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
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.
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,
- 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
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
- 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.
An organochlorine insecticide no longer registered for use in the United
- 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
- 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
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
- The interacting populations
of plants, animals, and microorganisms occupying an area, plus their physical
- 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
- 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
- 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
- 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)
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)
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
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
- Any or all forms of
water particles that fall from the atmosphere, such as rain, snow, hail,
- 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
- 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)
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
- 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
- The amount (concentration) of undissolved material in a water-sediment
mixture. It is associated with the material retained on a 0.45-micrometer
- 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
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
- 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)
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
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
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"
- 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.