From The Changing Illinois Environment: Critical Trends, Summary Report of the Critical Trends Assessment Project.

Words set in small caps are defined elsewhere in the glossary.


ACID RAIN. More accurately, acid precipitation that is created when airborne SULFATES and NITRATES react with water in the atmosphere to form dilute sulfuric and nitric acids that return to the surface, mainly in rain and snow.

ACRE. Area measuring 4,840 square yards. An American football field covers one and one-third acres.

ADSORB. To attach, as gases or dissolved substances such as pesticides and fertilizers attach themselves to the surface of soil particles.


AGRICULTURAL LIME. Ground limestone, applied to buffer or neutralize excess acidity in farm soils.

ALGAE. A group of green plants without roots, stems, or leaves; algae are found in water and damp places and include seaweeds, pond scum, etc.

AMMONIA. Water-soluble compound of nitrogen and hydrogen in common use as a fertilizer; also a pollutant formed when nitrogenous organic matter decays.

AMPHIPODS. Large group of crustaceans comprising beach fleas and related forms.

ANGLING DAY. A measure of recreational pressure on fishable waters equivalent to one day spent by one fisherman trying to catch a fish.

AQUIFER. Water-bearing stratum of permeable sand, gravel, or rock.

ATMOSPHERIC DEPOSITION. The movement of gases and dust in various forms from the air to the surface. Wet deposition delivers pollutants to the surface by precipitation; dry deposition occurs as airborne pollutants settle onto the surface, are blown onto it by winds, are intercepted by fogs, and so on.


BALLAST. Broken stone laid in railroad track beds. Also, anything heavy carried in a ship to give it stability. Zebra mussels are presumed to have reached North America in ballast waters from Europe.

BARREL. Basic measure of petroleum production equivalent to 42 gallons.

BEDROCK. General term for the rock that underlies the surface soil or other unconsolidated surface material. In some parts of Illinois bedrock lies at the surface.

BENTHIC. Relating to all the plants and animals living on or closely associated with the bottom of a body of water.


BIOLOGICAL OXYGEN DEMAND (BOD). Measurement of the amount of organic pollution in water, reported as the amount of oxygen that can be taken up by a given volume of water. A low BOD indicates little pollution.

BIOLOGICAL DIVERSITY. The world's living organisms along with their associated HABITATS and ecological systems.

BIOTA. The animal and plant life of a region.

BUFFERING CAPACITY. The ability to neutralize acids and bases in solution.


CADMIUM. Metallic element found in a variety of chemical forms; can affect human kidneys and liver. Most humans are exposed to cadmium via food or cigarette smoke; direct air and water exposure accounts for less than 10% of the total exposures.

CALCAREOUS WATER. Water rich in CALCIUM carbonate.

CALCIUM. Soft metallic element, very common in combination in certain minerals and rocks. An essential constituent of plant and animal cells.

CAMBRIAN. The first geological period in the Paleozoic Era, beginning 550 million years ago and lasting roughly 70 million years.

CARBON DIOXIDE (CO2). Heavy colorless gas produced by the decomposition (including via combustion) of organic matter. Essential to plant photosynthesis.

CARBON MONOXIDE (CO). Colorless, odorless gas that reduces the blood's ability to carry oxygen. Formed during the incomplete combustion of virtually all fuels; most of it comes from motor vehicles.

CARBONACEOUS OXYGEN DEMAND (COD). The weight of oxygen taken up by the organic matter in a sample of water. A test used to assess the strength of sewage. Similar to BOD.

CHANNELIZATION. Artificial straightening of a stream channel to increase the rate of land drainage.

CHIRONOMID. Member of a family of tiny two-winged flies.

CHLORDANE. An organochlorine insecticide much used from the 1950s to the mid-1970s for control of soil insects, especially termites. Its use was greatly restricted in the 1970s.

CHLORIDE. A compound of chlorine combined with another element.

CHLORINE RESIDUAL. Total amount of chlorine (combined and free available chlorine) remaining in wastewater at the end of a specified contact period following its chlorination.

CHLOROFORM. A colorless, volatile, heavy toxic liquid used chiefly as a solvent.

CHLOROFLUOROCARBONS (CFCs). Stable gaseous compounds used as working fluids in refrigeration systems, solvents, and aerosol propellants, and as "blowing agents" in the manufacture of insulation and packaging foams. In the upper atmosphere the chlorine molecules in CFCs act as catalysts to break apart OZONE molecules.

CHLORINATED HYDROCARBONS. Organic chemicals widely used as pesticides. See HYDROCARBONS.

CLAY PAN. Compacted layer of soil that hampers root penetration.

CLEAR-CUTTING. Method of harvesting forest trees in which all trees are cut down rather than just selected trees.

COMMERCIAL FOREST. Any FOREST that may be harvested and that is capable of producing more than 20 cubic feet of wood per ACRE when managed.

CONSTRUCTION AGGREGATE. Rock of various size mixed with cement to form concrete.

CORD. Quantity of wood equal to a stack of logs that measures 4 feet x 4 feet x 8 feet, or 128 cubic feet.

CRITERIA POLLUTANTS. Pollutants for which national or state air quality standards have been set. See CARBON MONOXIDE; NITROGEN DIOXIDE; OZONE; SULFUR DIOXIDE.

CROWN DIEBACK. The death of some of the upper branches on a tree; caused by a variety of diseases and other stress factors.

CURIE. Unit of radioactivity equal to 3.7 X 1010 disintegrations per second.


DDT. PERSISTENT organochlorine compound used widely as a pesticide from the mid-1940s to the 1960s.

DEFOLIATION. Loss of many or most of the leaves on a plant. May be caused by leaf-feeding insects, chemical treatments, or the effects of weather.


DIELDRIN. PERSISTENT organochlorine used widely as a pesticide from the 1950s to the 1960s.

DRIFT. Rock material transported by a glacier.



ECOLOGY. The branch of biology that deals with the interrelations among living organisms and their environment.

ECOSYSTEM. A relatively self-contained and interconnected system of living plants and animals along with certain essential features of their HABITAT (e.g., water, oxygen, mineral nutrients).

EDGE. Margin between different kinds of HABITAT, such as between FOREST and cultivated fields.

EFFLUENT. Discharged liquid waste.

ENDANGERED. As applied to any species that is in danger of extinction throughout all or a significant portion of its geographical range. See EXTINCT; THREATENED.

ENTOMOLOGIST. A scientist who specializes in insects.

EUTROPHICATION. As applied to bodies of water, the process of becoming rich in dissolved nutrients, often leading to seasonal oxygen deficiencies. Often caused in Illinois by runoff into LAKES and ponds from fertilized farm fields or septic systems.


EXTINCT. As applied to any SPECIES that has died out and no longer exists.

EXTIRPATED. No longer living in the state. Many species that are extirpated in Illinois are not EXTINCT, as they may thrive elsewhere.


FAUNAL STUDIES. Investigations of the animals of a specified region or time.

FECAL COLIFORM BACTERIA. Any of a group of colon bacteria typified by Escherichia coli. Their presence is a standard indicator of the pollution of water by fecal matter.

FISH KILL. Visible, mass die-off of fish, usually but not always caused by human activity.

FLATWOODS FOREST. Forest type usually occurring on poorly drained level uplands and stream terraces. In Illinois, commonly dominated by post oak and having a closed SAVANNA-like structure.

FLOCCULENT. Consisting of loosely aggregated particles; soft.

FLOODPLAIN. Land formed by an adjacent river and periodically flooded by it.

FLOOD PULSE. Natural, seasonal rise and fall of river level that inundates the river's plain.

FLOW. Quantity of water that moves through a stream under specified conditions.

FORAGE CROPLAND. Cropland used to raise oats, hay, and similar crops fed to livestock.

FORAGE SPECIES. As applied to lakes and streams, those SPECIES of animal preferred by PREDATOR species.

FOREST. Generally, land with trees on it. Foresters define as forestland any land stocked with trees of any size that cover 16.7% of the land area.

FUGITIVE EMISSIONS. Emissions that could not reasonably pass through a stack, chimney, vent, or other functionally equivalent opening.



GOB PILE. Waste coal, rock pyrites, slate, and other material of relatively large size that is separated from coal and other mined materials in the cleaning process.

GREENHOUSE GASES. Common air pollutants thought to contribute to global warming, including CARBON DIOXIDE (CO2), METHANE, NITROUS OXIDE (N2O), NITROGEN OXIDES (NOx), and CARBON MONOXIDE (CO).

GROUNDWATER. Water found underground in porous rock strata and soils. See AQUIFER; WATER TABLE.

GROWING STOCK. In forestry, the net volume in cubic feet of sound wood in the central stem of live timber trees from one foot off the ground to a stem diameter a minimum of four inches in size.


HABITAT. The kind of locality in which a plant or animal naturally grows or lives, such as forest, prairie, or wetland, and which provides a particular set of environmental and ecological conditions.

HALONS. Chemicals used in fire-fighting equipment; halons are present in much smaller amounts than CFCs but they have a much higher OZONE-depleting potential per molecule.

HARDNESS. Degree to which water contains certain dissolved calcium and magnesium salts that react with soap to form an insoluble precipitate or scum.

HERBACEOUS. Plants that are nonwoody and die back to the ground each year.


HYDRIC. As applied to soils, wet and low in oxygen.

HYDROCARBONS. Strictly, chemical compounds composed only of hydrogen and carbon; more loosely, many carbon-based compounds that also contain other elements.

HYDROPHYTES. Plant SPECIES adapted to life in water or in saturated soils.

HYDROLOGY. Science dealing with the properties, distribution, and circulation of water.


IMPOUNDMENT. A manmade pond or lagoon used to store, process, or dispose of wastes. Also any manmade pond or lake. See SLURRY POND.

INBREEDING DEPRESSION. A reduction in vigor of plants or animals caused by inbreeding (i.e., matings between related individuals).

INDIGENOUS. Native, or natural to a particular land, region, or environment.

INTRODUCED. In ecological terms, any plant or animal not native to a region and thought to have been brought in by humans.

INVERTEBRATES. Animals without backbones. Includes insects, worms, mussels, crayfish, and many other groups.


KETTLE. Bowl-shaped depression without surface drainage. Kettles formed in northeastern Illinois when blocks of ice buried in glacial drift melted.

KILOGRAM. Metric measure of weight equivalent to 2.205 pounds.


LAKE. Inland body of water lacking an appreciable directional water current. See KETTLE; MANMADE LAKE; RESERVOIR.

LANDFILL. Facility at which wastes are buried.

LEACHATE. In environmental terms, a liquid or some other polluted medium that has percolated through a landfill.

LOAM. Humus-rich topsoil consisting of clay, silt, and sand.

LOESS. Widespread, homogenous, usually unstratified and unconsolidated fine-grained dust usually considered to be composed of material transported by the wind during and after the most recent glacial period. The mineral basis of most Illinois soils.



MACROPHYTE. Large aquatic plants, as distinct from PHYTOPLANKTON and other small ALGAE.

MANMADE LAKE. Any surface impoundment created by damming a watercourse, from flood control reservoirs to farm ponds. See LAKE.

METHANE. Explosive gaseous hydrocarbon produced by the decomposition of organic matter. Methane is the principal constituent of natural gas and a major "greenhouse gas."

MISSISSIPPIAN. Subperiod of the Carboniferous geological period, during which coal formations were laid down in Illinois, beginning some 305 million years ago.

MITIGATE. As used in environmental statutes, to repair or compensate for losses or degradation of farmland, wetlands, etc.

MORTALITY RATES. Proportion or percentage of deaths in a POPULATION during a specified period of time.


NATURAL SUCCESSION. Sequence of ecological changes in which one dominant group of plant or animal SPECIES is replaced by another over time. This sequence is consistent and predictable for any given physical environment.

NEMATODE. Any of a class of (usually microscopic) elongated worms.

NITRATES. Any of the highly soluble, negatively charged compounds consisting of one atom of nitrogen and three of oxygen. Very important contributor to rapid growth in green plants. Associated with farm fertilizer applications, feedlot runoff, or leaking septic tanks.


NITROGEN DIOXIDE (NO2). A pungent, brownish-red gas. Can combine with water to produce nitric acid, which is harmful to plants and animals.

NITROGEN OXIDE (NOx). Any of several compounds of nitrogen produced when fossil fuels are burned. Two of them, nitric oxide and NITROGEN DIOXIDE, are quite reactive and are precursors of OZONE.

NON-NATIVE. Any SPECIES that does not occur naturally in a geographical region, but was INTRODUCED either deliberately or accidentally, by the actions of humans.

NONPOINT SOURCES. As defined in environmental protection laws, indirect sources of pollution. A farm field is a nonpoint water polluter; automobiles are nonpoint air polluters. See POINT SOURCES.

NONTARGET ORGANISMS. Those plants or animals not meant to be killed by applications of pesticides.


ORDOVICIAN. Geological period beginning roughly 480 million years ago and lasting for 85 million years.

ORGANIC COMPOUNDS. Any chemical compound containing carbon. In nature, most organic compounds can only be produced by living organisms.

OVERSTORY. Layer of foliage in a FOREST canopy.

OZONE. A corrosive gas created when atmospheric NITROGEN OXIDES are bombarded by ultraviolet light energy from the sun. A principal component of smog in the lower atmosphere; in the upper atmosphere, ozone absorbs harmful ultraviolet radiation from the sun.


PARTICULATE MATTER. Very small bits of airborne metal, fibers, stone dust, ash, and soot. Because it can be a health hazard, state and national air quality regulations set standards for total suspended particulate matter and for very small particulate matter.

PCBS. Polychlorinated biphenyls, widely used until the 1970s as insulating fluids, among other things; suspected of causing human birth defects and cancer. Production was banned in the U.S. in 1976.


PENNSYLVANIAN. Subperiod of the Carboniferous geological period, during which coal formations were laid down in Illinois, beginning some 305 million years ago.


PERSISTENT. Long-lasting. Applied to pesticides, the term refers to a compound's ability to be lethal for more than a few weeks.

PH. Measure of how acidic or alkaline a substance is, according to the concentration of hydrogen ions in a solution.

PHENOLS. An aromatic hydrocarbon widely used in manufacturing.

PHOSPHOROUS. Widely occurring element and one of three primary ingredients of commercial agricultural fertilizers.

PHOTOSYNTHESIS. Chemical process by which water and carbon are transformed in the presence of light into carbohydrates by chlorophyll cells in plants.

PHYTOPLANKTON. Plankton consisting of plant life.

PLANARIA. Small freshwater flatworms.

PLANKTON. Minute plant and animal life of open waters.

POINT SOURCES. Facilities (municipal or industrial) that discharge wastes directly into the air or surface waters. A sewer pipe is a point source, as is a factory smokestack. See NONPOINT SOURCES.

POPULATION. All the individuals of a particular species living in a given area.

POTW. Publicly-owned treatment works, or municipal sewage treatment plants.

PRAIRIE. Biological community occurring in central North America where the landscape is flat to rolling and is largely devoid of trees, and where most plants are herbaceous, with an abundance of grasses.

PRECURSOR. A substance from which another substance is formed. NITROGEN DIOXIDE and VOC are pre-cursors of OZONE.

PREDATOR. Any organism that catches and kills other organisms for food.

PROTOZOA. Subkingdom of animals consisting of minute creatures such as amoeba. Present in virtually all Illinois habitats.


RADON. Naturally occurring chemical element of atomic weight 222, produced by the radioactive decay of radium-226 and uranium-238. Radon occurs in trace amounts in most geologic materials, including soils.

REACTIVE. Any chemical that is quick to form new compounds with other substances.

RECREATION DAY. One day spent by one person in recreational activity; a measure of use pressure on recreation facilities.

RELICT. Surviving as a remnant of a vanished type or SPECIES.

REMEDIATION. In environmental terms, the undoing of past environmental damage, as in cleaning up a hazardous waste site.

RESERVOIR. Large manmade lake constructed to control floods or supply drinking water.

RETENTION POND. Manmade body of water typically used to trap sediments and/or excessive runoff.

RIPARIAN. Of or relating to the banks of a watercourse, usually a stream or river.

ROW CROP. A crop planted in rows sufficiently far apart to be cultivated for weed control. Corn and soybeans are the most common row crops planted in Illinois.


SAND FOREST. Forest occurring on soil that contains substantial amounts of sand.

SAVANNA. Mixture of trees, shrubs, and prairie vegetation, sometimes regarded as a transition community between forest and prairie. One of eight natural communities found in Illinois.

SECONDARY-GROWTH FOREST. Forest that has grown up in an area after the forest that existed prior to European settlement was logged or otherwise destroyed.

SECONDARY RECOVERY. Methods of petroleum production such as flooding old wells with water to force more oil toward nearby production wells.

SEDIMENTATION. Accumulation in one location of soil particles eroded from different locations.


SILICA. Sand-sized particles of quartz used in the manufacture of glass and in polishing.

SILTATION. The accumulation of silt. Distinct from sedimentation in that siltation usually involves only finer particles.

SLUDGE. The watery residue left by secondary sewage treatment processes.

SLURRY POND. Surface impoundment in which fine particles suspended in water, as from coal-cleaning operations, can settle out of solution.

SNAG. Standing dead tree.

SPECIES. A group or class of plants or animals (usually constituting a subdivision of a genus) having certain common and permanent characteristics that clearly distinguish it from other groups.

SPECIES ASSOCIATION. Group of species of plants or animals that usually occur together in the same kind of habitat.

SPOIL. Material excavated during mining or dredging.

STANDARD METROPOLITAN STATISTICAL AREA (SMSA) Unit of population measurement used by the U.S. Census Bureau, corresponding roughly to a city's metropolitan area.

STRIP MINING. The excavation of shallow deposits of coal or other minerals by the removal of surface soils.

SUBSIDENCE. Lowering of the land surface as a result of the collapse of subsurface tunnels, as from mining.

SULFATES. Compounds containing the sulfate ion, which consists of one sulfur atom and four oxygen atoms.

SULFUR DIOXIDE (SO2). Pungent, colorless gas that can be produced during petroleum refining or when fuels containing sulfur compounds are burned.

SULFUR OXIDE (SOX). Any of several oxides of sulfur. Oxidized and combined with water in the atmosphere, sulfur dioxide can produce an ultrafine mist of sulfur trioxide (SO3) or sulfuric acid.


THREATENED. In preservation law, of or relating to any species that is likely to become an endangered species within the foreseeable future throughout all or a significant part of its range.

TILING. Installation of tiles (usually earthenware or plastic pipe sections) under a farm field to drain away excess water.

TILL. Unsorted and unstratified glacial drift consisting of a mixture of clay, sand, gravel, and boulders of varying sizes and shapes.

TILLABLE. Capable of being cultivated.

TIMBER. Live trees of commercial species at least five inches in diameter.

TOPOGRAPHY. Configuration of the land surface, including both its natural and manmade features.

TOPSOIL. Uppermost soil layer, also known as the A-horizon.

TOTAL DISSOLVED SOLIDS. Measure of inorganic salts and other substances dissolved in water.

TRANSMISSIVITY. As applied to groundwater, the degree to which water may diffuse through deposits of sands, gravels, or rock in an aquifer.

TURBIDITY. Haziness or muddiness. Applied to water and the atmosphere.


UNDERSTORY. Vegetation layer occurring in a forest below the canopy formed by the largest trees.


VASCULAR PLANTS. Plants that contain special conducting tissue (xylem and phloem); these include ferns, conifers, and flowering plants.

VECTOR. Agent capable of transmitting a pathogen, or disease-carrier, from one organism to another.

VERTEBRATES. Animals with a backbone.

VINYL CHLORIDE. Flammable gaseous compound used chiefly for making vinyl resins.

VMT. Vehicle miles traveled.

VOLATILE ORGANIC COMPOUNDS (VOC). Large family of substances in common industrial use, including toluene, acetaldehyde, benzene, hexane, etc. Some are toxic; also PRECURSORS of OZONE.

VOLATILIZE. Evaporate, or pass off in vapor.


WATCH LIST. Unofficial list kept by the staff of the Illinois Endangered Species Protection Board of SPECIES that are not currently listed as ENDANGERED or THREATENED, but that are nevertheless rare or vulnerable and could eventually qualify for listing as endangered or threatened if current trends continue.

WATERSHED. The area of land drained by a given stream or stream system.

WATER TABLE. Zone of total saturation near the surface.


WINDTHROW. Uprooting of trees by the wind.

WOODY PLANTS. Plants that have woody stems and live for several to many years, i.e. trees, shrubs, and woody vines.

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