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 one foot in depth and covering one 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.
- Base flow
- Sustained, low flow in a stream; ground-water discharge is the source of base flow in most places.
- Best management practice (BMP)
- An agricultural practice that has been determined to be an effective, practical means of preventing or reducing nonpoint source pollution.
- Breakdown product
- A compound derived by chemical, biological, or physical action upon a pesticide; also called "metabolite." The breakdown is a natural process which may result in a compound that is more or less toxic and more or less persistent.
- Dissolved solids
- Amount of minerals, such as salt, that are dissolved in water; amount of dissolved solids is an indicator of salinity or hardness.
- Eutrophication
- The process by which water becomes enriched with plant nutrients, most commonly phosphorus and nitrogen, thereby causing excessive growth of aquatic plants.
- Flow path
- An underground route for ground-water movement, extending from a recharge (intake) zone such as a hill to a discharge (output) zone such as a shallow stream.
- Freshwater-chronic criteria
- The highest concentrations of contaminants that freshwater aquatic organisms can be exposed to for an extended period of time (4 days) without adverse effects. See also Water-quality criteria.
- Fumigant
- A substance or mixture of substances that produces gas, vapor, fume, or smoke intended to destroy insects, bacteria, or rodents.
- Furrow irrigation
- A type of surface irrigation where water is applied at the upper end of a field and flows in furrows to the lower end.
- Headwaters
- The source and upper part of a stream.
- Health advisory
- A nonregulatory level of a contaminant in drinking water or edible fish that may be used as guidance in the absence of a regulatory limit. 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 pesticide that is applied primarily for the purpose of killing undesirable plants.
- Insecticide
- A pesticide intended to prevent, destroy, or repel insects.
- Load
- General term that refers to the amount of a material or constituent in solution, in suspension, or in transport; usually expressed in terms of mass or volume.
- Loess
- A homogeneous, fine-grained sediment made up primarily of silt and clay, and deposited over a wide area (probably by wind).
- Maximum contaminant level (MCL)
- The 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 (USEPA).
- Median
- The middle or central value in a distribution of data ranked in order of magnitude. The median is equal to the 50th percentile.
- Metabolite
- See breakdown product.
- Method detection limit (MDL)
- The minimum concentration of a substance that can be accurately identified and measured with present laboratory technologies.
- 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.
- 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. See point source.
- 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 pesticide
- A class of organic pesticides 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 or severely restricted in usage because of their carcinogenicity, tendency to bioaccumulate, and toxicity to wildlife.
- Organophosphate pesticide
- A class of pesticides 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.
- Perennial stream
- A stream that normally has water in its channel at all times.
- Pesticide
- A chemical applied to crops, rights of way, lawns or residences to control weeds, insects, fungi, nematodes, rodents, or other "pests." See also herbicide, insecticide, fumigant.
- Point source
- A source at a discrete location such as a discharge pipe, drainage ditch, tunnel, well, concentrated livestock operation, or floating craft. See nonpoint source.
- Riparian
- The area adjacent to rivers or streams with a high density, diversity, and productivity of plant and animal species relative to nearby uplands.
- Sediment guideline
- Threshold concentration above which there is a high probability of adverse effects on aquatic life from sediment contamination, determined using modified USEPA (1996) procedures.
- 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).
- Subsurface drain
- A slotted or porous drainage pipe 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.
- 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.
- Synoptic site
- A site 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.
- 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.
- Triazine herbicide
- A class of herbicides containing a symmetrical triazine ring. Examples include atrazine, propazine, metribuzin, and simazine.
- Volatile organic compound (VOC)
- An organic chemical that has a high vapor pressure relative to its 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.
- Wasteway
- A waterway used to drain excess irrigation water dumped from the irrigation delivery system.
- 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 refer 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 guideline
- A specific level 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 standard
- A legally-enforceable state-adopted and U.S. Environmental Protection Agency-approved ambient standard 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 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 Study Unit.
- 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.
