This glossary is provided as a reference for technical terms found within the ACE Basin Characterization. It should be noted that many words have multiple usage and all definitions (usages) may not be provided here. Following each term in the list below is a number that refers to the reference (source material) for the definition. The references are listed following the definitions. In many cases, the definitions have been modified from those found in the source material. Use the "back button" to return to the narrative text from the glossary.

• TERM - Source Number - DEFINITION
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• abdomen - 46 - In Arthropoda, main division of body behind thorax; in crayfish and lobsters, often miscalled the tail. Mammalian abdomen lies behind diaphragm and contains liver, stomach, and intestines.
  
  
• abiotic - 8 - Describing the nonliving components of an ecosystem.
  
  
• acacia - 2 - A genus of leguminous trees of the tropics and subtropics, especially Australia, that may form the dominant vegetation in arid areas. Dyes, perfumes, timber and many other commercial products are derived from acacias, and some (e.g., Acacia albida) might be exploited more as a species of great value to people living in arid regions.
  
  
• actinarians - 14 - An order of Zoantharia, commonly called sea anemones, which are solitary, without a skeleton, and have complete and incomplete septa in multiples of six.
  
  
• acute toxicity - 20 - The ability of a substance to cause severe biological harm or death soon after a single exposure or dose. Also, any poisonous effect resulting from a single short-term exposure to a toxic substance.
  
  
• aeolian - 8 - Referring to mineral particles moved and sorted by wind, usually fine sands and coarse silt; also eolian.
  
  
• aerobic - 6 - Organisms, activities, and conditions that exist only in the presence of free oxygen. Aerobic organisms require oxygen for their life processes.
  
  
• algae - 42 - Simple plants, many microscopic, containing chlorophyll; forming the base of the food chain in aquatic environments; some species may create a nuisance when environmental conditions are suitable for prolific growth..
  
  
• aliphatic - 10 - Referring to an organic compound with properties similar to those of the alkanes, alkenes, and alkynes and their derivatives. Most aliphatic compounds have an open chain structure, but some have rings. The term is used in distinction to aromatic compounds.
  
  
• allochthonus - 48 - Refers to rocks or materials formed elsewhere than in their present position, such as particulate matter originating outside and carried into a new body of water.
  
  
• ammonium ion - 2 - The ion NH4+, formed by the relationship between NH3 and H+. .
  
  
• amnion - 39 - A thin membrane forming a closed sac surrounding the embryos of reptiles, birds, and mammals. It contains a serous fluid, the amniotic fluid, in which the embryo is immersed, and is usually formed by folds ( the amniotic folds) arising from the ectoderm and outer layer of the mesoderm of the extraembryonic part of the blastoderm. The folds unite over the back of the embryo, called the amniotic cavity. Only that layer of the folds is called the false amnion and forms part of the chorion. In parturition the amnion is ruptured and the amniotic fluid escapes.
  
  
• amniotic eggs - 40 - The type of eggs produced by birds, reptiles and prototherian (egg laying) mammals in which the embryo develops inside an amnion. The shell of the egg is either calcium-based or leathery.
  
  
• amphibians - 1 - (Amphibia). Class of vertebrates including newts, salamander, frogs and toads. The adults are aquatic or live in damp situations, and have moist, smooth skins, often used as well as lungs for respiratory purposes. Apart from a few viviparous species, most have to return to the water to breed, because the eggs have no shell to prevent desiccation. The larvae have gills. The earliest (Carboniferous) Amphibia resembled osteolepid fishes, from which they differed in having pentadactyl limbs instead of fins, and middle ear apparatus.
  
  
• amphipods - 1 - (Amphipoda). Order of Crustacea including the freshwater shrimps and sandhoppers. Most are marine and have laterally compressed bodies.
  
  
• anadromous - 4 - A form of life cycle among fishes in which maturity is attained in the ocean, and the adults ascend streams and rivers to spawn in freshwater. Salmon and shad are examples.
  
  
• anaerobic - 8 - Occurring in the absence of oxygen as applied to chemical and biochemical processes; opposite of aerobic.
  
  
• anal fin - 46 - In fish, a mid-ventral fin behind the anus.
  
  
• androgens - 40 - A class of male hormones (which includes testosterone and androsterone) responsible for the development of male secondary characteristics.
  
  
• anoxia - 2 - A severe deficiency of oxygen in tissues, blood or a body of water, causing harm to living organisms.
  
  
• anoxic - 40 - Lacking or not involving or requiring oxygen.
  
  
• anthesis - 38 - The time or action of a flower opening; full bloom.
  
  
• anthropogenic - 2 - Produced as a result of human activities.
  
  
• anthropomorphic - - Of or pertaining to anthropomorphism. See anthropomorphism.
  
  
• anthropomorphism - 2 - The projection on to non-humans, especially mammals, of motives, emotions or thoughts that a human might experience in circumstances apparently similar to those affecting the individual animal being observed. It is a common attitude for a person to hold when confronting a non-human, but it has no scientific validity.
  
  
• aquaculture - 2 - The breeding and rearing of freshwater or marine organisms in a controlled manner; frequently in captivity.
  
  
• aquifer - 2 - A geologic formation through which water can percolate, sometimes very slowly, for long distances. Springs and wells are charged from aquifers and the contamination of an aquifer may lead to the contamination of wells and springs over a wide area. .
  
  
• archaeology - 7 - The study of human cultures through the recovery and analysis of their material relics.
  
  
• archaic - 7 - Related or belonging to an earlier (and usually more primitive) time. In new world archaeology, a prehistoric cultural stage that follows the Lithic.
  
  
• argillaceous - 6 - Applied to rocks and substances composed of clay minerals or having a notable proportion of clay in their composition.
  
  
• argillic - 6 - Pertaining to clay or clay minerals.
  
  
• aromatic hydrocarbons - 35 - A major group of unsaturated cyclic hydrocarbons containing one or more rings, typified by benzene, which has a 6-carbon ring containing three double bonds. The vast number of compounds of this important group, derived chiefly from petroleum and coal tar, are rather highly reactive and chemically versatile. The name is due to the strong and not unpleasant odor characteristic of most substances of this nature. Certain 5-membered cyclic compounds such as the furan group (heterocyclic) are analogous to aromatic compounds.
  
  
• Arthropoda - 2 - The largest phylum of animals, containing more than 700,000 species, and the only major invertebrate phylum with members adapted for life in truly dry land. Arthropods are characterized by the possession of a jointed exoskeleton containing chitin, paired jointed limbs, a well-developed head and a haemocoelic (blood-containing) body cavity.
  
  
• arthropods - 2 - Animals belonging to the phylum Arthropoda (see Arthropoda).
  
  
• assimilation - 2 - The incorporation of food substances into the cells, tissues or organs of a living organism.
  
  
• assimilation rates - 2 - The rate at which food substances are incorporated into the cells, tissues and organs of a living organism.
  
  
• autolysis - 40 - The process of self-destruction of a cell, cell organelle, or tissue, occurring by the action of enzymes.
  
  
• autolytic - - See autolysis.
  
  
• autotrophs - 9 - An organism that is able to synthesize all needed organic molecules from simple inorganic substances (e.g., H2O, CO2, NH3) and some energy source (e.g., sunlight); in contrast to heterotroph. Plants, algae, and some bacteria are autotrophs.
  
  
• avifauna - 41 - Members of the vertebrate class Aves or birds; usually referring to birds within a specific community.
  
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• bacterivore - 42 - An organism that feeds on bacteria.
  
  
• bacterivorous - 42 - Relating to feeding upon bacteria.
  
  
• barbels - 46 - Thin, sensory appendages found near mouths of some fishes, e.g., catfishes. Barbels are sensitive to touch giving the fish tactile awareness.
  
  
• barrier islands - 6 - Elongate coastal islands, generally parallel to the coastline and fronting the ocean, barrier islands are formed of rows of parallel ridges of sand created by repeated deposition and erosion. Generally have beaches, dunes, vegetated terrains and swampy areas. Barrier islands tend to change shape and migrate in response to sea level rise and fall and erosion/deposition processes.
  
  
• bathymetric - 4 - Of or pertaining to the science of measuring ocean depths in order to determine the sea floor topography.
  
  
• beach facies - 3 - The section of the beach normally exposed to the action of the wave uprush. The foreshore of a beach.
  
  
• benthic - 4 - That portion of an aquatic environment inhabited by organisms which live permanently in or on the bottom sediments.
  
  
• berm - 46 - Generally flat part of beach leveled by previous erosion and sometimes bounded at lower side by ridge; occur above high water mark; formed by deposition of material by wave action.
  
  
• bioaccumulated - - See bioaccumulation.
  
  
• bioaccumulation - 42 - A build up of specific organic or inorganic compounds within tissues of given organisms; usually applied to certain heavy metals, pesticides, or metabolites.
  
  
• bioavailable - 18 - Available for uptake by living organisms.
  
  
• Biochemical oxygen demand - 2 - The amount of oxygen taken up by aerobic microbes that decompose organic matter in a unit volume of water over a given time. It is used as a measure of the degree of organic pollution of water. The more organic matter the water contains, the more oxygen is used by microorganisms.
  
  
• biodiversity - 8 - Totality of the richness of biological variation, ranging form within-species genetic variation, through subspecies and species, to communities, and the pattern and dynamics of these within the landscape.
  
  
• biogeochemical - 40 - (Biogeochemical cycle). The circulation (cycling) of chemical elements such as nitrogen, carbon, etc. in specific pathways from the abiotic (non-living) portions of the environment into living components and then back again into abiotic forms.
  
  
• biogeochemistry - 6 - Study of the effects of life processes on the distribution and fixation of chemical elements in the biosphere, e.g. nitrogen or sulfur cycling.
  
  
• biological bench-marking - 2 - The use of plant or animal species to measure pollution based on assessments (bench marks) of population level and fitness, against which changes can be evaluated. Also, The natural process by which a water body purifies itself of organic pollution, largely by the action of microorganisms.
  
  
• biological indicator - 42 - A species or organism that is used to grade environmental quality or change.
  
  
• biological oxygen demand - 7 - The amount of oxygen, measured in parts per million, that is removed from aquatic environments rich in organic material by the metabolic requirements of aerobic microorganisms. Used as a standardized test to measure nutrient pollution.
  
  
• biomass - 40 - The total mass (weight or volume) of all the organisms of a given type and/or in a given area; for example, the biomass of fishes in a pond.
  
  
• biomedicine - 38 - The study of medicine in relationship to all biological systems. The branch of medicine that deals with human response to environmental stress.
  
  
• biomolecules - 40 - Any molecule that is involved in the maintenance and metabolic processes living organisms.
  
  
• biosphere - 2 - That part of the Earth and its atmosphere in which organisms live.
  
  
• biospheric - - Of or pertaining to the biosphere. See biosphere.
  
  
• biostabilizer - 42 - A machine used to convert solid waste into compost by grinding and aeration.
  
  
• biota - 2 - The flora and fauna of an area.
  
  
• biotoxins - 15 - A toxin (poison) which originates from a living thing (a plant, animal, fungi, bacteria, etc.).
  
  
• bioturbation - 27 - The stirring of sediment by animal life.
  
  
• bivalve - 4 - One of a class (Pelecypoda or Lamellibranch) of molluscs generally sessile or burrowing into soft sediment, rock, wood, or other materials. Individuals possess a hinged shell and a hatchet-shaped foot, which in some is used in digging. Many molluscs are notable fouling organisms; several are marine borers. The clams, oysters, and mussels are bivalves.
  
  
• blackwater - 42 - Swamp, stream and river water that is dark in color because of tannins (complex organic molecules) that have leached from organic matter such as leaves and bark.
  
  
• bottomland - 15 - Lowlands along streams and rivers, usually on alluvial floodplains, that are periodically flooded.
  
  
• boundary layer (effect) - 2 - The layer of fluid that is influenced by its proximity to a rigid boundary. Frequently, but not always, refers to the slower motion of flowing water proximal to a solid surface (e.g. the bottom) compared to the mainstream flow..
  
  
• brackish - 4 - Water in which salinity values range from approximately 0.50 to 17.00 parts per thousand.
  
  
• bryozoans - 4 - One of a phylum (Bryozoa or Polyzoa) of minute, mostly colonial, aquatic animals with body walls often hardened by calcium carbonate and growing attached to aquatic plants, rocks, and other firm surfaces. Colonies may be encrusting, creeping, or erect branching. Encrusting colonies may be white, yellowish, or brick red and consist of many tiny, beautifully formed shells. Members of the phylum are widespread and notable fouling organisms.
  
  
• butylbenzyl phthalate - 35 - Clear, oily liquid; slight odor. Combustible. Plasticizer for polyvinyl and cellulosic resins, organic intermediate.
  
  
• bycatch - 43 - Bycatch is defined as marine life caught during fishing operations that is not targeted. While most bycatch is thrown back into the ocean, it is almost always either dead, or too weak to survive. Biomass of bycatch may exceed that of targeted organisms in some fisheries.
  
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• carapace - 4 - A chitinous or bony shield covering the whole or part of the back of certain animals, such as many crustaceans and turtles.
  
  
• carbamate pesticides - 28 - A class of new-age pesticides that attack the nervous system of organisms.
  
  
• carbonates - 6 - Mineral compounds created by weathering of minerals by carbon dioxide and having a characteristic anionic structure. Sediments formed of carbonate minerals (e.g. limestone).
  
  
• carnivore - 1 - A flesh-eating animal or plant (e.g. sundew). A secondary consumer in a food chain.
  
  
• catadromous - 4 - A form of life cycle among fishes in which maturity is attained in fresh waters, and the adults migrate into the ocean to spawn. The common eel is an example.
  
  
• catadromy - - See catadromous.
  
  
• cation exchange capacity - 42 - The total of exchangeable cations that a soil can absorb; expressed in milliequivalents per gram to 100 grams of soil (or other exchanges, such as clay).
  
  
• caudal fin - 46 - The posterior fin of a fish, associated with the caudal bones of the tail.
  
  
• caviar - 26 - Processed salted roe of large fish (such as sturgeon).
  
  
• cheliped - 46 - Large, grasping claw in many crustaceans.
  
  
• chemical oxygen demand - 1 - The amount of oxygen taken up by the organic matter in a sample of water, expressed as parts per million of oxygen taken up from a solution of boiling potassium dichromate in two hours. The test is used to assess the strength of sewage and trade wastes.
  
  
• chemoautotrophs - - See chemosynthetic.
  
  
• chemolithotrophic - 40 - Describing an organism that is able to obtain its energy from the oxidation of inorganic compounds, including those of iron, nitrogen and sulphur.
  
  
• chemoorganotrophs - 15 - An organism which oxidizes chemical bonds for energy but requires organic carbon compounds to grow. A type of heterotroph.
  
  
• chemosynthetic - 1 - Applied to organisms that produce organic material from inorganic compounds using simple inorganic reactions as a source of energy. The process is chemosynthesis. For example, Thiobacillus obtains energy by oxidizing hydrogen sulphide to sulpher; other bacteria utilize energy from the oxidation of ferrous salts to their ferric form..
  
  
• chlorinated organics - 15 - Any organic chemical which includes chlorine atoms. A class of water pollutants. Chlorinated organic compounds, along with other halogenated organics, are believed to cause health risks such as cancer, endocrine system disruption, birth defects, compromised immune systems, and reduced fertility. Examples of chlorinated organics include trichloroethylene, ethylene dichloride, vinyl chloride, PCBs chlorobenzene, and many chlorinated solvents and biocides.
  
  
• chlorophenoxy - 20 - A class of herbicides that may be found in domestic water supplies and cause adverse health effects.
  
  
• chlorophyll - 1 - A green pigment, present in algae and higher plants, that absorbs light energy and thus plays a vital role in photosynthesis. Except in Cyanophyta (blue-green algae), chlorophyll is confined to chloroplasts. There are several types of chlorophyll, but all contain magnesium and iron. Some plants (e.g., brown algae, red algae, copper beach trees) contain additional pigments that mask the green of their chlorophyll.
  
  
• chlorphenolic acids - - See chlorophenoxy.
  
  
• chordate - 1 - A phylum (Chordata) of animals characterized by the possession, at least in the early stages of development, of a notochord ( a longitudinal supporting rod or vacuolated cells, enclosed in a firm sheath, lying just below the central nervous system), pharyngeal ('gill') pouches and a hollow, dorsal, nerve chord. The phylum includes the vertebrates (vertebrata) and the more primitive Protochordata (extinct forms lacking shells and vertebrae).
  
  
• chronic toxicity - 20 - The capacity of a substance to cause long-term poisonous health effects in humans, animals, fish, and other organisms.
  
  
• cilia - 46 - Hair-like appendages that can move together in a waving motion; used for locomotion in various one-celled animals and to produce a current in a fluid in higher animals or their larvae.
  
  
• ciliates - 7 - Any protozoan belonging to the class Ciliata and characterized by the presence of cilia throughout its life cycle. Known range, Upper Jurassic to the present.
  
  
• circumpolar - 41 - Located around one of the polar regions of earth.
  
  
• clearcutting - 42 - A method of forest cutting that removes the entire timber stand on the area cut.
  
  
• clotting factor - 40 - A group of substances present in blood plasma that, under certain circumstances, undergo a series of chemical reactions leading to the conversion of blood from a liquid to a solid state.
  
  
• clupeid - 43 - A member of the fish family Clupeidae which includes herrings, alewives, menhaden and sardines in the United States. Clupeids are generally deep-bodied, silvery fishes that have relatively large, easily-shed scales and often associate in large schools. They have rough scales, or scutes, along the ventral edge of the body, a single dorsal fin midway along the body, and a deeply forked caudal fin. In addition, clupeids have no lateral line and lack spines on all their fins.
  
  
• cnidarians - 2 - A phylum of aquatic, mostly marine animals, that are usually radially symmetrical. They have simple, two-layered bodies with only one opening to the gut (the coelenteron) and characteristically they bear stinging cells (nematoblasts) on tentacles. Colonial forms are common. This group includes sea-anemones, corals, and jellyfish. .
  
  
• coliform bacteria - 40 - A group of Gram-negative rod-shaped bacteria that are found in the vertebrate gastrointestinal tract; their presence in water is an indication of fecal pollution. Well known coliform bacteria include Escherichia coli and Salmonella.
  
  
• colloidal - - See colloids.
  
  
• colloids - 40 - Substances which exist as a system of two or more phases, with one (the dispersed phase) distributed in the other (the continuous phase). At least one of the phases has very small dimensions. Colloids include sols, emulsions, gels, foams and aerosols.
  
  
• comminuter (or) - 42 - A device that breaks solids into smaller pieces. For sewage treatment, to make solid wastes easier to treat.
  
  
• comminution - 40 - The act of breaking solids into smaller pieces; grinding; pulverization.
  
  
• compound eye - 38 - The eye of most insects and crustaceans, composed of many light sensitive units, the ommatidia, each with its own refractive system which forms a portion of the image.
  
  
• concretions - 2 - A solid mass of matter formed by the cohesion or coalescence of its constituent particles.
  
  
• conservation - 12 - The continuing protection and management of natural renewable resources- e.g. soil, water, wildlife, forest- in accordance with principles that assure their optimum economic and social enjoyment.
  
  
• convection - 38 - Heat transfer by the movement of a heated gas or liquid between regions of unequal density.
  
  
• convective cooling - - Cooling of a substance by the process of convection (see convection).
  
  
• copepods - 40 - Members of the crustacean subclass Copepoda. These are a group of small (0.5-2.0 mm), freshwater and marine crustacea that lack a carapace and compound eye. Some are free swimming and may form a major part of the plankton (e.g., Calanus on which herrings feed). Some are parasitic. Many have enlarged first antennae, used for swimming. Cyclops, with a single median eye, is common in ponds.
  
  
• coppice selection - 12 - Silvicultural systems in which the crops originate mainly from stools but sometimes in small part from suckers or seed, and the rotation is generally comparatively short.
  
  
• Cretaceous - 6 - In the geologic time scale, the final period of the Mesozoic era (after the Jurassic and before the Tertiary period of the Cenozoic era), thought to have covered the span of time between 135 and 65 million years ago.
  
  
• critical area - 42 - An area that, because of its size, location, condition, or value, must be treated with special consideration because of inherent site factors and difficulty of management.
  
  
• crustacean - 46 - One of group (Crustacea) of mostly aquatic (freshwater and marine) arthropods which breathe by means of gills; segmented body commonly covered by hard shell or crust. Group includes barnacles, copepods, crabs, shrimps, and lobsters.
  
  
• cryoturbation - 2 - The disturbance of material by frost action, frost heaving and differential mass movements.
  
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• DBH - 13 - Diameter Breast Height. The stem diameter of a tree measured at breast height (1.3 m above ground level).
  
  
• decapod - 40 - A member of the crustacean order Decapoda, characterized by the presence of five pairs of walking legs, the first of which may be modified as a grasping pincer. Includes crabs, shrimps, and lobsters.
  
  
• deltaic - 39 - Pertaining to or characterized by a delta; e.g. "deltaic sedimentation". Also, constituting a delta; e.g. a "deltaic coast".
  
  
• demersal - 43 - Describes animals that live near (but not in) water bottoms. Examples are flounder and croaker.
  
  
• demographic - 2 - The study of the age and sex structure, geographical distribution, rate of change of size, etc. of populations.
  
  
• dendritic - 9 - Of or pertaining to nerve fiber, typically branched, that conducts impulses toward the cell body of a neuron. In reference to drainage pattern, an arrangement of surface drainage in which streams branch randomly at almost any angle, resembling in plan the branching habit of trees.
  
  
• denitrification - 2 - The breakdown of nitrates by soil bacteria (e.g., Bacterium denitrifications), resulting in the release of free nitrogen. This process takes place under anaerobic conditions, such as are found in water-logged soil, and it reduces soil fertility.
  
  
• dentine - 46 - Hard, bone-like material that is major component of teeth. Mainly composed of type of calcium phosphate, dentine contains tiny tubules leading to soft pulp cavity deep inside tooth where there are nerves and blood vessels.
  
  
• dentition - 40 - The type, number, and arrangement of teeth in a species.
  
  
• depocenter - 7 - An area or site of maximum deposition; the thickest part of any specified stratigraphic unit in a depositional basin.
  
  
• depolymerization - - See depolymerize.
  
  
• depolymerize - 39 - To separate a polymer into simpler substances of the same percentage composition.
  
  
• deposition - 7 - The laying, placing, or throwing down of any material; specifically, the constructive process of accumulation into beds, veins, or irregular masses of any kind of loose rock material by any natural agent, such as the mechanical settling of sediment from suspension in water, the chemical precipitation of mineral matter by evaporation from solution, or the accumulation of organic material on the death of plants and animals.
  
  
• depredate - 38 - To prey upon, plunder or lay waste by force.
  
  
• depredation - 38 - The act of preying upon or destroying.
  
  
• desorbes - - See desorption.
  
  
• desorption - 40 - The removal of adsorbed atoms, molecules, or ions from a surface.
  
  
• detritivores - 9 - Organisms that live on dead and discarded organic matter; including large scavengers, smaller animals such as earthworms and some insects, and decomposers (fungi and bacteria).
  
  
• detritus - 45 - Small particles of organic matter resulting from the decay of dead animals and plants.
  
  
• diabase - 6 - A fine-grained, intrusive, crystalline rock consisting essentially of labradorite and pyroxene, and characterized by ophitic texture.
  
  
• diabase dikes - - See diabase. See dikes.
  
  
• diel - 38 - Referring to a 24-hour period that usually involves the day and an adjoining night; used most frequently in ecology.
  
  
• dikes - 6 - 1. A tabular body of igneous rock that cuts across the structure of adjacent rocks. 2. A wall or mound built around a low-lying area to prevent flooding.
  
  
• Dimorphic - 46 - Occurring in two forms as differently shaped shells of males and females or minerals identical in composition but having different crystal forms (calcite, aragonite). Sexual dimorphism describes a species in which male and female take two distinct, different forms.
  
  
• dinoflagellates - 15 - The members of this class of fire algae (Division Pyrrophyta) are a major component of marine algae. Dinoflagellates, many of which have a very strange appearance, usually move via two flagella that beat in grooves along their bodies. These organisms, which are often red in color, can produce strong toxins; they are responsible for the deadly red tides that can kill many fish and other marine organisms. One dinoflagellate, Gessnerium catenellum, often causes red tides on the Pacific coast and Gulf of Mexico. Filter-feeding molluscs such as clams and oysters sometimes become toxic to humans and other animals due to their eating dinoflagellates. Many species of dinoflagellates are bioluminescent; they produce a faint light when they are disturbed, thus sometimes causing nighttime waves breaking against the shore to be faintly luminous.
  
  
• dioxin - 2 - (2,3,7,-tetraclorodibenzo-p-dioxin) A by product formed during the preparation of the herbicide 2,4,5-T, and sometimes produced by the incineration of chlorinated organic compounds. It may also occur naturally and is distributed widely in the environment, except locally in extreme low concentrations. Substantial amounts were released by the industrial incident at Seveso in 1976. Exposure to high concentrations causes chloracne. Although dioxin is suspected of causing more lasting damage, including chromosome malformation, there is no conclusive evidence for this.
  
  
• dissolved organic carbon - 15 - Organic material in an aquatic medium having a least dimension smaller than 0.45 micron (passes through a 0.45 micron filter).
  
  
• dorsal fin - 46 - Pertaining to fish, the fin on the back or upper surface.
  
  
• down warping - 7 - Subsidence of a regional area of the Earth's crust, as in an orogenic belt or a cratonic basin.
  
  
• draping - 7 - The general structural concordance of warped strata, lying above a limestone reef or other hard core, to the upper surface of that reef or core, due to initial dip, to differential compaction, or to both.
  
  
• drift fences - 12 - Any fence designed to prevent drift, constituting a barrier rather than an enclosure, is termed a drift fence.
  
  
• duff - 42 - The more or less firm organic layer on top of mineral soil, consisting of fallen vegetative matter in the process of decomposition, including everything from pure humus below the litter on the surface; a general, nonspecific term.
  
  
• duff depth - - The depth of the duff layer (see duff).
  
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• ebb - 38 - To decline or recede. Also see ebb tide.
  
  
• ebb tide - 46 - That stage of the tide when water is outgoing, receding, or falling; the period between high water and a succeeding low water.
  
  
• echinoderms - 2 - A phylum (Echinodermata) of marine invertebrate animals, most of which exhibit five-rayed symmetry as adults. The skin bears calcareous plates. The coelom is intricate and large, with extensions into the many tube feet which protrude from the body surface. The pelagic larvae have affinities with those of the Hemichordata. Includes sea stars, brittle stars, sand dollars and sea cucumbers.
  
  
• ecological characterization - 32 - A study which compiles existing available information utilizing a holistic approach that identifies functional relationships among natural processes and components of ecosystems. This study is designed primarily to integrate environmental and socioeconomic information useful for planning , impact assessment, and analysis, and to identify research needs.
  
  
• ecotonal - - See ecotone.
  
  
• ecotone - 7 - A transition zone that exists between two ecologic communities. Members of both communities may compete within this zone, yielding an apparent enrichment known as the edge effect.
  
  
• edge habitat - 42 - The transitional zone where one cover type ends and another begins.
  
  
• effluent - 2 - Generally, any fluid emitted by a source. More specifically, a waste fluid (usually liquid) produced by an agricultural or industrial process.
  
  
• egress - 38 - The act of going out from a place of actual or seeming confinement; emergence.
  
  
• electron acceptors - - Substance that accepts or receives electrons in an oxidation-reduction reaction, becoming reduced in the process.
  
  
• elongate - 26 - Stretched out, slender. To make or become longer.
  
  
• embankment - 7 - 1. A narrow depositional feature, such as a spit, barrier, or bar, built out from the shore of a sea or lake by the action of waves and currents that deposit excess material at its deep end; it may be emerged or submerge. 2. A dike, seawall or other linear structure of earth built to retain water or tailings, or to carry a roadway or railroad.
  
  
• endangered species - 42 - Any species that is in danger or extinction through all or significant portion of its range; a species of native fish, wildlife, or plants threatened with extinction because its habitat is threatened with destruction, drastic modification, or severe curtailment, or because of over-exploitation, disease, predation, or other factors affecting its survival.
  
  
• endemic - 40 - 1. Describing a plant or animal species that is restricted to one or a few localities in its distribution. 2. Describing a disease or a pest that is always present in an area.
  
  
• endogenous - 7 - Originating or produced from within. Said of a geologic process, or of its resultant feature or rock, that originates within the Earth, e.g. volcanism, volcanoes, extrusive rocks. The term is also applied to chemical precipitates, e.g. evaporites, and to ore deposits that originate within the rocks that contain them. In biology, describing a substance, stimulus, organ, etc. that originates from within an organism.
  
  
• endotoxin - 40 - A poisonous substance produced by a living organism (usually a bacteria) which resides inside the cell and is released only on disintegration of the cell.
  
  
• energetics - 4 - The branch of study dealing with the systematic description of the energy conversion and transfer processes which take place within a physical system
  
  
• Entisols - 2 - Young soils, characterized by dominance of mineral soil materials and absence of distinct horizons.
  
  
• environmental sustainability - 20 - Maintenance of ecosystem components and functions for future generations.
  
  
• Eocene - 7 - An epoch of the early Tertiary period, after the Paleocene and before the Oligocene; also, the corresponding worldwide series of rocks. It is sometimes considered to be a period, when the Tertiary is designated as an era.
  
  
• eolian - 8 - Referring to mineral particles moved and sorted by wind, usually fine sands and coarse silt; also aeolian.
  
  
• epifauna - 15 - Animals living on the surface of the substrate.
  
  
• epiphyte - 2 - A plant that grows on the outside of another plant, using it for support only and not as a source of nutrients. An example is lichen on trees.
  
  
• epiphytic - - Of or pertaining to an epiphyte. See epiphyte.
  
  
• epizootiology - 39 - Veterinary science treating of epizootic diseases.
  
  
• equilibrium state - 44 - In ecology, the condition in which a population or community is maintained with only minor fluctuations in composition over an extended period of time; sometimes called dynamic equilibrium. In chemistry, refers to the state of a reversible chemical reaction in which the forward and reverse reactions are taking place at the same rate.
  
  
• ER-L - 37 - Effects Range - Low. ER-L values are sediment quality guidelines for potentially toxic substances based upon empirical analyses of matching chemical and biological data. The ER-L values represented chemical concentrations below which adverse effects on sediment-dwelling fauna were rarely observed, and, therefore, estimated the low end of the effects range.
  
  
• ER-M - 37 - Effects Range - Median. ER-M values are sediment quality guidelines (SQG's) for potentially toxic substances based upon empirical analyses of matching chemical and biological data. The ER-M values represented the chemical concentrations toward the middle of the effects range and above which adverse effects on sediment-dwelling fauna would be likely to occur.
  
  
• estuarine - - Pertaining to an estuary (see estuary).
  
  
• estuary - 46 - A partially enclosed area where freshwater from a river or stream comes into contact with salty oceanic water; characterized by water whose salt content is between that of fresh and marine environments, tidal effects are evident, and by a population of animals and plants which is distinct from either the freshwater or oceanic environments.
  
  
• Euclidian zoning - - See zoning, euclidian.
  
  
• euhaline - 2 - Applied to full-strength seawater or to water of nearly equivalent salinity (i.e. to water containing about 35 parts salt per thousand parts of water (ppt)). Coastal waters have a salinity of about 30 ppt.
  
  
• eukaryotic - 9 - A cell having a membrane-bound nucleus, membrane-bound organelles, and chromosomes in which DNA is combined with special proteins; an organism composed of such cells.
  
  
• euryhaline - 7 - Said of marine organisms that tolerate a wide range of salinities.
  
  
• eustatic sea level - 7 - Pertaining to worldwide changes of sea level that affect all the oceans due to absolute changes in the quantity of seawater. Eustatic changes may have various causes, but the changes dominant in the last few million years were caused by additions of water to, or removal of water from, the continental icecaps.
  
  
• eutrophic - 2 - Applied to waters that are rich in plant nutrients and therefore highly productive; the large number of planktonic organisms (see plankton) sometimes rendering them cloudy. Eutrophic water bodies are frequently characterized by a deficiency of oxygen because of the decay of plant material.
  
  
• eutrophication - 6 - The process whereby a body of water becomes highly productive of aquatic plants, such as algae, due to the input of large quantities of nutrients. Eutrophication may happen naturally, but it often results from pollution. See eutrophic.
  
  
• evapotranspiration - 2 - The combined evaporation of water from the soil surface and transpiration from plants.
  
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• facies - 2 - The sum total characteristics of a rock (e.g., its texture, mineral or organic composition, form and structure) from which its environment of deposition and subsequent history can be deduced.
  
  
• facultative anaerobes - 40 - Organisms, such as bacteria, fungi and some internal parasites, that are able to alter their metabolism to grow in either the presence or absence of oxygen..
  
  
• facultative anaerobic bacteria - - See facultative anaerobes.
  
  
• faults - 2 - In geology, a fracture in the Earth along which there has been displacement of the sides relative to one another parallel to the fault plane. Faults are classified by the relative motions of the faulted blocks as: (a) dipnslip faults (e.g., normal faults, reverse faults, and thrusts) in which the movement is parallel to the dip of the fault plane; (b) strike-slip faults (e.g., wrench, tear and transform faults) in which movement is parallel to the strike of the fault plane; and (c) oblique slip faults in which movement is at an appreciable angle to both dip and strike. .
  
  
• fauna - 2 - The animals of a particular region or period of time.
  
  
• fecal coliform - 42 - A group of bacteria normally present in large numbers in the intestinal tracts of humans and other warm-blooded animals. Frequently used as an indicator of sewage pollution.
  
  
• Federal Register - - The Federal Register is the official newspaper of the United States government. Issued daily by the U.S. Government Printing Office (excepting weekends and official holidays), it is the vehicle through which all federal agencies publish their regulations and legal notices. The size of the Federal Register varies from 200 to 600 pages (or more), depending on the number and length of announcements. The Federal Register is comprised of two major publications, the daily Federal Register and the annually revised Code of Federal Regulations (CFR). The daily Federal Register and CFR work together to provide an up-to-date version of any federal agency regulation. The Federal Register is published every Federal working day and includes rules and regulations that businesses must follow.
  
  
• FEMA - 22 - Federal Emergency Management Agency- federal agency that implements the National Flood Insurance Program and provides disaster assistance to coastal states and local governments. Key authorizing legislation includes National Flood Insurance Act, Flood Disaster Protections Act and the Stafford Disaster Relief and Emergency Assistance Act. FEMA's stated mission is to reduce loss of life and property and protect our nation's critical infrastructure from all types of hazards through a comprehensive, risk-based, emergency management program of mitigation, preparedness, response and recovery..
  
  
• filter feeder - 46 - An animal that obtains food by straining organisms from water passed through some portion of its body; e.g. corals, mussels, sponges, and baleen whales.
  
  
• filter strips - 42 - A strip or area of vegetation for removing sediment, organic material, organisms, nutrients, and chemicals from runoff or wastewater.
  
  
• filter-feeding - - See filter feeder.
  
  
• finfish - 46 - True fish as opposed to shellfish.
  
  
• flagellates - 7 - Organisms, especially protozoans or algae, that bear flagella.
  
  
• flatfish - 46 - Member of fish order Heterosomata. It swims or lies on one side of its body; sides are greatly flattened and compressed. As young flatfish mature, lower eye "migrates" to upper side so that both eyes are on one side of head. Mainly marine animals, flatfish include such commercially valuable food fish as flounder, sole and halibut.
  
  
• flexure - 7 - A bend or turn; an act of bending. In Geology, a hinge.
  
  
• flood tide - 46 - Incoming or rising tide.
  
  
• floodplain - 2 - A relatively level part of a river valley, adjacent to the river channel, formed from sediments deposited by the river during periods of flooding or as river meanders cut into the leading edge of the channel, deposit silt at the trailing edge, and so advance across level ground.
  
  
• floodway - 42 - A channel, either natural, excavated, or bounded by dikes and levees, used to carry excessive flood flows to reduce flooding. Sometimes considered to be the transitional area between the active channel and the floodplain.
  
  
• fluvial - 8 - Related to stream or river flow and its associated erosional/depositional processes.
  
  
• flux - 42 - The rate of movement of liquid, particles, or energy over a given surface area; the act of flowing.
  
  
• fluxes - - See flux.
  
  
• food webs - 45 - The interlocking pattern interconnecting the sequences of food chains. In a food web a particular organism may feed at more than one trophic level.
  
  
• foot - 46 - In ordinary usage, terminal portion of walking appendage that contacts substrata. In molluscs, ventral surface of body, variously modified in different groups for creeping or digging or to serve as prehensile arms. Also, a unit of measurement in the United States system equal to 12 inches (30 cm).
  
  
• forb - 2 - A herbaceous plant, not including grasses and those resembling grasses (e.g., sedges).
  
  
• forbs - 2 - All herbaceous plants, except for grasses and those resembling grasses (e.g., sedges).
  
  
• fungivorous - 36 - Feeding on mushrooms or fungi.
  
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• gastropod molluscs - 4 - One of a class (Gastropoda) of molluscs in which the animals possess a distinct head, generally with eyes and tentacles, and a broad flat foot and usually are enclosed in a spiral shell.
  
  
• genus - 40 - A category used in the binomial classification system of organisms that consists of a number of similar or closely related species. Similar genera are grouped into families.
  
  
• geographic information system (GIS) - 20 - A system of computer hardware and software designed for storing, manipulating, analyzing, and displaying data in a geographic context.
  
  
• geomorphic - 6 - Pertaining to the form of the earth or its surface features. Pertaining to geomorphology (see geomorphology).
  
  
• geomorphology - 8 - The study of landforms and their origin.
  
  
• geotextiles - 31 - Any woven material used with rock or soil in a manmade product or structure.
  
  
• gig - 38 - A fish spear with two or more barbed prongs (fishgig).
  
  
• gigging - 38 - The act of using a gig (see gig) to capture fish.
  
  
• gill net - 46 - Net which is set upright in water to capture fish. Gills of fish become entangled in its meshes.
  
  
• gill raker - 46 - One of small, bony structures on inside edge of fish's gill arches which support gills; they prevent solid particles from injuring gills and stop food from escaping with the water which flows in through fish's mouth, over gills and out again through opening in animal's skin.
  
  
• GIS - - An acronym for Geographic Information System (see geographic information system).
  
  
• glacioeustatic - 4 - Pertaining to the worldwide changes in sea level produced by the successive withdrawal and return of water in the oceans accompanying the formation and melting of ice sheets
  
  
• gobblers - 38 - Male turkeys.
  
  
• granivore - 2 - An animal that eats mainly grain.
  
  
• granivorous - - Pertaining to a granivore (see granivore).
  
  
• greenbelt - 38 - An extensive area of largely undeveloped or sparsely occupied land surrounding a community; often associated with a community program to contain development, preserve the character of the countryside and community and provide open space.
  
  
• greenhouse effect - 2 - Worldwide changes in climate and sea levels caused by a warming of the atmosphere due to the release of gases, principally carbon dioxide, which are transparent to short-wave radiation, but absorb radiation at longer wavelengths. Thus the gases form a 'blanket' trapping outgoing heat, much as the glass or plastic does in a greenhouse. The burning of fossil fuels and clearance forests, releasing carbon dioxide held in forest soils, has increased the atmospheric concentration of carbon dioxide..
  
  
• greenspace - - See greenbelt.
  
  
• greenways - - See greenbelt.
  
  
• ground water - 44 - Water within the earth that supplies wells and springs. Specifically, water in the zone of saturation where all openings in soils and rocks are filled, the upper surface of which forms the water table.
  
  
• Grylloblattaria - 14 - (Grylloblatta) An order of insects secondarily without wings, with incomplete metamorphosis, small or absent eyes, and fairly long, filiform antennae.
  
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• halocline - 4 - Layer of water in which salinity change is maximal.
  
  
• halophilic - 4 - Said of an organism that prefers a saline environment.
  
  
• halophytes - 40 - Plants that naturally grow in salty water or soil with a high salt content.
  
  
• halophytic - - Of or pertaining to halophytes. See halophytes.
  
  
• heavy metals - 44 - Metals having a specific gravity (i.e., weight in comparison to weight of an equal volume of water) of 5.0 or over, and generally toxic in relatively low concentrations to plant and animal life. Such metals can persist in animal tissue and are capable of increasing in concentration as they pass upward through the food chain. Major sources of heavy metal contamination are pesticides, limestone, and phosphate fertilizers, manures and sewage sludges, and mine wastes. Examples include lead, mercury, cadmium, and arsenic.
  
  
• hemicellulose - 40 - A large polysaccharide which helps give structure to plant cells. Along with pectin, it forms a matrix in which cellulose fibrils from the plant cell walls are embedded..
  
  
• herbaceous - 2 - (herbaceous plant). A non-woody vascular plant having no parts that persist above the ground.
  
  
• hermaphroditic - 46 - Possessing both male and female reproductive organs.
  
  
• herpetofaunal - - Referring to reptiles and amphibians.
  
  
• herpetology - 38 - The scientific description of reptiles and amphibians.
  
  
• heterocercal tail - 46 - Unsymmetrical tail, upper lobe of which is often longer than lower. Backbone may extend into upper lobe or merely curve upward before reaching it as in mudfish.
  
  
• heterotroph - 9 - An organism that must feed on organic materials formed by other organisms in order to obtain energy; in contrast to autotroph. Animals, fungi, and many unicellular organisms are heterotrophs.
  
  
• heterotrophic - - See heterotroph.
  
  
• heterotrophic bacteria - 42 - Bacteria that are dependent on organic material for food (see heterotroph).
  
  
• heterotrophic protists - - See heterotrophic. See protists.
  
  
• high water mark - 4 - An established reference mark on a structure or natural object which indicates the maximum observed stage of tide.
  
  
• highstand - 7 - The interval of time during one or more cycles of relative change of sea level when sea level is above the shelf edge in a given local area.
  
  
• histopathology - 15 - The science concerned with the study of microscopic changes in diseased tissues.
  
  
• Histosols - 2 - Taxonomic soil classification. Organic soils developed largely by the accumulation of organic matter in a waterlogged site. Most Histosols are saturated or nearly saturated most of the year and include bog soils, half-bog and peat soils.
  
  
• Holocene - 7 - An epoch of the Quaternary period, from the end of the Pleistocene, approximately 10,000 years ago, to the present time; also, the corresponding rocks and deposits. When the Quartenary is designated as an era, the Holocene is considered to be a period.
  
  
• horizon - 2 - An approximately horizontal layer within a solid or sediment that is clearly distinct and distinguishable from the layers above and below it.
  
  
• humate - 7 - A salt or ester of humic acid.
  
  
• humic - 7 - Pertaining to or derived from humus (see humus).
  
  
• humus - 2 - The more or less decomposed organic matter in the soil. Besides being the source of most of the mineral salts needed by plants, humus improves the texture of the soil and holds water, so reducing the loss of nutrients by leaching. Mild humus (mull) is produced in soil containing abundant earthworms where decay is rapid.
  
  
• hybrid - 2 - An organism produced by crossing parents of different taxa (e.g., different species, subspecies or varieties) and thus different genotypes. Hybrids are often sterile.
  
  
• hydrocarbons - 2 - Strictly, chemical compounds composed only of hydrogen and carbon; more loosely, many organic (i.e.,. carbon-based) compounds that contain other elements (e.g., fossil fuels are sometimes described as hydrocarbon fuels).
  
  
• hydrochemistry - 39 - The chemistry of water, especially that of natural waters.
  
  
• hydrography - 4 - That science that deals with the measurement and description of the physical features of the oceans, seas, lakes, rivers, and adjoining coastal areas, with particular reference to their use for navigational purposes.
  
  
• hydrologic unit - 28 - A geographic area representing part or all of a surface drainage basin or distinct hydrologic feature.
  
  
• hydrological - 42 - Pertaining to the science dealing with the properties, distribution, and circulation of water, specifically the study of water on the surface of the land, in the soil and underlying rocks, and in the atmosphere , particularly with respect to evaporation and precipitation.
  
  
• hydrological units - - See hydrologic unit.
  
  
• hydrolysis - 6 - A decomposition reaction involving water; a reaction in which water reacts with a substance (frequently silicate minerals) to break it into components.
  
  
• hydroperiod - 39 - The period during which the water table occupies a definite vertical zone or layer next to the surface.
  
  
• hydrophytic - 40 - Of or pertaining to a plant that typically lives in water or very wet soils.
  
  
• hydrosphere - 7 - The waters of the Earth, as distinguished from the rocks (lithosphere), living things (biosphere), and the air (atmosphere). Includes the waters of the ocean; rivers, lakes, and other bodies of surface water in liquid form on the continents; snow, ice, and glaciers; and liquid water, ice, and water vapor in both the unsaturated and saturated zones below the land surface. Included by some, but excluded by others, is water in the atmosphere, which includes water vapor, clouds, and all forms of precipitation while still in the atmosphere.
  
  
• hyphae (tubes) - 2 - In Fungi, one of the mass of filaments that make up a mycelium. Hyphae are tubular and branched and may have crosswalks.
  
  
• hypoxia - 40 - A deficiency of oxygen in body tissues, which can result from living in an oxygen-deficient environment.
  
  
• hypoxic - - See hypoxia.
  
  
• hypsography - 2 - The science of measuring or describing elevation above or below a datum (usually sea level).
  
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• ichthyoplankton - 5 - The small fish (mostly larval forms) that float or drift in water.
  
  
• impoundment - 6 - The process of forming a lake, or pond by a dam, dike or other barrier; also, the body of water so formed.
  
  
• impoundments - - See impoundment.
  
  
• Inceptisols - 2 - In soil classification, young soils with horizons weakly developed, occurring in variable climates, including brown earths and tundra soils.
  
  
• indicator species - 2 - Species whose presence indicates certain environmental conditions.
  
  
• indicator taxa - - See indicator species.
  
  
• indigenous - 2 - Native or original to an area.
  
  
• indigo - 38 - A blue dye obtained from the decomposition of any of several plants.
  
  
• infauna - 34 - Animals living within a soft sediment and being large enough to displace sediment grains.
  
  
• infaunal - - See infauna.
  
  
• inferior mouth - 29 - The type of mouth that opens on the ventral surface (like sturgeon).
  
  
• influent - 42 - Flowing in (e.g., influent water). Water that flows into other bodies of water (a stream into a lake) or into the ground through sinkholes or other openings.
  
  
• infrastructure - 42 - The services and facilities that are an integral part of the life of an urban community; includes transport facilities and communications, power, shopping facilities, housing, schools, and recreational facilities.
  
  
• ingress - 39 - Act of entering; entrance; as, the ingress of air into the lungs or fish into an estuary.
  
  
• inlet - 4 - A short, narrow waterway connecting a bay or lagoon with the sea. When it is a natural inlet maintained by tidal currents, the name tidal inlet or tidal outlet is applied.
  
  
• inoculation - 39 - The introduction of a pathogen or antigen into a living organism to stimulate the production of antibodies.
  
  
• inorganic - 7 - Pertaining to or relating to a compound that contains no carbon.
  
  
• interfluves - 7 - The area between rivers; esp. the relatively undissected upland or ridge between two adjacent valleys containing streams flowing in the same general direction
  
  
• intertidal - 4 - The benthic zone between high and low water marks. According to some authorities the benthic zone between the shore and water depths of approximately 100 fathoms (200 meters).
  
  
• intertidal zone - 4 - Also called the littoral zone. Generally considered to be the zone between mean high water and mean low water levels.
  
  
• invasive species - 15 - A species which when introduced to a new area spreads rapidly disrupting and replacing native species.
  
  
• invertebrate - 42 - Referring to an animal without an internal skeletal backbone composed of vertebra, for example, insects molluscs, crayfish.
  
  
• invertebrates - 42 - See invertebrate.
  
  
• ion - 38 - An atom, group of atoms or molecule that has acquired a net electric charge by gaining or losing electrons from a neutral configuration.
  
  
• ionic form - - See ion.
  
  
• isohalines - 27 - In physical oceanography, a contour of constant salinity..
  
  
• isomorphous - 36 - Having the property of crystallizing in the same or closely related geometric forms; said especially of two compounds or groups of compounds of different elements, but analogous composition.
  
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• Jurassic - 7 - The second period of the Mesozoic era (after the Triassic and before the Cretaceous), thought to have covered the span of time between 190 and 135 million years ago; also, the corresponding system of rocks. It is named after the Jura Mountains between France and Switzerland, in which rocks of this age were first studied.
  
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• Kjeldahl nitrogen - - See Kjeldahl's method.
  
  
• Kjeldahl's method - 10 - A method for measuring the percentage of nitrogen in an organic compound. The compound is boiled with concentrated sulphuric acid and copper(II) sulphate catalyst to convert any nitrogen to ammonium sulphate. Alkali is added and the mixture heated to distil off ammonia. This is passed into a standard acid solution, and the amount of ammonia can then be found by estimating the amount of unreacted acid by titration. The amount of nitrogen in the original specimen can then be calculated. The method was developed by a Danish chemist Johan Kjeldahl (1849-1900).
  
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• labile - 6 - Constantly undergoing or likely to undergo chemical change; unstable; said of rocks, minerals and plant and animal matter that is easily decomposed.
  
  
• lability - - See labile.
  
  
• lacustrine - 6 - Of or pertaining to a lake or a region of lakes, or of plants and animals growing in or inhabiting lakes.
  
  
• larvae - 4 - Plural form of larva. Embryos which become self-sustaining and independent before assuming the characteristic features of parents.
  
  
• lateral line - 4 - A system of sense organs possessed by fishes, usually arranged in a single series along the side of the body, and functioning in part to detect low frequency vibrations such as those produced by local disturbances in the water.
  
  
• laws of thermodynamics - 2 - Laws describing relationships between heat and mechanical forms of energy.
  
  
• laymen - 38 - Someone who does not belong to a particular profession or specialty.
  
  
• life histories - - See life history.
  
  
• life history - 40 - The complete sequence of events undergone by organisms of a particular species from the fusion of gametes in one generation to the same stage in the following generation.
  
  
• ligand - 38 - A group, ion, or molecule coordinated to the central atom in a coordination complex.
  
  
• lignin - 38 - An amorphous substance or mixture that together with cellulose forms the woody cell walls of plants and the cementing material between them and thus gives them added mechanical strength. Any of various usually brown substances derived from the breakdown of wood.
  
  
• lignocellulose - 14 - Essential constituent of woody tissue, lignin and cellulose combined.
  
  
• lignocellulosic - - See lignocellulose.
  
  
• limnetic - 7 - Relating to the pelagic or open part of a body of fresh water (having salinity less than 0.5 parts per thousand).
  
  
• liposolubility - 38 - Liposoluble. Refers to a substance that is soluble in fats or oils.
  
  
• lithogenous - 14 - Rock-forming, or rock-building, as certain corals.
  
  
• lithosphere - 7 - The solid portion of the Earth, as compared with the atmosphere and the hydrosphere..
  
  
• lowcountry - 36 - A region whose level is lower than that of the surrounding country. Local term for the South Carolina coastal area south of Georgetown.
  
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• macrobenthic - - See macrobenthos.
  
  
• macrobenthos - 34 - Organisms (animals or plants) living in or on aquatic substrates and whose shortest dimension is greater than 0.5 mm (usually large enough to be seen with the unaided eye).
  
  
• macrofauna - 34 - Animals whose shortest dimension is greater than 0.5 mm (usually large enough to be seen with the unaided eye).
  
  
• macrophyte - 34 - An individual alga or aquatic plant large enough to be seen with the unaided eye.
  
  
• mafic - 6 - Term used to describe an igneous rock composed chiefly of dark-colored iron and magnesium minerals; also, said of those minerals..
  
  
• mafic-ultramafic intrusions - - See mafic.
  
  
• mantle - 6 - In biology, portion of body wall in molluscs that lines shell and contains shell-secreting glands. In geology, the zone of the earth below the crust and above the core.
  
  
• mantle cavity - 46 - Space containing respiratory organs between mantle and body of a mollusc or brachiopod.
  
  
• mariculture - 46 - Controlled cultivation of marine plants or animals (similar to aquaculture, but for marine species only).
  
  
• marl - 2 - A calcareous mudstone formed under aquatic conditions.
  
  
• megalopae - - Plural of megalops (see megalops).
  
  
• megalops - 46 - In crustaceans, larval stage just before adult stage of marine crabs. Transitional stage between larval and juvenile forms.
  
  
• meiofauna - 34 - Animals whose shortest dimension is less than 0.5 mm but greater than or equal to 0.1 mm.; the size class of transition from micro- to macrofauna.
  
  
• mesofauna - 40 - Small soil-dwelling animals such as worms and insects.
  
  
• mesohaline - 28 - Term to characterize waters with salinity of 5 to 18 0/00 (parts per thousand), due to ocean-derived salts.
  
  
• mesotidal - 7 - Said of a coast with a tidal range of 2 to 4 meters.
  
  
• Mesozoic - 7 - An era of geologic time, from the end of the Paleozoic to the beginning of the Cenozoic, or from about 225 to about 65 million years ago.
  
  
• metabolism - 2 - The sum of all chemical reactions occurring within a cell or organism.
  
  
• micro - 47 - A prefix denoting very small or minute in size. In the metric system, a prefix meaning 1/1,000,000. A microgram is 1/1,000,000 of a gram.
  
  
• microalgae - - Microscopic algae (see algae).
  
  
• microbiota - 38 - The microscopic flora and fauna of a region.
  
  
• microsiemens - 30 - One millionth of a siemens (practical unit of conductance equal to the reciprocal of the ohm and formerly called a mho). The microsiemens is the practical unit of measurement for conductivity, and is used to approximate the total dissolved solids content of water..
  
  
• microzooplankton - - Microscopic zooplankton (see zooplankton).
  
  
• middens - 42 - In archeology, an accumulation of waste materials that mark the site of a dwelling, usually kitchen midden.
  
  
• Miocene - 7 - An epoch of the upper Tertiary period, after the Oligocene and before the Pliocene; also, the corresponding worldwide series of rocks. It is considered to be a period when the Tertiary is designated an era.
  
  
• mitigation - 38 - Reduction of the adverse effects of an action.
  
  
• Mollisols - 2 - Grassland soils characterized by a thick, organic-rich surface layer, covering a wide variety of profiles with strong structural development, including the brown chestnut, chernozem, prairie (brunizem), red prairie, rendzina and brown forest soils.
  
  
• mollusks - 2 - Also spelled molluscs. Members of the phylum Mollusca, a large phylum of soft-bodied, unsegmented, mainly aquatic animals, most of which have calcareous shells. Locomotion of an individual is usually by means of a large muscular 'foot'.
  
  
• molt - 38 - To cast or shed periodically the outer body covering, including hair, feathers, horns, outer skin or shell in a process of growth or renewal. Permits an increase in size in invertebrates such as crabs.
  
  
• monoculture - 46 - The cultivation of a crop of the same type in successive years to the exclusion of all other crops.
  
  
• monosulfides - 38 - A compound of sulfur analogous to an oxide in which the sulfur molecule contains a single atom of sulfur.
  
  
• monotypic - 15 - Including a single representative; containing only one taxon of the next lower rank (e.g., applied to a family containing only one genus or a genus with only one species).
  
  
• mucilage - 38 - A gelatinous substance that contains protein and polysaccharides secreted by certain plants or plant organs.
  
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• NPDES - 20 - National Pollutant Discharge Elimination System. A provision of the Clean Water Act which prohibits discharge of pollutants into waters of the United States unless a special permit is issued by EPA, a state, or, where delegated, a tribal government on an Indian reservation..
  
  
• natural areas - 7 - An area of land or water that has retained its wilderness character, although not necessarily completely natural and undisturbed, or that has rare or vanishing flora, fauna, archaeological , scenic, historical, or similar features of scientific or educational value; e.g. a "research natural area" where natural processes are allowed to predominate and which is preserved for the primary purposes of research and education.
  
  
• neap tide - 4 - Tide of decreased range which occurs about every two weeks when the moon is in quadrature (not new or full).
  
  
• nematodes - 2 - Members of the phylum Nematoda, the roundworms. A very large group (usually regarded as a phylum) of unsegmented worms without a coelom and usually pointed at both ends. Some are free-living in soil or water and play an important role in recycling of organic matter. Many are parasites, (e.g., potato root eelworm, sugarbeet eelworm, pinworms of vertebrates).
  
  
• nemerteans - 2 - Members of the phylum Nemertea (Nemertinea, Nemertini), the probiscis worms and ribbon worms. A small phylum of flattened, unsegmented mainly marine animals with a large, reversible probiscis, used for catching prey.
  
  
• neotropical - 45 - The area embracing South America, Central America, the West Indies, and the coasts of Mexico; Mexico being for the most part a transition tract between the Neotropical and the Nearctic.
  
  
• nephelometric - 15 - Measure of the concentration or size of suspended particles (cloudiness) based on the scattering of light transmitted or reflected by the medium.
  
  
• neritic - 2 - Applied to the parts of the sea lying over the continental shelf, usually less than 200 meters deep.
  
  
• nitrate - 2 - A salt (NO3-), or ester of nitric acid (HNO3). Nitrates are the chief source of the nitrogen used by plants in their synthesis of proteins (see nitrification). They are highly soluble in water and so prone to leaching from land supporting vegetation. Where nitrogen is supplied as a soluble fertilizer the rate of leaching may increase, leading to nitrate pollution.
  
  
• nitrifiaction - 2 - The conversion by aerobic soil bacteria (nitrifying bacteria) of organic nitrogen compounds into nitrates (NO3-), which can be absorbed by green plants. Dead organic matter is broken into substances such as ammonia, which reacts with calcium carbonate. Ammonium carbonate is oxidized to nitrite (NO2-) by nitrite bacteria (Nitrosomonas), then into nitrate.
  
  
• nitrite - 2 - A salt (NO2-) or ester of nitric acid (HNO3).
  
  
• nitrogen fixation - 2 - Any reaction as a result of which gaseous nitrogen forms a soluble compound that is available as a plant nutrient either directly or after it has engaged in further reactions. In soils, certain nitrogen-fixing bacteria and Cyanophyta utilize gaseous nitrogen and release it for the use of other organisms as metabolic waste products or as a decay product following their death. Some nitrogen-fixing bacteria are free-living in the soil; others live symbiotically in the root nodules of legume plants. .
  
  
• non-point source pollution - 42 - Pollution arising from an ill-defined and diffuse source, such as runoff from cultivated fields, grazing land, or urban areas.
  
  
• nonpoint source runoff - - See non-point source pollution.
  
  
• non-point sources - 42 - Sources of pollution that cannot be defined as discrete points, such as areas of crop production, timber, surface mining, disposal of refuse, and construction.
  
  
• non-polar - 38 - Describing a molecule in which two or more atoms with incomplete outer shells combined to share an electron, thus achieving greater stability. Molecules having no separation of centers of positive and negative electrical charge that would make the molecule assume certain orientations more than other in an electric field.
  
  
• nontidal - 4 - Areas of waterbodies not exhibiting changes in height or current as a result of tidal influence. Also, any current that is caused by other than tide-producing forces. This includes all permanently established oceanic currents as well as all temporary ocean currents generated by winds.
  
  
• nursery habitat - 16 - The complex environmental area for maturation of young organisms that may migrate out of the habitat of maturity; nutrition and protection from predators are afforded by plants and their by-products.
  
  
• nutrient loadings - 42 - The amount of nutrients (e.g., nitrogen and phosphorous) entering into a defined geographic area, such as a watershed.
  
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• obligate aerobes - 40 - Organisms that must use free oxygen for respiration.
  
  
• obligate anaerobes - 41 - A microorganism which can not use free oxygen for respiration and finds the presence of oxygen harmful.
  
  
• Odonata - 2 - An order of large, often highly colored insects (division: Exopterygota) whose members have two similar pairs of membranous wings. The adults are strong fliers, preying on insects which they seize while on the wing. The nymphs are aquatic and predatory with a lower lip (labium) modified as an extensible, prehensile mask used to catch prey. Includes dragonflies and damselflies..
  
  
• offlap - 7 - The progressive offshore regression of the updip edges of sedimentary units within a conformable sequence of rocks, in which each successively younger unit leaves exposed a portion of the older unit on which it lies. Also, the successive contraction in the lateral extent of strata (as seen in an upward sequence) due to their being deposited in a shrinking sea or on the margin of a rising landmass.
  
  
• Oligocene - 7 - An epoch of the early Tertiary period, after the Eocene and before the Miocene; also, the corresponding worldwide series of rocks. It is considered to be a period when the Tertiary is designated as an era.
  
  
• oligochaetes - 2 - Members of a class (Oligochaeta) of mostly terrestrial and freshwater worms (Annelida) whose members (e.g., earthworm) have few bristles (chaetae), no muscular, lateral projections (parapodia) along the body and no specialized head appendages. Oligochaetes are hermaphrodites, and the eggs develop inside a cocoon. Earthworms are very important in the maintenance of soil fertility because their tunnels aerate and drain the soil, and some species continually bring to the surface fresh soil containing humus. .
  
  
• oligohaline - 2 - Applied to slightly brackish waters whose salinity is 0.5 - 5 parts per thousand.
  
  
• omnivore - 2 - An animal which eats both plant and animal food items (e.g., raccoon, man).
  
  
• onlap - 7 - An overlap characterized by the regular and progressive pinching out, toward the margins or shores of a depositional basin, of the sedimentary units within a conformable sequence of rocks, in which the boundary of each unit is transgressed by the next overlying unit and each unit in turn terminates farther from the point of reference. Also, the successive extension in the lateral extent of strata (as seen in an upward sequence) due to their being deposited in an advancing sea or on the margin of a subsiding landmass.
  
  
• opithosoma - 40 - The posterior section of the body of arachnids and other arthropods of the subphylum Chelicerata, which consists of those body segments that do not bear legs.
  
  
• optimal sustained yield - 42 - The yield that a renewable resource can produce continuously at a given intensity of management; implies a balance at the earliest practical time between increment (growth) and harvesting.
  
  
• organic material - 7 - Pertaining or relating to material containing carbon, especially as an essential component. Material derived from plants and animals.
  
  
• organochlorine - 47 - Organochlorines are chlorinated hydrocarbon molecules and include the best known of all the synthetic poisons: endrin, heptaclor, aldrin, toxaphene, dieldrin, lindane, DDT, chlordane, and methoxychlor. There is no clear understanding of just how organochlorines work. Apparently, the central nervous system is affected, for typical symptoms of acute poisoning are tremors and convulsions. Chronic levels have various effects. In aquatic organisms, which are especially sensitive to this class of compounds, the uptake of oxygen through the gills is disrupted and death is associated with suffocation, rather than with a nervous disorder.
  
  
• organochlorine pesticides - - See organochlorine.
  
  
• organo-metallic - 10 - A compound in which a metal atom or ion is bound to an organic group.
  
  
• organophosphates - 42 - A group of pesticide chemicals that contain phosphorus, such as malathion and parathion, that are formulated as insecticides; they are short lived and normally do not reach environmentally toxic concentrations; some of these chemicals are initially, extremely toxic and can be environmentally dangerous.
  
  
• organophosphorous pesticides - - See organophosphates.
  
  
• orogenic - - Of or pertaining to orogeny (see orogeny).
  
  
• orogeny - 6 - The process of mountain building. In present usage, the process by which structures in fold-belt mountains areas were formed, including thrusting, folding, and faulting in the outer and higher layers and metamorphism and plutonism in the inner and deeper layers. May also refer to the period in which orogeny occurs.
  
  
• orthophosphate - 10 - Naturally occurring phosphates of the form M3PO4; these are salts or esters of orthophosphoric acid.
  
  
• osmoregulate - 2 - See osmoregulation.
  
  
• osmoregulation - 40 - Regulation of the osmotic pressure within a body via control of water content and the concentration of salts.
  
  
• ostracods - 2 - Members of the subclass Ostracoda, a small subclass of Crustacea whose members have a bivalve carapace enclosing the body and reduced trunk limbs. They live in fresh and salt water and may be pelagic or bottom-dwellers.
  
  
• overwinter - 38 - To pass or last through the winter.
  
  
• ovigerous - 38 - Bearing eggs or modified for the purpose of bearing eggs.
  
  
• ovoviviparous - 46 - Reproductive pattern in which eggs develop within mother's body without further nutritive aid from mother.
  
  
• oxidation - 9 - Gain of oxygen, loss of hydrogen, or loss of an electron by an atom, ion, or molecule. Oxidation and reduction take place simultaneously, with the electron lost by one reactant being transferred to another reactant.
  
  
• ozone - 2 - A form of oxygen (O3) in which the molecule consists of three atoms rather than two. It is very reactive chemically and is an irritant to eyes and respiratory tissues. It occurs naturally at about 0.01 ppm of air; 0.1 ppm is considered toxic. As a pollutant, it is harmful to plants and is involved in the formation of photochemical smog. It is formed by the recombination of oxygen following its ionization (e.g., by electrical discharges or ultraviolet radiation).
  
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• Paleocene - 7 - An epoch of the early Tertiary period, after the Gulfian epoch of the Cretaceous period and before the Eocene; also the corresponding worldwide series of rocks.
  
  
• paleoenvironmental - 7 - Referring to an environment in the geologic past.
  
  
• paleogeographic - - See paleogeography.
  
  
• paleogeography - 6 - The study of the physical geography of all or a part of the earth's surface at some time in the geologic past.
  
  
• Paleoindian - 38 - One of a hypothetical mixed Asian group that migrated to North America.
  
  
• palustrine - 7 - Pertaining to material growing or deposited in a marsh or marsh-like environment or to the environment itself.
  
  
• Pangea - 7 - A super continent that existed from about 300 to about 200 million years ago and included most of the continental crust of the Earth, from which the present continents were derived by fragmentation and continental displacement. During an intermediate stage of the fragmentation, between the existence of Pangea and that of the present continents, Pangea is believed to have split into two large fragments, Laurasia on the north and Gondwana on the south. .
  
  
• parasitoids - 2 - An animal whose mode of life is intermediate between parasitism and predation because the parasitoid ultimately kills its host. An example is ichneumons (e.g., Aculeata) which lay eggs inside the larvae or eggs of other insects.
  
  
• particulate feeders - 34 - Aquatic organisms (usually sedentary) that feed by capturing particles from the water column; also called suspension feeders.
  
  
• particulate matter - 38 - Existing in the form of minute particles that may be transported in the air or water.
  
  
• pathogen - 42 - An organism capable of producing disease.
  
  
• PCBs - 2 - Polychlorinated biphenyls. A group of closely related chlorinated hydrocarbons whose principal use has been as liquid insulators in high-voltage transformers. Their use is being reduced due to the evidence of their persistence and toxicity in the environment.
  
  
• pectoral fin - 40 - Anterior paired fins of fish that are attached to the pectoral (shoulder) girdle, usually of the upper thoracic region.
  
  
• pelagic - 34 - Refers to organisms living in the water column seaward of the shelf-slope break. Also see pelagic zone.
  
  
• pelagic zone - 4 - Living in the water column. Also, a primary division of the sea which includes the whole mass of water. The division is made up of the neritic province which includes the water shallower than 100 fathoms (200 meters), and the oceanic province which includes that water deeper than 100 fathoms.
  
  
• pelvic fin - 40 - Posterior paired fins, attached to the pelvic (hip) girdle and located in the abdominal position.
  
  
• penaeid shrimp - 24 - Primitive shrimps, members of the family Penaeidae; constitute the backbone of the shrimp fishing industry in North and South America and in many parts of Asia. Penaeid shrimps are the basis of the shrimping industry in South Carolina.
  
  
• periopod - - A walking leg of crabs, shrimps and lobsters.
  
  
• periphyton - 7 - Micro-organisms that coat rocks, plants, and other surfaces on the water bottom.
  
  
• pharyngeal teeth - 46 - Specialized dentition on various gill arch elements in fishes; in some species these teeth are used in sound production.
  
  
• phenols - 42 - A group of organic compounds that in very low concentrations produce a taste and odor problem in water and at higher levels are toxic to aquatic life; they are by products of petroleum refining, tanning, and other manufacturing processes.
  
  
• photoautotrophs - 14 - Organisms using light as an energy source and carbon dioxide as the main source of carbon; includes green plants and some bacteria.
  
  
• photolysis - 40 - A chemical reaction produced by exposure to light or ultraviolet radiation. Chemical decomposition or dissociation by the action of radiant energy (light). The photolysis of water is a key reaction in photosynthesis.
  
  
• photoperiod - 7 - The relative number of alternating daylight and dark hours in a 24-hour period. The photoperiod has a significant effect on the development of certain organisms, especially flowering plants.
  
  
• photoreceptor - 40 - A sensory cell or group of cells that reacts to the presence of light, usually resulting in a chemical transformation.
  
  
• photosynthesis - 9 - The conversions of light energy to chemical energy; the synthesis of organic compounds from carbon dioxide and water in the presence of chlorophyll, using light energy.
  
  
• photosynthesize - - See photosynthesis.
  
  
• photosynthetic - - See photosynthesis.
  
  
• physiochemical - 38 - Of or relating to physiological chemistry, the chemistry of living things.
  
  
• physiographic - - See physiography.
  
  
• physiography - 38 - Description of nature or natural phenomena or features; usually applied to the description and origin of land forms. May be used synonymously with physical geography and geomorphology.
  
  
• phytobenthos - 4 - The bottom of a sea or lake that supports plant life, anywhere from the high-water mark down to the deepest level; the organisms living there. .
  
  
• phytoflagellates - 11 - Unicellular photosynthesizing organisms in the plankton that posses a flagella (whip-like structure used for locomotion).
  
  
• phytoplankton - 34 - The photosynthesizing organisms (plant forms) residing in the plankton; includes dinoflagellates and diatoms.
  
  
• piedmont - 6 - Located or formed at the base of a mountain range; an example would be a piedmont terrace. In the southeast U.S., refers to the area between the blue ridge mountains and the coastal plain.
  
  
• piedmont basement - 6 - The crust of the earth (undifferentiated rocks) underlying sedimentary rocks in the piedmont region (see piedmont).
  
  
• pigment - 40 - A compound that gives color to a tissue. Pigments perform a variety of functions and include hemoglobin in mammals and chlorophyll in plants.
  
  
• pigmentation - 38 - The natural coloring of plants and animals
  
  
• pioneer species - 14 - The organisms which first establish themselves on bare ground at the start of a primary succession, including plants, microorganisms, and small animals.
  
  
• piscivorous - 38 - Feeding on fishes.
  
  
• pitfall traps - 38 - A pit with the opening masked, into which animals may fall and be captured.
  
  
• planktivore - 34 - An organism that feeds on planktonic organisms.
  
  
• planktivorous - 34 - Feeding on planktonic organisms.
  
  
• plankton - 4 - The passively drifting or weakly swimming organisms in marine and fresh waters. Members of this group range in size from microscopic plants to jellyfishes measuring up to 6 feet across the bell, and include the eggs and larval stages of the nekton and benthos.
  
  
• planktonic - - Of or pertaining to plankton (see plankton).
  
  
• plastron - 46 - Lower shell of a turtle.
  
  
• Pleistocene - 7 - An epoch of the Quaternary period, after the Pliocene of the Tertiary and before the Holocene; also, the corresponding worldwide series of rocks. It began two to three million years ago and lasted until the start of the Holocene some 10,000 years ago. When the Quaternary is designated as an era, the Pleistocene is considered to be a period.
  
  
• pleopod - 46 - One of paired abdominal appendages among some crustaceans; pleopods may be used in swimming, fanning water, respiration or reproduction (some decapod females carry eggs on pleopods).
  
  
• Pliocene - 7 - An epoch of the Tertiary period, after the Miocene and before the Pleistocene; also, the corresponding worldwide series of rocks. It is considered to be a period when the Tertiary is designated as an era.
  
  
• point sources - 42 - In reference to pollution, a stationary, identifiable pollution source, such as a smoke stack or discharge pipe. In contrast to non-point sources of pollution, such as farm fields.
  
  
• polar - 9 - Having parts or areas with opposed or contrasting properties, such as positive and negative charges, head and tail.
  
  
• polyaromatic hydrocarbons - - See polycyclic aromatic hydrocarbons.
  
  
• polychaete - 2 - A member of the group of bristle worms. An order (Polychaeta) of mainly marine annelid worms whose members have numerous bristles (chaetae) borne on flat outgrowths (parapodia) of the body segments. Their heads bear sense organs and tentacles. Males and females are separate, and fertilization is external. Some (e.g., ragworms) are free-swimming; others (e.g., tubeworms, lugworms) live in tubes or burrows.
  
  
• polychaetes - - See polychaete.
  
  
• polycyclic aromatic hydrocarbons - 2 - A major group of cyclic hydrocarbons known as PAHs. The vast number of compounds of this important group, derived chiefly from petroleum and coal tar, are rather highly reactive and chemically versatile. The name is due to the strong and not unpleasant odor characteristic of most substances of this nature. Includes benz-a-pyrene, debenzopyrene and dibenzoacridine, that are carcinogenic to humans. Also see aromatic hydrocarbons.
  
  
• polygamy - 2 - The condition of bearing both unisex and hermaphrodite flowers on the same or different plants. The condition of having more than one mate at one time.
  
  
• polyhaline - 2 - Applied to brackish waters whose salinity approaches that of seawater (i.e., 18 to 30 parts per thousand salt).
  
  
• pore waters - 7 - Subsurface water in the voids of a rock.
  
  
• postemergence herbicides - 42 - Chemicals applied to kill undesired plants (herbicides) after the desired crop has emerged through the soil surface.
  
  
• postlarva - 46 - In Crustacea, a developmental stage between larval and juvenile stages. Form is usually more like juvenile and adult form than preceding larval forms.
  
  
• postlarvae - - Plural of postlarva (see postlarva).
  
  
• postlarval - - Of or pertaining to a postlarva (see postlarva).
  
  
• preemergence herbicides - 42 - Chemicals applied to kill undesired plants (herbicides) before the desired crop has emerged through the soil surface.
  
  
• primary producers - 34 - Organisms capable of using the energy derived from light or a chemical substance in order to manufacture energy-rich organic compounds.
  
  
• primary production - 42 - The rate at which organic matter is stored by photosynthetic and chemosynthetic activity of producer organisms (autotrophs), usually measured in grams per day.
  
  
• primary productivity - 40 - The total amount of organic matter synthesized by the primary producers of an ecosystem.
  
  
• progradation - 41 - Seaward buildup of a beach, delta, or fan by near-shore deposition of sediments transported by a river, by accumulation of material thrown up by waves, or by material moved by longshore drifting.
  
  
• prokaryote - 9 - A cell lacking a membrane-bound nucleus and membrane-bound organelles; a bacterium or a cyanobacterium.
  
  
• prosoma - 40 - The anterior section of the body of arachnids and other arthropods of the subphylum Chelicerata (includes horseshoe crabs), which consists of the fused head and thorax (cephalothorax) and bears the chelicerae and other appendages.
  
  
• protists - 40 - Members of the (former) kingdom Protista. In older classifications, all organisms of simple biological organization were classified in this kingdom and included algae, bacteria, fungi, and protozoa. It was later restricted, and in modern classification it has been replaced by the Protoctista. See Protoctista.
  
  
• Protoctista - 40 - A kingdom consisting of unicellular or simple multicellular organisms that possess nuclei and cannot be classified as animals, plants or fungi. Includes protozoa, algae, dinoflagellates, and slime molds.
  
  
• Protozoa - 40 - A group of unicellular or acellular, usually microscopic, organisms now classified in various phyla of the kingdom Protoctista. They were formally regarded either as a phylum of simple animals or as members of the kingdom Protista. They are very widely distributed in most marine, freshwater, and terrestrial habitats.
  
  
• pseudofeces - 14 - Excess particles of food discharged by bivalve molluscs. Also spelled pseudofaeces.
  
  
• pseudohermaphrodism - 38 - The condition of having the gonads of one sex and the external genitalia and other sex organs so variably developed that the sex of the individual is uncertain. Also spelled pseudohermaphroditism.
  
  
• pyrene - 38 - A pale yellow crystalline hydrocarbon (C16H10) that consists structurally of a cluster of four compactly fused benzene rings. It is obtained from coal-tar distillation, from petroleum cracking, and is made synthetically.
  
  
• pyrite - 7 - A common , pale-bronze or brass-yellow, isometric mineral: FeS2. Pyrite has a brilliant metallic luster and an absence of cleavage, and has been mistaken for gold (which is softer and heavier). Pyrite is the most widespread and abundant of the sulfide minerals and occurs in all kinds of rocks, such as in nodules in sedimentary rocks and coal seams or as a common vein material associated with many different minerals. Pyrite is an important ore of sulfur, less so of iron, and is burned in making sulfur dioxide and sulfuric acid; it is sometimes mined for the associated gold and coppe.
  
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• Quarternary - 2 - Geological time since the end of the Pliocene (i.e., the Pleistocene and the Holocene) and ranked either as an era, following the Cenozoic era, or a period of the Cenozoic era, following the Tertiary period. Quaternary also refers to rocks formed during this time.
  
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• radionuclides - 10 - A nuclide that is radioactive. A nuclide is a nuclear species with a given number of protons and neutrons.
  
  
• raptors - 42 - Birds of prey, such as hawks and eagles.
  
  
• recruit - 43 - In ecology, an individual fish or other animal that has moved into a certain class, such as the spawning class, fishing-size class, or in a specific geographic region. General usage, to seek out someone for work or service; one who has been recruited.
  
  
• recruitment - 45 - The number of young annually added to the population. The number of individuals added to a certain class of the population, such as recruitment to the spawning stock or recruitment to the fishery. General usage, the act of recruiting.
  
  
• redox - 10 - Of or relating to oxidation-reduction reactions where there is a transfer of electrons; one atom gives up electrons (oxidation) and the other receives electrons (reduction). See redox layer.
  
  
• redox potential - 10 - The inherent tendency of a compound to act as an electron donor or an electron acceptor. Normally expressed as reduction potentials, they are obtained by electrochemical measurements. Also called standard electrode potential.
  
  
• redox layer - 27 - Also called the redox potential discontinuity. A zone of rapid transition between areas of aerobic and anaerobic decomposition in oceanic sediments. Its depth within the sediment depends on the quantity of organic matter available for decomposition and the rate at which oxygen can diffuse down from the overlying water. For example, in organic muds, relatively impermeable to oxygen-carrying water, the upper aerobic layer may only be a couple of millimeters deep, while in permeable sands with a low rate of organic input aerobic conditions can extend for tens of centimeters.
  
  
• redox state - - See redox.
  
  
• refractory - 38 - Said of a substance that is resistant to decay or corrosion. Said of any substance that is notably resistant to heat. Said of an ore from which it is difficult or expensive to recover its valuable constituents.
  
  
• refractory compounds - - See refractory.
  
  
• regeneration - 44 - Renewal, regrowth or restoration. In forestry, the renewal of a tree crop, whether by natural or artificial means.
  
  
• regressive - 2 - Applied to a body of water or to sediments associated with a lowering of sea level.
  
  
• relict - 6 - Said of a community, mineral, or landform or fragment of these that has survived some important change, remaining after other parts have disappeared, often to become in appearance an integral part of the existing community, rock, or topography.
  
  
• relict marsh - - See relict.
  
  
• remineralization - 31 - The process by which inorganic nutrients are released to seawater during the consumption of organic matter by the processes involved in respiration.
  
  
• reptiles - 2 - A class of essentially terrestrial vertebrates, whose modern representatives are poikilothermic (cold blooded) and scaly-skinned, with embryos protected by an amnion and an allantos. Most lay large eggs with leathery shells. Includes snakes, lizards, and turtles.
  
  
• residence times - 7 - The average amount of time a particular substance spends within a designated earth system. The residence time is inversely proportional to the rate of movement within the system and directly proportional to the size of the system.
  
  
• resource allocation - 39 - The action of apportioning the supply of a resource to specific uses or to particular persons or organizations.
  
  
• resource conservation - 2 - Preservation or protection of resources from decay or destruction, usually in reference to natural resources such as trees and rivers.
  
  
• riparian - 38 - Of or related to or living or located on the land bordering a water body, especially a stream, river or lake.
  
  
• riverine - 46 - Pertaining to a river. A natural stream, larger than a brook, creek, or rivulet, flowing into a lake, sea, or other stream.
  
  
• roe - 38 - The eggs of a fish, especially when still enclosed in the ovarian membrane. May also be applied to invertebrate eggs. Often eaten by humans, such as shad roe or sturgeon roe (caviar).
  
  
• rookery - 42 - The breeding place of a group of birds or seals.
  
  
• rostrum - 46 - In Crustacea, forward prolongation of carapace beyond the head.
  
  
• rotenone - 38 - A crystalline pentacyclic compound that is toxic to many animals. Used as an insecticide and for capturing fish. Of low toxicity to mammals.
  
  
• rotifers - 2 - Members of a phylum (Rotifera) of minute animals that move and feed by means of a crown of cilia. They have no true coelom. Most live in fresh water, a few occur in the sea. The great majority are free-swimming, a few are sedentary, colonial or parasitic..
  
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• scarp - 6 - A line of cliffs produced by faulting or erosion. The term is an abbreviation of escarpment, and the two terms have essentially the same meaning. A more or less continuous line of cliffs or steep slopes facing in one general direction which are caused by erosion or faulting.
  
  
• scute - 46 - External horny plate found on some fish and many reptiles.
  
  
• sea-floor spreading - 31 - A theory that the oceanic crust is increasing in area by upwelling of magma along the mid-ocean ridges or world rift system, and by a moving-away of the new material at rates of one to ten centimeters per year. This movement provides the source of dynamic thrust in the hypothesis of plate tectonics.
  
  
• sediment - 6 - Solid material that has settled down from a state of suspension in liquid or other fluid medium. More generally, solid, fragmented material transported and deposited by wind, water or ice, chemically precipitated from solution or excreted by organisms, and that forms in layers in loose, unconsolidated form..
  
  
• seine - 46 - Type of net used to catch fish by encirclement, usually by active closure of 2 ends but also including closure or pursing of the bottom (purse seine). Also as a verb, to use a net of this sort.
  
  
• seismic reflector - - See seismic-reflection profiles.
  
  
• seismic-reflection profiles - 41 - A subsurface profile that is generated by seismic data and indicates a distinctive type of sediment geometry produced by sea-level changes; used to correlate stratigraphic sequences.
  
  
• semi-diurnal - 6 - Occurring approximately every half day. Descriptive of a tide that has a cycle of approximately one-half a tidal day, i.e., with two high and two low waters per tidal day.
  
  
• sequential hermaphrodite - 46 - During the course of its life, when an animal or plant possesses both male and female reproductive organs, but only one set is functional at a time. An unusual condition in higher vertebrates, it is common in many worms and some molluscs and echinoderms.
  
  
• setback - 39 - A withdrawal of the face of a building to a line some distance to the rear of the building line, or to the rear of the wall below. The steplike profile of tall buildings is now required by many buildings codes to reduce the obstruction the upper stories offer to sunlight reaching the streets and the lower stories of adjacent buildings.
  
  
• sheetflow - 42 - Water, usually storm runoff, flowing in a thin layer over the ground surface; also called overland flow.
  
  
• shards - 6 - Fragments or broken pieces of pottery. Also spelled sherds.
  
  
• shoal - 6 - Noun - A relatively shallow region in a body of water; a submerged ridge, bank or bar made of deposited sediments and rising to near the waters surface. Verb - to make shallow or to come to a shallow part of a water body.
  
  
• shoaling - - See shoal.
  
  
• shrink-swell clays - - See shrink-swell potential.
  
  
• shrink-swell potential - 42 - The susceptibility of soil to volume change due to loss or gain in moisture content.
  
  
• silicates - 38 - Any of numerous insoluable often complex metal salts that contain silicon and oxygen; silicates constitute the largest chemical group of minerals and with quartz make up the greater part of the earth's crust.
  
  
• silicoflagellates - 7 - Any chrysomonad protozoan belonging to the family Silicoflagellidae and characterized by a skeleton composed of siliceous rings and spines. Range Cretaceous to present.
  
  
• siltation - 42 - The process of depositing silt.
  
  
• silviculture - 38 - The phase of forestry that deals with the establishment, reproduction and care of forest trees.
  
  
• simple eye - 38 - An eye with a single lens, in contrast to compound eyes of insects. .
  
  
• sinkholes - 42 - Depressions in the earth's surface caused by dissolving of underlying limestone, salt, or gypsum; drainage is through underground channels; may be enlarged by collapse of a cover roof.
  
  
• siphon - 46 - Specialized tube of mantle of certain bivalve, gastropod and cephalopod molluscs, or test of tunicates for entrance of water.
  
  
• slump - 6 - The downward slipping of a mass of rock or unconsolidated material, moving as a unit; the sliding down of a mass of sediment shortly after its deposition on an underwater slope. The mass of material produced by a slump.
  
  
• slump areas - - See slump.
  
  
• slumping - - See slump.
  
  
• snags - 13 - A dead tree or portion thereof, from which most of the branches have fallen.
  
  
• socio-ecological characterization - 33 - A structured approach to the synthesis of current knowledge about ecosystems and human activity for management purposes. In general, ecological characterizations synthesize interdisciplinary knowledge about ecosystems including their biological resources, physical environment, key processes and important human interactions. Ecological characterizations may also include descriptions or analyses of anticipated resource uses, proposed development scenarios, an management response options. May also be called environmental characterization.
  
  
• sondes - 2 - Any of various devices for testing and measuring physical conditions, including measurements of atmosphere, ground water and surface water.
  
  
• spat - 4 - The spawn or young of bivalve molluscs, especially used for young that have recently attached to a hard substrate.
  
  
• spawn - 42 - In aquatic animals, to produce or deposit eggs or sperm. Also, collective term for the eggs and sperm so produced or deposited.
  
  
• species richness - 34 - The number of species in an area or biological collection.
  
  
• specific gravities - 42 - The relative weight of a given volume of any kind of matter (volume occupied by solid phase, pore space excluded) compared with an equal volume of distilled water at a specified temperature; average specific gravity for soil is about 2.65.
  
  
• spermatophore - 46 - Packet of sperm within complicated case secreted by male, as in crustaceans, copepods and cephalopods.
  
  
• spodosols - 2 - Soils with a diagnostic iron oxide and/or organic-enriched B horizon underlying an ashy grey, leached layer in the A horizon, associated with a cool and cool-humid climate, a forest or heath vegetation cover.
  
  
• spreading centers - - See sea-floor spreading.
  
  
• spring tide - 4 - Tide of increased range; occurs about every two weeks when the moon is new or full.
  
  
• stable isotopes - 7 - A nuclide that does not undergo radioactive decay (also see radionuclide).
  
  
• standing crop - 8 - The amount of biomass that occurs on a given site at a particular rime without reference to rate of accumulation.
  
  
• standing stocks - - See standing crop.
  
  
• standstill - 7 - Stability of an area of land, as a continent or island, with reference to the Earth's interior or mean sea level, as might be reflected, for example, by a relatively unvarying base level of erosion between periods of crustal movement. Also called stillstand.
  
  
• stenohaline - 7 - Said of a marine organism that tolerates only a narrow range of salinity.
  
  
• storage capacity - 42 - The capacity to store water available for use by plants, usually expressed in linear depths of water per unit depth of soil; the difference between the percentage of soil water at field capacity and the percentage at wilting point. Also, the volume of water normally available for release from a reservoir below the stage of the maximum controllable level.
  
  
• strand-line - 7 - The ephemeral line or level at which a body of standing water (e.g., the sea) meets the land; the shoreline, especially a former shoreline now elevated above the present water level.
  
  
• stratification - 6 - The arrangement of sedimentary rocks in strata; bedding. Also, the layering of waters of different densities, usually because of heating of the surface layer.
  
  
• stratigraphy - 7 - The arrangement of strata, especially as to geographic position and chronologic order of sequence. The science of rock strata.
  
  
• stream gradient - 6 - The angle between the water surface or the channel floor of a stream and the horizontal, measured in the direction of flow; the general slope, or rate of vertical drop per unit of length, of a flowing stream.
  
  
• strike-slip - 7 - In a fault, the component of the movement or slip that is parallel to the strike of the fault.
  
  
• structural feature - 7 - A feature produced by deformation or displacement of the rocks, such as a fold or fault. For such features, the more colloquial term structure (used as a specific noun) is now generally accepted.
  
  
• stumpage - 12 - Standing timber as viewed by a potential harvester.
  
  
• subadult - 29 - A developmental life stage when the individual exhibits most but not all traits of an adult; usually is similar in appearance to an adult, but is not yet sexually mature.
  
  
• sub-basin - 28 - A portion of a subregion or basin drained by a single stream or group of minor streams; the smallest unit into which the land surface is subdivided for hydrologic study purposes.
  
  
• substrate - 7 - The substance, base, or nutrient on which, or the medium in which, an organism lives and grows, or the surface to which a fixed organism is attached; e.g., soil, rocks, water, and leaf tissues, or perhaps a gel for the accumulation and preservation of prebiologic organic matter.
  
  
• subtidal - 25 - A marine or estuarine environment that lies below extreme low water of the spring tides; any substratum that is continuously submerged within a tidally-influenced water body.
  
  
• sub-watershed - 28 - Drainage area composed of two or more sub-basins. (Also see sub-basins).
  
  
• succession - 40 - The sequence of communities that develops in an area from the initial stages of colonization until a stable mature climax community is achieved. Many factors, including climate and changes brought about by the colonizing organisms, influence the nature of a succession..
  
  
• sulphides - 6 - Mineral compounds characterized by the linkage of sulfur with a metal. Also spelled sulfides.
  
  
• supercontinent - - See Pangea.
  
  
• surfactants - 10 - A substance that lowers surface tension and has properties of wetting, foaming, detergency, dispersion, and emulsification (e.g., a soap or other detergent).
  
  
• surficial - 7 - Pertaining to, or occurring on, a surface, especially the surface of the Earth.
  
  
• suspended particulates - 28 - A sample drawn from natural water or from a wastewater stream consists of a mixture of both dissolved and suspended matter. Those solid materials that are retained on a filter prescribed by the specific technique being followed are referred to as particulate matter. The suspended particulate matter can be subdivided into two fractions: volatile and fixed. The volatile particulates are those that are lost when the filter is heated to about 550C (1,022F), and the fixed particulates are those that are not lost upon being so heated. The volatile substances are generally considered to be of biological origin, and the fixed solids are considered to be minerals.
  
  
• suspended solids - 28 - Solids which are not in true solution and which can be removed by filtration. Such suspended solids usually contribute directly to turbidity. Also see suspended particulates.
  
  
• sustainable - 23 - A state or process that can be maintained indefinitely. The principles of sustainability integrate three closely interlined elements - the environment, the economy and the social system - into a system that can be maintained in a healthy state indefinitely.
  
  
• swales - 6 - Swale (singular). A long, narrow, generally shallow natural depression between two beach ridges. A slight depression, sometimes swampy, in the midst of generally level land.
  
  
• swim bladder - 4 - A membranous sac of atmospheric gases lying in the body cavity between the vertebral column and the alimentary tract of certain fishes. It serves a hydrostatic function in most fishes that possess it (to regulate buoyancy); in some it participates in sound production. Also called an air bladder.
  
  
• symbiosis - 9 - An intimate and protracted association between two or more organisms of different species. Includes mutualism, in which the association is beneficial to both; commensalism, in which one benefits and the other is neither harmed nor benefited; and parasitism, in which one benefits and the other is harmed.
  
  
• symbiotic - - Of or pertaining to symbiosis. See symbiosis
  
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• tactile - 38 - Of, pertaining to, or issuing from the sense of touch. Used for feeling (i.e. a tactile organ).
  
  
• taxonomy - 42 - The science of classification; laws and principles governing the classifying of objects, particularly living and extinct organisms.
  
  
• tectonics - 6 - A branch of geology dealing with the broad architecture of the outer part of the earth, that is, the major structural or deformational features and their relations, origin, and historical evolution.
  
  
• tectonism - 7 - A general term for all movement of the crust produced by tectonic processes, including the formation of ocean basins, continents, plateaus, and mountain ranges. Similar to diastrophism..
  
  
• telson - 38 - The terminal segment of the body of some arthropods and segmented worms; in some crustaceans (shrimps, lobsters) it forms the middle lobe of the tail.
  
  
• tertiary treatment - 44 - Wastewater treatment processes, beyond primary and secondary wastewater treatment, which remove or reduce the amount of nitrate and phosphate nutrients still present in their effluents. Tertiary treatment may consist of extensions or modifications of secondary treatment processes, additional forms of chemical treatment, electrochemical processing, carbon filtration, and other more complex procedures.
  
  
• Tertiary - 2 - That part of geological time from the end of the Cretaceous (65 mya) to the beginning of the Pleistocene (2 mya), comprising the Paleocene, Eocene, Miocene, Oligocene and Pliocene. Tertiary also refers to rocks formed during this time. In some usage's Tertiary is synonymous with Cenozoic, whereas in other usages, Tertiary and Quaternary together make up the Cenozoic.
  
  
• tetrapods - 40 - Members of the superclass Tetrapoda, the jawed chordates comprising all vertebrates with four limbs (2 pairs). Includes amphibians, reptiles, birds, and mammals.
  
  
• thermocline - 4 - A vertical, negative gradient of temperature that is characteristic of the layer of ocean water under the mixed layer; also, the layer in which this gradient occurs. A thermocline may be either seasonal or permanent.
  
  
• threatened species - 44 - Any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range and which has been designated in the Federal Registry by the Secretary of Interior as a threatened species.
  
  
• tidewater region - 46 - Region where water is affected by tides or sometimes that part of it which covers tideland. Term is sometimes used broadly to designate the seaboard.
  
  
• topographic - - Of or pertaining to topography. See topography.
  
  
• topography - 6 - The general configuration of a land surface, including its relief and the position of natural and man-made features.
  
  
• topology - 7 - Study of the properties of geometric configurations. In digital cartography, it is concerned with the characteristics of data that describe the spatial relationships, such as dimensionality, adjacency, and connectivity, of map elements to each other. The detailed study of minor landforms, requiring fairly large scales of mapping. The topographic study of a particular place, specifically, the history of a region as indicated by its topography.
  
  
• trace metals - 18 - Trace elements regulated because of their potential for human, plant, or animal toxicity, including cadmium (Cd), copper (Cu), chromium (Cr), mercury (Hg), nickel (Ni), lead (Pb) and Zinc (Zn).
  
  
• trammel nets - 38 - A rectangular net made of a middle layer that is slack and of fine mesh and two outer layers that are stretched and of coarse mesh so arranged that fish attempting to pass in either direction carry some of the fine net through the coarse net and are thus pocketed.
  
  
• transgression - 6 - In geology, the spread of sea over land areas; also, any change that brings offshore, deep-water environments to areas formerly occupied by nearshore, shallow-water conditions, or that shifts the boundary between marine and non-marine deposition outward from the center of a marine basin. The resulting sequence of strata would be a transgressive sequence. Also, a discrepancy in the boundary lines of continuous strata.
  
  
• transgressive - - See transgression.
  
  
• trawl - 46 - Noun - Bag or funnel-shaped net to catch bottom-dwelling animals (e.g. fish, crustaceans) by dragging it along the bottom. Large research net designed on bottom trawl principles to catch large zooplankton and fish by towing in intermediate depths. Verb - the act of pulling a trawl net.
  
  
• treeline - 38 - Timberline. The height or limit beyond which trees do not grow in mountainous or artic regions.
  
  
• Triassic - 7 - The first period of the Mesozoic era (after the Permian of the Paleozoic era, before the Jurassic), thought to have covered the span of time between 250 and 190 million years ago; also, the corresponding system of rocks. The Triassic is so named because of its threefold division in the rocks of Germany.
  
  
• triazine herbicides - 42 - Herbicides that inhibit photosynthesis, leading to yellowing of leaves, followed by death of leaf tissue; uptake can occur through leaves but there is little movement inside the plant; when applied to soils, they are taken up by the roots and move in the xylem to plant leaves.
  
  
• tributaries - 42 - Secondary or branch of a stream or other channel that contributes flow to the primary or main channel.
  
  
• trochophore - 46 - Free-swimming, pelagic larval stage in certain aquatic invertebrates (some annelids and molluscs), distinguished by ciliated, pear-shaped body.
  
  
• trophic - - See trophic levels.
  
  
• trophic levels - 40 - The position that an organism occupies in a food chain. For example, green plants are primary producers; herbivores are primary consumers and secondary producers; a carnivore that eats only herbivores is a secondary consumer and tertiary producer. Many animals feed at several different trophic levels.
  
  
• turbellarians - 2 - Members of a class (Turbellaria) of mainly free-living flatworms (phylum Platyhelminthes) that move by means of cilia which cover the body. Some (e.g., Planaria) live in fresh water, others are marine, and a few are terrestrial..
  
  
• turbid - 7 - Stirred up or disturbed, such as by sediment; not clear or translucent, being opaque with suspended matter, such as of a sediment-laden stream flowing into a lake; cloudy or muddy in physical appearance.
  
  
• turbidity - - The quality or state of being turbid. See turbid.
  
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• unconformities - 7 - A substantial break or gap in the geologic record where a rock unit is overlain by another that is not next in stratigraphic succession, such as an interruption in the continuity of a depositional sequence of sedimentary rocks or a break between eroded igneous and younger sedimentary strata. It results from a change that caused deposition to cease for a considerable span of time, and it normally implies uplift and erosion with loss of the previously formed record. Also, the structural relationship between two groups of rocks that are not in normal succession.
  
  
• understory - 38 - A foliage layer lying beneath and shaded by the main canopy of a forest. The plants that form the foliage understory. Also, a layer of low vegetation underlying a layer of taller vegetation.
  
  
• uropod - 38 - Flattened, life-like, paired appendage of the last abdominal segment of various crustaceans (as the lobster) that with the telson forms the fantail. Used for swimming by some crustaceans.
  
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• veliger - 4 - The planktonic, larval second stage of many gastropods.
  
  
• velum - 40 - In zoology, circular, muscular, locomotory membrane of hydromedusans; ciliated, swimming organ of a trochophore larva; or any of various ring-shaped structures in animals, such as the segments of earthworms or other annelids.
  
  
• vertebrates - 40 - Any of a large group of animals comprising all those members of the phylum Chordata that have backbones. Vertebrates include the fishes, amphibians, reptiles, birds and mammals.
  
  
• vertical stratification - - See stratification.
  
  
• viviparous - 38 - Giving birth to living offspring that develop inside the body of the mother rather than hatching from an egg. Synonymous with viviparity.
  
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• water column - 28 - A hypothetical column of water from the surface to the bottom of a stream, lake, or ocean within which the physical and/or chemical properties can be measured.
  
  
• water quality indicators - 28 - Constituents or characteristics of water that can be measured to determine its suitability for use.
  
  
• watershed - 28 - All lands enclosed by a continuous hydrologic drainage divide and lying upslope from a specified point on a stream. Also referred to as a water basin or drainage basin. Also, a ridge of relatively high land dividing two areas that are drained by different river systems.
  
  
• wattles - 38 - Fleshy, often vividly colored flaps of skin hanging from the head or neck of certain lizards and birds (e.g., turkey). Also, sticks and twigs, branches, reeds, etc. woven into a construction material, as for walls or fences.
  
  
• weir - 38 - A damn built to direct or back up the flow of water. A fence or barrier, as of branches or a net, placed in a stream to catch or retain fish.
  
  
• WQ indicators - - See water quality indicators
  
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• xenobiota - 20 - Any substance foreign to living systems. Xenobiotics include drugs, pesticides, and carcinogens. Also, any biota displaced from its normal habitat.
  
  
• xenobiotics - - See xenobiota.
  
  
• xeriscape - 19 - Shortened form of xeric landscape. Landscaping designed for water and energy efficiency and lower maintenance. The seven xeriscape principles are: good planning and design; practical lawn areas; efficient irrigation; soil improvement; use of mulches; low water demand plants; good maintenance.
  
  
• xeriscaping - - See xeriscape.
  
  
• year class - 29 - Fish in a stock born in the same year. For example, the 1987 year class of cod includes all cod born in 1987, which would be age 1 in 1988. Occasionally, a stock produces a very small or very large year class which can be pivotal in determining stock abundance in later years.
  
  
• zoning, Euclidian - 44 - Zoning of the type adopted by the city of Euclid, Ohio, and made famous in 1926 by the United States Supreme Court decision in village of Euclid vs. Ambler Realty company, upholding the nation's first comprehensive zoning ordinance. The Euclid zoning ordinance restricted the location of trades, industries, apartment houses, two-family houses, single-family houses, the lot area to be built upon, the size and height of buildings, etc. The court found these restrictions neither "unreasonable" nor "arbitrary." Since that time the term has come to describe the most common form of zoning in the United States, in which "use districts" are designated (I.e., light manufacturing, commercial, single-family residential) and only the permitted use or a "higher" one is allowed. Thus in an area zoned for heavy industry, all other uses would theoretically be permitted (though there are some exceptions to this under the principle of exclusive zoning), whereas in an area of single-family residences, no other uses are likely to be permitted.
  
  
• zoomorphic - 38 - Having, or represented as having, the form of an animal.
  
  
• zooplankton - 40 - The animal component of the plankton (see plankton). All major animal phyla are represented in zooplankton as adults, larvae, or eggs; some are just visible to the unaided eye but most can not be seen without magnification. Near the surface of the sea there may be many thousands of such animals per cubic meter of water.
  

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