Glossary of Environmental Science - H

H

  • habitat - an ecological or environmental area that is inhabited by a particular species.
  • hard waste - household garbage which is not normally accepted into rubbish bins by local councils, e.g. old stoves, mattresses.
  • heat– energy derived from the motion of molecules; a form of energy into which all other forms of energy may be degraded.
  • herbicide – a chemical the kills or inhibits growth of a plant.
  • herbivory - predation in which an organism known as an herbivore, consumes principally autotrophs such as plants, algae and photosynthesizing bacteria.
  • heterotroph (chemoorganotrophy) - an organism that requires organic substrates to obtain its carbon for growth and development.
  • hierarchy – an organisation of parts in which control from the top (generally with few parts), proceeds through a series of levels (ranks) to the bottom (generally of many parts) cf. heterarchy.
  • high density polyethylene (HDPE) - A member of the polyethylene family of plastics and is used to make products such as milk bottles, pipes and shopping bags. HDPE may be coloured or opaque.
  • homoclime – a region with the same climate as the one under investigation.
  • horsepower (hp) = 745.7 watts.
  • homeostasis - the property of either an open system or a closed system, especially a living organism, that regulates its internal environment so as to maintain a stable, constant condition.
  • Horton overland flow - the tendency of water to flow horizontally across land surfaces when rainfall has exceeded infiltration capacity and depression storage capacity.
  • house energy rating - an assessment of the energy efficiency of residential house or unit designs using a 5 star scale.
  • household metabolism - the passage of food, energy, water, goods, and waste through the household unit in a similar way to the metabolic activity of an organism cf. industrial metabolism.
  • humus - organic material in soil lending it a bark brown or black colouration.
  • human equivalent (He) - the approximate human daily energy requirement of 12,500 kJ or its approximate energy generating capacity at basal metabolic rate which is equivalent to about 80 watts (3.47222kWh/day). A 100 watt light bulb therefore runs at 1.25 He.
  • humus – semi-persistent organic matter in the soil that can no longer be recognised as tissue.
  • hydrocarbons - chemicals made up of carbon and hydrogen that are found in raw materials such as petroleum, coal and natural gas, and derived products such as plastics.
  • hydroelectric power - the electrical power generated using the power of falling water.
  • hydrological cycle (water cycle) - the natural cycle of water from evaporation, transpiration in the atmosphere, condensation (rain and snow), and flows back to the ocean (e.g. rivers).
  • hydrosphere - all the Earth's water; this would include water found in the sea, streams, lakes and other waterbodies, the soil, groundwater, and in the air.

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