| Habitat
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| The specific environment (woods, desert, swamp) in which an organism lives.
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| Habitat Conservation Plan (HCP)
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| Under the Endangered Species Act, a plan that may be drafted by the U.S. Fish and Wildlife Service in working with landowners to help mitigate conflicts over the Act.
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| Hadley cells
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| Circulation patterns of atmospheric convection currents as they sink and rise in several intermediate bands.
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| Half-life
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| The time required for one-half of a sample to decay or change into some other form.
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| Halogenated hydrocarbon
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| Synthetic organic compound contaming one or more atoms of the halogen group, which includes chlorine, fluorine, and bromine.
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| Hard water
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| Water that contains relatively large amounts of calcium and/or certain other minerals that cause soap to precipitate. (Gontrast soft water.)
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| Hazard
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| Anything that can cause (1) injury, disease, or death to humans; (2) damage to property; or (3) degradation of the environment. Cultural hazards refer to factors that are often a matter of choice, like smoking or sunbathing. Biological hazards are pathogens and parasites that infect humans. Physical hazards are natural disasters like earthquakes and tornadoes. Chemical hazards refer to the chemicals in use in different technologies and household products.
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| Hazard assessment
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| The process of examining evidence linking a particular hazard to its harmful effects.
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| Hazardous
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| Describes chemicals that are - dangerous, including flammables, explosives, irritants, sensitizers, acids, and caustics; may be relatively harmless in diluted concentrations.
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| Hazardous materials (HAZMAT)
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| Any material having one or more of the following attributes: ignitability, corrosivity, reactivity, toxicity.
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| Hazardous waste
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| Any potentially harmful solid, liquid, or gaseous waste product of manufacturing or other human activities.
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| Health
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| A state of physical and emotional well-being; the absence of disease or ailment.
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| Heap-leach extraction
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| A technique for separating gold from extremely low-grade ores. Crushed ore is piled in huge heaps and sprayed with a dilute alkaline-cyanide solution, which percolates through the pile to extract the gold, which is separated from the effluent in a processing plant. This process has a high potential for water pollution.
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| Heat
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| A form of energy transferred from one body to another because of a difference in temperatures.
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| Heat capacity
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| The amount of heat energy that must be added or subtracted to change the temperature of a body; water has a high heat capacity.
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| Heat of vaporization
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| The amount of heat energy required to convert water from a liquid to a gas.
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| Heavy metals
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| Any of the high atomic weight metals, such as lead, mercury, cadmium, and zinc. All may be serious pollutants in water or soil because they are toxic in relatively low concentrations and they tend to bioaccumulate.
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| Herbicide
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| Chemical agent used to control weeds.
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| Herbivore
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| Heterotrophic organism that feeds exclusively on plants.
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| Herbivore/Herbivorous
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| An organism such as rabbit or deer that feeds primarily on green plants or plant products such as seeds or nuts. Such an organism is said to be herbivorous. Synonym: primary consumer.
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| Herbivory
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| The feeding on plants that occurs in an ecosystem. The total feeding of all plant-eating organisms.
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| Heteroculture
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| Agriculture in which several plant species are grown simultaneously to reduce insect infestation and disease.
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| Heterotroph/Heterotrophic
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| Any organism that consumes organic matter as a source of energy. Such an organism is said to be beterotrophic.
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| HHW (household hazardous wastes)
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| An important component of the hazardous waste problem in the United States.
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| High-level waste repository
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| A place where intensely radioactive wastes can be buried deep in the ground and remain unexposed to groundwater and earthquakes for tens of thousands of years. The first such site chosen in the United States is Yucca Mountain, Nevada, although it is not certain that a waste repository will ever be built there.
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| High-quality energy
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| Intense, concentrated, and high-temperature energy that is considered high-quality because of its usefulness in carrying out work.
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| Highway Trust Fund
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| The monies collected from the gasoline tax designated for construction of new highways. hormones. Natural chemical substances that control development, physiology, and/or behavior of an organism. Hormones are produced internally and affect only that individual. Hormones are coming into use in pest control. (See also pheromones.)
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| Homeostasis
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| Maintaining a dynamic, steady state in a living system through opposing, compensating adjustments.
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| Homestead Act
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| Legislation passed in 1862 allowing any citizen or applicant for citizenship over twenty-one years old and head of a family to acquire 160 acres of public land by living on it and cultivating it for five years.
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| Host organism
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| An organism that provides lodging for a parasite.
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| Host
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| In feeding relationships, particularly parasitism, refers to the organism that is being fed upon, i.e., supporting the feeder.
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| Host-parasite relationship
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| The combination of a parasite and the organism upon which it feeds.
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| Host-specific
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| Referring to insects, fungal diseases, and other parasites that are unable to attack species other than their particular host.
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| Hot desert
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| Deserts of the American Southwest and Mexico; characterized by extreme summer heat and cacti.
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| Hot-rock zones
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| Most widespread geothermal resource. Regions where bedrock is heated by underlying magma.
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| Human ecology
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| The study of the interactions of humans with the environment.
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| Human resources
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| Human wisdom, experience, skill, labor, and enterprise.
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| Human system
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| The entire system that humans have created for their own support, consisting of agriculture, industry, transportation, and communications networks, etc.
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| Humidity
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| The amount of water vapor in the air. (See also relative humidity.)
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| Humus
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| Sticky, brown, insoluble residue from the bodies of dead plants and animals; gives soil its structure, coating mineral particles and holding them together; serves as a major source of plant nutrients.
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| Hunger
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| A general term referring to the lack of basic food required for meeting nutritional and energy needs, such that the indivdual is unable to lead a normal, healthy life.
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| Hunter-gatherers
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| Humans surviving by hunting wild game and gathering seeds, nuts, berries, and other edible things from the natural environment.
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| Hurricanes
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| Large cyclonic oceanic storms with heavy rain and winds exceeding 119 km/hr (74 mph).
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| Hybrid electric vehicle (HEy)
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| An automobile with a small gaso. line motor and batteries capable of getting over 60 mpg and producing only 1/10 the pollution of a comparable gasoline car.
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| Hybrid
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| A plant or animal resulting from a cross between two closely related species that do not normally cross.
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| Hybridization
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| Cross-mating between two more or less closely re lated species.
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| Hydrocarbon emissions
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| Exhaust of various hydrogen-carbon compounds due to incomplete combustion of fuel. They are a major contribution to photochemical smog.
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| Hydrocarbons
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| Organic molecules containing hydrogen and carbon. Released during the incomplete combustion of organic fuels. React with nitrogen oxides and sunlight to form photo- chemical oxidants in photochemical smog.
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| Hydroelectric dam
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| A dam and associated reservoir used to produce electrical power by letting the high-pressure water behind the dam flow through and drive a turbogenerator.
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| Hydroelectric power
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| Electrical power that is produced from hydroelectric dams or, in some cases, natural waterfalls.
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| Hydrogen bonding
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| A weak attractive force that occurs between a hydrogen atom of one molecule and, usually, an oxygen atom of another molecule. It is responsible for holding water molecules together to produce the liquid and solid states.
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| Hydrogen ions
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| Hydrogen atoms that have lost their electrons. Chemical symbol, H+.
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| Hydrologic cycle
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| The movement of water from points of evaporation through the atmosphere, through precipitation, and through or over the ground, returning to points of evaporation.
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| Hydroponics
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| The culture of plants without soil. The method uses water with the required nutrients in solution.
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| Hydrosphere
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| The watery portion of the planet. Contrast with atmosphere and lithosphere.
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| Hydrothermal convection zone
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| Rock strata containing large amounts of water heated by underlying magma and driven to the surface through cracks and fissures in overlying rock layers. Forms hot springs and geysers.
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| Hydroxyl radical
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| The hydroxyl group (OH) missing the electron. It is a natural cleansing agent of the atmosphere. It is highly reactive and readily oxidizes many pollutants on contact and thus contributes to their removal.
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| Hypothesis
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| An educated guess concerning the cause of an observed phenomenon that is then subjected to experimental tests to prove its accuracy or inaccuracy.
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| Hypothyroidism
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| Listlessness and other metabolic symptoms caused by low thyroid hormone levels.
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