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Principles of Environmental Science
William P. Cunningham, University of Minnesota
Mary Ann Cunningham, Vassar College


acid precipitation  Acidic rain, snow, or dry particles deposited from the air due to increased acids released by anthropogenic or natural resources.
acids  Substances that release hydrogen atoms in water.
active solar system  A mechanical system that uses moving substances to collect and transfer solar energy.
acute effects  A sudden onset of symptoms or effects of exposure to some factor.
acute poverty  Insufficient income or access to resources needed to provide the basic necessities for life such as food, shelter, sanitation, clean water, medical care, and education.
adaptive management  A management plan designed from the outset to "learn by doing," and to actively test hypotheses and adjust treatments as new information becomes available.
administrative law  Executive orders, administrative rules and regulations, and enforcement decisions by administrative agencies and special administrative courts.
aerosols  Minute particles or liquid droplets suspended in the air.
agency rule-making  The formal process of establishing rules and standards by administrative agencies.
albedo  A description of a surface's reflective properties.
allergens  Substances that activate the immune system and cause an allergic response; may not be directly antigenic themselves but may make other materials antigenic.
ambient air  The air immediately around us.
analytical thinking  A way of systematic analysis that asks, "How can I break this problem down into its constituent parts?"
anemia  Low levels of hemoglobin due to iron deficiency or lack of red blood cells.
anthropocentric  Believing that humans hold a special place in nature; being centered primarily on humans and human affairs.
antigens  Substances that stimulate the production of, and react with, specific antibodies.
aquifers  Porous, water-bearing layers of sand, gravel, and rock below the earth's surface; reservoirs for groundwater.
arbitration  A formal process of dispute resolution in which there are stringent rules of evidence, cross-examination of witnesses, and a legally binding decision made by the arbitrator that all parties must obey.
arithmetic growth  A pattern of growth that increases at a constant amount per unit time, such as 1, 2, 3, 4 or 1, 3, 5, 7.
atmospheric deposition  Sedimentation of solids, liquids, or gaseous materials from the air.
atom  The smallest unit of matter that has the characteristics of an element; consists of three main types of subatomic particles: protons, neutrons, and electrons.
atomic number  The characteristic number of protons per atom of an element.
autotroph  An organism that synthesizes food molecules from inorganic molecules by using an external energy source, such as light energy.
barrier islands  Low, narrow, sandy islands that form offshore from a coastline.
bases  Substances that readily bond with hydrogen ions in an aqueous solution.
Batesian mimicry  Evolution by one species to resemble the coloration, body shape, or behavior of another species that is protected from predators by a venomous stinger, bad taste, or some other defensive adaptation.
benthos  The bottom of a sea or lake.
bioaccumulation  The selective absorption and concentration of molecules by cells.
biocentrism  The belief that all creatures have rights and values; being centered on nature rather than humans.
biochemical oxygen demand (BOD)  A standard test for measuring the amount of dissolved oxygen utilized by aquatic microorganisms.
biodegradable plastics  Plastics that can be decomposed by microorganisms.
biodiversity  The genetic, species, and ecological diversity of the organisms in a given area.
biogeochemical cycles  Movement of matter within or between ecosystems; caused by living organisms, geological forces, or chemical reactions. The cycling of nitrogen, carbon, sulfur, oxygen, phosphorus, and water are examples.
biogeographical area  A region or ecosystem with characteristic biological, water, and land resources.
biological community  The populations of plants, animals, and microorganisms living and interacting in a certain area at a given time.
biological controls  Use of natural predators, pathogens, or competitors to regulate pest populations.
biomagnification  Increase in concentration of certain stable chemicals (for example, heavy metals or fat-soluble pesticides) in successively higher trophic levels of a food chain or web.
biomass  The total mass or weight of all the living organisms in a given population or area.
biomass fuel  Organic material produced by plants, animals, or microorganisms that can be burned directly as a heat source or converted into a gaseous or liquid fuel.
biomass pyramid  A metaphor or diagram that explains the relationship between the amounts of biomass at different trophic levels.
biome  A broad, regional type of ecosystem characterized by distinctive climate and soil conditions and a distinctive kind of biological community adapted to those conditions.
bioremediation  Use of biological organisms to remove pollution or restore environmental quality.
biosphere  The zone of air, land, and water at the surface of the earth that is occupied by organisms.
biosphere reserves  World heritage sites identified by the IUCN as worthy for national park or wildlife refuge status because of high biological diversity or unique ecological features.
biota  All organisms in a given area.
biotic potential  The maximum reproductive rate of an organism, given unlimited resources and ideal environmental conditions. Compare with environmental resistance.
birth control  Any method used to reduce births, including celibacy, delayed marriage, contraception; devices or medication that prevent implantation of fertilized zygotes, and induced abortions.
bog  An area of waterlogged soil that tends to be peaty; fed mainly by precipitation; low productivity; some bogs are acidic.
boreal forest  A broad band of mixed coniferous and deciduous trees that stretches across northern North America (and also Europe and Asia); its northernmost edge, the taiga, intergrades with the arctic tundra.
brownfields  Abandoned or underused urban areas in which redevelopment is blocked by liability or financing issues related to toxic contamination.
cancer  Invasive, out-of-control cell growth that results in malignant tumors.
capital  Any form of wealth, resources, or knowledge available for use in the production of more wealth.
carbohydrate  An organic compound consisting of a ring or chain of carbon atoms with hydrogen and oxygen attached; examples are sugars, starches, cellulose, and glycogen.
carbon cycle  The circulation and reutilization of carbon atoms, especially via the processes of photosynthesis and respiration.
carbon monoxide (CO)  Colorless, odorless, nonirritating but highly toxic gas produced by incomplete combustion of fuel, incineration of biomass or solid waste, or partially anaerobic decomposition of organic material.
carbon sink  Places of carbon accumulation, such as in large forests (organic compounds) or ocean sediments (calcium carbonate); carbon is thus removed from the carbon cycle for moderately long to very long periods of time.
carcinogens  Substances that cause cancer.
carnivores  Organisms that mainly prey upon animals.
carrying capacity  The maximum number of individuals of any species that can be supported by a particular ecosystem on a long-term basis.
case law  Precedents from both civil and criminal court cases.
cellular respiration  The process in which a cell breaks down sugar or other organic compounds to release energy used for cellular work; may be anaerobic or aerobic, depending on the availability of oxygen.
chain reaction  A self-sustaining reaction in which the fission of nuclei produces subatomic particles that cause the fission of other nuclei.
chaparral  A biological community characterized by thick growth of thorny, evergreen shrubs typical of a Mediterranean climate.
chemical bond  The force that holds molecules together.
chemical energy  Potential energy stored in chemical bonds of molecules.
Chipko Andolan movement  A group of village women in India who mobilized to save the forest on which their livelihoods depended. The name means to hug trees to protect them.
chlorofluorocarbons  Chemical compounds with a carbon skeleton and one or more attached chlorine and fluorine atoms. Commonly used as refrigerants, solvents, fire retardants, and blowing agents.
chloroplasts  Chlorophyll-containing organelles in eukaryotic organisms; sites of photosynthesis.
chronic effects  Long-lasting results of exposure to a toxin; can be a permanent change caused by a single, acute exposure or a continuous, low-level exposure.
citizen science  Projects in which trained volunteers work with scientific researchers to answer real-world questions.
city  A differentiated community with a sufficient population and resource base to allow residents to specialize in arts, crafts, services, and professional occupations.
civil law  A body of laws regulating relations between individuals or between individuals and corporations concerning property rights, personal dignity and freedom, and personal injury.
classical economics  Modern, western economic theories of the effects of resource scarcity, monetary policy, and competition on supply and demand of goods and services in the marketplace. This is the basis for the capitalist market system.
clear-cutting  Cutting every tree in a given area, regardless of species or size; an appropriate harvest method for some species; can be destructive if not carefully controlled.
climate  A description of the long-term pattern of weather in a particular area.
climax community  A relatively stable, long-lasting community reached in a successional series; usually determined by climate and soil type.
closed-canopy  A forest where tree crowns spread over 20 percent of the ground; has the potential for commercial timber harvests.
cloud forests  High mountain forests where temperatures are uniformly cool and fog or mist keeps vegetation wet all the time.
coevolution  The process in which species exert selective pressure on each other and gradually evolve new features or behaviors as a result of those pressures.
cogeneration  The simultaneous production of electricity and steam or hot water in the same plant.
cold front  A moving boundary of cooler air displacing warmer air.
coliform bacteria  Bacteria that live in the intestines (including the colon) of humans and other animals; used as a measure of the presence of feces in water or soil.
commensalism  A symbiotic relationship in which one member is benefited and the second is neither harmed nor benefited.
common law  The body of court decisions that constitute a working definition of individual rights and responsibilities where no formal statutes define these issues.
communal resource management systems  Resources managed by a community for long-term sustainability.
community ecology  The study of interactions of all populations living in the ecosystem of a given area.
community-based planning  Involving community stake-holders in pluralistic, adaptive, inclusive, proactive planning.
competitive exclusion  A theory that no two populations of different species will occupy the same niche and compete for exactly the same resources in the same habitat for very long; disputed by some ecologists who see biological communities as highly individualistic and variable.
complexity (ecological)  The number of species at each trophic level and the number of trophic levels in a community.
composting  The biological degradation of organic material under aerobic (oxygen-rich) conditions to produce compost, a nutrient-rich soil amendment and conditioner.
compound  A molecule made up of two or more kinds of atoms held together by chemical bonds.
conifers  Needle-bearing trees that produce seeds in cones.
conservation of matter  In any chemical reaction, matter changes form; it is neither created nor destroyed.
conspicuous consumption  A term coined by economist and social critic Thorstein Veblen to describe buying things we don't want or need to impress others.
consumer  An organism that obtains energy and nutrients by feeding on other organisms or their remains. See also heterotroph.
consumption  The fraction of withdrawn water that is lost in transmission or that is evaporated, absorbed, chemically transformed, or otherwise made unavailable for other purposes as a result of human use.
contour plowing  Plowing along hill contours; reduces erosion.
control rods  Neutron-absorbing material inserted into spaces between fuel assemblies in nuclear reactors to regulate fission reaction.
convection currents  Rising or sinking air currents that stir the atmosphere and transport heat from one area to another. Convection currents also occur in water.
conventional (or criteria) pollutants  The seven substances (sulfur dioxide, carbon monoxide, particulates, hydrocarbons, nitrogen oxides, photochemical oxidants, and lead) that make up the largest volume of air quality degradation; identified by the Clean Air Act as the most serious threat of all pollutants to human health and welfare; also called criteria pollutants.
convergent evolution  Species evolve from different origins but under similar environmental conditions to have similar traits.
coral reefs  Prominent oceanic features composed of hard, limy skeletons produced by coral animals; usually formed along edges of shallow, submerged ocean banks or along shelves in warm, shallow, tropical seas.
core  The dense, intensely hot mass of molten metal, mostly iron and nickel, thousands of kilometers in diameter at the earth's center.
Coriolis effect  The tendency for air above the earth to appear to be deflected to the right (in the northern hemisphere) or the left (in the South) because of the earth's rotation.
corridor  A strip of natural habitat that connects two adjacent nature preserves to allow migration of organisms from one place to another.
cost-benefit analysis  An evaluation of large-scale public projects by comparing the costs and benefits that accrue from them.
cover crops  Plants, such as rye, alfalfa, or clover, that can be planted immediately after harvest to hold and protect the soil.
creative thinking  Original, independent thinking that asks, "How might I approach this problem in new and inventive ways?"
criminal law  A body of court decisions based on federal and state statutes concerning wrongs against persons or society.
criteria pollutants  See conventional pollutants.
critical factor  The single environmental factor closest to a tolerance limit for a given species at a given time. See limiting factors.
critical thinking  An ability to evaluate information and opinions in a systematic, purposeful, efficient manner.
crude birthrate  The number of births in a year divided by the midyear population.
crude death rate  The number of deaths per thousand persons in a given year; also called crude mortality rate.
crust  The cool, lightweight, outermost layer of the earth's surface that floats on the soft, pliable underlying layers; similar to the "skin" on a bowl of warm pudding.
cultural eutrophication  An increase in biological productivity and ecosystem succession caused by human activities.
debt-for-nature swap  Forgiveness of international debt in exchange for nature protection in developing countries.
deciduous  Trees and shrubs that shed their leaves at the end of the growing season.
decline spiral  A catastrophic deterioration of a species, community, or whole ecosystem; accelerates as functions are disrupted or lost in a downward cascade.
decomposers  Fungi and bacteria that break complex organic material into smaller molecules.
deductive reasoning  A series of logical steps that attempt to derive understanding of specific case from a general principle or law.
deep ecology  A philosophy that calls for a profound shift in our attitudes and behavior based on rejection of anthropocentric attitudes; a belief in the sacredness of nature; and direct personal action to protect nature.
delta  Fan-shaped sediment deposit found at the mouth of a river.
demanufacturing  Disassembly of products so components can be reused or recycled.
demographic transition  A pattern of falling death rates and birthrates in response to improved living conditions; could be reversed in deteriorating conditions.
demography  Vital statistics about people: births, marriages, deaths, etc.; the statistical study of human populations relating to growth rate, age structure, geographic distribution, etc., and their effects on social, economic, and environmental conditions.
dependency ratio  The number of nonworking members compared to working members for a given population.
desalinization (or desalination)  Removal of salt from water by distillation, freezing, or ultrafiltration.
desert  A type of biome characterized by low moisture levels and infrequent and unpredictable precipitation. Daily and seasonal temperatures fluctuate widely.
desertification  Denuding and degrading a once-fertile land, initiating a desert-producing cycle that feeds on itself and causes long-term changes in soil, climate, and biota of an area.
detritivore  Organisms that consume organic litter, debris, and dung.
dew point  The temperature at which condensation occurs for a given concentration of water vapor in the air.
dieback  A sudden population decline; also called a population crash.
disability adjusted life years (DALYs)  A health measure that assesses the total burden of disease by combining premature deaths and loss of a healthy life that result from illness or disability.
discharge  The amount of water that passes a fixed point in a given amount of time; usually expressed as liters or cubic feet of water per second.
discount rate  The amount we discount or reduce the value of a future payment. When you borrow money from the bank at 10 percent annual interest, you are in effect saying that having the money now is worth 10 percent more to you than having the same amount one year from now.
disease  A deleterious change in the body's condition in response to destabilizing factors, such as nutrition, chemicals, or biological agents.
dissolved oxygen (DO) content  Amount of oxygen dissolved in a given volume of water at a given temperature and atmospheric pressure; usually expressed in parts per million (ppm).
diversity (species diversity, biological diversity)  The number of species present in a community (species richness), as well as the relative abundance of each species.
DNA  Deoxyribonucleic acid; the long, double-helix molecule in the nucleus of cells that contains the genetic code and directs the development and functioning of all cells.
drip irrigation  Uses pipe or tubing perforated with very small holes to deliver water one drop at a time directly to the soil around each plant.
earth charter  A set of principles for sustainable development, environmental protection, and social justice developed by a council appointed by the United Nations.
earthquakes  Sudden, violent movement of the earth's crust.
ecocentric (ecologically centered)  A philosophy that claims moral values and rights for both organisms and ecological systems and processes.
ecofeminism  A pluralistic philosophy of respect for nature based on feminist philosophies of justice and egalitarianism.
ecological development  A gradual process of environmental modification by organisms.
ecological economics  Application of ecological insights to economic analysis; incorporating ecological principles and priorities into economic accounting systems.
ecological niche  The functional role and position of a species in its ecosystem, including what resources it uses, how and when it uses the resources, and how it interacts with other species.
ecological services  Processes or materials such as clean water, energy, climate regulation, and nutrient cycling provided by ecosystems.
ecological succession  The process by which organisms gradually occupy a site, alter its ecological conditions, and are eventually replaced by other organisms.
ecology  The scientific study of relationships between organisms and their environment. It is concerned with the life histories, distribution, and behavior of individual species as well as the structure and function of natural systems at the level of populations, communities, and ecosystems.
economic development  A rise in real income per person; usually associated with new technology that increases productivity or resources.
economic growth  An increase in the total wealth of a nation; if population grows faster than the economy, there may be real economic growth, but the share per person may decline.
ecosystem  A specific biological community and its physical environment interacting in an exchange of matter and energy.
ecosystem management  An integration of ecological, economic, and social goals in a unified systems approach to resource management.
ecosystem restoration  To reinstate an entire community of organisms to as near its natural condition as possible.
ecotone  A boundary between two types of ecological communities.
ecotourism  A combination of adventure travel, cultural exploration, and nature appreciation in wild settings.
edge effects  A change in species composition, physical conditions, or other ecological factors at the boundary between two ecosystems.
El Niño  A climatic change marked by shifting of a large warm water pool from the western Pacific Ocean towards the east. Wind direction and precipitation patterns are changed over much of the Pacific and perhaps around the world.
electron  A negatively charged subatomic particle that orbits around the nucleus of an atom.
element  A substance that cannot be broken into simpler units by chemical means.
emergent disease  A new disease or one that has been absent for at least 20 years.
emigration  The movement of members from a population.
emission standards  Regulations for restricting the amounts of air pollutants that can be released from specific point sources.
endangered species  A species considered to be in imminent danger of extinction.
endemism  A state in which species are restricted to a single region.
energy  The capacity to do work (that is, to change the physical state or motion of an object).
energy recovery  Incineration of solid waste to produce useful energy.
environment  The circumstances or conditions that surround an organism or group of organisms as well as the complex of social or cultural conditions that affect an individual or community.
environmental ethics  A search for moral values and ethical principles in human relations with the natural world.
environmental hormones  Chemical pollutants that substitute for, or interfere with, naturally-occurring hormones in our bodies; these chemicals may trigger reproductive failure, developmental abnormalities, or tumor promotion.
environmental impact statement (EIS)  An analysis of the effects of any major program or project planned by a federal agency; required by provisions in the National Environmental Policy Act of 1970.
environmental indicators  Organisms or physical factors that serve as a gauge for environmental changes. Indicator organisms, which cannot survive beyond certain environmental limits, are known as bioindicators.
environmental justice  Fair access to a clean, healthy environment, regardless of class, race, or income level, or other status.
environmental law  Legal rules, decisions, and actions concerning environmental quality, natural resources, and ecological sustainability.
environmental literacy  A basic understanding of ecological principles and the ways society affects, or responds to, environmental conditions.
environmental policy  The official rules or regulations concerning the environment adopted, implemented, and enforced by some governmental agency.
environmental racism  Decisions that unfairly expose people to polluted or degraded environments on the basis of race.
environmental resistance  All the limiting factors that tend to reduce population growth rates and set the maximum allowable population size or carrying capacity of an ecosystem.
environmental science  The systematic, scientific study of our environment as well as our role in it.
enzymes  Molecules, usually proteins or nucleic acids, that act as catalysts in biochemical reactions.
epidemiology  The study of the distribution and causes of disease and injuries in human populations.
epiphyte  A plant that grows on a substrate other than the soil, such as the surface of another organism.
equilibrium community  Also called a disclimax community; a community subject to periodic disruptions, usually by fire, that prevent it from reaching a climax stage.
estuary  A bay or drowned valley where a river empties into the sea.
eutrophic  Rivers and lakes rich in organic material (eu = well; trophic = nourished).
evolution  A theory that explains how random changes in genetic material and competition for scarce resources cause species to change gradually.
exhaustible resources  Materials present in fixed amounts in the environment, especially the earth's geologic endowment: minerals, nonmineral resources, fossil fuels.
exotic organisms  Alien species introduced by human agency into biological communities where they would not naturally occur.
exponential growth  Growth at a constant rate of increase per unit of time; can be expressed as a constant fraction or exponent. See geometric growth.
externalizing costs  Shifting expenses, monetary or otherwise, to someone other than the individuals or groups who use a resource.
extinction  The irrevocable elimination of species; can be a normal process of the natural world as species out-compete or kill off others or as environmental conditions change.
extirpate  To destroy totally; extinction caused by direct human action, such as hunting, trapping, etc.
family planning  Controlling reproduction; planning the timing of birth and having only as many babies as are wanted and can be supported.
famines  Acute food shortages characterized by large-scale loss of life, social disruption, and economic chaos.
fauna  All of the animals present in a given region.
fecundity  The physical ability to reproduce.
federal laws (statutes)  Laws passed by the federal legislature and signed by the chief executive.
fen  A wetland fed mainly by groundwater.
feral  A domestic animal that has taken up a wild existence.
fertility  The actual number of offspring produced through sexual reproduction; usually described in terms of number of offspring of females, since paternity can be difficult to determine.
fetal alcohol syndrome  A tragic set of permanent physical and mental and behavioral birth defects that result when mothers drink alcohol during pregnancy.
fire-climax community  An equilibrium community maintained by periodic fires; examples include grasslands, chaparral shrubland, and some pine forests.
first law of thermodynamics  States that energy is conserved; that is, it is neither created nor destroyed under normal conditions.
First World  The industrialized capitalist or market-economy countries of Western Europe, North America, Japan, Australia, and New Zealand.
flood  An overflow of water onto land that normally is dry.
floodplains  Low lands along riverbanks, lakes, and coastlines subjected to periodic inundation.
flora  All of the plants present in a given region.
food chain  A linked feeding series; in an ecosystem, the sequence of organisms through which energy and materials are transferred, in the form of food, from one trophic level to another.
food security  The ability of individuals to obtain sufficient food on a day-to-day basis.
food web  A complex, interlocking series of individual food chains in an ecosystem.
fossil fuels  Petroleum, natural gas, and coal created by geological forces from organic wastes and dead bodies of formerly living biological organisms.
fragmentation  Disruption of habitat into small, isolated fragments.
freshwater ecosystems  Ecosystems in which the fresh (nonsalty) water of streams, rivers, ponds, or lakes plays a defining role.
fuel assembly  A bundle of hollow metal rods containing uranium oxide pellets; used to fuel a nuclear reactor.
fuel cells  Mechanical devices that use hydrogen or hydrogen-containing fuel such as methane to produce an electric current. Fuel cells are clean, quiet and highly efficient sources of electricity.
fugitive emissions  Substances that enter the air without going through a smokestack, such as dust from soil erosion, strip mining, rock crushing, construction, and building demolition.
fungi  One of the five kingdom classifications; consists of nonphotosynthetic, eukaryotic organisms with cell walls, filamentous bodies, and absorptive nutrition.
fungicide  A chemical that kills fungi.
gamma rays  Very short wavelength forms of the electromagnetic spectrum.
gap analysis  A biogeographical technique of mapping biological diversity and endemic species to find gaps between protected areas that leave endangered habitats vulnerable to disruption.
gasohol  A mixture of gasoline and ethanol.
gene  A unit of heredity; a segment of DNA nucleus of the cell that contains information for the synthesis of a specific protein, such as an enzyme.
general fertility rate  Crude birthrate multiplied by the percentage of reproductive age women.
genetic assimilation  The disappearance of a species as its genes are diluted through crossbreeding with a closely related species.
genetic engineering  Laboratory manipulation of genetic material using molecular biology.
geometric growth  Growth that follows a geometric pattern of increase, such as 2, 4, 8, 16, etc. See exponential growth.
geothermal energy  Energy drawn from the internal heat of the earth, either through geysers, fumaroles, hot springs, or other natural geothermal features, or through deep wells that pump heated groundwater.
grassland  A biome dominated by grasses and associated herbaceous plants.
green plans  Integrated national environmental plans for reducing pollution and resource consumption while achieving sustainable development and environmental restoration.
green political parties  Political organizations based on environmental protection, participatory democracy, grassroots organization, and sustainable development.
green pricing  Plans in which consumers can voluntarily pay premium prices for renewable energy.
green revolution  Dramatically increased agricultural production brought about by "miracle" strains of grain; usually requires high inputs of water, plant nutrients, and pesticides.
greenhouse effect  Trapping of heat by the earth's atmosphere, which is transparent to incoming visible light waves but absorbs outgoing long-wave infrared radiation.
greenhouse gas  A gas that traps heat in the atmosphere.
gross domestic product (GDP)  The total economic activity within national boundaries.
gross national product (GNP)  The sum total of all goods and services produced in a national economy. Gross domestic product (GDP) is used to distinguish economic activity within a country from that of off-shore corporations.
groundwater  Water held in gravel deposits or porous rock below the earth's surface; does not include water or crystallization held by chemical bonds in rocks or moisture in upper soil layers.
gully erosion  Removal of layers of soil, creating channels or ravines too large to be removed by normal tillage operations.
habitat  The place or set of environmental conditions in which a particular organism lives.
habitat conservation plans  Agreements under which property owners are allowed to harvest resources or develop land as long as habitat is conserved or replaced in ways that benefit resident endangered or threatened species in the long run. Some incidental "taking" or loss of endangered species is generally allowed in such plans.
Hadley cells  Circulation patterns of atmospheric convection currents as they sink and rise in several intermediate bands.
half-life  The time required for one-half of a sample to decay or change into some other form.
hazardous waste  Any discarded material containing substances known to be toxic, mutagenic, carcinogenic, or teratogenic to humans or other life-forms; ignitable, corrosive, explosive, or highly reactive alone or with other materials.
health  A state of physical and emotional well-being; the absence of disease or ailment.
heap-leach extraction  A technique for separating gold from extremely low-grade ores. Crushed ore is piled in huge heaps and sprayed with a dilute alkaline-cyanide solution, which percolates through the pile to extract the gold, which is separated from the effluent in a processing plant. This process has a high potential for water pollution.
heat  Total kinetic energy of atoms or molecules in a substance not associated with the bulk motion of the substance.
herbicide  A chemical that kills plants.
herbivore  An organism that eats only plants.
heterotroph  An organism that is incapable of synthesizing its own food and, therefore, must feed upon organic compounds produced by other organisms.
high-level waste repository  A place where intensely radioactive wastes can be buried and remain unexposed to groundwater and earthquakes for tens of thousands of years.
high-quality energy  Intense, concentrated, and high-temperature energy that is considered high-quality because of its usefulness in carrying out work.
holistic science  The study of entire, integrated systems rather than isolated parts. Often takes a descriptive or interpretive approach.
homeostasis  Maintaining a dynamic, steady state in a living system through opposing, compensating adjustments.
humus  Sticky, brown, insoluble residue from the bodies of dead plants and animals; gives soil its structure, coating mineral particles and holding them together; serves as a major source of plant nutrients.
hurricanes  Large cyclonic oceanic storms with heavy rain and winds exceeding 119 km/hr (74 mph).
hypothesis  A conditional explanation that can be verified or falsified by observation or experimentation.
igneous rocks  Crystalline minerals solidified from molten magma from deep in the earth's interior; basalt, rhyolite, andesite, lava, and granite are examples.
inbreeding depression  In a small population, an accumulation of harmful genetic traits (through random mutations and natural selection) that lowers viability and reproductive success of enough individuals to affect the whole population.
inductive reasoning  A series of logical steps that attempt to derive general principles or laws by studying specific cases.
industrial revolution  Advances in science and technology that have given us power to understand and change our world.
infiltration  The process of water percolation into the soil and pores and hollows of permeable rocks.
inherent value  Ethical values or rights that exist as an intrinsic or essential characteristic of a particular thing or class of things simply by the fact of their existence.
inholdings  Private lands within public parks, forests, or wildlife refuges.
insecticide  A chemical that kills insects.
insolation  Incoming solar radiation.
instrumental value  Value or worth of objects that satisfy the needs and wants of moral agents. Objects that can be used as a means to some desirable end.
intangible resources  Factors such as open space, beauty, serenity, wisdom, diversity, and satisfaction that cannot be grasped or contained. Ironically, these resources can be both infinite and exhaustible.
integrated pest management (IPM)  An ecologically based pest-control strategy that relies on natural mortality factors, such as natural enemies, weather, cultural control methods, and carefully applied doses of pesticides.
internalizing costs  Planning so that those who reap the benefits of resource use also bear all the external costs.
international treaties and conventions  Agreements between nations on important issues.
interspecific competition  In a community, competition for resources between members of different species.
intraspecific competition  In a community, competition for resources among members of the same species.
ionizing radiation  High-energy electromagnetic radiation or energetic subatomic particles released by nuclear decay.
ionosphere  The lower part of the thermosphere.
ions  Electrically charged atoms that have gained or lost electrons.
irruptive growth  See Malthusian growth.
island biogeography  The study of rates of colonization and extinction of species on islands or other isolated areas based on size, shape, and distance from other inhabited regions.
isotopes  Forms of a single element that differ in atomic mass due to a different number of neutrons in the nucleus.
J curve  A growth curve that depicts exponential growth; called a J curve because of its shape.
jet streams  Powerful winds or currents of air that circulate in shifting flows; similar to oceanic currents in extent and effect on climate.
joule  A unit of energy. One joule is the energy expended in 1 second by a current of 1 amp flowing through a resistance of 1 ohm.
keystone species  A species whose impacts on its community or ecosystem are much larger and more influential than would be expected from mere abundance. This could be a top predator, a plant that shelters or feeds other organisms, or an organism that plays a critical ecological role.
kinetic energy  Energy contained in moving objects such as a rock rolling down a hill, the wind blowing through the trees, or water flowing over a dam.
kwashiorkor  A widespread human protein deficiency disease resulting from a starchy diet low in protein and essential amino acids.
landscape ecology  The study of the reciprocal effects of spatial pattern on ecological processes.
landslides  Mass wasting or mass movement of rock or soil downhill. Often triggered by seismic events or heavy rainfall.
LD50  A chemical dose lethal to 50 percent of a test population.
legal standing  The right to take part in legal proceedings.
less-developed countries (LDC)  Non-industrialized nations characterized by low per capita income, high birthrates and death rates, high population growth rates, and low levels of technological development.
life expectancy  The average age that a newborn infant can expect to attain in a particular time and place.
life span  The longest period of life reached by a type of organism.
limiting factors  Chemical or physical factors that limit the existence, growth, abundance, or distribution of an organism.
limits to growth  A belief that the world has a fixed carrying capacity for humans.
lobbying  Using personal contacts, public pressure, or political action to persuade legislators to vote in a particular manner.
logical thinking  A rational way of thought that asks, "How can orderly, deductive reasoning help me think clearly?"
logistic growth  Growth rates regulated by internal and external factors that establish an equilibrium with environmental resources. See S curve.
longevity  The length or duration of life; compare to survivorship.
low-quality energy  Diffuse, dispersed energy at a low temperature that is difficult to gather and use for productive purposes.
LULUs  Locally Unwanted Land Uses such as toxic waste dumps, incinerators, smelters, airports, freeways, and other sources of environmental, economic, or social degradation.
magma  Molten rock from deep in the earth's interior; called lava when it spews from volcanic vents.
malnourishment  A nutritional imbalance caused by lack of specific dietary components or inability to absorb or utilize essential nutrients.
Malthusian growth  A population explosion followed by a population crash; also called irruptive growth.
Man and Biosphere (MAB) program  A design for nature preserves that divides protected areas into zones with different purposes. A highly protected core is surrounded by a buffer zone and peripheral regions in which multiple-use resource harvesting is permitted.
mantle  A hot, pliable layer of rock that surrounds the earth's core and underlies the cool, outer crust.
marasmus  A widespread human protein deficiency disease caused by a diet low in calories and protein or imbalanced in essential amino acids.
marginal costs  The cost to produce one additional unit of a good or service.
marsh  Wetland without trees; in North America, this type of land is characterized by cattails and rushes.
mass burn  Incineration of unsorted solid waste.
matter  Anything that takes up space and has mass.
mediation  An informal dispute resolution process in which parties try to reach agreement through discussion and compromise; often used as an alternative to resolving disputes through lawsuits.
Mediterranean climate areas  Regions defined by warm, dry summers and cool, wet winters; these areas may have distinctive and endemic species.
megacity  See megalopolis.
megalopolis  Also known as a megacity or supercity; megalopolis indicates an urban area with more than 10 million inhabitants.
megawatt (MW)  Unit of electrical power equal to one thousand kilowatts or one million watts.
mesosphere  The atmospheric layer above the stratosphere and below the thermosphere; the middle layer; temperatures are usually very low.
metabolism  All the energy and matter exchanges that occur within a living cell or organism; collectively, the life processes.
metamorphic rock  Igneous and sedimentary rocks modified by heat, pressure, and chemical reactions.
methane hydrate  Small bubbles or individual molecules of methane (natural gas) trapped in a crystalline matrix of frozen water.
midoceanic ridges  Mountain ranges on the ocean floor where magma wells up through cracks and creates new crust.
Milankovitch cycles  Periodic variations in tilt, eccentricity, and wobble in the earth's orbit; Milutin Milankovitch suggested these are responsible for cyclic weather changes.
mineral  A naturally occurring, inorganic, crystalline solid with definite chemical composition, a specific internal crystal structure, and characteristic physical properties.
mitigation  Repairing or rehabilitating a damaged ecosystem or compensating for damage by providing a substitute or replacement area.
molecule  A combination of two or more atoms.
monitored, retrievable storage  Holding wastes in underground mines or secure surface facilities such as dry casks where they can be watched and repackaged, if necessary.
monoculture forestry  Intensive planting of a single species; an efficient wood production approach, but one that encourages pests and disease infestations and conflicts with wildlife habitat or recreation uses.
monsoon  A seasonal reversal of wind patterns caused by the different heating and cooling rates of the oceans and continents.
montane coniferous forests  Coniferous forests of the mountains consisting of belts of different forest communities along an altitudinal gradient.
morals  A set of ethical principles that guide our actions and relationships.
morbidity  Illness or disease.
more-developed countries (MDC)  Industrialized nations characterized by high per capita incomes, low birth and death rates, low population growth rates, and high levels of industrialization and urbanization.
mortality  Death rate in a population, e.g., number of deaths per thousand people per year.
mulch  Protective ground cover that protects the soil, saves water, and prevents weed growth; often straw, seaweed, leaves, or synthetic materials, such as heavy paper or plastic.
Müllerian (or Muellerian) mimicry  Evolution of two species, both of which are unpalatable and, have poisonous stingers or some other defense mechanism, to resemble each other.
multiple use  Many uses that occur simultaneously; used in forest management; limited to mutually compatible uses.
mutagens  Agents, such as chemicals or radiation, that damage or alter genetic material (DNA) in cells.
mutation  A change, either spontaneous or by external factors, in the genetic material of a cell; mutations in the gametes (sex cells) can be inherited by future generations of organisms.
mutualism  A symbiotic relationship between individuals of two different species in which both species benefit from the association.
National Environmental Policy Act (NEPA)  The law that established the Council on Environmental Quality and that requires environmental impact statements for all federal projects with significant environmental impacts.
natural increase  Crude death rate subtracted from crude birthrate.
natural resources  Goods and services supplied by the environment.
natural selection  The mechanism for evolutionary change in which environmental pressures cause certain genetic combinations in a population to become more abundant; genetic combinations best adapted for present environmental conditions tend to become predominant.
negative feedbacks  Factors that result from a process and, in turn, reduce that same process.
neo-classical economics  A branch of economics that attempts to apply the principles of modern science to economic analysis in a mathematically rigorous, non-contextual, abstract, predictive manner.
neo-Malthusian  A belief that the world is characterized by scarcity and competition in which too many people fight for too few resources. Named for Thomas Malthus, who predicted a dismal cycle of misery, vice, and starvation as a result of human overpopulation.
net energy yield  Total useful energy produced during the lifetime of an entire energy system minus the energy used, lost, or wasted in making useful energy available.
neurotoxins  Toxic substances, such as lead or mercury, that specifically poison nerve cells.
neutron  A subatomic particle, found in the nucleus of the atom, that has no electromagnetic charge.
NIMBY  Not-In-My-Back-Yard: the position of those opposed to LULUs.
nitrogen cycle  The circulation and reutilization of nitrogen in both inorganic and organic phases.
nitrogen oxides  Highly reactive gases formed when nitrogen in fuel or combustion air is heated to over 650° C (1200° F) in the presence of oxygen or when bacteria in soil or water oxidize nitrogen-containing compounds.
nitrogen-fixing bacteria  Bacteria that convert nitrogen from the atmosphere or soil solution into ammonia that can then be converted to plant nutrients by nitrite- and nitrate-forming bacteria.
noncriteria pollutants  See unconventional air pollutants.
nongovernmental organizations (NGOs)  A term referring collectively to pressure and research groups, advisory agencies, political parties, professional societies, and other groups concerned about environmental quality, resource use, and many other issues.
nonpoint sources  Scattered, diffuse sources of pollutants, such as runoff from farm fields, golf courses, construction sites, etc.
nonrenewable resources  Minerals, fossil fuels, and other materials present in essentially fixed amounts (within human time scales) in our environment.
nuclear fission  The radioactive decay process in which isotopes split apart to create two smaller atoms.
nuclear fusion  A process in which two smaller atomic nuclei fuse into one larger nucleus and release energy; the source of power in a hydrogen bomb.
nucleic acids  Large organic molecules made of nucleotides that function in the transmission of hereditary traits, in protein synthesis, and in control of cellular activities.
nucleus  The center of the atom; occupied by protons and neutrons. In cells, the organelle that contains the chromosomes (DNA).
numbers pyramid  A diagram showing the relative population sizes at each trophic level in an ecosystem; usually corresponds to the biomass pyramid.
offset allowances  A controversial component of air quality regulations that allows a polluter to avoid installation of control equipment on one source with an "offsetting" pollution reduction at another source.
oil shale  A fine-grained sedimentary rock rich in solid organic material called kerogen. When heated, the kerogen liquefies to produce a fluid petroleum fuel.
old-growth forests  Forests free from disturbance for long enough (generally 150 to 200 years) to have mature trees, physical conditions, species diversity, and other characteristics of equilibrium ecosystems.
oligotrophic  Condition of rivers and lakes that have clear water and low biological productivity (oligo = little; trophic = nourished); are usually clear, cold, infertile headwater lakes and streams.
omnivore  An organism that eats both plants and animals.
open access system  A commonly held resource for which there are no management rules.
open canopy  A forest where tree crowns cover less than 20 percent of the ground; also called woodland.
open system  A system that exchanges energy and matter with its environment.
organic compounds  Complex molecules organized around skeletons of carbon atoms arranged in rings or chains; includes biomolecules, molecules synthesized by living organisms.
overnutrition  Receiving too many calories.
overshoot  The extent to which a population exceeds the carrying capacity of its environment.
oxygen sag  Oxygen decline downstream from a pollution source that introduces materials with high biological oxygen demands.
ozone  A highly reactive molecule containing three oxygen atoms; a dangerous pollutant in ambient air. In the stratosphere, however, ozone forms an ultraviolet absorbing shield that protects us from mutagenic radiation.
paradigms  Overarching models of the world that shape our worldviews and guide our interpretation of how things are.
parasite  An organism that lives in or on another organism, deriving nourishment at the expense of its host, usually without killing it.
particulate material  Atmospheric aerosols, such as dust, ash, soot, lint, smoke, pollen, spores, algal cells, and other suspended materials; originally applied only to solid particles but now extended to droplets of liquid.
parts per billion (ppb)  Number of parts of a chemical found in one billion parts of a particular gas, liquid, or solid mixture.
parts per million (ppm)  Number of parts of a chemical found in one million parts of a particular gas, liquid, or solid mixture.
parts per trillion (ppt)  Number of parts of a chemical found in one trillion parts of a particular gas, liquid, or solid mixture.
passive heat absorption  The use of natural materials or absorptive structures without moving parts to gather and hold heat; the simplest and oldest use of solar energy.
pastoralist  Someone who lives by herding domestic animals.
patchiness  Within a larger ecosystem, the presence of smaller areas that differ in some physical conditions and thus support somewhat different communities; promotes diversity in a system or area.
pathogen  An organism that produces disease in a host organism, disease being an alteration of one or more metabolic functions in response to the presence of the organism.
peat  Deposits of moist, acidic, semi-decayed organic matter.
perennial species  Plants that grow for more than two years.
permafrost  A permanently frozen layer of soil that underlies the arctic tundra.
permanent retrievable storage  Placing waste storage containers in a secure building, salt mine, or bedrock cavern where they can be inspected periodically and retrieved, if necessary, for repacking or for transfer if a better means of disposal or reuse is developed.
persistent organic pollutant (POP)  Chemical compounds that persist in the environment and retain biological activity for a long time.
pest  Any organism that reduces the availability, quality, or value of a useful resource.
pest resurgence  Rebound of pest populations due to acquired resistance to chemicals and nonspecific destruction of natural predators and competitors by broadscale pesticides.
pesticide  Any chemical that kills, controls, drives away, or modifies the behavior of a pest.
pesticide treadmill  A need for constantly increasing doses or new pesticides to prevent pest resurgence.
pH  A value that indicates the acidity or alkalinity of a solution on a scale of 0 to 14, based on the proportion of H+ ions present.
phosphorus cycle  The movement of phosphorus atoms from rocks through the biosphere and hydrosphere and back to rocks.
photochemical oxidants  Products of secondary atmospheric reactions. See smog.
photodegradable plastics  Plastics that break down when exposed to sunlight or to a specific wavelength of light.
photosynthesis  The biochemical process by which green plants and some bacteria capture light energy and use it to produce chemical bonds. Carbon dioxide and water are consumed while oxygen and simple sugars are produced.
photovoltaic cell  An energy-conversion device that captures solar energy and directly converts it to electrical current.
phytoplankton  Microscopic, free-floating, autotrophic organisms that function as producers in aquatic ecosystems.
pioneer species  In primary succession on a terrestrial site, the plants, lichens, and microbes that first colonize the site.
plankton  Primarily microscopic organisms that occupy the upper water layers in both freshwater and marine ecosystems.
plasma  A hot, electrically neutral gas of ions and free electrons.
poaching  Hunting wildlife illegally.
point sources  Specific locations of highly concentrated pollution discharge, such as factories, power plants, sewage treatment plants, underground coal mines, and oil wells.
policy  A societal plan to statement of intentions intended to accomplish some social or economic goal.
policy cycle  The process by which problems are identified and acted upon in the public arena.
pollution  To make foul, unclean, dirty; any physical, chemical, or biological change that adversely affects the health, survival, or activities of living organisms or that alters the environment in undesirable ways.
pollution charges  Fees assessed per unit of pollution based on the "polluter pays" principle.
population  A group of individuals of the same species occupying a given area.
population crash  A sudden population decline caused by predation, waste accumulation, or resource depletion; also called a dieback.
population explosion  Growth of a population at exponential rates to a size that exceeds environmental carrying capacity; usually followed by a population crash.
population momentum  A potential for increased population growth as young members reach reproductive age.
positive feedbacks  Factors that result from a process and, in turn, increase that same process.
positivism  A philosophy that says we should depend only on testable facts and direct physical observation.
potential energy  Stored energy that is latent but available for use. A rock poised at the top of a hill or water stored behind a dam are examples of potential energy.
power  The rate of energy delivery; measured in horsepower or watts.
precautionary principle  The rule that we should leave a margin of safety for unexpected developments. This principle implies that we should strive to prevent harm to human health and the environment even if risks are not fully understood.
precedent  An act or decision that can be used as an example in dealing with subsequent similar situations.
predator  An organism that feeds directly on other organisms in order to survive; live-feeders, such as herbivores and carnivores.
primary pollutants  Chemicals released directly into the air in a harmful form.
primary productivity  Synthesis of organic materials (biomass) by green plants using the energy captured in photosynthesis.
primary standards  Regulations of the 1970 Clean Air Act; intended to protect human health.
primary succession  Ecological succession that begins in an area where no biotic community previously existed.
primary treatment  A process that removes solids from sewage before it is discharged or treated further.
principle of competitive exclusion  A result of natural selection whereby two similar species in a community occupy different ecological niches, thereby reducing competition for food.
producer  An organism that synthesizes food molecules from inorganic compounds by using an external energy source; most producers are photosynthetic.
prokaryotic  Cells that do not have a membrane-bounded nucleus or membrane-bounded organelles.
pronatalist pressures  Influences that encourage people to have children.
prospective study  A study in which experimental and control groups are identified before exposure to some factor. The groups are then monitored and compared for a specific time after the exposure to determine any effects the factor may have.
proteins  Chains of amino acids linked by peptide bonds.
proton  A positively charged subatomic particle found in the nucleus of an atom.
pull factors (in urbanization)  Conditions that draw people from the country into the city.
push factors (in urbanization)  Conditions that force people out of the country and into the city.
radioactive decay  A change in the nuclei of radioactive isotopes that spontaneously emit high-energy electromagnetic radiation and/or subatomic particles while gradually changing into another isotope or different element.
rain shadow  Dry area on the downwind side of a mountain.
rainforest  A forest with high humidity, constant temperature, and abundant rainfall (generally over 380 cm [150 in] per year); can be tropical or temperate.
rangeland  Grasslands and open woodlands suitable for livestock grazing.
rational choice  Public decision making based on reason, logic, and science-based management.
reasoned judgment  Thoughtful decisions based on careful, logical examination of available evidence.
recharge zone  Area where water infiltrates into an aquifer.
reclamation  Chemical, biological, or physicalclean-up and reconstruction of severely contaminated or degraded sites to return them to something like their original topography and vegetation.
recycling  Reprocessing of discarded materials into new, useful products; not the same as reuse of materials for their original purpose, but the terms are often used interchangeably.
red tide  A population explosion or "bloom" of single-celled marine organisms called dinoflagellates. Billions of these cells can accumulate in protected bays where the toxins they contain can poison other marine life.
reduced tillage systems  Farming methods that preserve soil and save energy and water through reduced cultivation; includes minimum till, conserve-till, and no-till systems.
reflective thinking  A thoughtful, contemplative analysis that asks, "What does this all mean?"
reformer  A device that strips hydrogen from fuels such as natural gas, methanol, ammonia, gasoline, or vegetable oil so they can be used in a fuel cell.
refuse-derived fuel  Processing of solid waste to remove metal, glass, and other unburnable materials; organic residue is shredded, formed into pellets, and dried to make fuel for power plants.
regenerative farming  Farming techniques and land stewardship that restore the health and productivity of the soil by rotating crops, planting ground cover, protecting the surface with crop residue, and reducing synthetic chemical inputs and mechanical compaction.
regulations  Rules established by administrative agencies; regulations can be more important than statutory law in the day-to-day management of resources.
rehabilitation  Rebuilding basic structure or function in an ecological system without necessarily achieving complete restoration to its original condition.
relative humidity  At any given temperature, a comparison of the actual water content of the air with the amount of water that could be held at saturation.
relevé  A rapid assessment of vegetation types and biodiversity in an area.
remediation  Cleaning up chemical contaminants from a polluted area.
renewable resources  Resources normally replaced or replenished by natural processes; resources not depleted by moderate use; examples include solar energy, biological resources such as forests and fisheries, biological organisms, and some biogeochemical cycles.
renewable water supplies  Annual freshwater surface runoff plus annual infiltration into underground freshwater aquifers that are accessible for human use.
residence time  The length of time a component, such as an individual water molecule, spends in a particular compartment or location before it moves on through a particular process or cycle.
resilience  The ability of a community or ecosystem to recover from disturbances.
resistance (inertia)  The ability of a community to resist being changed by potentially disruptive events.
resource  In economic terms, anything with potential use in creating wealth or giving satisfaction.
resource partitioning  In a biological community, various populations sharing environmental resources through specialization, thereby reducing direct competition. See also ecological niche.
restoration  To bring something back to a former condition. Ecological restoration involves active manipulation of nature to re-create conditions that existed before human disturbance.
restoration ecology  Seeks to repair or reconstruct ecosystems damaged by human actions.
retrospective study  A study that looks back in history at a group of people (or other organisms) who suffer from some condition to try to identify something in their past life that the whole group shares in common but that is not found in the histories of a control group as near as possible to those being studied but who do not suffer from the same condition.
riders  Amendments attached to bills in conference committee, often completely unrelated to the bill to which they are added.
rill erosion  The removing of thin layers of soil as little rivulets of running water gather and cut small channels in the soil.
risk  Probability that something undesirable will happen as a consequence of exposure to a hazard.
risk assessment  Evaluation of the short-term and long-term risks associated with a particular activity or hazard; usually compared to benefits in a cost-benefit analysis.
rock  A solid, cohesive, aggregate of one or more crystalline minerals.
rock cycle  The process whereby rocks are broken down by chemical and physical forces; sediments are moved by wind, water, and gravity, sedimented and reformed into rock, and then crushed, folded, melted, and recrystallized into new forms.
rotational grazing  Confining grazing animals in a small area for a short time to force them to eat weedy species as well as the more desirable grasses and forbes.
runoff  The excess of precipitation over evaporation; the main source of surface water and, in broad terms, the water available for human use.
S curve  A curve that depicts logistic growth; called an S curve because of its shape.
salinity  Amount of dissolved salts (especially sodium chloride) in a given volume of water.
salinization  A process in which mineral salts accumulate in the soil, killing plants; occurs when soils in dry climates are irrigated profusely.
saltwater intrusion  Movement of saltwater into freshwater aquifers in coastal areas where groundwater is withdrawn faster than it is replenished.
sanitary landfills  A landfill in which garbage and municipal waste is buried every day under enough soil or fill to eliminate odors, vermin, and litter.
scientific method  A systematic, precise, objective study of a problem. Generally this requires observation, hypothesis development and testing, data gathering, and interpretation.
scientific theory  An explanation or idea accepted by a substantial number of scientists.
second law of thermodynamics  States that, with each successive energy transfer or transformation in a system, less energy is available to do work.
secondary pollutants  Chemicals modified to a hazardous form after entering the air or that are formed by chemical reactions as components of the air mix and interact.
secondary succession  Succession on a site where an existing community has been disrupted.
secondary treatment  Bacterial decomposition of suspended particulates and dissolved organic compounds that remain after primary sewage treatment.
secure landfill  A solid waste disposal site lined and capped with an impermeable barrier to prevent leakage or leaching. Drain tiles, sampling wells, and vent systems provide monitoring and pollution control.
sedimentary rock  Rock composed of accumulated, compacted mineral fragments, such as sand or clay; examples include shale, sandstone, breccia, and conglomerates.
sedimentation  The deposition of organic materials or minerals by chemical, physical, or biological processes.
selective cutting  Harvesting only mature trees of certain species and size; usually more expensive than clear-cutting, but less disruptive for wildlife and often better for forest regeneration.
selective pressure  Limited resources or adverse environmental conditions that tend to favor certain adaptations in a population. Over many generations, this can lead to genetic change, or evolution.
sheet erosion  Peeling off thin layers of soil from the land surface; accomplished primarily by wind and water.
sinkholes  A large surface crater caused by the collapse of an underground channel or cavern; often triggered by groundwater withdrawal.
sludge  Semisolid mixture of organic and inorganic materials that settles out of wastewater at a sewage treatment plant.
smelting  Roasting ore to release metals from mineral compounds.
smog  The term used to describe the combination of smoke and fog in the stagnant air of London; now often applied to photochemical pollution.
social justice  Equitable access to resources and the benefits derived from them; a system that recognizes inalienable rights and adheres to what is fair, honest, and moral.
soil  A complex mixture of weathered rock material, partially decomposed organic molecules, and a host of living organisms.
soil horizons  Horizontal layers that reveal a soil's history, characteristics, and usefulness.
species  A population of morphologically similar organisms that can reproduce sexually among themselves but that cannot produce fertile offspring when mated with other organisms.
species diversity  The number and relative abundance of species present in a community.
species recovery plan  A plan for restoration of an endangered species through protection, habitat management, captive breeding, disease control, or other techniques that increase populations and encourage survival.
specific heat  The amount of heat energy needed to change the temperature of a body. Water has a specific heat of 1, which is higher than most substances.
stability  In ecological terms, a dynamic equilibrium among the physical and biological factors in an ecosystem or a community; relative homeostasis.
stable runoff  The fraction of water available year-round; usually more important than total runoff when determining human uses.
Standard Metropolitan Statistical Area (SMSA)  An urbanized region with at least 100,000 inhabitants with strong economic and social ties to a central city of at least 50,000 people.
statutory law  Rules passed by a state or national legislature.
steady-state economy  Characterized by low birth and death rates, use of renewable energy sources, recycling of materials, and emphasis on durability, efficiency, and stability.
stewardship  A philosophy that holds that humans have a unique responsibility to manage, care for, and improve nature.
stomates  The small openings in leaves, herbaceous stems, and fruits through which gases and water vapor pass.
strategic lawsuits against public participation (SLAPP)  Lawsuits that have no merit but are brought merely to intimidate and harass private citizens who act in the public interest.
strategic metals and minerals  Materials a country cannot produce itself but that it uses for essential materials or processes.
stratosphere  The zone in the atmosphere extending from the tropopause to about 50 km (30 mi) above the earth's surface; temperatures are stable or rise slightly with altitude; has very little water vapor but is rich in ozone.
stress  Physical, chemical, or emotional factors that place a strain on an animal. Plants also experience physiological stress under adverse environmental conditions.
strip-cutting  Harvesting trees in strips narrow enough to minimize edge effects and to allow natural regeneration of the forest.
strip-farming  Planting different kinds of crops in alternating strips along land contours; when one crop is harvested, the other crop remains to protect the soil and prevent water from running straight down a hill.
strip-mining  Extracting shallow mineral deposits (especially coal) by scraping off surface layers with giant, earth-moving equipment; creates a huge open-pit; an alternative to underground or deep open pit mines.
subsidence  Settling of the ground surface caused by the collapse of porous formations that result from withdrawal of large amounts of groundwater, oil, or other underground materials.
subsoil  A layer of soil beneath the topsoil that has lower organic content and higher concentrations of fine mineral particles; often contains soluble compounds and clay particles carried down by percolating water.
sulfur cycle  The chemical and physical reactions by which sulfur moves into or out of storage and through the environment.
sulfur dioxide  A colorless, corrosive gas directly damaging to both plants and animals.
Superfund  A fund established by Congress to pay for containment, cleanup, or remediation of abandoned toxic waste sites. The fund is financed by fees paid by toxic waste generators and by cost-recovery from cleanup projects.
surface mining  Some minerals are also mined from surface pits. See strip-mining.
surface tension  The tendency for a surface of water molecules to hold together, producing a surface that resists breaking.
survivorship  The percentage of a population reaching a given age or the proportion of the maximum life span of the species reached by any individual.
sustainability  Ecological, social, and economic systems that can last over the long term.
sustainable agriculture  Ecologically sound, economically viable, socially just agricultural system. Stewardship, soil conservation, and integrated pest management are essential for sustainability.
sustainable development  A real increase in well-being and standard of life for the average person that can be maintained over the long-term without degrading the environment or compromising the ability of future generations to meet their own needs.
sustained yield  Utilization of a renewable resource at a rate that does not impair or damage its ability to be fully renewed on a long-term basis.
swamp  Wetland with trees, such as the extensive swamp forests of the southern United States.
symbiosis  The intimate living together of members of two different species; includes mutualism, commensalism, and, in some classifications, parasitism.
synergism  When an injury caused by exposure to two environmental factors together is greater than the sum of exposure to each factor individually.
taiga  The northernmost edge of the boreal forest, including species-poor woodland and peat deposits; intergrading with the arctic tundra.
tailings  Mining waste left after mechanical or chemical separation of minerals from crushed ore.
taking  Unconstitutional confiscation of private property.
technological optimists  Those who believe that technology and human enterprise will find cures for all our problems. Also called Promethean environmentalism.
tectonic plates  Huge blocks of the earth's crust that slide around slowly, pulling apart to open new ocean basins or crashing ponderously into each other to create new, larger landmasses.
temperate rainforest  The cool, dense, rainy forest of the northern Pacific coast; enshrouded in fog much of the time; dominated by large conifers.
temperature  A measure of the speed of motion of a typical atom or molecule in a substance.
teratogens  Chemicals or other factors that specifically cause abnormalities during embryonic growth and development.
terracing  Shaping the land to create level shelves of earth to hold water and soil; requires extensive hand labor or expensive machinery, but it enables farmers to farm very steep hillsides.
tertiary treatment  The removal of inorganic minerals and plant nutrients after primary and secondary treatment of sewage.
thermal pollution  Artificially raising or lowering the temperature of a water body in a way that adversely affects the biota or water quality.
thermocline  In water, a distinctive temperature transition zone that separates an upper layer that is mixed by the wind (the epilimnion) and a colder, deep layer that is not mixed (the hypolimnion).
thermodynamics  A branch of physics that deals with transfers and conversions of energy. The first law of thermodynamics is that energy can be transformed and transferred, but cannot be destroyed or created. The second law states that with each successive energy transfer or transformation, less energy is available to do work.
thermosphere  The highest atmospheric zone; a region of hot, dilute gases above the mesosphere extending out to about 1,600 km (1,000 mi) from the earth's surface.
Third World  Less-developed countries that are not capitalistic and industrialized (First World) or centrally-planned socialist economies (Second World); not intended to be derogatory.
thorn shrub  A dry, open woodland or shrubland characterized by sparse, spiny shrubs.
threatened species  While still abundant in parts of its territorial range, this species has declined significantly in total numbers and may be on the verge of extinction in certain regions or localities.
tolerance limits  See limiting factors.
topsoil  The first true layer of soil; layer in which organic material is mixed with mineral particles; thickness ranges from a meter or more under virgin prairie to zero in some deserts.
total fertility rate  The number of children born to an average woman in a population during her entire reproductive life.
total growth rate  The net rate of population growth resulting from births, deaths, immigration, and emigration.
total maximum daily loads (TMDL)  The amount of particular pollutant that a water body can receive from both point and non-point sources and still meet water quality standards.
toxic release inventory  A program created by the Superfund Amendments and Reauthorization Act of 1984 that requires manufacturing facilities and waste handling and disposal sites to report annually on releases of more than 300 toxic materials. You can find out from the EPA whether any of these sites are in your neighborhood and what toxics they release.
toxins  Poisonous chemicals that react with specific cellular components to kill cells or to alter growth or development in undesirable ways; often harmful, even in dilute concentrations.
tradable permits  Pollution quotas or variances that can be bought or sold.
tragedy of the commons  An inexorable process of degradation of communal resources due to selfish self-interest of "free riders" who use or destroy more than their fair share of common property. See open access system.
transpiration  The evaporation of water from plant surfaces, especially through stomates.
trophic level  Step in the movement of energy through an ecosystem; an organism's feeding status in an ecosystem.
tropical rainforest  Forest near the equator in which rainfall is abundant-more than 200 cm (80 in) per year-and temperatures are warm to hot year-round.
tropical seasonal forest  Semi-evergreen or partly deciduous forests tending toward open woodlands and grassy savannas dotted with scattered, drought-resistant trees.
tropopause  The boundary between the troposphere and the stratosphere.
troposphere  The layer of air nearest to the earth's surface; both temperature and pressure usually decrease with increasing altitude.
tundra  Treeless arctic or alpine biome characterized by cold, dark winters, a short growing season, and potential for frost any month of the year; vegetation includes low-growing perennial plants, mosses, and lichens.
unconventional air pollutants  Toxic or hazardous substances, such as asbestos, benzene, beryllium, mercury, polychlorinated biphenyls, and vinyl chloride, not listed in the original Clean Air Act because they were not released in large quantities; also called noncriteria pollutants.
undernourished  Those who receive less than 90 percent of the minimum dietary intake over a long-term time period; they lack energy for an active, productive life and are more susceptible to infectious diseases.
urban renewal  Programs to revitalize old, blighted sections of inner cities.
urbanization  An increasing concentration of the population in cities and a transformation of land use to an urban pattern of organization.
utilitarian conservation  A philosophy that resources should be used for the greatest good for the greatest number for the longest time.
values  An estimation of the worth of things; a set of ethical beliefs and preferences that determine our sense of right and wrong.
vertical stratification  The vertical distribution of specific subcommunities within a community.
visible light  A portion of the electromagnetic spectrum that includes the wavelengths used for photosynthesis.
vitamins  Organic molecules essential for life that we cannot make for ourselves; we must get them from our diet; they act as enzyme cofactors.
volatile organic compounds (VOCs)  Organic chemicals that evaporate readily and exist as gases in the air.
volcano  A vent in the earth's surface through which molten lava (magma), gases, and ash escape to create a mountain.
vulnerable species  Naturally rare organisms or species whose numbers have been so reduced by human activities that they are susceptible to actions that could push them into threatened or endangered status.
warm front  A long, wedge-shaped boundary caused when a warmer advancing air mass slides over neighboring cooler air parcels.
waste stream  The steady flow of varied wastes, from domestic garbage and yard wastes to industrial, commercial, and construction refuse.
water cycle  The recycling and reutilization of water on Earth, including atmospheric, surface, and underground phases and biological and nonbiological components.
water stress  A situation when residents of a country don't have enough accessible, high-quality water to meet their everyday needs.
water table  The top layer of the zone of saturation; undulates according to the surface topography and subsurface structure.
waterlogging  Water saturation of soil that fills all air spaces and causes plant roots to die from lack of oxygen; a result of over-irrigation.
watershed  The land surface and groundwater aquifers drained by a particular river system.
weather  Description of the physical conditions of the atmosphere (moisture, temperature, pressure, and wind).
weathering  Changes in rocks brought about by exposure to air, water, changing temperatures, and reactive chemical agents.
wetlands  Ecosystems of several types in which rooted vegetation is surrounded by standing water during part of the year. See also swamp, marsh, bog, fen.
wicked problems  Problems with no simple right or wrong answer where there is no single, generally agreed on definition of or solution for the particular issue.
wilderness  An area of undeveloped land affected primarily by the forces of nature; an area where humans are visitors who do not remain.
wildlife refuges  Areas set aside to shelter, feed, and protect wildlife; due to political and economic pressures, refuges often allow hunting, trapping, mineral exploitation, and other activities that threaten wildlife.
wind farms  Large numbers of windmills concentrated in a single area; usually owned by a utility or large-scale energy producer.
Wise Use Movement  A coalition of ranchers, loggers, miners, industrialists, hunters, off-road vehicle users, land developers, and others who call for unrestricted access to natural resources and public lands.
withdrawal  A description of the total amount of water taken from a lake, river, or aquifer.
woodland  A forest where tree crowns cover less than 20 percent of the ground; also called open canopy forest.
work  The application of force through a distance; requires energy input.
world conservation strategy  A proposal for maintaining essential ecological processes, preserving genetic diversity, and ensuring that utilization of species and ecosystems is sustainable.
World Trade Organization (WTO)  An association of 135 nations that meet to regulate international trade.
X ray  Very short wavelength in the electromagnetic spectrum; can penetrate soft tissue; although it is useful in medical diagnosis, it also damages tissue and causes mutations.
zero population growth (ZPG)  A condition in which births and immigration in a population just balance deaths and emigration.
zone of aeration  Upper soil layers that hold both air and water.
zone of leaching  The layer of soil just beneath the topsoil where water percolates, removing soluble nutrients that accumulate in the subsoil; may be very different in appearance and composition from the layers above and below it.
zone of saturation  Lower soil layers where all spaces are filled with water.