Water Quality in the Lower Susquehanna River Basin, Pennsylvania and Maryland, 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.

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 also Water-quality criteria.

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

Atmospheric deposition
The transfer of substances from the air to the surface of the Earth, either in wet form (rain, fog, snow, dew, frost, hail) or in dry form (gases, aerosols, particles).

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.

General term for consolidated (solid) rock that underlies soils or other unconsolidated material.

Best management practice (BMP)
An agricultural practice that has been determined to be an effective, practical means of preventing or reducing nonpoint source pollution.

The biological sequestering of a substance at a higher concentration than that at which it occurs in the surrounding environment or medium. Also, the process whereby a substance enters organisms through the gills, epithelial tissues, dietary, or other sources.

The capacity of a chemical constituent to be taken up by living organisms either through physical contact or ingestion.

Breakdown product
A compound derived by chemical, biological, or physical action upon a pesticide. The breakdown is a natural process that may result in a more or less toxic and a more or less persistent compound.

Carbonate rocks
Rocks (such as limestone or dolostone) that are composed primarily of minerals (such as calcite and dolomite) containing the carbonate ion (CO32-).

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 microgram per liter (water sample) or micrograms per kilogram (sediment or tissue sample).

Concentrated animal operation
Operation where the animal density exceeds two animal units per acre on an annual basis as defined for the Pennsylvania nutrient management legislation. An animal unit is 1,000 pounds of live weight.

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

Crystalline rocks
Rocks (igneous or metamorphic) consisting wholly of crystals or fragments of crystals.

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

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.

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.

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

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

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

FDA action level
A regulatory level recommended by the U.S. Environmental Protection Agency for enforcement by the FDA when pesticide residues occur in food commodities for reasons other than the direct application of the pesticide. Action levels are set for inadvertent pesticide residues resulting from previous legal use or accidental contamination. Applies to edible portions of fish and shellfish in interstate commerce.

Fish community
See Community.

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

Human health advisory level
Guidance provided by U.S. Environ-mental 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 substance or mixture of substances intended to prevent, destroy, or repel insects.

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.

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

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.

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

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 milligram per liter.

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.

An ion consisting of nitrogen and oxygen (NO-). 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. See also Point source.

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

Occurrence and distribution assessment
Characterization of the broad-scale spatial and temporal distributions of water-quality conditions in relation to major contaminant sources and background conditions for surface water and ground water.

Organochlorine compound
Synthetic organic compound containing chlorine. As generally used, the 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.

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

Point source
A source at a discrete location such as a discharge pipe, drainage ditch, well, or concentrated livestock operation. See also Nonpoint source.

The area adjacent to a stream or river with a high density, diversity, and productivity of plant and animal species relative to nearby uplands.

Species diversity
An ecological concept that incorporates both the number of species in a particular sampling area and the evenness with which individuals are distributed among the various species.

Species (taxa) richness
The number of species (taxa) present in a defined area or sampling unit.

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.

Tier 1 sediment guideline
Threshold concentration above which there is a high probability of adverse effects on aquatic life from sediment contamination, determined by using modified procedures from the U.S. Environmental Protection Agency (1996b).

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.

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 byproducts 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.

The mass of a material or constituent transported by a river in a specified period of time divided by the drainage area of the river basin.

U.S. Geological Survey Circular 1168

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Suggested citation:
Lindsey, B.D., Breen, K.J., Bilger, M.D., and Brightbill, R.A., 1998, Water Quality in the Lower Susquehanna River Basin, Pennsylvania and Maryland, 1992-95: U.S. Geological Survey Circular 1168, on line at <URL:>, updated June 22, 1998 .

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Last modified: Wed Jul 1 16:17:06 1998