Water Quality in the San Joaquin-Tulare Basins, California, 1992-95

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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.

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.

Deposits of clay, silt, sand, gravel or other particulate rock material left by a river in a streambed, on a flood plain, delta, or at the base of a mountain.

A compound of nitrogen and hydrogen (NH3) that is a common byproduct of animal waste. Ammonia readily converts to nitrate in soils and streams.

As related to fish, externally visible skin or subcutaneous disorders, including deformities, eroded fins, lesions, and tumors.

Aquatic life criteria
Water-quality guidelines for protection of aquatic life. Often refers to U.S. Environmental Protection Agency water-quality criteria for protection of aquatic organisms. See Water-quality guidelines, Water-quality criteria, and Freshwater chronic criteria.

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.

Base flow
Sustained, low flow in a stream; ground-water discharge is the source of base flow in most places.

Basic Fixed Sites
Sites on streams at which streamflow is measured and samples are collected for temperature, salinity, suspended sediment, major ions and metals, nutrients, and organic carbon to assess the broad-scale spatial and temporal character and transport of inorganic constituents of stream water in relation to hydrologic conditions and environmental settings.

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 invertebrates
Insects, mollusks, crustaceans, worms, and other organisms without a backbone that live in, on, or near the bottom of lakes, streams, or oceans.

Living organisms.

Octachloro-4,7-methanotetrahydroindane. An organochlorine insecticide no longer registered for use in the United States. Technical chlordane is a mixture in which the primary components are cis- and trans-chlordane, cis- and trans-nonachlor, and heptachlor.

A class of volatile compounds consisting of carbon, chlorine, and fluorine. Commonly called freons, which have been used in refrigeration mechanisms, as blowing agents in the fabrication of flexible and rigid foams, and, until several years ago, as propellants in spray cans.

In ecology, the species that interact in a common area.

The amount or mass of a substance present in a given volume or mass of sample. Usually expressed as micrograms per liter (water sample) or micrograms per kilogram (sediment or tissue sample).

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

Degradation of water quality compared to original or natural conditions due to human activity.

A standard rule or test on which a judgment or decision can be based.

Cubic foot per second
(ft3/s, or cfs) is the rate of water discharge representing a volume of a 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.

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.

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

dichloro-diphenyl-trichloro-ethane. An organochlorine insecticide no longer registered for use in the United States.

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

Rate of fluid flow passing a given point at a given moment in time, expressed as volume per unit of time.

Dissolved solids
Amount of minerals, such as salt, that are dissolved in water; amount of dissolved solids is an indicator of salinity or hardness.

Drainage basin
The portion of the surface of the Earth that contributes water to a stream through overland 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. 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.

Ecological studies
Studies of biological communities and habitat characteristics 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 in NAWQA Study Units.

An area of similar climate, landform, soil, potential natural vegetation, hydrology, or other ecologically relevant variables.

The interacting populations of plants, animals, and microorganisms occupying an area, plus their physical environment.

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.

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
A stream or part of a stream that flows only in direct response to precipitation or snowmelt. Its channel is above the water table at all times.

The process whereby materials of the Earth's crust are loosened, dissolved, or worn away and simultaneously moved from one place to another.

The process by which water becomes enriched with plant nutrients, most commonly phosphorus and nitrogen.

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.

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.

Freshwater chronic criteria
The highest concentration of a contaminant that freshwater aquatic organisms can be exposed to for an extended period of time (4 days) without adverse effects. See Water-quality criteria.

A substance or mixture of substances that produce gas, vapor, fume, or smoke intended to destroy insects, bacteria, or rodents.

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.

The part of the physical environment where plants and animals live.

A chemical or other agent applied for the purpose of killing undesirable plants. See also Pesticide.

Graph showing variation of water elevation, velocity, streamflow, or other property of water with respect to time.

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.

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

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.

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 Study-Unit Survey.

The removal of materials in solution from soil or rock to ground water; refers to movement of pesticides or nutrients from land surface to ground water.

General term that refers to a material or constituent in solution, suspension, or in transport; usually expressed in terms of mass or volume.

Main stem
The principal course of a river or a stream.

Maximum contaminant level (MCL)
Maximum permissible level of a contaminant in water that is delivered to any user of a public water system. MCL's are enforceable standards established by the U.S. Environmental Protection Agency.

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

Mean discharge (MEAN)
The arithmetic mean of individual daily mean discharges during a specific period, usually daily, monthly, or annually.

The middle or central value in a distribution of data ranked in order of magnitude. The median is also known as the 50th percentile.

A substance produced in or by biological processes.

Method detection limit
The minimum concentration of a sub-stance 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 µg/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 streamwater and ground water. One thousand micrograms per liter equals 1 mg/L.

Monitoring well
A well designed for measuring water levels and testing ground-water quality.

The place where a stream discharges to a larger stream, a lake, or the sea.

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.

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

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.

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.

A chemical applied to crops, rights of way, lawns or residences to control weeds, insects, fungi, nematodes, rodents or other "pests."

A nutrient essential for growth that can play a key role in stimulating aquatic growth in lakes and streams.

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

A naturally occurring, colorless, odorless, radioactive gas formed by the disintegration of the element radium; damaging to human lungs when inhaled.

Water that infiltrates the ground and reaches the saturated zone.

Relative abundance
The number of organisms of a particular kind present in a sample relative to the total number of organisms in the sample.

Areas adjacent to rivers and streams with a high density, diversity, and productivity of plant and animal species relative to nearby uplands.

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

Particles, derived from rocks or biological materials, that have been transported by a fluid or other natural process, 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 (PAH).

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

Specific conductance
A measure of the ability of a liquid to conduct an electrical current.

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.

Study Unit Survey
Broad assessment of the water-quality conditions of the major aquifer systems of each Study Unit. The Study-Unit Survey relies primarily on sampling existing wells and, wherever possible, on existing data collected by other agencies and programs. Typically, 20 to 30 wells are sampled in each of three to five aquifer subunits.

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.

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.

Suspended sediment
Particles of rock, sand, soil, and organic detritus carried in suspension in the water column, in contrast to sediment that moves on or near the streambed.

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).

Synoptic sites
Sites sampled during a short-term investigation of specific water-quality conditions during selected seasonal or hydrologic conditions to provide improved spatial resolution for critical water-quality conditions.

Total DDT
The sum of DDT and its metabolites (breakdown products), including DDD and DDE.

Trace element
An element found in only minor amounts (concentrations less than 1.0 milligram per liter) in water or sediment; includes arsenic, cadmium, chromium, copper, lead, mercury, nickel, and zinc.

Urban Site
A site that has greater than 50 percent urbanized and less than 25 percent agricultural area.

Volatile organic compounds (VOC)
Organic chemicals that have a high vapor pressure relative to their water solubility. VOCs include components of gasoline, fuel oils, and lubricants, as well as organic solvents, fumigants, some inert ingredients in pesticides, and some by-products of chlorine disinfection.

Water-quality criteria
Specific levels of water quality which, if reached, are expected to render a body of water unsuitable for its designated use. Commonly refers to water-quality criteria established by the U.S. Environmental Protection Agency. Water-quality criteria are based on specific levels of pollutants that would make the water harmful if used for drinking, swimming, farming, fish production, or industrial processes.

Water-quality guidelines
Specific levels of water quality which, if reached, may adversely affect human health or aquatic life. These are nonenforceable guidelines issued by a governmental agency or other institution.

Water-quality standards
State-adopted and U.S. Environmental Protection Agency-approved ambient standards for water bodies. Standards include the use of the water body and the water-quality criteria that must be met to protect the designated use or uses.

See Drainage basin.

Water table
The point below the land surface where ground water is first encountered and below which the earth is saturated. Depth to the water table varies widely across the country.

Water year
The continuous 12-month period, October 1 through September 30, in U.S. Geological Survey reports dealing with the surface-water supply. The water year is designated by the calendar year in which it ends and which includes 9 of the 12 months. Thus, the year ending September 30, 1980, is referred to as the "1980" water year.

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

The act or process of removing; such as removing water from a stream for irrigation or public water supply.

U.S. Geological Survey Circular 1159

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Suggested citation:
Dubrovsky, N.M., Kratzer, C.R., Brown, L.R., Gronberg, J.M., and Burow, K.R., 1998, Water Quality in the San Joaquin-Tulare Basins, California, 1992-95: U.S. Geological Survey Circular 1159, on line at <URL:>, updated April 17, 1998

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Last modified: April 17, 1998