Water Quality in the Central Nebraska Basins, Nebraska, 1992-95

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Glossary

The terms in this glossary were compiled from numerous sources. Some definitions have been modified and may not be the only valid ones for these terms.

Acre-foot

A volume of water equal to 1 foot in depth and covering 1 acre; equivalent to 43,560 cubic feet or 325,851 gallons.

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.

Alluvial aquifer

A water-bearing deposit of unconsolidated material (sand and gravel) left behind by a river or other flowing water.

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.

Aquifer

A water-bearing layer of soil, sand, gravel, or rock that will yield usable quantities of water to a well.

Background concentration

A concentration of a substance in a particular environment that is indicative of minimal influence by human (anthropogenic) sources.

Bank

The sloping ground that borders a stream and confines the water in the natural channel when the water level, or flow is normal.

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.

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.

Benthic

Refers to plants or animals that live on the bottom of lakes, streams, or oceans.

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.

Best Management Practice (BMP)

An agricultural practice that has been determined to be an effective, practical means of preventing or reducing nonpoint-source pollution.

Biota

Living organisms.

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.

Confluence

The flowing together of two or more streams; the place where a tributary joins the main stream.

Constituent

A chemical or biological substance in water. sediment, or biota that can be measured by an analytical method.

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.

Detection limit

The concentration below which a particular analytical method cannot determine, with a high degree of certainty, a concentration.

DDT

Dichloro-diphenyl-trichloroethane. An organochlorine insecticide no longer registered for use in the United States.

Dieldrin

An organochlorine insecticide no longer registered for use in the United States. Also a degradation product of the insecticide aldrin.

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.

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.

Drainage basin

The portion of the surface of the Earth that contributes water to a stream through overland runoff, 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. Environ-mental Protection Agency regulations that specify the maximum contamina-tion levels for public water systems required to protect the public welfare; guidelines have no regulatory status and are issued in an advisory capacity.

Environmental setting

Land area characterized by a unique combination of natural and human-related factors, such as row-crop cultivation or glacial-till soils.

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.

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.

Flood

Any relatively high streamflow that overtops the natural or artificial banks of a stream.

Flood plain

The relatively level area of land bordering a stream channel and inundated during moderate to severe floods.

Flow path

An underground route for ground-water movement, extending from a recharge (intake) zone to a discharge (output) zone such as a shallow stream.

Fungicide

A substance or mixture of substances intended for the purpose of killing undesirable fungi.

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 levels (HALs)

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.

Index of Biotic Integrity (IBI)

An aggregated number, or index, based on several attributes or metrics of a fish community that provides an assessment of biological conditions.

Infiltration

Movement of water, typically downward, into soil or porous rock.

Insecticide

A substance or mixture of substances intended to destroy or repel insects.

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.

Intolerant organisms

Organisms that are not adaptable to human alterations to the environment and thus decline in numbers where human alterations occur. See also Tolerant species.

Invertebrate

An animal having no backbone or spinal column. See also Benthic invertebrate.

Land-use study

A network of existing shallow wells in an area having a relatively uniform land use. These studies are a subset of the Study-Unit Survey and have the goal of relating the quality of shallow ground water to land use. See also Study-Unit Survey.

Loess

Homogeneous, fine-grained sediment made up primarily of silt and clay, and deposited over a wide area (probably by wind).

Macroinvertebrate

An animal that is large enough to be seen without magnification and has no backbone or spinal column. See Invertebrate.

Main stem

The principal course of a river or a stream.

Major ions

Constituents commonly present in concentrations exceeding 1.0 milligram per liter. Dissolved cations generally are calcium, magnesium, sodium, and potassium; the major anions are sulfate, chloride, fluoride, nitrate, and those contributing to alkalinity, most generally assumed to be bicarbonate and carbonate.

Maximum contaminant level (MCL)

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. Environ-mental Protection Agency.

Mean

The average of a set of observations, unless otherwise specified.

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.

Method detection limit

The minimum concentration of a substance that can be accurately identified and measured with present laboratory technologies.

Micrograms per liter (µg/L)

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 1 mg/L.

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 stream water and ground water. One thousand micrograms per liter equals 1 mg/L.

Minimum reporting level (MRL)

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.

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 available aquatic toxicity studies, and were considered preliminary even at the time (1972). The guidelines used in the summary reports are for freshwater.

Natural Resources Districts (NRDs)

Local districts created in 1969 by the Nebraska legislature and charged with properly conserving and developing the State of Nebraska's natural resources. The NRDs' boundaries were established primarily in accordance with Nebraska's natural river basin boundaries. The activities of the 23 NRDs include the management of surface-water and ground-water resources, the construction and operation of flood-control structures, and the administration of land-management plans to prevent soil erosion and sediment problems. The NRDs also have some responsibility for drainage and stream-channel improvement, forestry and range management, management of fish and wildlife habitat, recreational and park facility management, and solid waste disposal and sanitary drainage.

Nitrate

An ion consisting of nitrogen and oxygen (NO₃^-). Nitrate is a plant nutrient and is very mobile in soils.

Nonpoint source

A pollution source that cannot be defined as originating from discrete points such as pipe discharge. Areas of fertilizer and pesticide applications, atmospheric deposition, manure, and natural inputs from plants and trees are types of nonpoint-source pollution.

Nutrient

Element or compound essential for animal and plant growth. Common nutrients in fertilizer include nitrogen, phosphorus, and potassium.

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.

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

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."

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.

Point source

A source at a discrete location such as a discharge pipe, drainage ditch, tunnel, well, concentrated livestock operation, or floating craft.

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.

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.

Polycyclic aromatic hydrocarbon (PAH)

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.

Precipitation

Any or all forms of water particles that fall from the atmosphere, such as rain, snow, hail, and sleet.

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.

Recharge

Water that infiltrates the ground and reaches the saturated zone.

Runoff

Excess rainwater or snowmelt that is transported to streams by overland flow, tile drains, or ground water.

Sediment

Particles, derived from rocks or biological materials, that have been transported by a fluid or other natural process and are suspended or settled in water.

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).

Species

Populations of organisms that may interbreed and produce fertile offspring having similar structure, habits, and functions.

Stage

The 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 near the channel floor.

Streamflow

A type of channel flow, applied to that part of surface runoff in a stream whether or not it is affected by diversion or regulation.

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.

Surface water

An open body of water, such as a lake, river, or stream.

Suspended (as used in tables of chemical analyses)

The amount (concentration) of undissolved material in a water

sediment mixture. It is associated with the material retained on a 0.45-micrometer filter.

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.

Tolerant species

Those species that are adaptable to (tolerant of) human alterations to the environment.

Total concentration

Refers to the concentration of a constituent regardless of its form (dissolved or bound) in a sample.

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.

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 it undergoes.

Unconfined aquifer

An aquifer whose upper surface is a water table; an aquifer containing unconfined ground water.

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.

Watershed

See Drainage basin.

Wetlands

Ecosystems whose soil is saturated for long periods seasonally or continuously, including marshes, swamps, and ephemeral ponds.

U.S. Geological Survey Circular 1163

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