Environmental Problems, Their Causes, and Sustainability 1

adioactive decay Change of a radioisotopeto a different isotope by the emissionof radioactivity.radioactive isotope See radioisotope.radioactive waste Waste products ofnuclear power plants, research, medicine,weapon production, or other processesinvolving nuclear reactions. See radioactivity.radioactivity Nuclear change in whichunstable nuclei of atoms spontaneouslyshoot out “chunks” of mass, energy, or bothat a fixed rate. The three principal types ofradioactivity are gamma rays and fastmovingalpha particles and beta particles.radioisotope Isotope of an atom thatspontaneously emits one or more types ofradioactivity (alpha particles, beta particles,gamma rays).rain shadow effect Low precipitation onthe far side (leeward side) of a mountainwhen prevailing winds flow up and over ahigh mountain or range of high mountains.This creates semiarid and arid conditions onthe leeward side of a high mountain range.range See distribution.rangeland Land that supplies forage orvegetation (grasses, grasslike plants, andshrubs) for grazing and browsing animalsand is not intensively managed. Comparefeedlot, pasture.range of tolerance Range of chemical andphysical conditions that must be maintainedfor populations of a particularspecies to stay alive and grow, develop, andfunction normally. See law of tolerance.rare species A species that has naturallysmall numbers of individuals (oftenbecause of limited geographic ranges or lowpopulation densities) or has been locallydepleted by human activities.realized niche Parts of the fundamentalniche of a species that are actually used bythat species. See ecological niche, fundamentalniche.recharge area Any area of land allowingwater to pass through it and into an aquifer.See aquifer, natural recharge.reconciliation ecology The science ofinventing, establishing, and maintainingnew habitats to conserve species diversityin places where people live, work, or play.recycling Collecting and reprocessing aresource so that it can be made into newproducts. An example is collecting aluminumcans, melting them down, andusing the aluminum to make new cans orother aluminum products. Compare reuse.reforestation Renewal of trees and othertypes of vegetation on land where treeshave been removed; can be done naturallyby seeds from nearby trees or artificially byplanting seeds or seedlings.reliable runoff Surface runoff of waterthat generally can be counted on as a stablesource of water from year to year. See runoff.renewable resource Resource that can bereplenished rapidly (hours to severaldecades) through natural processes. Examplesare trees in forests, grasses in grasslands,wild animals, fresh surface waterin lakes and streams, most groundwater,fresh air, and fertile soil. If such a resourceis used faster than it is replenished, it can bedepleted and converted into a nonrenewableresource. Compare nonrenewableresource and perpetual resource. See also environmentaldegradation.replacement-level fertility Number ofchildren a couple must have to replace them.The average for a country or the world usuallyis slightly higher than 2 children percouple (2.1 in the United States and 2.5 insome developing countries) because somechildren die before reaching their reproductiveyears. See also total fertility rate.reproduction Production of offspring byone or more parents.reproductive isolation Long-term geographicseparation of members of a particularsexually reproducing species.reproductive potential See biotic potential.reserves Resources that have been identifiedand from which a usable mineral canbe extracted profitably at present priceswith current mining technology. See identifiedresources, undiscovered resources.resilience Ability of a living system torestore itself to original condition afterbeing exposed to an outside disturbancethat is not too drastic. See constancy, inertia.resource Anything obtained from the livingand nonliving environment to meethuman needs and wants. It can also beapplied to other species.resource partitioning Process of dividingup resources in an ecosystem so that specieswith similar needs (overlapping ecologicalniches) use the same scarce resources at differenttimes, in different ways, or in differentplaces. See ecological niche, fundamentalniche, realized niche.resource productivity See materialefficiency.respiration See aerobic respiration.response The amount of health damagecaused by exposure to a certain dose of aharmful substance or form of radiation. Seedose, dose-response curve, median lethal dose.restoration ecology Research and scientificstudy devoted to restoring, repairing,and reconstructing damaged ecosystems.restorationist Scientist or other persondevoted to the partial or complete restorationof natural areas that have beendegraded by human activities. Compareconservation biologist, conservationist, ecologist,environmental scientist, preservationist.reuse Using a product over and overagain in the same form. An example is collecting,washing, and refilling glass beveragebottles. Compare recycling.Richter scale A measurement used byscientists to determine the magnitude ofearthquakes.riparian zones Thin strips and patches ofvegetation that surround streams. They arevery important habitats and resources forwildlife.risk The probability that something undesirablewill result from deliberate oraccidental exposure to a hazard. See riskanalysis, risk assessment, risk–benefit analysis,risk management.risk analysis Identifying hazards, evaluatingthe nature and severity of risks (riskassessment), using this and other informationto determine options and make decisionsabout reducing or eliminating risks(risk management), and communicatinginformation about risks to decision makersand the public (risk communication).risk assessment Process of gathering dataand making assumptions to estimate shortandlong-term harmful effects on humanhealth or the environment from exposure tohazards associated with the use of a particularproduct or technology. See risk–benefitanalysis.risk–benefit analysis Estimate of theshort- and long-term risks and benefits ofusing a particular product or technology.See risk assessment.risk communication Communicatinginformation about risks to decision makersand the public. See risk, risk analysis,risk–benefit analysis.risk management Using risk assessmentand other information to determine optionsand make decisions about reducing or eliminatingrisks. See risk, risk analysis, risk–benefitanalysis, risk communication.rock Any material that makes up a large,natural, continuous part of the earth’s crust.See mineral.rock cycle Largest and slowest of theearth’s cycles, consisting of geologic, physical,and chemical processes that form andmodify rocks and soil in the earth’s crustover millions of years.r-selected species Species that reproduceearly in their life span and produce largenumbers of usually small and short-livedoffspring in a short period. Compare K-selected species.r-strategists See r-selected species.rule of 70 Doubling time (in years) =70/(percentage growth rate). See doublingtime, exponential growth.ruminants Grazing animals with complexdigestive systems that enable them to convertgrass and other roughage into meatand milk.runoff Freshwater from precipitation andmelting ice that flows on the earth’s surfaceinto nearby streams, lakes, wetlands, andreservoirs. See reliable runoff, surface runoff,surface water. Compare groundwater.rural area Geographic area in the UnitedStates with a population of less than 2,500.The number of people used in this definitionmay vary in different countries. Compareurban area.salinity Amount of various salts dissolvedin a given volume of water.GLOSSARYG15