Glossary

In systems analysis, refers to an increase in the amount of material being measured. It results when rate of input of that material to a system exceeds rate of output from that system. See Chapter 2 for more. Accumulation can have another, distinct, meaning; see bioaccumulation for that usage (and Chapter 15).

The correctness of a measurement in relation to a universally accepted standard. Contrast with precision and sensitivity. See Chapter 2 for details.

Biological entities that lack cells (e.g., viruses). See Chapter 3 for more.

An important environmental consequence of mining. Materials that were buried in low-oxygen environments are brought to the surface and exposed to oxygen and water. The resulting chemical reactions produce sulfuric acid that can flow to streams and other waterways. See Chapter 10 for more.

Rain, snow, ice, etc., that has a pH lower than is natural. It can be caused by natural and human activity. See Chapter 10 for more.

A chemical substance released into the atmosphere that is converted into an acid. For example, sulfur dioxide gas emitted in coal combustion will react to form sulfuric acid. See Chapter 14 for more.

In response to environmental pressures, organisms develop strategies that allow them to survive and reproduce in a particular area. In ecology, a characteristic or trait that an organism develops in response to pressures placed on it by its environment is called an 'adaptation'.  Well-adapted organisms posses the traits that allow them to be present in their current environment.  Organisms with the best adaptations will be most successful in their environment (barring a random event that could disrupt them).  Some simple examples of adaptations:  fish have gills to extract oxygen from water, thus they can survive in water; cheetahs are very fast, thus they can catch prey in open landscapes; certain bacteria can withstand very acidic conditions, thus they can live inside the human stomach.  See Chapters 1, 5, and 6 for more.

In ecology, a characteristic or trait that an organism develops in response to pressures placed on it by its environment.  Well-adapted organisms posses the traits that allow them to be present in their current environment.  Organisms with the best adaptations will be most successful in their environment (barring a random event that could disrupt them).  Some simple examples of adaptations:  fish have gills to extract oxygen from water, thus they can survive in water; cheetahs are very fast, thus they can catch prey in open landscapes; certain bacteria can withstand very acidic conditions, thus they can live inside the human stomach.  See Chapters 1, 5, and 6 for more.

A reason several species resemble each other physically. In this case, organisms from a single population took on somewhat different forms as they specialized within a small space. They look similar and are closely related genetically, but they are separate species occupying separate niches. Compare to convergent evolution and divergent evolution. See Chapter 6 for more.

A substance intentionally put into food. Compare to contaminant. See Chapter 15 for more.

In ecology, refers to a trait that helps an organism survive and reproduce better than competitors. See Chapters 1, 5, and 6 for more.

More formally, 'aerobic organisms', they require dioxygen gas for survival. See Chapter 1, especially Box 1.1, for more.

An adjective referring to an organism that uses dioxygen in its metabolism. "Aerobe" is the noun, the organism itself. Contrast with anaerobic. See Chapter 1 for more.

Aerosol is a general term referring to any fine particle or droplet suspended in air.

The increase in forested area compared to the current situation. In other words, forests would encroach upon un-forested areas. See Chapter 12 for details.

The human practice of cultivating crops and growing animals to produce food for human consumption. It involves extensive manipulations of natural environments and ecological processes. See Chapter 9 for details.

A term used by environmental scientists to refer to a farm. It reflects the nature of agriculture: humans harness natural ecological processes to artificially produce more food than would otherwise grow in an area. See Chapter 9 for more.

The amount of solar radiation reflected off any planetary body. See Chapters 4 and 14 for details.

A group of organisms that are eukaryotic, phototrophic, and autotrophic. Some are unicellular, but most are colonial. Note: some scientists include certain prokaryotic cells in this group, the so-called "blue-green algae"; others classify those prokaryotic organisms as bacteria (known as "cyanobacteria"). We will follow the latter convention in this book. See Chapter 3 for more.

A term often used to describe renewable energy sources such as solar, wind, and hydro power. See Chapter 10 for more.

A chemical form of N that is biologically available to the biosphere. It is produced by fixation of nitrate and ammonium by plants, algae, and certain microorganisms. Amino acids are the building blocks of proteins. See Chapter 4 for more.

An inorganic form of nitrogen with the formula NH4+. It is biologically available to plants, algae, and certain microorganisms. It is the product of the fixation of dinitrogen and can be further fixed to amino acids. See Chapter 4 for more.

More formally, 'anaerobic organisms.' They do not require dioxygen gas; in fact, many anaerobes are poisoned by O2. See Chapter 1, especially Box 1.1, for more.

An adjective referring to organisms that do not use dioxygen as part of their metabolism. Many such organisms die in the presence of oxygen gas. "Anaerobe" is the noun. Compare to aerobic. See Chapter 1 for more.

Refers to an area that lacks dioxygen gas. Anaerobic organisms would be found in an anoxic environment. Compare to oxic and aerobic.

An adjective that means of human origin. See Chapter 7 for details.

A population of bacteria that is no longer susceptible to the toxic effects of a particular antibiotic. Note it was once dominated by pesticide-sensitive individuals, but rapid evolution led to its ability to survive in the presence of the poison. See Chapters 5 and 6 for details.

Generally, a kind of chemical substance that kills living cells. In practice, 'antibiotic' refers to a drug designed to kill harmful bacteria without appreciably harming the host taking the drug. See Chapters 1 and 5 for more.

In ecology, an organism that sits at the highest trophic level. In principle, no organism feeds on it. See Chapter 5 for details.

An adjective that refers to organisms that live in water. Compare to terrestrial. See Chapter 4 for more.

A geologic structure that can store and transmit usable quantities of water. See Chapters 4 and 11 for more.

An inland freshwater sea in Central Asia. It is an example of how competing demands for water can lead to adverse consequences. In this case, diversions of the rivers that fed the Aral in the interest of agriculture led to profound shrinking of this formerly enormous body of water. See Chapter 11, especially Box 11.2, for more about conflicts over water.

One of the three domains of living things. It is made up of prokaryotes that tend to live in relatively extreme environments (e.g., temperature, acidity, pressure). Compare to Bacteria and Eukarya. See Chapter 6 for more.

Constructed by humans to treat sewage. See Chapter 11 for more.

A type of reproduction in which a individual can reproduce without a mate.  Bacteria and protozoa, for example, reproduce this way:  a single cell divides into two identical cells.  Contrast this strategy with sexual reproduction.  See Chapter 6 for more.

When an organism takes up a nutrient and incorporates it into its cells. See Chapter 4 for more.

The thick layer of the Earth that lies beneath the lithosphere. It consists of much of the middle and lower mantle and behave plastically when stressed. See Chapter 3 for more.

One of Earth's four spheres, this is the envelope of gases that surrounds the Earth. See Chapter 4 for more.

Also known as a thermal inversion. This is a natural phenomenon whereby cool air is trapped near Earth's surface by layers of warmer air. Inversions can exacerbate local air pollution problems like smog because pollutants released at the surface do not disperse. See Chapter 14 for more.

A chemistry term, atoms are the building blocks of everything in the universe. They are the smallest units into which an element can be divided. Atoms consist of even smaller, subatomic particles, such as protons, electrons, and neutrons. See Chapter 4 for more.

In toxicology, an endpoint caused by exposure to certain xenobiotics: the immune system inappropriately attacks the cells of its own body. See Chapter 15 for details.

A type of organism that fix its own carbon, that is, it can convert unavailable carbon dioxide into useable glucose to meet its nutrient needs. Includes plants, algae, and some bacteria. Autotrophic an adjective. Compare to heterotroph. See Chapter 5 for more.

In demography, the mean length of life, in years, of a population. See Chapter 8 for more.

An important consideration when scientists make measurements. Background levels refer to the normal condition of whatever variable is under consideration. For example, normal human body temperature is 37 degrees C (98.6 F). Put another way, background is 37 (i.e., not 0); we use a thermometer to determine if temperature is ABOVE background (say 39) when a person is sick. Background levels can affect measurements and interpretations of experimental results. This idea is specifically referenced in Chapter 14 but is relevant for all scientific measurements and ideas described in the book.

Refers to the many different kinds of microscopic organisms that are single celled and prokaryotic (i.e., do not possess distinct cellular organelles). Collectively, bacteria are extremely diverse, are the oldest organisms on Earth, and are critical to many environmental cycles and processes. See Chapter 3 for more.

With a Capital B, refers to one of the three domains of living things. It is made up of prokaryotes that tend to be found in relatively moderate environments. Compare to Archaea and Eukarya. See Chapter 6 for more.

The site of a major accident at a Indian chemical manufacturing plant in 1984. Thousands of people were killed and hundreds of thousands were sickened. This event raised many questions about corporate responsibility and environmental contamination. See Chapter 1 for more.

Dietary and non-dietary uptake of pollutants by organisms; can be thought of as bioconcentration + biomagnification. See Chapter 15 for more.

Refers to how usable an atom is. For example, some C atoms are not directly available for use (as in carbon dioxide) whereas others are directly available for use (as in glucose). See Chapter 4 for details.

An important water quality parameter. In simple terms, BOD is a measurement of the amount of aerobic metabolism occurring in a water sample, that is, the level of decomposition of organic materials by microorganisms. High BOD will drive down levels of dissolved oxygen in the water and, in some cases, lead to the deaths of fish and other aerobic animals. BOD can be thought of as an indirect way to measure water quality: when there is a lot of organic matter in the water, a lot of oxygen will be required by decomposing organisms to digest that organic matter. See Chapter 11 for more.

Uptake of a substance (generally, some kind of pollutant) from a non-living medium like soil or water into an organism. See Chapter 15 for more.

A process analogous to decomposition of natural compounds, but this term is generally used to refer to chemical decomposition of synthetic products by organisms; fungi and bacteria are responsible for most of the relevant biodegradation seen in contaminated environments. See Chapter 15 for more.

A broad term that refers to the number of different organisms in an ecosystem or, often, the whole Earth. There are several specific ways to measure and express biodiversity. See Chapters 5 and 6 for details.

Methane-containing gases produced by anaerobic decomposition in landfills, sewage treatment plants, and farms. It can be burned as a fuel. See Chapter 10 for more.

Holds that populations change with time in response to a number of factors, including mutations, natural selection, and random chance. Biological evolution is the main scientific explanation for the development of life on Earth. See Chapter 6 for many more details.

Differences in metabolism, physiology, behavior, etc., among different organisms. It adds uncertainty to scientific measurements. See Chapter 2 for details on uncertainty.

Uptake of a compound (generally, some kind of pollutant) into an organism via diet. See Chapter 15 for more.

A term referring to the total amount of living material in a place.

In ecology, a type of ecosystem. Depending upon who you ask, Earth has between 5 and 15 biomes, and each is characterized and classified according to dominant organisms present and environmental conditions. See Chapter 5 for details.

Produced by medical facilities like hospitals, this includes body fluids and tissues from humans. Due to its potential to spread disease, it is handled more carefully than is municipal solid waste. See Chapter 13 for more.

A general term that refers to the use of organisms to clean up polluted water or soil. See Chapter 15 for more.

One of Earth's four spheres, refers to all living things. See Chapter 4 for more.

A set of physiological features that provides extra protection for the central nervous system against penetration by xenobiotics. It is not 100% effective, but it does prevent the entry of many potential poisons into the CNS. See Chapter 15 for details.

The total dose of a xenobiotic in a whole organism. See Chapter 15 for details.

In chemistry, one of several attractive forces that hold atoms together. See Chapter 4 for more.

A chemistry term related to acids and bases. It refers to how resistant a water-based solution is to pH changes following addition of strong acid or base. High buffering capacity indicates a solution that will resist changes--that is, its pH does not change appreciably--after acid or base is added. See Chapters 9 and 10 for more, including context and relevance.

A procedure to assess the accuracy of a scientific instrument. Accomplished by measuring a standard of known properties. For example, a balance could be calibrated through the use of a calibration weight, a carefully constructed object of known mass. A calibration weight with a mass = 1.00000 g could be used to assess the accuracy of a laboratory balance; if the mass of the object is determined to be 0.99880, we know the balance needs to be calibrated. Put informally, we need to remind the balance what 1.00000 g actually looks like! See also accuracy and Box 2.2.

In ecology, refers to the nearly continuous layer of leaves and branches in a mature forest that blocks much of the incoming sunlight that would otherwise strike the forest floor. See Chapter 5 for details.

A strategy used to reduce use and release of pollutants by a group of emitters. A limit on the total amount of the targeted substance is established and lowered each year. Individual polluters (i.e., companies) need to buy allowances to continue to emit the pollutant or may change their processes to eliminate missions all together. See Chapter 14 for more.

A group of chemical compounds that include sugars like glucose as well as polymers like starch and cellulose. See Chapter 4 for more.

One of the known elements in the Universe, carbon (C) atoms consist of 6 protons and 6 electrons. Carbon is an important element for living things; organic C compounds make up the skeleton of biological systems. See Chapter 4 for details.

A proposed strategy to reduce the amount of carbon dioxide moving to the atmosphere. In principle, the CO2 gas would be collected and moved to underground rock layers. See Chapter 14 for more.

A strategy that would collect carbon dioxide gas generated from fossil fuel combustion before it moves to the atmosphere. The captured carbon would then be used in the manufacturing of plastics. It is an idea that is in early stages of development. See Chapter 14 for more.

A gas made up of one carbon atom and two oxygen atoms, it is one of the many forms carbon can take. This gas is the product of aerobic respiration as well as combustion of fossil fuels, wood, and other materials containing organic carbon. It is not directly usable as a carbon source but can be fixed into useable forms of carbon, for example glucose, by autotrophic organisms. See Chapters 4 and 14 for more.

The process of converting C from non-biologically available forms to forms that can be used by organisms. Typically, carbon dioxide molecules are converted to glucose. C fixation is carried out by organisms that possess the proper machinery to do so: plants, algae, and some bacteria. Fixation is a general term that indicates an increase in the biological availability of any atom.  See Chapter 4 for more details.

In toxicology, a xenobiotic that causes cancer. See Chapter 15 for details.

An organism that eats the flesh of consumers. That is, carnivores usually do not eat primary producers. See Chapter 5 for more.

Equal to the number of individuals of a species that can be sustainably supported by an ecosystem. See Chapter 1 for more.

Environmental scientist and activist, author of the book Silent Spring (1962). She was an important voice in the environmental movement and helped raise awareness about the potential dangers of indiscriminate use of pesticides like DDT. See Chapter 1 for more.

A broad term referring to a substance that accelerates a chemical reaction without being affected by that chemical reaction.

An approach to studying Earth's history characterized by the belief that Earth was shaped by fast, dramatic upheavals, not slow processes. It is used to explain how a young Earth could contain so many seemingly ancient features. Importantly, no objective evidence supports catastrophism. Contrast with uniformitarianism. See Chapter 3 for more.

Two events are linked mechanistically; one is influenced by the other. Compare to correlation. See Chapter 2 for more.

The basic microscopic unit that makes up living things. Cells are systems made up of component parts and receive inputs and produce outputs. Different organisms are built of different types of cells, but cells have many things in common. All are enclosed by cell membranes, some have an extra rigid layer outside the membrane known as a cell wall. Some organisms consist of just one cell (e.g., bacteria) whereas others are made up of billions or trillions (e.g., animals and plants). See Chapter 3 for more.

The semi-permeable boundary that encloses all cells. Its chemical properties give it some control over what enters and exits a cell. See Chapter 3, especially Figure 3.9, for details.

The rigid layer found outside the cell membrane in the cells of plants and many microorganisms (but not animals). See Chapter 3 for more.

Refers to the brain and nerves in the body. See Chapter 15 for details.

A process whereby the fission of a single unstable atom can lead to subsequent fission of more and more unstable atoms. See Chapter 10 for more.

The site of a major nuclear accident in 1986. Located in Ukraine, this power plant exploded due to multiple user and design errors. The environmental effects of this accident persist to this day. See Chapter 1 for more.

A class of chemical compounds built of C atoms bonded to some number of Cl and F atoms. CFCs are important greenhouse gases and also contribute to ozone depletion because they travel to the stratosphere and release Cl atoms; those Cl atoms are highly reactive and catalyze ozone destruction. See Chapter 14, including Figure 14.31, for more.

A law first passed in the U.S. in 1970, it was intended to reduce air pollution. Several subsequent amendments have strengthened it over the years. See Chapters 1 and 13 for more.

When all the trees in an area are cut down at one time. See Chapters 7 and 12 for more.

The long-term, average atmospheric conditions that prevail in an area. Temperature (ranges and averages) and precipitation patterns are two important climatic characteristics. Compare to weather. See Chapter 14 for more.

In ecology, the group of species in ecological succession that are not replaced as a matter of course. See Chapter 5 for details.

See central nervous system.

An important fossil fuel, coal is a term that refers to several types of soil rocks that were derived from ancient plants. See Chapter 10 for more.

Where coal lies within the Earth. It is essentially a series of layers of coal that can be accessed through mines and then extracted. See Chapter 10 for more.

A way to categorize coal by sulfur content: high emits less sulfur upon burning than does does low. See Chapter 10 for more.

There are several different types of coal arranged according to their age and energy content, that is, rank. See Chapter 10 for more.

Refers to organisms that are built of multiple cells, but those cells do not specialize and communicate with each other to the same extent as cells in true multicellular organisms. Compare to unicellular and multicellular. See Chapter 3 for more.

In ecology, organisms that can live on barren landscapes and begin the process of ecological succession. They are pioneer species. See Chapter 5 for more.

In ecology, a group of interacting populations. See Chapter 5 for details.

An interaction among organisms characterized by rivalry for limited resources. All participants are harmed as a result. See Chapter 5 for details.

In ecology, states that two organisms with the same requirements cannot coexist in the same space and time indefinitely. Eventually, the organism that is best adapted to survive will dominate and force the weaker competitor out. See Chapter 5 for details.

A practice that involves the accelerated decomposition of non-animal waste such as plant scraps, leaves, and related objects. Materials are collected in a structure known as a composter in which environmental conditions are maintained to stimulate aerobic decomposition. Compost, the product, is an organic- and nutrient-rich material that can be used as fertilizer. See Chapters 9 and 13 for more.

In chemistry, a molecule that is built of more than one type of atom. Two oxygen atoms make up the molecule dioxygen, a pairing that is not a compound, whereas two hydrogen atoms bonded to one oxygen make up the molecule water, a group that is also called a compound. See Chapter 4 for more.

A scientific notion derived from a limited amount of data. Conclusions are likely to be tested and profoundly modified with repeated experimentation
Compare to theory and law. See Chapter 2 for more.

A pathway of the hydrologic cycle. Water changes from gas to liquid. See Chapter 4 for more.

In the context of groundwater extraction by humans, the shape the water table takes around a well once pumping from it commences. See Chapter 11, especially Figure 11.5, for more.

In ecology, refers to an approach to wildlife and ecosystem protection. The goal of conservation is to manage wild living resources so they persist indefinitely and provide humans with specific benefits. Compare to preservation. See Chapter 6 for more.

A process whereby an organism ingests nutrients through diet. An organism that carries it out is a consumer. See Chapters 4 and 5 for details.

A type of off-stream water use that does not immediately return the water to the reservoir from which it is removed. For example: human consumption. See Chapter 11 for more.

Refers to any one of several structures and strategies that restrict the movement of waste from its management facility (e.g., landfill) to water, air, or organisms. See Chapter 13 for more.

Broadly, substances present in food, air, water, or soil that that do not belong where they are found (i.e., are out of place, should NOT be present).  Compare with 'pollution', a word with a related, if distinct, meaning.  In short, a contaminant can be thought of as any substance that does not belong where it is found (i.e., a metal dissolved in water).  A pollutant is a contaminant that has reached a high enough concentration to bring on adverse effects (i.e., that metal noted in the previous sentence is at such a high level that it is killing fish; see Chapter 11 for more).  Note that the terms are often used interchangeably by scientists and members of the public alike.

In the context of toxicology (Chapter 15) a contaminant is a substance that is inadvertently put into food. Compare to additive, something that is knowingly and intentionally added to food.

In geology, the theory that Earth's continents have not always been in their current locations; rather, due to plate movements, continents have slowly changed position through history. See Chapter 3 for more.

Controls help establish causation.  If controls and test subjects respond the same way, the factor tested likely is not responsible for the reactions noted.  Essential, a control is deliberately left alone--it goes untreated--so a researcher can compare its reaction to that of subjects that ARE treated. See Chapter 2 for more.

Consisting of neutron-absorbing material, these are used to keep a nuclear reaction running at a more or less constant rate; they also can be lowered into a reactor to slow it in an emergency. See Chapter 10 for more.

Controls or control subjects help establish causation.  These are subjects that are untreated in an experiment; in other words, they provide the baseline against which test subjects are compared. Controls are essential to experimental science. If controls and test subjects respond the same way, the factor tested likely is not responsible for the reactions noted. See Chapter 2 for more.

In geology, circular motion in the mantle that is thought to propel lithospheric plates. They are caused by the rising and falling of hot material. See Chapter 3 for more.

The most widely used technique to recover petroleum from beneath Earth's surface. It involves drilling into reservoir rocks and then pumping the fluids to the surface. Compare to unconventional oil drilling. See Chapter 10 for more.

In geology, a location where two lithospheric plates move toward each other or collide. See Chapter 3 for more.

One reason members of different species can resemble each other physically: organisms that were not related genetically lived in the same environment and therefore developed the same physical adaptations. Compare with divergent evolution. See Chapter 6 for more.

A geology term referring to the innermost region of the Earth. It is partially solid and partially molten and made up of relatively dense elements. See Chapter 3 for more.

Two phenomena may occur at the same time but they may or may not have any influence over each other. Compare to causation. See Chapter 2 for more.

An evaluation of the advisability of a course of action that weighs the adverse consequences--the costs--of it against its potential advantages--the benefits. Inherent to a cost-benefit analysis is the assumption that any choice involves risks of some kind, and careful collection and interpretation of data can help us make a decision that poses the least risk. See Chapter 1 for more.

A type of mass wasting event during which materials on Earth's surface move downhill extremely slowly. The movement is not perceptible in real time, but certain clues at the surface can indicate it is occurring. See Chapter 7 for more.

Both too little and too much of an essential nutrient can harm natural systems. See Chapters 4 and 15 for details.

In agriculture, the amount of food produced from a field of a particular crop. See Chapter 9 for more.

The raw material extracted from the Earth's crust by conventional or unconventional means. Except in very rare cases, crude is not immediately usable as an energy source; rather, it must be processed at a refinery to produce multiple fuels from it. See Chapter 10 for more.

A geology term referring to the thin, brittle outer layer of the Earth. It is composed of relatively low-density elements. See Chapter 3 for more.

Dichlorodiphenyltrichloroethane, 1,1′- (2,2,2-trichloroethylidene) bis(4-chlorobenzene), or DDT is a pesticide designed to kill insects (i.e., it is an insecticide). It was used widely in the 1940s, 1950s, and 1960s but banned in the U.S. and largely phased out of use in the early 1970s. See Chapters 1 and 15 for more.

Remains and waste products of organisms are grouped together as dead organic matter. It contains a lot of stored nutrients that can be used and recycled by decomposers. See Chapters 4 and 5 for more.

Refers to a low-oxygen region of a body of water such as the Gulf of Mexico. Runoff from human activities such as agriculture introduces excess nutrients into the water; fish and other oxygen-requiring organisms die off in such a zone. See Chapters 1 and 4 for more.

A general word that refers to the breaking down of relatively large, complex materials into relatively small, simple materials. Certain organisms, known as decomposers, break down the remains and waste products of other organisms and use those products as nutrient sources. Decomposers are critical to the health of ecosystems because they aid in the recycling of materials. Fungi and some bacteria are important decomposers. See Chapters 4 and 5 for more.

A strategy used by scientists in which specific cases are compared to previously developed and accepted principles. It is often used to categorize organisms or objects into preexisting groups. See Chapter 2 for more.

A waste-management strategy whereby liquid waste is pumped underground into geologic layers deemed stable and appropriate for such materials. Site choice must be made carefully and waste must be stored below groundwater to minimize adverse consequences of this practice. See Chapter 13 for more.

The removal of forest ecosystems. Multiple forces, anthropogenic and natural, can cause deforestation. See Chapter 12 for details.

A general term that refers to the breakdown of a relatively large, complex compound into smaller, simpler products. It involves the breaking of chemical bonds by biological or non-biological means.  See Chapter 15 for details.

Energy is converted from high to low grade forms, meaning it becomes less capable of doing work. See Chapter 4 for more.

Refers to a change in the relative size of different age cohorts within a population. For example, many human populations are experiencing a decline in the size of younger cohorts relative to the size of older cohorts. See Chapter 8 for more.

The science of births, deaths, and other forces that affect population size. See Chapter 8 for more.

Bacteria that convert ammonia and/or nitrate to dinitrogen. In other words, they reduce the biological availability of N. See Chapter 4 for more.

Density is a term that essentially refers to how much solid material is packed into a given space, or it can be thought of as the relative amount of air space present in a particular substance.  For example, a 1-liter bottle of foam packing peanuts will have a lower density than a 1-liter bottle of sugar which in turn will have a lower density than a 1-liter bottle of copper pennies. See Chapter 3 for more.

In systems analysis, refers to a decline in the amount of material being measured. It results when rate of output of that material from a system exceeds rate of input to that system. See Chapter 2 for more.

In geology, refers to processes that lay sediments onto the surface of the Earth. Typically, water or wind carries sediments until the velocity of the moving medium is insufficient to continue transport. See Chapter 3 for more.

An adjective that refers to skin. In toxicology, dermal exposure occurs when a xenobiotic comes into contact with skin. See Chapter 15 for more.

In toxicology, movement of a xenobiotic into an organism through the skin. See Chapter 15 for details.

The removal of salt (by one of several methods) from water. See Chapter 11 for more.

Small organisms that feed on the decaying remains of other organisms. See Chapter 5 for details.

Refers to nations that have relatively large amounts of technology, wealth, and infrastructure compared to the developing world.  See Chapter 8 for details.

Refers to nations that have relatively small amounts of technology, wealth, and infrastructure compared to the developed world.  See Chapter 8 for details.

The movement of a material that is unequally spread throughout some medium (e.g., air or water) from areas of high concentration of the material to areas of low concentration of the material.  See Chapter 4 for details.

The process by which a small amount of a relatively concentrated material is spread out within a large body or water or air.

Two N atoms bonded together via a triple bond. It makes up nearly 80% of the gases in the atmosphere. Not biologically available, must be fixed before organisms can the N atoms in it. See Chapter 4 for more.

Two oxygen atoms are bonded to form O2, dioxygen. This is the gas required by aerobic organisms, including humans; it makes up approximately 20% of the gasses in the atmosphere. See Chapter 1, especially Box 1.1, and Chapters 3 and 4 for more.

A broad term referring to a process that inhibits and/or kills unwanted microorganisms in water, food, or on surfaces. In the context of sewage treatment, it tends to be the last phase, one which reduces the number of pathogenic microorganisms in treated sewage before it is released into a natural water reservoir. See Chapter 11 for more.

In geology, a location where two lithospheric plates move away from each other. See Chapter 3 for more.

One reason different species resemble each other physically. In this case, individuals from the same species were separated from each other and moved into different environments. Since they developed in different environments, they developed different adaptations as time went by. Modern organisms that diverged into different species are still closely related genetically. Compare to convergent evolution. See Chapter 6 for more.

A biochemical molecule containing the code that makes every organism unique.  See Chapter 6 for details.

A term used to refer to one of the three major categories of living things based on genetic relatedness. See Chapter 6 for more.

The concentration of a xenobiotic inside an organism, usually expressed as mg of compound per kg of body mass. See Chapter 15 for details.

In the context of groundwater usage, the depth to which the water table is lowered by pumping. See Chapter 11, especially Figure 11.5, for more.

In ecology, organisms that resemble pioneer species more than climax-community species. They appear early in the process of succession. See Chapter 5 for more.

Vertical shaking of the Earth's surface that results from movement along faults. See Chapter 7 for more.

Refers to the amount of resources used per person. See Chapter 8 for more.

A phenomenon whereby the dominant organisms in an area change with distance away from a pollution source. The most resistant to the adverse effects of the pollutant are found at highest-concentration areas. See Chapter 15 for more.

Determines the likelihood that a planned activity will cause adverse effects to natural systems. See Chapter 15 for more.

In ecology, the sequential replacement of dominant species in an area; it is mechanism by which an ecological community comes into being. See Chapter 5 for details.

The science of interactions among organisms and between organisms and their environments. See Chapter 5 for more.

In ecology, all of the living and non-living entities present in a defined space. See Chapter 5 for more.

One of the processes carried out by organisms in an ecosystem. Important functions include C fixation, decomposition, and consumption. See Chapter 5 for details.

Essentially, the benefits we derive from ecosystems. They include carbon fixation, provision of habitat for valued species, enhancement of water supply, and others.  See Chapters 5, 6 and 12 for details.

In ecology, refers to the specific identity of organisms present in an ecosystem. This property varies widely among ecosystems. See Chapter 5 for details.

Describes many different types of energy; often shown on a plot where they are arranged along a continuum according to their wavelengths. See Chapter 14, especially Figure 14.17, for more.

In chemistry, a negatively charged subatomic particle that orbits an atom's nucleus. Neutral atoms contain the same number of protons and electrons. See Chapter 4 for more.

In chemistry, refers to a substance that cannot be broken down into simpler units. Each element is made up of the atoms that have the same number of protons. For example, all atoms in the universe with 8 protons in their nuclei are grouped together as the element oxygen. See Chapter 4 for more.

In toxicology, refers to processes that expel unwanted waste products from the body, including the xenobiotics. See Chapter 15 for more.

An organism that is native to its current habitat. See Chapter 5 for details.

One of the systems in the body, it uses hormones to regulate important processes and functions controlling mood, development, reproduction, and growth. See Chapter 15 for more.

An adjective that refers to something that originates from within an organism. For example, endogenous errors in DNA are not caused by external agents but by some forces associated with the body. See Chapter 6 for a little more.

An explanation of the way modern eukaryotic cells possess organelles such as mitochondria. In short, it holds that ancient prokaryotes engulfed other, smaller, prokaryotes in a way that the two organisms ended up living together. See Chapter 6 for more.

In toxicology, the outcome caused by a xenobiotic. It is often what is measured or assessed by a toxicologist. Endpoints include paralysis, blindness, death, and others. See also response, See Chapter 15 for details.

Formally, energy is the capacity to perform work. It enables changes to be made to matter. For example, energy allows you to move a box from the floor to a table. See Chapter 4 for more.

A graphical representation of the way usable energy dramatically declines from lowest to highest trophic levels. See Chapter 5 for more.

All energy conversions increase the amount of disorder, or entropy, in the universe. Entropy is related to the second law of thermodynamics. See Chapter 4 for details.

A term that refers to all of the factors that surround, influence, and sustain an organism. Earth is made up of many different environments. See Chapter 1, for more.

U.S. federal agency tasked with protection of soil, air, water, and ecosystems. See Chapter 1 for more.

Objective study of Earth's natural systems. Compare to environmentalism. See Chapter 1 for more.

A governing rule in environmental science that states, in short:  all systems are connected to all other systems.  The principle of environmental unity also implies that changes made to any system can bring about changes to other systems, even if those other systems are very distant from the initial change.  Importantly, the resultant changes can be hard to predict and often are undesirable. See Chapter 1 for more.

Advocacy-based, subjective approach to protecting earth's natural systems; may or may not be informed by objective data or science. Compare to environmental science. See Chapter 1 for more.

Refers to processes that transport the products of erosion. Typically, sediments are carried in water, wind, or ice. Compare to weathering. See Chapter 3 for more.

A kind of alcohol that is generally produced through the fermentation of plant materials like corn or sugar. Ethanol is an important ingredient in alcoholic beverages like wine and beer and can also be used as a liquid fuel. See Chapter 10 for more.

One of the three domains of living things. It contains all eukaryotic organisms. Compare to Archaea and Bacteria. See Chapter 6 for more.

A cell that consists of discreet, membrane-enclosed subcellular structures like nucleus, chloroplast, ribosomes, and mitochondria. Contrast with prokaryotic cell.  Also known simply as 'eukaryote'. See Chapter 3 for more.

A process whereby a relatively clear aquatic system is transformed to first a murky then swampy then, potentially, a dry terrestrial system. It is caused by the accumulation of excess nutrients (nitrogen and/or phosphorus). See Chapters 4 and 11 for details.

A pathway of the hydrologic cycle. Water changes from liquid to gas. See Chapter 4 for more.

A term that refers to the combination of nonbiological evaporation and transpiration. Together, these pathways move water from the lithosphere and hydrosphere into the atmosphere. See Chapter 4 for more.

A general term that refers to change with time. In ecology, it is used to describe the heritable changes of organisms. See biological evolution, theory of, for more; also see Chapter 6.

In ecology, an organism that is not native to an area in which it currently lives. See Chapters 5 and 6 for more.

An organism that is not native to its currents habitat. If it outcompetes native organisms in its new space it is termed 'invasive'.  See Chapter 5 for details.

In science, the difference between the actual value and the measured value. For example, if the length of a line is 3.2 cm but we measure it as 3.4 cm, the experimental error = 0.2 cm. Experimental error can result from many sources and contributes to uncertainty. See Chapter 2 for more.

Research that examines the effects of stimuli or stressors (phenomena that could be defined as causes) on test subjects (systems that react to or are influenced by stressors). See Chapter 2 for more.

A rapid increase in size of a property being measured due to positive feedback.  It results from a constant rate of increase, i.e., a constant % of a growing number.  See Chapter 2 for details.

In toxicology, when an organism comes into contact with a xenobiotic. Also see routes of exposure. See Chapter 15 for details.

A process that leads to the complete disappearance of a species from Earth. See Chapter 6 for more.

Refers to the removal or recovery of oil and natural gas from underground reservoirs. Pumping is used to extract these fluids. See Chapter 10 for more.

A type of mass wasting event in which material moves downhill; in this case, the falling rocks, etc., do not contact the Earth's surface as they descend. See Chapter 7 for more.

A surface along which there is displacement of rocks. The movement is generally sudden and results from tectonic stress. Movement along faults can cause earthquakes. See Chapter 7 for more.

In systems analysis, feedback is defined as a system's response to its own output. See negative and positive feedback. See Chapter 2 for more.

A natural process carried out by certain microorganisms like yeast. In short, yeast can metabolize plant materials like corn into several products, including ethyl alcohol (i.e., ethanol). Fermentation requires anoxic (i.e., not dioxygen) conditions. See Chapter 10 for more information about and context for ethanol.

In agriculture, a term that refers generally to nutrients added to enhance the growth of crops. Fertilizers can be produced synthetically or can be natural products (e.g., manure). See Chapter 9 for more.

States that the amount of energy in the universe is conserved, that is, energy cannot be created or destroyed. Conversions among different forms of energy is allowed, though. See Chapter 4 for more.

A general term related to biogeochemical cycles. It refers to any process that increases the biological availability of an atom. See Chapter 4 for details.

The largely flat areas adjacent to either side of a stream channel. Water moves into a flood plain during floods; flood plains are also caused and expanded by repeated flooding. See Chapter 7 for more.

A graphical representation of feeding relationships in an ecosystem. See Chapter 5 for details.

The remains of an ancient organism. Such remains can take many forms, including impressions in rocks or chemical remnants that were transformed into fuels such as coal, oil, and gas. See Chapters 3 and 10 for more.

Formed from the remains of ancient organisms. These include coal, oil, and natural gas. They contain a lot of organic carbon compounds that are converted to inorganic products like CO2 when the fuels are burned.  See Chapters 3 and 10 for details.

Classed as eukaryotic microorganisms. Some are unicellular (e.g., yeast), many are multicellular (e.g., mushroom). They are are heterotrophic and tend to act as important decomposers in ecosystems. See Chapter 3 for more.

An adjective that indicates digestive system. In toxicology, gastrointestinal or GI exposure occurs when a xenobiotic is swallowed. See Chapter 15 for more.

A term used to refer to the total amount of genetic information within the DNA of all members of a species. See chapter 6 for more.

In ecology, an organism that occupies a broad niche, that is, it can live under a wide range of conditions and meet its needs with varying strategies. Contrast with specialist. See Chapter 6 for more.

How many different genetic codes are present in an area. See Chapter 6 for more.

Through the use of one of several techniques, the DNA sequence of an organism can be altered. For example, cross breeding of related species can produce offspring with desired traits; genetic engineering that involves direct manipulation of DNA sequences is a modern way to alter the genome of an organism. Genetically modified organisms are often used in agriculture to increase food production, but they are controversial. See Chapter 9 for more.

Refers to all the information that can be used to copy cells. See Chapter 6 for more.

An approach to understanding Earth's history. It is a modification of uniformitarianism and holds that Earth's past was like the present day in that most features arise from slow and steady processes but allows that occasional short-lived catastrophes can also play roles. See Chapter 3 for more.

Associated with the Earth's molten core and responsible for the tectonic cycle. See Chapter 4 for more.

A large mass of ice that persists for many years (up to hundreds of thousands) despite changing seasons. It is formed through accumulation and compression of snow into ice. Glaciers can profoundly shape the surface as they slowly move, store a lot of freshwater, and contain clues about past climatic and atmospheric conditions. See Chapters 4 and 14 for more.

One of the major consequences of global warming. As the name suggests, climates around Earth are altered in subtle and dramatic ways, e.g., amount of rainfall, average temperature, cloud cover. Notably, because of the complexity of Earth's systems, some local areas can become cooler even as the overall temperature of the planet increases. See Chapter 14 for more.

Refers to the way water circulates around the globe. Notably, warm waters moves northward from the equator to northern latitudes. See Chapter 14 for more.

An increase in the average temperature of the Earth. See Chapter 14 for more.

GWP. How much warming a gas can cause relative to that caused by carbon dioxide. So, carbon dioxide has a GWP = 1, methane has a GWP = 24, and nitrous oxide has a GWP = 3007, meaning one methane causes as much warming as 24 carbon dioxide molecules and one nitrous oxide causes as much warming as 3007 carbon dioxide molecules. See Chapter 14 for details.

A form of carbon that is biologically available to the whole biosphere. It is organic, having the formula C6H12O6. It is produced by fixation of carbon dioxide.

Associated with the pull all objects in space have on each other, e.g., the way the moon and Earth are attracted. It is responsible for the tides. See Chapter 4 for more.

A natural atmospheric phenomenon. It leads to a warmer planet than Earth would be without it. Certain gases (known as greenhouse gases) absorb outgoing heat and then re-radiate much of that energy back to the surface; as a result, Earth's surface warms. Human activity increases the amount of greenhouse gases in the atmosphere and intensify the greenhouse effect. See Chapter 14, especially Figure 14.18, for more.

A group of gases found in Earth's troposphere. They absorb heat (i.e., infrared energy) that is released from Earth's surface and re-radiate some of that energy back to Earth. Greenhouse gases come from both synthetic and natural origins and include carbon dioxide, nitrous oxide, water vapor, and several industrial products. See Chapter 14 for more.

A reservoir of the hydrologic cycle located below the Earth's surface. See Chapter 4 for details.

In demography, the net change in the size of a population; it is generally expressed as a percentage. See Chapter 8 for more.

Bird excrement that tends to be rich in phosphorus. See Chapter 4 for more.

See Global Warming Potential.

In ecology, refers to the physical location in which an organism lives. Compare to niche. See Chapter 5 for details.

The physical environment in which an organism lives is rendered incapable of supporting that organism; the term generally refers to human activity. In the case of species with very specific needs, habitat destruction can lead to extinction. See Chapter 6 for more.

Barriers to the movement of organisms can effectively cut up a large habitat into small sections. Highways, railways, and pipelines are among the structures that can fragment habitat. In some cases, it can endanger organisms.  See Chapter 6 for details.

The length of time required for half of the unstable atoms in a space to decay to stable products. See Chapter 10 for more.

A group of elements that have similar chemical properties. Among others, the halogens contain environmentally important bromine (Br) and chlorine (Cl).

An intrinsic property of a substance or an activity related to how much harm it will cause. Also, certain substances or devices are referred to as hazards (e.g., a step ladder or laboratory solvent). See Chapter 15 for more.

Refers to waste that poses more risk to human and environmental health than does domestic waste. Some waste from industry, hospitals, universities, and other facilities is classified as hazardous if it meets certain criteria. See Chapter 13 for details.

A low-grade form of energy that is the result of degradation of high-grade energy. See Chapter 4 for details.

A type of pesticide that specifically targets unwanted plants (i.e., weeds). See Chapters 9 and 15 for details.

An organism that consumes plants. See Chapter 5 for details.

Passed from parents to offspring. See Chapter 6 for more.

A type of organism that relies on preformed, organic carbon to meet its nutrient needs. Includes animals, fungi, and many bacteria.  Heterotrophic an adjective. Compare to autotroph. See Chapter 5 for more.

In toxicology, the idea that there is an optimum dose of a xenobiotic; both low and high doses can cause harm. See Chapter 15 for details.

Named after an American geologist who predicted a rise and then fall in petroleum production, also the notion of "peak oil". See Chapter 10, especially Box 10.3, for more.

One widely used unconventional petroleum-recovery technique. It involves injection of fluids to free up fluids stored in pores of reservoir rocks. See Chapter 10, especially Figure 10.11,  for more.

A term used to refer to the ways humans can capture the energy of moving water to generate power. See Chapter 10 for more.

A general chemical term that refers to chemical compounds made up of hydrogen and carbon atoms bonded together. This term encompasses a large array of compounds with different numbers of C and H atoms connected in different ways. See Chapter 10 for details and context.

A facility that uses moving water to spin turbines and generate electricity. See Chapter 10 for more.

A chemical element made up of atoms that have 1 proton and 1 electron. It is an important building block for organisms and is the most abundant element in the universe.

Describes the pathways and reservoirs of Earth's water. See Chapters 4 and 11 for more.

One of Earth's four spheres, this one contains all of Earth's water. See Chapter 4 for more.

In toxicology, an endpoint caused by exposure to certain xenobiotics: the immune system has a more pronounced and inappropriate reaction to substances that enter the body. It is similar to allergic reaction. See Chapter 15 for details.

A proposed explanation for an observed phenomenon. See Chapter 2 for more.

In geology, rocks formed directly from cooling magma or lava. See Chapter 3 for more.

In toxicology, an endpoint that may be caused by xenobiotic exposure: the immune system does not work as well as it once did, meaning the affected organism is more susceptible to infectious agents and cancers. See Chapter 15 for details.

In toxicology, refers to damage done to the immune system by a xenobiotic. See Chapter 15 for details.

When humans go to a reservoir and utilize the water in place (rather than removing the water from the reservoir to use it elsewhere). Examples include boating, swimming, fishing. See Chapter 11 for more.

Combustion of waste at very high temperature in a structure known as an incinerator. These facilities are designed to reduce the volume of waste and release minimal air pollution. See Chapter 13 for more.

An organism that is native to an area. An exotic organism would be the opposite, one that came into an area from an outside system. See Chapter 5 for more.

A strategy used by scientists in their study of the natural world. It involves the observation of specific, representative phenomena to develop general conclusions or rules that govern the universe. See Chapter 2 for more.

In demography, refers to the number of pregnancies that end in a stillborn baby; it is generally expressed as a number per 1000, e.g., 20 / 1000. See Chapter 8 for more.

A pathway of the hydrologic cycle. Water flows vertically downward due to gravity. See Chapter 4 for more.

Also known as heat, it is a type of energy that behaves differently than light and ultraviolet energy (and all the other energy types on the electromagnetic spectrum). See Chapter 14 for more.

When an airborne substance enters a body through the respiratory system (i.e., nose/mouth). In toxicology, exposure via inhalation is of concern for gaseous and particulate xenobiotics. See Chapter 15 for more.

In chemistry, refers to chemical compounds that lack at least one of the following: a C atom and at one C-H bond. Compare to organic. See Chapter 4 for details.

The portion of soil that was derived from rocks. See Chapter 9 for more.

The simultaneous use of multiple strategies to collect, handle, and minimize waste. See Chapter 13 for more.

An important concept related to water quality. It refers to the way a given quantity of water will be utilized by humans. Different uses include consumption, irrigation, cleaning; different uses tend to require different levels of water quality. See Chapter 11 for more.

A group of scientists working through the United Nations. It evaluates scientific data from studies of climate change to predict future trends and make recommendations. See Chapter 14 for more.

Rivalry among different populations, that is, among organisms that are not from the same species. See Chapter 5 for more.

Rivalry among members of a species, that is, those in the same population. Compare to interspecific competition. See Chapter 5 for more.

Refers to injection into a blood vessel. In toxicology, intravenous or IV exposure is of concern because a xenobiotic can quickly enter the bloodstream. See Chapter 15 for more.

In ecology, exotic species that outcompete native organisms. Often, invasives can take over an area. See Chapters 5 and 6 for more.

An animal that lacks a backbone.  This is a large group, and includes worms, jellyfish, and spiders.  Compare to vertebrate.

In chemistry, when a neutral atom gains or loses electrons, thereby gaining or losing negative charge, it becomes a charged ion. Loss of electrons produces a positive ion, gain of electrons produces a negative ion. See Chapter 4 for more.

In agriculture, the application of water onto crop fields. See Chapter 9 for more.

Atoms with the same number of protons but a different number of neutrons in the nuclei. For example, U235 and U239 are different isotopes of uranium.  Each has 92 protons (as well as 92 electrons), but the former has 143 neutrons and the latter has 146 neutrons. See Chapter 4 for details and Chapter 10 for some relevance and context.

In ecology, the reproductive strategy that involves producing a small number of offspring that are cared for by their parents. See Chapter 5, especially Box 5.2 for more.

A waxy intermediate between dead organisms and petroleum. It forms from remains of buried marine microorganisms; it can undergo further transformations into petroleum. See Chapter 10 for more.

In ecology, an organism that plays a uniquely critical role in an ecosystem. If such an organism disappears, the affected system is likely to undergo dramatic adverse changes. See Chapter 6 for details.

Energy in motion. See Chapter 4 for details.

A structure designed to contain waste. See chapter 13 for details.

One type of mass wasting event: it involves the rapid movement of materials downhill; those materials slide along a slope. See Chapter 7 for more.

A larva (plural: larvae) is an immature form of an animal, one that can undergo a dramatic metamorphosis and develop into an adult.  For example, caterpillars are butterfly larvae. 

In ecology, organisms that are more like climax-community species than pioneer species. See Chapter 5 for more.

In geology, molten rock that flows on top of Earth's surface. See Chapter 3 for more.

A theory that has persisted for many years and continues to persist in the face of attempts to discredit it may be elevated to the status of scientific law. Generally, laws can be expressed by a (relatively) simple mathematical formula. Few scientific notions are given this standing. The laws of thermodynamics and the law of gravitation are two examples. Although widely supported by data and history, a law may be subject to review or change as our understanding of the universe increases. Compare to theory and conclusion. See Chapter 2 for more.

A process whereby a pollutant is carried vertically downward in moving water. It is of concern because it can lead to groundwater pollution. See Chapters 11 and 15 for details.

In toxicology, the tissue concentration of a xenobiotic that causes death in an exposed organism. See Chapter 15 for details.

A ridge of material that lies at the edge of a stream channel; levees run parallel to a stream. A levee forms via flooding and grows with each flood. See Chapter 7 for more.

An example of a very close mutualistic relationship involving algae and fungi. This association is so evolved and so close that lichens take on a form that is distinct from that of each partner. See Chapter 5 for details,

The one requirement for growth that is least abundant relative to demand for it. It is a concept and problem relevant for both natural and agricultural systems. See Chapter 9 for details.

In geology, the multiple processes that produce sedimentary rocks from unconsolidated sediments. See Chapter 3 for more.

One of Earth's four sphere.  This term refers to the brittle, outer layer of the Earth made up of the entire crust and the upper portion of the mantle. It is nonliving and lies on top of the asthenosphere. See Chapter 3 for more.

The organ in which most xenobiotic metabolism occurs. See Chapter 15 for details.

A type of population growth curve that is more or less S-shaped. It is characterized by an initial slow phase which is followed by a rapid, exponential phase, and then another slow, nearly flat phase. See Chapter 8, especially Figure 8.2, for more.

City in western New York State (USA) that became famous when hazardous waste buried beneath it came to the surface. National attention and outrage led to new environmental protection laws. See Chapter 1, especially Table 1.1, for more.

In geology, molten rock that moves below the Earth's surface. See Chapter 3 for more.

A potentially deadly disease caused by a kind of protozoan; that microorganism is itself spread by a certain type of mosquito.

18th-Century economist and cleric who predicted that the human population would exceed carrying capacity and therefore suffer war, starvation, and other adverse consequences. He is credited with the 'Prophecy of Malthus.' See Chapter 8, especially Box 8.6, for more.

A geology term that refers to the middle zone of the Earth that sits between the crust and core. It is thick, mostly plastic in behavior, and has a higher density than does the crust. See Chapter 3 for more.

A U.S. law passed in 1988 that, among other things, restricted the dumping of waste into the ocean. See Chapter 13 for more.

Refers to a relatively short period of geologic time during which 75% or more of existing species ceased to exist on Earth. See Chapter 6 for more.

Generally, the gravity-driven downward movement of Earth's materials from high to low elevation. There are several different types of mass wasting events. See Chapter 7 for more.

Physical matter that takes up space and has mass. This term is very general and includes many things, for example, individual atoms, chemical compounds, water, soil, and fossil fuels.

A formal chemical term that refers to anything that takes up space and has mass. See Chapter 4 for more.

In agriculture, the largest amount of a crop that can be sustainably grown in a field. See Chapter 9 for more.

One way to represent multiple readings of the same phenomena. For example, five separate readings of the temperature of a container of water could yield five different readings. The mean is often chosen as the best representation of the answer in such a situation. Calculated by adding up the values of all measurements made and then dividing by the number of measurements; equivalent to average. See also standard deviation. See Chapter 2 for more.

Two meanings are relevant to environmental scientists. 1: chemical breakdown of food so nutrients can be obtained by the organism ingesting that food. See Chapter 5 for details. 2: In toxicology, the chemical breakdown of a xenobiotic; usually done to increase the likelihood of elimination (i.e., excretion) of the xenobiotic. See Chapter 15 for details.

In geology, one of the three rock types. These are formed from rocks subjected to solid-state changes. Increased temperature and/or pressure will alter existing rocks into new, metamorphic rocks. See Chapter 3 for more.

A gaseous form of C consisting of 4 H atoms bonded to 1 C atom. See also natural gas. See Chapters 4, 10, and 13 for more.

Anything that is too small to be seen without the aid of a magnifier. Microorganisms are living microbes. See Chapter 3 for more.

A metric unit of length that is equal to 0.0000001 meter. The abbreviation for this unit is µm. See Chapters 2 and 3 for more.

Refers to organisms that are too small to be seen without the aid of a magnifier, including bacteria, protozoa, fungi, algae, and viruses. In the case of algae and fungi, some of the forms are large enough to be seen with the naked eye, but they are included here because some of their forms are microscopic. See Chapters 1, 3, and 4 for more.

Very small plastic particles. These are classified as between 1 micron and 5 millimeter in size. They can be generated through the disintegration of larger plastic trash that is improperly disposed of and are also manufactured for inclusion in certain products. Microplastics pollute water and food. See Chapter 13 for more.

In ecology, organisms that dominate during the intermediate stages of ecological succession. See Chapter 5 for more.

King of Pontus during the last century, BC. Important to modern-day toxicologists because of the way he built up his resistance to poisons by daily ingestion of low doses of all known toxic substances (to thwart would-be assassins). See Chapter 15, especially Box 15.1, for more.

An important subunit or organelle in eukaryotic cells that converts energy into usable forms for a cell. See Chapter 3 for more.

In chemistry, two or more atoms held together by bonds. See Chapter 4 for more.

In agriculture, the practice of growing a single crop in one field. See Chapter 9 for more.

A term that refers to an organism that can move under its own power. Motility is the noun. See Chapter 3 for more.

A type of surface mining of coal which involves the clearing of existing mountain peaks to expose a coal seam. See Chapter 10 for more.

An adjective that refers to an organism made up of many cells that communicate with each other. Humans and plants, for example, are multicellular whereas bacteria are unicellular. See Chapter 3 for more.

Refers to garbage produced by households and other domestic activities. See Chapter 13 for more.

Refers to a change from the normal or original genetic code. Mutations tend to damage or kill affected organisms but may impart new and helpful traits.  See Chapter 6 for details.

In ecology, a relationship among organisms in which all participants benefit.  See Chapter 5 for details.

In the context of environmental science, a phenomenon or process that occurs in the absence of human activity. See Chapter 7 for more.

An important fossil fuel, it is mostly comprised of gaseous methane. See methane for more. See also Chapter 10 and 13.

In evolutionary theory, individuals that are best adapted to survive in their environments will reproduce better than those are less well adapted. See Chapter 6 for details.

In a system, output attenuates or cancels previous output such that a system does not change appreciably from initial conditions. Compare to positive feedback. See Chapter 2 for more.

In chemistry, a subatomic particle found in the nucleus of an atom. These are uncharged. Different atoms of the same element may vary in the number of neutrons they possess, even as they must have the same number of protons. Atoms having the same number of protons but different numbers of neutrons are called isotopes. See Chapters 4 and 10 for more.

The role an organism plays in its habitat.  A niche can be narrow, that is, organisms occupying it have very specific needs and activities.  Slight changes to the conditions in an ecosystem could devastate such organisms.  On the other hand, a niche can be broad, meaning that organisms in it can use a wider variety of strategies to meet their needs.  In this latter case, organisms are more likely to survive changes to environmental conditions.  Compare to habitat. See Chapters 5 and 6 for more details.

A form of nitrogen with the formula NO3-. It is inorganic and biologically available to plants, algae, and some microorganisms. It can cause water pollution, including eutrophication. See Chapter 4 for more.

A chemical element made up of atoms with 7 protons and 7 electrons. Certain forms of N are essential for organisms' survival. See Chapter 4 for more.

Specialized bacteria that can convert dinitrogen into ammonium. They are crucial in providing biologically available N to most of the biosphere. See Chapters 4, 5, and 9 for more.

A type of off-stream use of water that quickly returns the removed water to the reservoir from which it was extracted. For example, water can be pumped from a river to cool an industrial process and then returned shortly thereafter. See Chapter 11 for more.

Diffuse, non-discreet sources of water pollution. Unlike point sources, they are difficult to identify and remediate. See Chapter 11 for details.

Contaminants that enter water from multiple, hard-to-identify outlets. Runoff from agriculture is a good example of non-point source pollution. Compare to point source pollution. See Chapter 11 for more.

Non-potable water is not safe for human consumption (opposite: 'potable water'). See Chapter 11 for more.

Those that are finite in that they cannot be replaced fast enough to keep up with their rate of usage. Examples include coal, oil, natural gas, and nuclear energy. See Chapter 10 for more.

An organism that humans do not intend to kill with pesticides, antibiotics, or other poisons; generally, an organism that provides some benefit to humans. However, non-target organisms often are affected nonetheless. See Chapters 9 and 15 for more.

The process that splits a single atom into several products; it releases an enormous amount of energy, some of which can be harnessed to generate electricity. See Chapter 10 for more.

Thin tubes packed with fissionable material such as uranium atoms. These rods undergo a chain reaction inside a nuclear reactor. See Chapter 10 for more.

An accident at a nuclear power plant that involves the uncontrolled heating of the reactor core such that it starts to melt. See Chapter 10 for more.

An approach to study used by scientists.  It is characterized by observation of phenomena without imposing judgements or other biases on the results.  Contrast with subjective. See Chapter 1 for more.

The status of a test subject at a moment in time is studied and reported. Observational science can be used to classify objects into previously established categories; for example, an unknown mineral sample could be evaluated and identified according to preexisting criteria and grouped accordingly. See Chapter 2 for more.

When humans extract water from a reservoir to utilize it elsewhere. For example: irrigation, domestic consumption. See Chapter 11 for more.

A natural opening in the seafloor through which small amounts of petroleum can enter ocean water. See Chapter 10 for more.

An impermeable geologic structure against which migrating petroleum is concentrated. See Chapter 10 for more.

Once a widely used practice to manage waste, ihis involves the simple incineration of trash without air pollution controls. See Chapter 13 for more.

A strategy for waste management that was used widely in the past. Garbage is dumped onto Earth's surface without containment. Note that open dumps are not the same as sanitary landfills. See Chapter 13 for more.

Subcellular structure such as nucleus, mitochondria, chloroplast, etc.  They are found in eukaryotic but not prokaryotic cells. See Chapter 3 for more.

In chemistry, an adjective that refers to chemical compounds that consist of at least one C atom that is bonded to at least one H atom. Compare to inorganic. See Chapter 4 for details.

The portion of soil that was derived from organisms' waste and remains; synonymous with SOM (soil organic matter). It consists of many sub fractions with specific chemical and physical properties. See Chapter 9 for more.

Comprised of about 15 nations (membership fluctuates) that control about 80% of Earth's oil reserves. See Chapter 10 for more.

The geologic material that lies on top of a coal seam; it must be either removed or penetrated by mines so the coal can be extracted. See Chapter 10 for more.

In the context of water usage, when water is extracted by humans from the groundwater reservoir faster than it is replaced by natural processes. See Chapter 11 for more.

In agriculture, when the feeding by livestock exceeds the carrying capacity of grasses in a field. See Chapter 9 for more.

A space that contains sufficient dioxygen gas to support aerobic organisms. Compare to anoxic and anaerobic.

A chemical element made up of atoms with 8 protons and 8 electrons. It is an important building block for organisms. Two O atoms bonded together makes up dioxygen, a gas which is essential to the survival of aerobic organisms.

A molecule made of e oxygen atoms bonded together. See Chapter 14 for details.

An area in the stratosphere in which there is less ozone than is typical. See Chapter 14 for more.

The ozone molecules located in the stratosphere. This layer absorbs much of the harmful ultra violet light that reaches the Earth from the sun. See Chapter 14 for more.

A broad term given to chemical compounds that can lead to destruction of stratospheric ozone. See Chapter 14 for more.

In geology, an ancient landmass made up of all Earth's continents. It started to break up due to movement of tectonic plates about 200 million years ago. See Chapter 3 for more.

16th-Century scientist whose work led to the dose-response principle in toxicology. See Chapter 15 for more.

In ecology, an association in between organisms in which one is harmed and one derives benefit. Typically, a smaller organism, the parasite, lives on or in a larger organisms, the host. See Chapter 5 for details.

Existing substances that can be modified into soil via natural physical, chemical, and biological processes. Parents include rocks and the remains / waste products of organisms. See Chapter 9 for more.

In toxicology, the form of the compound to which an organism is exposed, the form that enters an organism. The parent compound may be chemically altered within an organism. See Chapter 15 for details.

A general term that includes any disease-causing organism. Some bacteria, fungi, protozoa, and algae are on this list, as are many viruses. Certain worms and other larger organisms can act as pathogens as well. See Chapters 3 and 5 for more.

Refers to natural processes that move materials among earth's natural reservoirs. For example, evaporation moves water from surface reservoirs like the ocean to the atmosphere. See Chapter 1 for more.

A precursor to coal, formed from the decomposing remains of plants. See Chapter 10 for more.

The first antibiotic discovered by humans. Produced by a certain fungal species, it inhibits cell wall synthesis in many bacteria. Thus, penicillin can cure an infected person of a disease caused by susceptible bacterial pathogens. See Chapters 5, 6, and 15 for details.

Refers to a broad class of chemical compounds intended to kill unwanted organisms. Widely used in agriculture, they can kill pests such as weeds, certain insects, and others, but they also can harm organisms we wish to protect, including humans. See Chapters 1, 9, and 15 for more.

A laboratory tool in which microorganisms such as bacteria can be grown. See Chapter 3 for context.

A broad term that refers to fuels derived from ancient marine microorganisms. These fossil fuels include oil and, according to some, natural gas. See Chapter 10 for more.

In chemistry, a way to express the acidity of a water-based solution. The pH scale runs from 0-14, with the lower numbers (those below 7) indicating acids and higher numbers (those above 7) indicating bases. A neutral solution is pH 7. See Chapters 9 and 10.

A chemical element, P, made up of atoms have 15 protons and 15 electrons. It is an essential nutrient for organisms, but its relatively scarcity on Earth can limit production and growth in ecosystems. Excess P can cause eutrophication in water. See Chapter 4 for more.

Sometimes called Los Angeles smog. A local air pollution phenomenon caused by the specific conditions in LA, California (and other places): low wind, high sun, and high density of cars and trucks (which release hydrocarbons and nitrous oxide, two important primary pollutants).  Compare to sulfurous smog. See Chapter 14 for more.

A process carried out by certain organisms (plants, algae, and some bacteria) in which the energy of the sun is used to drive the fixation of carbon. See Chapters 4 and 5 for more details.

An organism that uses the sun as its energy source. See Chapter 5 for more.

Small constructed objects that contain specialized chemicals able to absorb and convert solar energy into electricity. Many cells can be combined to form a solar panel. See Chapter 10 for more.

A graphical representation of relationships among organisms based on comparisons of DNA sequences. See Chapter 6 for more.

Plant-like plankton that are producers; they are consumed by zooplankton.  They live in surface waters where sunlight is available.  They tend to be on the order of a few millimeters or so in size. See Chapter 5 for more.

The use of plants to clean up contaminated soil. See Chapter 15 for more.

In ecology, the organisms that can colonize barren landscape and thus initiate ecological succession. See Chapter 5 for more.

Physiological features within the placenta that protect a developing offspring from many xenobiotics. See Chapter 15 for details.

Small organisms that float at or near the surface of bodies of water.  They range in size from less than a millimeter to a centimeter.  See phytoplankton and zooplankton.

In geology, describes how the lithosphere of Earth is broken into several units called plates. These plates slowly move horizontally with respect to each other. Plate movements are responsible for continental drift, earthquakes, volcanoes, and other important phenomena. See Chapter 3 for details.

Discrete outlets that release contaminants into water reservoirs. For example, a pipe that drains from an industrial site is a point source of pollution. These are relatively easy to identify and remediate; compare to non-point sources of pollution. See Chapter 11 for more.

A general term that includes substances that can cause harm to living systems. See Chapter 15 for details.

The more or less triangular shape a contaminant in flowing water takes after it is released. Concentration is highest at the point at which the pollutant is introduced and diminishes with distance from the source. See Chapter 11, particularly Figure 11.7, for more.

Terms referring to something that degrades the quality of air, water, or soil.  The term 'pollutant' is used to refer to that material that degrades quality.  Compare with 'contaminant', a word with a related, if distinct, meaning.  In short, a contaminant can be thought of as any substance that does not belong where it is found (i.e., a metal dissolved in water).  A pollutant is a contaminant that has reached a high enough concentration to cause adverse effects (i.e., that metal noted in the previous sentence is at such a high level that it is killing fish; see Chapter 11 for more about water pollution).  Note that the terms are often used interchangeably by scientists and members of the public alike.

In ecology, a group of organisms that are all members of the same species. See Chapter 5 for details.

A cause of extinction of a species that stems from a low number of individuals of that species. See Chapter 6 for more.

In a system, current output accentuates or magnifies the effect of previous output. This type of feedback leads to change away from initial conditions. Compare to negative feedback. See Chapter 2 for more.

In toxicology, refers to the dose of a xenobiotic required to bring on an observable response. Low-potency compounds require high doses and high-potency compounds require low doses. See Chapter 15 for details.

Stored energy. See Chapter 4 for details.

A term related to energy and the capacity to do work.  It can be derived mathematically:  it is the amount of energy transferred per time unit.  Conceptually, power allows a certain amount of work to be done in a certain period of time.  It can be expressed with several different units, including the watt.  A power generation plant receives thermal power from the burning of a fuel like coal and releases mechanical power in the form of electricity. See Chapter 10 for context.

A collection of generation facilities and power lines that produce and distribute electricity to a large number of users. See Chapter 10 for more.

In short, it holds that new chemicals, technology (etc.) are assumed to be hazardous and risky until proven otherwise.  Often drives regulations on new substances and devices introduced into commerce. See Chapter 1 for more.

A pathway of the hydrologic cycle. Water that has condensed in the atmosphere falls to the surface as liquid or solid. See Chapter 4 for more.

How well multiple readings, or replicates, of the same phenomena agree with each other. Contrast with accuracy and sensitivity. See Chapter 2 for details.

Observable events that signal an earthquake is imminent. See Chapter 7 for more.

An interaction between organisms in which one is harmed and the other derives benefit. Specifically, a predator consumes a prey organism. See Chapter 5 for details.

In ecology, an association between organisms in which one, the predator, lives at the expense of the other, the prey. Predators consume prey. See Chapter 5 for details.

Their energy be converted directly into electricity or heat; oil, gasoline, coal, solar energy, and others are primary energy sources. See Chapter 10 for more.

A substance that has not been altered from its original form, that is, the form that is released into a natural environment. For example, carbon monoxide emitted from the tailpipe of car. See Chapter 14 for more.

Organisms that fix carbon for all members of an ecosystem; they are autotrophs. They also tend to convert non-biologically available energy into biologically available forms. For example, plants both fix carbon and convert the sun's energy to chemical bond energy. Consumers live off of the C and energy stored in primary producers. See Chapters 4 and 5 for more.

In ecology, ecological succession that follows a disturbance extreme enough to wipe out an existing community. Pioneer species can colonize a barren landscape in this case. Compare to secondary succession. See Chapter 5 for more.

One of the stages of sewage treatment, involves the physical separation of solids from liquids. See Chapter 11 for more.

Alaska (USA), the site of a major marine oil spill in 1989. This event raised many concerns about marine oil tankers, oil usage, and contamination of pristine environments. See Chapter 1 for more.

Foundational principle in toxicology that states the effects caused by a xenobiotic will depend on the concentration of that xenobiotic in a body or, more likely, at a target site within a body. See Chapter 15 for details.

A type of organism that lacks any membrane-bound organelles such as a nucleus. These tend to also be small and single celled. Bacteria are important prokaryotes.  Also known simply as 'prokaryote.' See Chapter 3 for more.

Positively charged subatomic particle found in the nucleus of an atom. The number of protons varies by, and defines, atom type (i.e., atoms of specific elements are defined by the number of protons in their nuclei). See Chapter 4 for more.

A group of organisms that are microscopic, eukaryotic, mobile (also known as "motile"), and usually heterotrophic. They are roughly ten times larger than bacteria; they also tend to prey on bacteria. See Chapter 3 for more.

The amount of any material that is known to exist and can be recovered (i.e., obtained) with existing technology. For example, "petroleum reserves" refers to the oil we can count on. See Chapter 10 for more.

In ecology, a reproductive strategy that involves the release of high numbers of offspring but little or no parental care. See Chapter 5, especially Box 5.2 for more.

A kind of energy that can travel at the speed of light from some source through air or even a vacuum. There are many different types of radiation. Some high energy radiation such as gamma rays can penetrate deep into objects (living and non living) and cause chemical changes. This kind of ionizing radiation can damage living cells. See Chapters 10 and 15 for more.

A process whereby an unstable atom emits energy and particles as it is transformed into a smaller atom. See Chapter 10 for more.

Products of nuclear fission, some of this emits low levels of radiation and some emits high levels of radiation. In the latter case, long-term containment is necessary to minimize risk of exposure of humans and other organisms to dangerous radiation. See Chapter 10 for more.

Cause measurements of a phenomena to be inaccurate in an inconsistent way (i.e., either above or below the actual value). For example, five different scientists might read a meter stick from five different angles and report five different answers; some of the answers will be too high and some will be too low. Contributes to scientific uncertainty. Compare to systematic errors. See Chapter 2 for details.

In chemistry, occurs when two or more atoms are brought close together and interact. Reactions can lead to breaking of existing bonds and formation of new bonds. In some cases, separate smaller units are combined into larger units via reactions. Energy released during some reactions can be captured by organisms and used to do the work of living. See Chapter 4 for more.

Refers to replacement of water in the groundwater reservoir. Recharge is largely the result of precipitation followed by infiltration of water downward. Melting snow and ice at the surface can also contribute. See Chapter 4 for more.

A process that combines genetic information from two parents into a new offspring; changes in a population are a result. See Chapter 6 for more.

An adjectival word that refers to a substance that is not medically necessary; a person may ingest it for pleasure. Compare to therapeutic. See Chapter 15 for more.

A waste management strategy characterized by the collection and reprocessing of paper, glass, plastics, metals, and other materials (including hazardous waste) so they can be used again. See Chapter 13, especially Figures 13.12 and 13.13, for more.

The process by which several different fuels are derived from crude oil. It involves heating and high pressure to yield such products as gasoline, motor oil, kerosene, and others. This work is done at a facility known as an oil refinery. See Chapter 10 for more.

Clean up or repair of an existing problem. See Chapter 15 for more.

Those that can be replaced in a relevant period or time and/or are so abundant that human usage has no appreciate effect on their supply. Solar energy is a good example because of the vastness of its supply. See Chapter 10 for more.

In demography, refers to the number of births required to maintain a population indefinitely. See Chapter 8 for more.

A shorthand word often used by scientists to refer to multiple measurements of the same phenomena: each reading is a replicate. Put another way, we replicate or repeat a measurement multiple times. See also precision. See Chapter 2 for more.

In ecology, refers to an approach to wildlife and ecosystem protection. The goal of preservation is to protect wild living entities for their own sake, not to provide direct benefits to humans. Compare to conservation. See Chapter 6 for more.

The amount of a material that is known to exist and can be obtained with existing technology. The term is often applied to oil and natural gas. See Chapter 10 for details.

Refers to natural sites in which important materials such as water, petroleum, nitrogen, and many others, are stored. See Chapter 1 for more.

The length of time an average unit of a particular material remains inside a system. It can be calculated as shown in Box 2.4.

The quantity of material that includes reserves as well as other, more tenuous pools of materials. Often used in reference to oil and natural gas. See Chapter 10 for details.

A process carried out by living things. The chemical bonds in relatively large molecules are broken with the following results: some energy is harnessed by the respiring organism and the large molecule is broken down into relatively small fragments. See Chapter 4 for more.

In toxicology, an outcome caused by a xenobiotic. See also endpoint. See Chapter 15 for details.

The likelihood that a substance or activity will cause harm. See Chapter 15 for more.

The final step or product of a risk assessment. Typically, it is a short statement of the risk or safety of a substance or activity. For example, a risk assessment of a new food additive might conclude with a statement like "the safe daily dose is 0.1 mg / kg body weight +/- 0.5 mg." See Chapter 15 for more.

People who regulate risky substances, devices, actions, and behaviors. They make laws (etc.) in response to risk assessment data; other inputs also contribute to their decision making, including politics and ideology. See Chapter 15 for more.

Defined by geologists as materials that are naturally occurring, solid, consolidated (i.e., grains glued together through some mechanism), and made up of some combination of inorganic minerals and remains of organisms. More about the three types of rocks and the rock cycle can be found in Chapter 3.

In toxicology, the possible ways a xenobiotic can enter an organism, including via diet, dermal (skin) contact, inhalation, and injection. See Chapter 15 for details.

A pathway of the hydrologic cycle. Water flows across the surface of the Earth; it moves with gravity and follows the contours of the surface. See Chapter 4 for more.

The likelihood that a substance or activity will not cause harm. It can be understood to be the inverse of risk. See Chapter 15 for more.

Refers to the salt content of water.

A type of water pollution that affects coastal groundwater reservoirs. Overdraft of coastal aquifers can draw saltwater from a nearby ocean into an aquifer and well. See Chapter 11, especially Figure 11.11, for more.

An example of ecological succession that transforms a barren sand dune into a small forest. Among other changes that occur with time: the dune is stabilized by grasses specifically adapted to grow in unstable sand. See Chapter 5 for details.

A widely used strategy to manage municipal solid waste (MSW). Large structures are excavated and divided into cells. Each cell is lined with impermeable plastic before trash is packed into it. Once full, a cell is sealed all around and the waste is contained indefinitely. See Chapter 13, especially Figures 13.7 and 13.8, for more.

A layer that can be found beneath the Earth's surface; it is below the water table. It consists of solids and pores, and the pores are completely filled with water. Groundwater is found in the saturated zone. See Chapter 4 for details.

A systematic strategy used by scientists to answer questions about the natural world.  It is designed to facilitate objectivity and repeatability. The specific steps used by scientists different somewhat among disciplines, but they generally include some variation on:  observation, hypothesis, experimentation, conclusion, repeat / refine hypothesis, share information with the scientific community.  Chapter 2 contains a detailed description.

In simple terms, describes how energy conversions must always go from higher to lower grade, i.e., conversions always lead to degradation of energy. See Chapter 4 for more.

Unlike primary energy sources, these are not sources of energy but instead can be used to carry power from a primary source to a user. Electricity is a good example of a secondary energy source. See Chapter 10 for more.

A product of reactions involving primary pollutants. For example, ozone gas, an important secondary air pollutant, can be produced from reactions involving hydrocarbons released from a car's tailpipe. See Chapter 14 for more.

In ecology, the recovery of an ecosystem after a relatively minor disturbance. Some remnants of previous communities are present. Compare to primary succession. See Chapter 5 for more.

An important step in the sewage treatment process, it involves the use of microorganisms to digest some of the decomposable organic pollutants in sewage. See Chapter 11 for more.

In the context of environmental science, refers to a major group of activities that are related to each other. Important sectors are industrial, agricultural, and domestic. For example, we can speak of water use by sector (as in Chapters 9 and 11).

Places at which hazardous waste is contained. See Chapter 13 for more.

On geology, one of the three rocks types. These are formed from weathering products of existing rocks. See Chapter 3 for more.

A fundamental concept in the science of toxicology. Different species, and even different individuals from the same species, will respond differently to the same poisonous substance. See Chapter 15 for more details.

Refers to the smallest change an instrument can detect; put another way, the smallest possible measurement that can be made by an instrument. Contrast with accuracy and precision, and see more details in Chapter 2.

One sewage treatment strategy used on a small scale. Typically, sewage from a single house is drained to a septic tank and then leach field as described in Chapter 11 (especially Figure 11.12).

Refers to the combination of biological, physical, and chemical waste that is flushed down toilets and washed down drains. Sewage is a major source of water pollution and can be cleaned up by sewage treatment. See Chapter 11 for more.

A pipe from which treated sewage is released into a natural reservoir of the hydrologic cycle. See Chapter 11 for more.

A general term that refers to clean up of water polluted with human excrement and other products flushed down toilets and other drains. Treatment involves a complex series of steps to minimize the presence of chemical, physical, and biological pollutants in water before it is released back to natural systems. See Chapter 11 for details.

A large-scale approach to the clean up of human sewage. Sewage treatment plants are typically operated by counties, cities, or other governmental organizations. See Chapter 11, especially Figure 11.13, for more.

Reproduction in which two separate individuals contribute genetic material to produce offspring.  In simple terms, two parents make one new individual.  Most animals employ this strategy.  Contrast with asexual reproduction.  See Chapter 6 for more.

An indoor air pollution phenomenon. Many people living or working in the same building become stricken with illnesses (often respiratory conditions) that are difficult to trace to a source. Materials in their common space are often to blame, although establishing cause and effect can be difficult. See Chapter 14 for more.

Unintended, and often harmful, consequence of ingestion of a therapeutic drug. See Chapter 15 for more.

A depression or opening in the Earth's surface resulting from a lack of underlying support. A common cause of sinkholes is dissolution of limestone beneath the surface. See Chapter 14, especially Box 14.2, for more.

A local air pollution problem generally seen in urban areas. Airborne products of fossil fuel combustion can get trapped near their sources and profoundly degrade air quality. See Chapter 14 for details.

Natural materials that are produced from chemical, biological, and physical transformations of rocks and organisms. True soil consists of layers or soil horizons. Soils consist of inorganic and organic materials + air and water. See Chapter 9 for details.

The horizontal layers that extend from Earth's surface downward for a few meters (it varies). Each layer is physically and chemically distinct from the other layers. See Chapter 9 for details.

An important component of soil. It is a complex material made up of the partially decomposed remains of organisms. It supplies nutrients to plants and helps retain moisture and soil structure. See Chapter 9 for details.

The layers in a true soil when viewed in cross section. See Chapter 9 for more.

Refers to the relative proportion of sand, silt, and clay in a given soil sample. See Chapter 9 for more.

High-grade energy emitted from the sun. It provides nearly all of Earth's energy. See Chapters 4 and 10 for more.

Refers to ways humans use the sun to generate electricity or to heat water or spaces. Distinct from indirect usage of solar energy such as photosynthesis. See Chapter 10 for more.

Areas at which many solar panels are concentrated; electricity generated at such a site could be distributed to multiple users. See Chapter 10 for more.

In ecology, an organism that occupies a narrow niche. It has strict requirements that can only be met in a small number of ways. Contrast with generalist. See Chapter 6 for more.

Broadly defined, the production of a new species. See Chapter 6 for more.

Refers to a group of organisms that are closely related enough that they can breed and produce fertile offspring. See Chapter 5 for more details.

A way to quantify how many different species dominate in an area. Unlike species richness, this property reflects the relative importance of different species, not the total number of different species. For example, in a hypothetical ecosystem there might be 10,000 different species (high richness) but low evenness because only 1 of those species dominates the area--the other 9,999 are essentially invisible and inactive. In a second case, an ecosystem might have 10 organisms--low richness--but high evenness if the relative number of each species is about the same. See Chapter 6 for more.

The total number of different species in an area. See chapter 6 for more.

Environmental scientists divide the outer portion of Earth into four zones or units for the ease of study; each is known as a sphere. They include the atmosphere, hydrosphere, biosphere, and lithosphere. See Chapter 4 for more.

The name of a theory that was once used to explain how organisms could end up in food, water, and other places. In short, these organisms were thought to spring up within non-living matter without any external source or aid. It was used to account for disease and food spoilage. The theory of spontaneous generation persisted for centuries, despite many attempts to discredit it, including some that cited compelling evidence. It was finally debunked completely in the late 19th Century by Louis Pasteur and some other scientists. See Chapter 3, especially Box 3.5,  for more.

A common strategy, but not the only way, to quantify uncertainty in a measurement. For example, 6.2 +/- 0.3 indicates the mean value from multiple readings (6.2) and the standard deviation (0.3). It can be reasonably understood to represent the range of possible values for a measurement; in the above example: 5.9 to 6.5. See also mean. See Chapter 2 for more.

A broad term referring to the money that must be spent to build a new facility. It is often used to describe challenges associated with power generation (Chapter 10) or waste management (Chapter 13) facilities, but it is appropriate for any new construction project.

In systems analysis, refers to a situation when the rate of input of a material to a system is equal to the rate of removal of that material from a system. It results in no net change in the amount of that material within a system. See Chapter 2 for more.

A object's response to stress applied to it; strain can be understood to be the way an object changes or breaks. See Chapter 7 for more.

The layer of the atmosphere that lies above the troposphere. Here is where the bulk of atmospheric ozone is located. See Chapters 4 and 14 for more.

The ability an object has to withstand stress applied to it without exhibiting strain. See Chapter 7 for more.

The force applied to an object, as in tectonic stress applied to rocks. See Chapter 7 for more.

One strategy to extract coal from the Earth. In short, rocks and soil on top of a coal seam are removed so the coal can be extracted at the surface. See Chapter 10 for more.

A term that refers to objects that are smaller than and associated with atoms. These include neutrons, protons, and electrons. See Chapter 4 for more.

In geology, an interaction between lithospheric plates: the more dense one dives below the the less dense one. See Chapter 3 for more.

In geology, a convergent plate boundary at which more dense crust slides below less dense crust. See Chapter 3 for more.

An approach that is characterized by values and biases; contrast with objective. See Chapter 1 for more.

Sometimes called London smog. A local air pollution phenomenon caused by the specific conditions in London, England (and other places): cool damp conditions, persistent cloud cover, and high density of manufacturing, cars, and trucks (which release sulfur oxides and other primary pollutants). See Chapter 14 for more.

A visible dark patch on the surface of the sun. The number of sunspots goes up and down in a regular 11-year cycle; there is a positive correlation between sunspot number and the amount of energy released by the sun. See Chapter 14 for more.

Related to the way current usage of a resource affects future availability of that resource. Sustainable practices ensure that materials are not used up faster than they are replaced. See Chapter 1 for more.

In ecology, a general term referring to two or more organisms living together. Symbiotic and symbiotically are related words. See Chapter 5 for more.

Formally defined as a collection of subunits that work together. A system responds to inputs and produces outputs. See Chapter 2 for more.

In science, cause all measurements of a particular phenomenon to be inaccurate in the same direction (i.e., either too high or too low). For example, if a balance is poorly calibrated, it could consistently read 0.2 g too high for all objects assessed. Contributes to scientific uncertainty. Compare to random errors. See Chapter 2 for details.

In toxicology, the part of the body affected by a xenobiotic. See Chapter 15 for details.

A geology term referring to distinct units of the lithosphere. Several of these large plates make up the lithosphere, and they move around, on top of the asthenosphere, with respect to each other. Their movements are responsible for many important phenomena, including continental drift, earthquakes, and volcanoes. See Chapter 3 for more.

In toxicology, a xenobiotic that induces birth defects. See Chapter 15 for details.

An adjective that refers to organisms that live primarily on land (i.e., not in water). Compare to aquatic organisms. See Chapter 4 for more.

A very important historical teratogen. It was used to treat morning sickness in the late 1950s and early 1960s but caused severe birth defects. See Chapter 15 for details.

An international agreement designed to eliminate the release of CFCs into the atmosphere because of the way they contribute to ozone destruction. It was initiated in 1987 by a small number of countries (including the U.S.) and signed by many more nations in subsequent years. See Chapter 14 for more.

A scientific notion that has developed after many experiments; often, several generations of scientists have tested and refined such a notion before it is elevated to the status of theory. It is reasonable to view a theory as a conclusion that has withstood many attempts to discredit it. Note that “theory” is used differently in science than it is in everyday life.  In the former, it is taken very seriously, whereas in the latter it indicates an idea that has little or no evidence to support it. Even well-supported theories could be modified with continued study, but a lot of new data would need to come to light in order to discredit one of them. Compare to conclusion and law. See Chapter 2 for more.

An adjectival word that refers to a substance that provides a benefit to the person who ingests it. Generally, therapeutic substances are assumed to be medically necessary. Compare to recreational. See Chapter 15 for more.

Refers to the way water takes up more space as its temperature goes up (at least above about 4 degrees C). See Chapter 14 for more.

When non-consumptive off-stream water use introduces heat into a stream. See Chapter 11 for more.

Describe how energy is used and converted among forms (e.g., potential, kinetic, and heat). See Chapter 4 for details.

A nuclear power plant near Harrisburg, PA (USA). An serious accident there in 1979 changed the way Americans viewed nuclear power. See Chapter 1 for more.

In toxicology, the dose of a xenobiotic below which no response is observable. See Chapter 15 for details.

Reservoirs of oil and natural gas that are locked in the pores of shales and other hard-to-access geologic structures are said to be "tight". They can only be recovered using hydraulic fracturing or other unconventional method. See Chapter 10 for more.

A term that refers to oil and natural gas that is difficult to extract from their reservoirs because it is tied up in solid rocks or sands. See Chapter 10 for more.

An informal term that refers to rapid, non-linear acceleration of change once a certain level of some property is reached. In the case of global warming and climate change, a tipping point could be reached at a particular concentration of carbon dioxide in the atmosphere or average global temperature. See Chapter 14 for more.

The layer, or soil horizon, that contains the most soil organic matter (SOM). It is is at or close to the surface. This is the most fertile part of the soil profile and is where plants grow; when it is lost, the remaining horizons cannot support plants, including crops.  See Chapter 9 for details.

In demography, the number of live births per woman during childbearing years; it is generally expressed as a number such as 2.3 or 5.6. See Chapter 8 for more.

The science of poisons. See Chapter 15 for more.

A poisonous substance produced by an organism. See Chapter 15 for details.

In geology, where two lithospheric plates slide side by side. See Chapter 3 for more.

Movement of material from one place to another; often used to refer to movement among reservoirs. See Chapters 1 and 4 for more.

A pathway of the hydrologic cycle. Water is drawn into plants via their roots. The water moves upwards and is released through openings in leaves as a vapor. See Chapter 4 for more.

A term that refers to clean up of an existing contaminated parcel of water or soil. Various strategies can be employed to clean up, or remediate, polluted materials. See Chapters 11 and 15 for more.

In ecology, refers to the hierarchical feeding relationships in ecosystems. See Chapter 5 for details.

In ecosystems, a group of organisms that all feed the same number of steps away from the original source of energy. For example, plants are all at the first trophic level because they get their energy directly from the sun, whereas deer and other herbivores are at the second trophic level because they get their energy from eating organisms at the first trophic level. Consult Chapter 5 for more details.

Refers to the movement of an environmental pollutant from one organism to another via predator-prey interactions. See Chapter 15 for more.

The inner-most layer of the atmosphere, this is where weather events occur and is the portion of the atmosphere that is in direct contact with Earth's surface and living things. See Chapters 4 and 14 for more.

An ocean wave that results from the sudden displacement of a large volume of water. Earthquakes are commonly responsible, but volcanic eruptions and meteorite impacts can also cause tsunamis. See Chapter 7 for more.

A kind of radiation emitted by the sun. It is higher energy than visible light and can damage living cells (particularly cells of the skin). See Chapter 14 for more.

A property of any scientific measurement, it represents the size of the error term for a measurement. Can be thought of as the range of possible answers to a question (often, from lowest to highest). May be expressed as a number, e.g., 5.0 +/- 0.5 which indicates an average value (or otherwise representative number) of 5 with a possible range of 4.5 to 5.5.  It arises from random and systematic errors. See Chapter 2 for more.

Refers to methods that are more costly and complicated than conventional methods. These can recover tight petroleum, fluids that are difficult to separate from the solid materials in which they are bound. Hydraulic fracturing is one example. See Chapter 10 for more.

An organism that consists entirely on a single cell. Bacteria are unicellular. Contrast with multicellular. See Chapter 3 for more.

An approach to studying Earth's history characterized by the phrase 'the present is the key to the past.' In other words it holds that slow, steady processes (like those active today) were responsible for the features we see on present-day Earth. It requires that Earth be ancient to be plausible.  Contrast with catastrophism. See Chapter 3 for more.

A layer that can be found beneath the Earth's surface; it is above the water table. It consists of solids and pores, and the pores are filled with some combination of water and air. See Chapter 4 for details.

In geology, refers to vertical movement upward of Earth's crust. It can be caused by one of several tectonic phenomena. See Chapter 3 for more.

A general term that refers to the entry of a xenobiotic into an organism. See Chapter 15 for details.

Refers to the medical administration of a substance--generally, some derivative or relative of an infectious agent--to induce a protective immune response. Vaccinations against polio, measles, COVID-19 and many others have prevented millions of deaths worldwide during the past century.

In simple terms, something that changes. In science, it refers to a stressor that is altered during an experiment. Generally, the way changes to a variable--for example temperature or light-- affect a test subject are studied. See Chapter 2 for more.

This is animal with a backbone (e.g., humans, snakes, cats, mice, barracuda). Compare to invertebrate.

An acellular biological entity. Viruses are not alive in the same sense that cellular plants, animals, fungi, bacteria, and protozoa are alive, but they carry genetic information and can reproduce using the machinery of cells in organism they invade. Viruses are extremely small, 100-1000 times smaller than most bacteria and 1000-10,000 times smaller than most eukaryotic cells. They are important agents of disease. See Chapter 3 for more.

A process that converts a substance in the liquid phase into a gas. See Chapter 15 for more.

A rather broad term that refers to materials unwanted by the organism or system that generates them. Individuals produce biological waste products that are partially decomposed remains of food. Such leftovers are toxic to the organism expelling them but can serve as nutrients for other organisms. The term also is applied to human systems and includes garbage from homes plus a range of other materials from industry, medical facilities, military installations, and farms. See Chapter 13 for more.

A broad term that refers to the generation of electricity through the utilization of products of human waste management. See Chapter 13 for more.

Water contaminated by human activities (e.g., agriculture, industry, domestic use). Literally, water that contains waste products. It can be treated to remove the pollutants that render it unfit for use. See Chapter 11 for more.

Essentially, a quantifiable property of water that refers to how clean it is. Generally, how clean is related to how much material (biological, physical, chemical) is present and the intended use of the water. See Chapter 11 for more.

The upper limit of the saturated zone. See Chapter 4 for details.

A transmissible illness caused by microorganisms that live in contaminated water. See Chapter 7 for more.

A soil science term that refers to the amount of water retained in soil after inputs (i.e., precipitation) ceases. Water held in soil is vital to the survival of soil organisms, including crops, because it can meet demand until the next rainfall event. See Chapter 9 for more.

Short-term temperature, precipitation, wind, and humidity conditions that affect an area. Weather changes daily and can fluctuate wildly. Compare to climate. See Chapter 14 for more.

In geology, a term that refers to chemical and physical processes that break down and transform rocks and the remains of living materials. Weathering products can be transported and incorporated into new rocks and soils.  Compare to erosion. See Chapter 3 for more.

An area in which many wind turbines are concentrated. See Chapter 10 for more.

A structure with spinning blades that captures the wind's energy and converts it into electricity. See Chapter 10, especially Figure 10.33, for more.

The relatively small portion of a landfill that actively receives trash. See Chapter 13 for more.

A substance that originates outside the body, that is, it is not produced by the body but from some source external to the body. See Chapter 15 for details.

Plankton that are consumers or chemoheterotrophs; they eat phytoplankton so live in surface waters. They tend to be several millimeters to a centimeter in size. See Chapter 5 for more.