Environmental Problems, Their Causes, and Sustainability 1

natural lawSee scientific law.natural radioactive decay Nuclear changein which unstable nuclei of atoms spontaneouslyshoot out particles (usually alphaor beta particles) or energy (gamma rays) ata fixed rate.natural rate of extinction See backgroundextinction.natural recharge Natural replenishmentof an aquifer by precipitation, whichpercolates downward through soil androck. See diagram on top half of back cover,recharge area.natural resources The earth’s naturalmaterials and processes that sustain life onthe earth and our economies. Comparehuman resources, manufactured resources.natural selection Process by which a particularbeneficial gene (or set of genes) isreproduced in succeeding generations morethan other genes. The result of natural selectionis a population that contains a greaterproportion of organisms better adapted tocertain environmental conditions. See adaptation,biological evolution, differential reproduction,mutation.negative feedback loop Situation inwhich a change in a certain direction providesinformation that causes a system tochange less in that direction. Compare positivefeedback loop.nekton Strongly swimming organismsfound in aquatic systems. Compare benthos,plankton.net energy Total amount of useful energyavailable from an energy resource or energysystem over its lifetime, minus the amountof energy used (the first energy law), automaticallywasted (the second energy law),and unnecessarily wasted in finding, processing,concentrating, and transporting it tousers.net primary productivity (NPP) Rate atwhich all the plants in an ecosystem producenet useful chemical energy; equal tothe difference between the rate at which theplants in an ecosystem produce usefulchemical energy (gross primary productivity)and the rate at which they use some ofthat energy through cellular respiration.Compare gross primary productivity.neutral solution Water solution containingan equal number of hydrogen ions (H )and hydroxide ions (OH ); water solutionwith a pH of 7. Compare acid solution, basicsolution.neutron (n) Elementary particle in thenuclei of all atoms (except hydrogen-1). Ithas a relative mass of 1 and no electriccharge. Compare electron, proton.niche See ecological niche.nitrogen cycle Cyclic movement of nitrogenin different chemical forms from theenvironment to organisms and then back tothe environment.nitrogen fixation Conversion of atmosphericnitrogen gas into forms useful toplants by lightning, bacteria, and cyanobacteria;it is part of the nitrogen cycle.noise pollution Any unwanted, disturbing,or harmful sound that impairs or interfereswith hearing, causes stress, hampersconcentration and work efficiency, or causesaccidents.nondegradable pollutant Materialthat is not broken down by naturalprocesses. Examples are the toxic elementslead and mercury. Compare biodegradablepollutant, degradable pollutant, slowly degradablepollutant.nonionizing radiation Forms of radiantenergy such as radio waves, microwaves,infrared light, and ordinary light that do nothave enough energy to cause ionization ofatoms in living tissue. Compare ionizingradiation.nonnative species Species that migrateinto an ecosystem or are deliberately oraccidentally introduced into an ecosystemby humans. Compare native species.nonpersistent pollutant See degradablepollutant.nonpoint source Large or dispersed landareas such as crop fields, streets, and lawnsthat discharge pollutants into the environmentover a large area. Compare pointsource.nonrenewable mineral resource A concentrationof naturally occurring nonrenewablematerial in or on the earth’s crust thatcan be extracted and processed into usefulmaterials at an affordable cost.nonrenewable resource Resource thatexists in a fixed amount (stock) in variousplaces in the earth’s crust and has thepotential for renewal by geological, physical,and chemical processes taking placeover hundreds of millions to billions ofyears. Examples are copper, aluminum,coal, and oil. We classify these resources asexhaustible because we are extracting andusing them at a much faster rate than theywere formed. Compare renewable resource.nontransmissible disease A disease thatis not caused by living organisms and doesnot spread from one person to another.Examples are most cancers, diabetes, cardiovasculardisease, and malnutrition.Compare transmissible disease.no-till farming See conservation-tillagefarming.nuclear change Process in which nuclei ofcertain isotopes spontaneously change, orare forced to change, into one or more differentisotopes. The three principal types ofnuclear change are natural radioactivity,nuclear fission, and nuclear fusion. Comparechemical change, physical change.nuclear energy Energy released whenatomic nuclei undergo a nuclear reactionsuch as the spontaneous emission of radioactivity,nuclear fission, or nuclear fusion.nuclear fission Nuclear change in whichthe nuclei of certain isotopes with largemass numbers (such as uranium-235 andplutonium-239) are split apart into lighternuclei when struck by a neutron. Thisprocess releases more neutrons and a largeamount of energy. Compare nuclear fusion.nuclear fusion Nuclear change in whichtwo nuclei of isotopes of elements with alow mass number (such as hydrogen-2and hydrogen-3) are forced together atextremely high temperatures until theyfuse to form a heavier nucleus (such ashelium-4). This process releases a largeamount of energy. Compare nuclear fission.nucleus Extremely tiny center of an atom,making up most of the atom’s mass. It containsone or more positively charged protonsand one or more neutrons with no electricalcharge (except for a hydrogen-1 atom,which has one proton and no neutrons in itsnucleus).nutrient Any food or element an organismmust take in to live, grow, or reproduce.nutrient cycle See biogeochemical cycle.oil sand Deposit of a mixture of clay,sand, water, and varying amounts of a tarlikeheavy oil known as bitumen. Bitumencan be extracted from tar sand by heating. Itis then purified and upgraded to syntheticcrude oil. See bitumen.oil shale Fine-grained rock containingvarious amounts of kerogen, a solid, waxymixture of hydrocarbon compounds. Heatingthe rock to high temperatures convertsthe kerogen into a vapor that can be condensedto form a slow-flowing heavy oilcalled shale oil. See kerogen, shale oil.old-growth forest Virgin and old, secondgrowthforests containing trees that areoften hundreds, sometimes thousands ofyears old. Examples include forests ofDouglas fir, western hemlock, giantsequoia, and coastal redwoods in the westernUnited States. Compare second-growthforest, tree plantation.oligotrophic lake Lake with a low supplyof plant nutrients. Compare eutrophic lake,mesotrophic lake.omnivore Animal that can use both plantsand other animals as food sources. Examplesare pigs, rats, cockroaches, and people.Compare carnivore, herbivore.open dumps Fields or holes in the groundwhere garbage is placed and sometimescovered with soil. They are rare in developedcountries, but widely used in manydeveloping countries. Compare santitarylandfill.open-pit mining Removing minerals suchas gravel, sand, and metal ores by diggingthem out of the earth’s surface and leavingan open pit. Compare area strip mining, contourstrip mining, dredging, mountaintopremoval, subsurface mining.open sea The part of an ocean that isbeyond the continental shelf. Comparecoastal zone.ore Part of a metal-yielding material thatcan be economically and legally extracted ata given time. An ore typically contains twoparts: the ore mineral, which contains thedesired metal, and waste mineral material(gangue).organic compounds Compounds containingcarbon atoms combined with each otherG12GLOSSARY