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Environmental Science: A Global Concern, 7/e
William P. Cunningham, University of Minnesota
Mary Ann Cunningham, Vassar College
Barbara Woodworth Saigo, St. Cloud State University

Glossary S-Z

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saltwater intrusion  Movement of saltwater into freshwater aquifers in coastal areas where groundwater is withdrawn faster than it is replenished.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.
saturation point  The maximum concentration of water vapor the air can hold at a given temperature.
scavenger  An organism that feeds on the dead bodies of other organisms.
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 supported by many tests and accepted by a general consensus of scientists.
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 recovery technique  Pumping pressurized gas, steam, or chemical-containing water into a well to squeeze more oil from a reservoir.
secondary standards  Regulations of the 1972 Clean Air Act intended to protect materials, crops, visibility, climate, and personal comfort.
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.
second law of thermodynamics  States that, with each successive energy transfer or transformation in a system, less energy is available to do work.
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  Deposited material that remains in place long enough or is covered with enough material to compact into stone; 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 it is less disruptive for wildlife and often better for forest regeneration.
seriously undernourished  Those who receive less than 80 percent of their minimum daily caloric requirements.
shallow ecology  A critical term applied to superficial environmentalists who claim to be green but are quick to compromise and who do little to bring about fundamental change.
shantytowns  Settlements created when people move onto undeveloped lands and build their own shelter with cheap or discarded materials; some are simply illegal subdivisions where a landowner rents land without city approval; others are land invasions.
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.
slums  Legal but inadequate multifamily tenements or rooming houses; some are custom built for rent to poor people, others are converted from some other use.
smart growth  Efficient use of land resources and existing urban infrastructure.
smog  The term used to describe the combination of smoke and fog in the stagnant air of London; now often applied to photochemical pollution products or urban air pollution of any kind.
social ecology  A socialist/humanist philosophy based on the communitarian anarchism of the Russian geographer Peter Kropotkin. It shares much with deep ecology except that it is more humanist in its outlook.
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 mineral materials from rocks, partially decomposed organic molecules, and a host of living organisms.
soil horizons  Horizontal layers that reveal a soil's history, characteristics, and usefulness.
southern pine forest  United States coniferous forest ecosystem characterized by a warm, moist climate.
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.
sprawl  Unlimited outward extension of city boundaries that lowers population density, consumes open space, generates freeway congestion, and causes decay in central cities.
spring overturn  Springtime lake phenomenon that occurs when the surface ice melts and the surface water temperature warms to its greatest density at 4 °C and then sinks, creating a convection current that displaces nutrient-rich bottom waters.
squatter towns  Shantytowns that occupy land without owner's permission; some are highly organized movements in defiance of authorities; others grow gradually.
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.
standing  The right to take part in legal proceedings.
statute law  Formal documents or decrees enacted by the legislative branch of government.
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.
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.
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  Removing surface layers over coal seams using giant, earth-moving equipment; creates a huge open-pit from which coal is scooped by enormous surface-operated machines and transported by trucks; an alternative to deep mines.
structure (in ecological terms)  Patterns of organization, both spatial and functional, in a community.
sublimation  The process by which water can move between solid and gaseous states without ever becoming liquid.
subsidence  A 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.
supply  The quantity of that product being offered for sale at various prices, other things being equal.
surface mining  Some minerals are also mined from surface pits. See strip mining.
surface tension  A condition in which the water surface meets the air and acts like an elastic skin.
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.
sustainable agriculture  An ecologically sound, economically viable, socially just, and humane 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.
swidden agriculture  See milpa agriculture.
symbiosis  The intimate living together of members of two different species; includes mutualism, commensalism, and, in some classifications, parasitism.
synergistic effects  When an injury caused by exposure to two environmental factors together is greater than the sum of exposure to each factor individually.
systemic  A condition or process that affects the whole body; many metabolic poisons are systemic.
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.
tar sands  Sand deposits containing petroleum or tar.
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.
territoriality  An intense form of intraspecific competition in which organisms define an area surrounding their home site or nesting site and defend it, primarily against other members of their own species.
tertiary treatment  The removal of inorganic minerals and plant nutrients after primary and secondary treatment of sewage.
thermal plume  A plume of hot water discharged into a stream or lake by a heat source, such as a power plant.
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.
thermodynamics, first law  Energy can be transformed and transferred, but cannot be destroyed or created.
thermodynamics, second law  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.
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.
tidal station  A dam built across a narrow bay or estuary traps tide water flowing both in and out of the bay. Water flowing through the dam spins turbines attached to electric generators.
timberline  In mountains, the highest-altitude edge of forest that marks the beginning of the treeless alpine tundra.
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.
tornado  A violent storm characterized by strong swirling winds and updrafts; tornadoes form when a strong cold front pushes under a warm, moist air mass over the land.
tort law  Court cases that seek compensation for damages.
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 colonialism  Shipping toxic wastes to a weaker or poorer nation.
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.
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.
transitional zone  A zone in which populations from two or more adjacent communities meet and overlap.
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 rainforests  Forests in which rainfall is abundant-more than 200 cm (80 in) per year-and temperatures are warm to hot year-round.
tropical seasonal forest  Semievergreen or partly deciduous forests tending toward open woodlands and grassy savannas dotted with scattered, drought-resistant tree species; distinct wet and dry seasons, hot year-round.
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.
tsunami  Giant seismic sea swells that move rapidly from the center of an earthquake; they can be 10 to 20 meters high when they reach shorelines hundreds or even thousands of kilometers from their source.
tundra  Treeless arctic or alpine biome characterized by cold, harsh 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.
unconventional oil  Resources such as shale oil and tar sands that can be liquefied and used like oil.
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.
undiscovered resources  Speculative or inferred resources or those that we haven't even thought about.
universalists  Those who believe that some fundamental ethical principles are universal and unchanging. In this vision, these principles are valid regardless of the context or situation.
upwelling  Convection currents within a body of water that carry nutrients from bottom sediments toward the surface.
urban area  An area in which a majority of the people are not directly dependent on natural resource-based occupations.
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.
utilitarianism  See utilitarian conservation.
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.
village  A collection of rural households linked by culture, custom, and association with the land.
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  Organic chemicals that evaporate readily and exist as gases in the air.
voluntary simplicity  Deliberately choosing to live at a lower level of consumption as a matter of personal and environmental health.
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 droplet coalescence  A mechanism of condensation that occurs in clouds too warm for ice crystal formation.
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 overirrigation.
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.
Wilderness Act  Legislation of 1964 recognizing that leaving land in its natural state may be the highest and best use of some areas.
wildlife  Plants, animals, and microbes that live independently of humans; plants, animals, and microbes that are not domesticated.
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.
windbreak  Rows of trees or shrubs planted to block wind flow, reduce soil erosion, and protect sensitive crops from high winds.
wind farms  Large numbers of windmills concentrated in a single area; usually owned by a utility or large-scale energy producer.
Wise Use Groups  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.
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.
yellowcake  The concentrate of 70 to 90 percent uranium oxide extracted from crushed ore.
zero population growth (ZPG)  The number of births at which people are just replacing themselves; also called the replacement level of fertility.
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.
zone of saturation  Lower soil layers where all spaces are filled with water.