caving and in the formation of narrow conduits, tunnels, or "pipes" through which soluble or granular soil material is removed.
Placer
Placer
A surficial mineral deposit formed by mechanical concentration of mineral particles from weathered debris.
Plankton
Plankton
Floating or weakly swimming organisms at the mercy of the waves and currents. Animals of the group are called zooplankton and the plants are called phytoplankton.
Playa
Playa
A dry, flat area at the lowest part of an undrained desert basin in which water accumulates and is quickly evaporated; underlain by stratified clay, silt, or sand and commonly by soluble salts; term used in Southwestern United States.
Playa lake
Playa lake
A shallow, temporary lake in an arid or semiarid region, covering or occupying a playa in the wet season but drying up in summer; temporary lake that upon evaporation leaves or forms a playa.
Pocosin
Pocosin
A local term along the Atlantic coastal plain, from Virginia south, for a shrub-scrub wetland located on a relatively flat terrain, commonly between streams.
Point source
Point source
Originating at any discrete source.
Point-source contaminant
Point-source contaminant
Any substance that degrades water quality and originates from discrete locations such as discharge pipes, drainage ditches, wells, concentrated livestock operations, or floating craft.
Pollutant
Pollutant
Any substance that, when present in a hydrologic system at sufficient concentration, degrades water quality in ways that are or could become harmful to human and/or ecological health or that impair the use of water for recreation, agriculture, industry, commerce, or domestic purposes.
Polychlorinated biphenyls
Polychlorinated biphenyls
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.
Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbon
A class of organic compounds with a fused-ring aromatic structure. PAHs result from incomplete combustion of organic carbon (including wood), municipal solid waste, and fossil fuels, as well as from natural or anthropogenic introduction of uncombusted coal and oil. PAHs include benzo(a)pyrene, fluoranthene, and pyrene.
Pool
Pool
A small part of a stream reach with little velocity, commonly with water deeper than surrounding areas.
Population
Population
A collection of individuals of one species or mixed species making up the residents of a prescribed area.
Porosity
Porosity
The ratio of the volume of voids in a rock or soil to the total volume.
Postemergence herbicide
Postemergence herbicide
Herbicide applied to foliage after the crop has sprouted to kill or significantly retard the growth of weeds.
Potable water
Potable water
Water that is safe and palatable for human consumption.
Potential evapotranspiration
Potential evapotranspiration
The amount of moisture which, if available, would be removed from a given land area by evapotranspiration; expressed in units of water depth.
Potentiometric surface
Potentiometric surface
An imaginary surface that represents the total head in an aquifer. It represents the height above a datum plane at which the water level stands in tightly cased wells that penetrate the aquifer.
Prairie pothole
Prairie pothole
A shallow depression, generally containing wetlands, occurring in an outwash plain, a recessional moraine, or a till plain; usually the result of melted blocks of covered glacial ice; occur most commonly in the North-Central United States and in States west of the Great Lakes from Wisconsin to eastern Montana.
Precipitation
Precipitation
Any or all forms of water particles that fall from the atmosphere, such as rain, snow, hail, and sleet. The act or process of producing a solid phase within a liquid medium.
Preemergence herbicide
Preemergence herbicide
Herbicide applied to bare ground after planting the crop but prior to the crop sprouting above ground to kill or significantly retard the growth of weed seedlings.
Pristine
Pristine
The earliest condition of the quality of a water body; unaffected by human activities.
Public-supply withdrawals
Public-supply withdrawals
Water withdrawn by public and private water suppliers for use within a general community. Water is used for a variety of purposes such as domestic, commercial, industrial, and public water use.
Q
Quality assurance
Quality assurance
Evaluation of quality-control data to allow quantitative determination of the quality of chemical data collected during a study. Techniques used to collect, process, and analyze water samples are evaluated.
R
Radon
Radon
A naturally occurring, colorless, odorless, radioactive gas formed by the disintegration of the element radium; damaging to human lungs when inhaled.
Rain shadow
Rain shadow
A dry region on the lee side of a topographic obstacle, usually a mountain range, where rainfall is noticeably less than on the windward side.
Reach
Reach
A continuous part of a stream between two specified points.
Real-time data
Real-time data
Data collected by automated instrumentation and telemetered and analyzed quickly enough to influence a decision that affects the monitored system.
Recessional moraine
Recessional moraine
An end moraine built during a temporary but significant pause in the final retreat of a glacier.
Recharge
Recharge
The process involved in the absorption and addition of water to the zone of saturation.
Recharge area
Recharge area
An area within which water infiltrates the ground and reaches the zone of saturation.
Recurrence interval
Recurrence interval
The average interval of time within which the magnitude of a given event, such as a storm or flood, will be equaled or exceeded once.
Reference site
Reference site
A NAWQA sampling site selected for its relatively undisturbed conditions.
Regolith
Regolith
The layer or mantle of fragmented and unconsolidated rock material, residual or transported, that nearly everywhere forms the surface of the land and overlies or covers the bedrock.
Regulation
Regulation
Artificial manipulation of the flow of a stream.
Relative abundance
Relative abundance
The number of organisms of a particular kind present in a sample relative to the total number of organisms in the sample.
Retrospective analysis
Retrospective analysis
Review and analysis of existing data in order to address NAWQA objectives, to the extent possible, and to aid in the design of NAWQA studies.
Return flow
Return flow
That part of irrigation water that is not consumed by evapotranspiration and that returns to its source or another body of water.
Riffle
Riffle
A shallow part of the stream where water flows swiftly over completely or partially submerged obstructions to produce surface agitation.
Riparian
Riparian
Pertaining to or situated on the bank of a natural body of flowing water.
Riparian rights
Riparian rights
A concept of water law under which authorization to use water in a stream is based on ownership of the land adjacent to the stream.
Riparian zone
Riparian zone
Pertaining to or located on the bank of a body of water, especially a stream.
Riverine wetlands
Riverine wetlands
Wetlands within river and stream channels; ocean-derived salinity is less than 0.5 part per thousand.
Rock
Rock
Any naturally formed, consolidated or unconsolidated material (but not soil) consisting of two or more minerals.
Runoff
Runoff
That part of precipitation or snowmelt that appears in streams or surface-water bodies.
Rural withdrawals
Rural withdrawals
Water used in suburban or farm areas for domestic and livestock needs. The water generally is self-supplied and includes domestic use, drinking water for livestock, and other uses such as dairy sanitation, evaporation from stock-watering ponds, and cleaning and waste disposal.
S
Salina
Salina
An area where deposits of crystalline salt are formed, such as a salt flat; a body of saline water, such as a saline playa or salt marsh.
Saline water
Saline water
Water that is considered unsuitable for human consumption or for irrigation because of its high content of dissolved solids; generally expressed as milligrams per liter (mg/L) of dissolved solids; seawater is generally considered to contain more than 35,000 mg/L of dissolved solids.
Saturated zone
Saturated zone
A subsurface zone in which all the interstices or voids are filled with water under pressure greater than that of the atmosphere. See also Water table.
Sea level
Sea level
Long-term average position of the sea surface. Sea level varies from place to place and with the time period for which the average is calculated. For the conterminous United States, sea level is most commonly referenced to the National Geodetic Vertical Datum of 1929.
Secondary maximum contaminant level
Secondary maximum contaminant level
The maximum level of a contaminant or undesirable constituent in public water systems that, in the judgment of the U.S. Environmental Protection Agency (USEPA), is required to protect the public welfare. SMCLs are secondary (nonenforceable) drinking water regulations established by the USEPA for contaminants that may adversely affect the odor or appearance of such water.
Sediment
Sediment
Particles, derived from rocks or biological materials, that have been transported by a fluid or other natural process, suspended or settled in water.
Sediment guideline
Sediment guideline
Threshold concentration above which there is a high probability of adverse effects on aquatic life from sediment contamination, determined using modified U.S. Environmental Protection Agency USEPA (1996) procedures.
Sedimentary rocks
Sedimentary rocks
Rocks formed by the consolidation of loose sediment that has accumulated in layers.
Sedimentation
Sedimentation
The act or process of forming or accumulating sediment in layers; the process of deposition of sediment.
Seep
Seep
A small area where water percolates (see percolation) slowly to the land surface.
Seiche
Seiche
A sudden oscillation of the water in a moderate-size body of water, caused by wind.
Selective herbicide
Selective herbicide
A compound that kills or significantly retards growth of an unwanted plant species without significantly damaging desired plant species.
Semipermeable membrane device
Semipermeable membrane device
A long strip of low-density, polyethylene tubing filled with a thin film of purified lipid such as triolein that simulates the exposure to and passive uptake of highly lipid-soluble organic compounds by biological membranes.
Semivolatile organic compound
Semivolatile organic compound
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).
Shale
Shale
A fine-grained sedimentary rock formed by the consolidation of clay, silt, or mud.
Shallows
Shallows
A term applied to a shallow place or area in a body of water; a shoal.
Shoal
Shoal
A relatively shallow place in a stream, lake, or sea.
Short-wave trough
Short-wave trough
A wave of low atmospheric pressure in the form of a trough that has a wave length of 600 to 1,500 miles and moves progressively through the lower troposphere in the same direction as that of the prevailing current of air motion.
Shrubland
Shrubland
Land covered predominantly with shrubs.
Sideslope gradient
Sideslope gradient
The representative change in elevation in a given horizontal distance (usually about 300 yards) perpendicular to a stream; the valley slope along a line perpendicular to the stream (near a water-quality or biological sampling point).
Siliciclastic rocks
Siliciclastic rocks
Rocks such as shale and sandstone that are formed by the compaction and cementation of quartz-rich mineral grains.
Siltation
Siltation
The deposition or accumulation of silt (or small-grained material) in a body of water.
Siltstone
Siltstone
An indurated silt having the texture and composition of shale but lacking its fine lamination.
Silviculture
Silviculture
The cultivation of forest trees.
Sinkhole
Sinkhole
A depression in an area underlain by limestone. Its drainage is subterranean.
Sinuosity
Sinuosity
The ratio of the channel length between two points on a channel to the straight-line distance between the same two points; a measure of meandering.
Skewness
Skewness
Numerical measure of the lack of symmetry of an asymmetrical frequency distribution.
Slough
Slough
A small marshy tract lying in a swale or other local shallow, undrained depression; a sluggish creek or channel in a wetland.
Soil
Soil
The layer of material at the land surface that supports plant growth.
Soil horizon
Soil horizon
A layer of soil that is distinguishable from adjacent layers by characteristic physical and chemical properties.
Soil moisture
Soil moisture
Water occurring in the pore spaces between the soil particles in the unsaturated zone from which water is discharged by the transpiration of plants or by evaporation from the soil.
Sole-source aquifer
Sole-source aquifer
As defined by the U.S. Environmental Protection Agency, an aquifer that supplies 50 percent or more of the drinking water of an area.
Solid-phase extraction
Solid-phase extraction
A procedure to isolate specific organic compounds onto a bonded silica extraction column.
Solution
Solution
Formed when a solid, gas, or another liquid in contact with a liquid becomes dispersed homogeneously throughout the liquid. The substance, called a solute, is said to dissolve. The liquid is called the solvent.
Sorb
Sorb
To take up and hold either by absorption or adsorption.
Sorption
Sorption
General term for the interaction (binding or association) of a solute ion or molecule with a solid.
Source rocks
Source rocks
The rocks from which fragments and other detached pieces have been derived to form a different rock.
Species
Species
Populations of organisms that may interbreed and produce fertile offspring having similar structure, habits, and functions.
Species diversity
Species diversity
An ecological concept that incorporates both the number of species in a particular sampling area and the evenness with which individuals are distributed among the various species.
Species richness
Species richness
The number of species (taxa) present in a defined area or sampling unit.
Specific capacity
Specific capacity
The yield of a well per unit of drawdown.
Specific conductance
Specific conductance
A measure of the ability of a liquid to conduct an electrical current.
Specific yield
Specific yield
The ratio of the volume of water that will drain under the influence of gravity to the volume of saturated rock.
Spit
Spit
A small point or low tongue or narrow embankment of land having one end attached to the mainland and the other terminating in open water.
Split sample
Split sample
A sample prepared by dividing it into two or more equal volumes, so that each volume is considered a separate sample but representative of the entire sample.
Spoil
Spoil
Overburden or other waste material removed in mining, quarrying, dredging, or excavating.
Spring
Spring
Place where a concentrated discharge of ground water flows at the ground surface.
Stage
Stage
Height of the water surface above an established datum plane, such as in a river above a predetermined point that may (or may not) be at the channel floor.
Standard deviation
Standard deviation
Statistical measure of the dispersion or scatter of a series of values. It is the square root of the variance, which is calculated as the sum of the squares of the deviations from the arithmetic mean, divided by the number of values in the series minus 1.
State climate division
State climate division
Geographic area in a State based primarily on crop-reporting districts. States can have 2 to 10 climate divisions.
Statistics
Statistics
A branch of mathematics dealing with the collection, analysis, interpretation, and presentation of masses of numerical data.
Storm surge
Storm surge
An abnormal and sudden rise of the sea along a shore as a result of the winds of a storm.
Stratification
Stratification
Subdivision of the environmental framework. NAWQA Study Units are divided into subareas that exhibit reasonably homogeneous environmental conditions, as determined by both natural and human influences.
Stream mile
Stream mile
A distance of 1 mile along a line connecting the midpoints of the channel of a stream.
Stream reach
Stream reach
A continuous part of a stream between two specified points.
Stream-aquifer interactions
Stream-aquifer interactions
Relations of water flow and chemistry between streams and aquifers that are hydraulically connected.
Streamflow
Streamflow
The discharge of water in a natural channel.
Streamline
Streamline
A line on a map that is parallel to the direction of fluid flow and shows flow patterns.
Study Unit
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.
Study-Unit Survey
Study-Unit Survey
Broad assessment of the water-quality conditions of the major aquifer systems of each NAWQA Study Unit. The Study-Unit Survey relies primarily on sampling existing wells and, wherever possible, on data collected by other agencies and programs. Typically, 20 to 30 wells are sampled in each of three to five aquifer subunits.
Submersed plant
Submersed plant
A plant that lies entirely beneath the water surface, except for flowering parts in some species.
Subsidence
Subsidence
The gradual downward settling or sinking of the Earth's surface with little or no horizontal motion.
Substrate
Substrate
The surface beneath a wetland, lake, or stream in which organisms grow or to which organisms are attached.
Substrate size
Substrate size
The diameter of streambed particles such as clay, silt, sand, gravel, cobble and boulders.
Subsurface drain
Subsurface drain
A shallow drain installed in an irrigated field to intercept the rising ground-water level and maintain the water table at an acceptable depth below the land surface.
Subtidal
Subtidal
Continuously submerged; an area affected by ocean tides.
Subtropical anticyclone
Subtropical anticyclone
A semipermanent anticyclone located, on the average, over oceans near
30 o N. and 30 o S. latitude.
Surface runoff
Surface runoff
Runoff that travels over the land surface to the nearest stream channel.
Surface water
Surface water
An open body of water such as a lake, river, or stream.
Survey
Survey
Sampling of a representative number of sites during a given hydrologic condition.
Suspended
Suspended
(as used in tables of chemical analyses)The amount (concentration) of undissolved material in a water-sediment mixture. Most commonly refer to that material retained on a 0.45- micrometer filter.
Suspended sediment
Suspended sediment
Sediment that is transported in suspension by a stream.
Suspended solids
Suspended solids
Different from suspended sediment only in the way that the sample is collected and analyzed.
Suspended-sediment concentration
Suspended-sediment concentration
The velocity-weighted concentration of suspended sediment in the sampled zone (from the water surface to a point approximately 0.3 foot above the bed); expressed as milligrams of dry sediment per liter of water-sediment mixture (mg/L).
Swale
Swale
A slight depression, sometimes filled with water, in the midst of generally level land.
Swamp
Swamp
An area intermittently or permanently covered with water, and having trees and shrubs.
Synoptic sites
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.
T
Tailings
Tailings
Rock that remains after processing ore to remove the valuable minerals.
Tarn
Tarn
A relatively small and deep, steep-sided lake or pool occupying an ice-gouged basin amid glaciated mountains.
Taxon
Taxon
Any identifiable group of taxonomically related organisms.
Tectonic activity
Tectonic activity
Movement of the Earth's crust resulting in the formation of ocean basins, continents, plateaus, and mountain ranges.
Terminal moraine
Terminal moraine
The end moraine extending across a glacial plain or valley as an arcuate or crescent ridge that marks the farthest advance or maximum extent of a glacier.
Terrane
Terrane
Area or surface over which a particular rock type or group of rock types is prevalent.
Terrestrial
Terrestrial
Pertaining to, consisting of, or representing the Earth.
Tertiary-treated sewage
Tertiary-treated sewage
The third phase of treating sewage that removes nitrogen and phosphorus before it is discharged.
Thermal loading
Thermal loading
Amount of waste heat discharged to a water body.
Thermoelectric power
Thermoelectric power
Electrical power generated by use of fossil-fuel (coal, oil, or natural gas), geothermal, or nuclear energy.
Thermokarst
Thermokarst
An irregular land surface formed in a permafrost region by melting ground ice and a subsequent settling of the ground.
Tidal flat
Tidal flat
An extensive, nearly horizontal, tract of land that is alternately covered and uncovered by the tide and consists of unconsolidated sediment.
Tide
Tide
The rhythmic, alternate rise and fall of the surface (or water level) of the ocean, and connected bodies of water, occurring twice a day over most of the Earth, resulting from the gravitational attraction of the Moon, and to a lesser degree, the Sun.
Tier 1 sediment guideline
Tier 1 sediment guideline
Threshold concentration above which there is a high probability of adverse effects on aquatic life from sediment contamination, determined using modified U.S. Environmental Protection Agency USEPA (1996) procedures.
Tile drain
Tile drain
A buried perforated pipe designed to remove excess water from soils.
Till
Till
Predominantly unsorted and unstratified drift, deposited directly by and underneath a glacier without subsequent reworking by meltwater, and consisting of a heterogeneous mixture of clay, silt, sand, gravel, and boulders.
Tinaja
Tinaja
A pocket of water developed below a waterfall; a term used in the Southwestern United States; used loosely to mean a temporary pool.
Tissue study
Tissue study
The assessment of concentrations and distributions of trace elements and certain organic contaminants in tissues of aquatic organisms.
Tolerant species
Tolerant species
Those species that are adaptable to (tolerant of) human alterations to the environment and often increase in number when alterations occur.
Topography
Topography
The general configuration of a land surface or any part of the Earth's surface, including its relief and the position of its natural and man-made features.
Total concentration
Total concentration
Refers to the concentration of a constituent regardless of its form (dissolved or bound) in a sample.
Total DDT
Total DDT
The sum of DDT and its metabolites (breakdown products), including DDD and DDE.
Total head
Total head
The height above a datum plane of a column of water. In a ground-water system, it is composed of elevation head and pressure head.
Trace element
Trace element
A chemical element that is present in minute quantities in a substance.
Tracer
Tracer
A stable, easily detected substance or a radioisotope added to a material to follow the location of the substance in the environment or to detect any physical or chemical changes that it undergoes.
Trade winds
Trade winds
A system of easterly winds that dominate most of the tropics. A major component of the general circulation of the atmosphere.
Tranmissivity
Tranmissivity
The rate at which water of the prevailing kinematic viscosity is transmitted through a unit width of an aquifer under a unit hydraulic gradient. It equals the hydraulic conductivity multiplied by the aquifer thickness.
Transpiration
Transpiration
The process by which water passes through living organisms, primarily plants, into the atmosphere.
Triazine herbicide
Triazine herbicide
A class of herbicides containing a symmetrical triazine ring (a nitrogen-heterocyclic ring composed of three nitrogens and three carbons in an alternating sequence). Examples include atrazine, propazine, and simazine.
Tributary
Tributary
A river or stream flowing into a larger river, stream or lake.
Tritium
Tritium
A radioactive form of hydrogen with atoms of three times the mass of ordinary hydrogen; can be used to determine the age of water.
Tropical cyclone
Tropical cyclone
A cyclone that originates over the tropical oceans. Tropical cyclones are classified according to their intensity and windspeed and, when fully mature, are characterized by extremely high-speed winds and torrential rains. In the United States, tropical cyclones that have windspeeds greater than 40 miles per hour are classified as tropical storms, and tropical cyclones that have windspeeds of 74 miles per hour or more are classified as hurricanes.
Troposphere
Troposphere
Lowest 6 to 12 miles of the atmosphere, characterized by a general decrease in temperature with height, appreciable water content, and active weather processes.
Tundra
Tundra
A vast, nearly level, treeless plain of the arctic and subarctic regions. It usually has a marshy surface which supports mosses, lichens, and low shrubs, underlain by mucky soils and permafrost.
Turbidity
Turbidity
The state, condition, or quality of opaqueness or reduced clarity of a fluid due to the presence of suspended matter.
U
Un-ionized
Un-ionized
The neutral form of an ionizable compound (such as an acid or a base).
Un-ionized ammonia
Un-ionized ammonia
The neutral form of ammonia-nitrogen in water, usually occurring as NH4OH. Un-ionized ammonia is the principal form of ammonia that is toxic to aquatic life. The relative proportion of un-ionized to ionized ammonia (NH4+) is controlled by water temperature and pH. At temperatures and pH values typical of most natural waters, the ionized form is dominant.
Unconfined aquifer
Unconfined aquifer
An aquifer whose upper surface is a water table free to fluctuate under atmospheric pressure.
Unconsolidated deposit
Unconsolidated deposit
Deposit of loosely bound sediment that typically fills topographically low areas.
Underground water
Underground water
Subsurface water in the unsaturated and saturated zones.
Understory
Understory
A foliage layer lying beneath and shaded by the main canopy of a forest.
Unsaturated zone
Unsaturated zone
A subsurface zone above the water table in which the pore spaces may contain a combination of air and water.
Upgradient
Upgradient
Of or pertaining to the place(s) from which ground water originated or traveled through before reaching a given point in an aquifer.
Upland
Upland
A general term for nonwetland; elevated land above low areas along streams or between hills; any elevated region from which rivers gather drainage.
Uranium
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.
Urban site
Urban site
A site that has greater than 50 percent urbanized and less than 25 percent agricultural area.
V
Vascular plant
Vascular plant
A plant composed of or provided with vessels or ducts that convey water or sap. A fern is an example of this type of plant.
Vernal pool
Vernal pool
A small lake or pond that is filled with water for only a short time during the spring.
Volatile organic compounds
Volatile organic compounds
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.
W
Wasteway
Wasteway
A waterway used to drain excess irrigation water dumped from the irrigation delivery system.
Water budget
Water budget
An accounting of the inflow to, outflow from, and storage changes of water in a hydrologic unit.
Water column
Water column
An imaginary column extending through a water body from its floor to its surface.
Water column studies
Water column studies
Investigations of physical and chemical characteristics of surface water, which include suspended sediment, dissolved solids, major ions, and metals, nutrients, organic carbon, and dissolved pesticides, in relation to hydrologic conditions, sources, and transport.
Water content of snow
Water content of snow
Amount of liquid water in the snow at the time of observation. Water equivalent of snow.
Water demand
Water demand
Water requirements for a particular purpose, such as irrigation, power, municipal supply, plant transpiration, or storage.
Water exports
Water exports
Artificial transfer (by pipes or canals) of freshwater from one region or subregion to another.
Water gap
Water gap
A deep, narrow pass in a mountain ridge through which a stream flows.
Water imports
Water imports
Artificial transfer (by pipes or canals) of freshwater to one region or subregion from another.
Water rights
Water rights
Legal rights to the use of water.
Water table
Water table
The top water surface of an unconfined aquifer at atmospheric pressure.
Water year
Water year
A continuous 12-month period selected to present data relative to hydrologic or meteorological phenomena during which a complete annual hydrologic cycle normally occurs. The water year used by the U.S. Geological Survey runs from October 1 through September 30, and is designated by the year in which it ends.
Water-quality criteria
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 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
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
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-resources region
Water-resources region
Natural drainage basin or hydrologic area that contains either the drainage area of a major river or the combined areas of a series of rivers. In the United States, there are 21 regions of which 18 are in the conterminous United States, and one each in Alaska, Hawaii, and the Caribbean.
Water-resources subregion
Water-resources subregion
Subdivision of a water-resources region. The 21 water-resources regions of the United States are subdivided into 222 subregions. Each subregion includes that area drained by a river system, a reach of a river and its tributaries in that reach, a closed basin(s), or a group of streams forming a coastal drainage area.
Weather
Weather
State of the atmosphere at any particular time and place.
Weathering
Weathering
Process whereby earthy or rocky materials are changed in color, texture, composition, or form (with little or no transportation) by exposure to atmospheric agents.
Weighted mean
Weighted mean
A value obtained by multiplying each of a series of values by its assigned weight and dividing the sum of these products by the sum of the weights. In the ordinary arithmetic mean, each value is assigned a weight of 1.
Wetland function
Wetland function
A process or series of processes that take place within a wetland that are beneficial to the wetland itself, the surrounding ecosystems, and people.
Wetlands
Wetlands
Ecosystems whose soil is saturated for long periods seasonally or continuously, including marshes, swamps, and ephemeral ponds.
Willow carr
Willow carr
A pool, or wetland dominated by willow trees or shrubs.
Withdrawal
Withdrawal
Water removed from the ground or diverted from a surface-water source for use. Also refers to the use itself; for example, public-supply withdrawals or public-supply use.
X
Xerophyte
Xerophyte
A plant adapted for growth under dry conditions.
Y
Yield
Yield
The mass of material or constituent transported by a river in a specified period of time divided by the drainage area of the river basin.