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.
- As related to fish, externally visible skin or
subcutaneous disorders, including deformities, eroded fins, lesions,
- Water-quality guidelines for protection
of aquatic life. Often refers to U.S. Environmental Protection Agency
water-quality criteria for protection of aquatic organisms. See also
Water-quality guidelines and Water-quality criteria.
- A water-bearing layer of soil, sand, gravel, or rock
that will yield usable quantities of water to a well.
- Insects, mollusks, crustaceans, worms,
and other organisms without a backbone that live in, on, or near the
bottom of lakes, streams, or oceans.
- The amount of living matter, in the form of
organisms, present in a particular habitat, usually expressed as weight
per unit area.
- A condition that can be caused by
ingestion of high amounts of nitrate resulting in the blood losing its
ability to effectively carry oxygen. It is most common in young infants
and certain elderly people.
- A compound derived by chemical, biological,
or physical action upon a pesticide. The breakdown is a natural process
which may result in a more toxic or a less toxic compound and a more
persistent or less persistent compound.
- 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.
- In ecology, the species that interact in a common
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.
- A standard rule or test on which a judgment or
decision can be based.
- The concentration below which a particular
analytical method cannot determine, with a high degree of certainty, a
- Amount of minerals, such as salt, that are
dissolved in water; amount of dissolved solids is an indicator of
salinity or hardness.
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
- 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
- The part of the physical environment where plants and
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.
- A type of topography that results from dissolution and
collapse of carbonate rocks such as limestone and dolomite, and
characterized by closed depressions or sinkholes, caves, and underground
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
- The middle or central value in a distribution of data
ranked in order of magnitude. The median is also known as the 50th
Method detection limit
- The minimum concentration of a
substance that can be accurately identified and measured with present
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.
National Academy of Sciences/National Academy of Engineering
(NAS/NAE) recommended maximum concentration in water
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
this report are for freshwater.
- A contamination 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
- A description of the surface features of the
Earth, with an emphasis on the origin of landforms.
- One trillionth (10-12) of the amount of
radioactivity represented by a curie (Ci). A curie is the amount of
radioactivity that yields 3.7 x 1010 radioactive disintegrations per
second (dps). A picocurie yields 2.22 disintegrations per minute (dpm)
or 0.037 dps.
Polychlorinated biphenyls (PCBs)
- A mixture of chlorinated
derivatives of biphenyl, marketed under the trade name Aroclor with a
number designating the chlorine content (such as Aroclor 1260). PCBs
were used in transformers and capacitors for insulating purposes and in
gas pipeline systems as a lubricant. Further sale for new use was banned
by law in 1979.
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.
- A naturally occurring, colorless, odorless, radioactive
gas formed by the disintegration of the element radium; damaging to
human lungs when inhaled.
- The number of organisms of a particular
kind present in a sample relative to the total number of organisms in
- Pertaining to or located on the bank of a body
of water, especially a stream.
- 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).
- 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
the water-quality or biological sampling point).
- 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.
- A ranking of the relative sizes of streams
within a watershed based on the nature of their tributaries. The
smallest unbranched tributary is called first order, the stream
receiving the tributary is called second order, and so on.
- The diameter of streambed particles such as
clay, silt, sand, gravel, cobble, and boulders.
- Those species that are adaptable to
(tolerant of) human alterations to the environment and often increase in
number when human alterations occur.
- 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
- 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.
- 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.
- 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
- 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.
Petersen, J.C., Adamski, J.C., Bell, Davis, J.V., Femmer, S.R., Freiwald,
D.A., and Joseph, R.L., 1998, U.S. Geological Survey Circular 1158, on
line at < URL: http://water.usgs.gov/pubs/circ1158>, updated
April 3, 1998
This page is a subpage of <URL:http://water.usgs.gov/pubs/circ1158>
Email questions and comments to GS-W_NAWQA_Outreach@usgs.gov
Last modified: 4/3/98