Cumulative Effect: the totality of a number of specific negative
impacts (e.g. clearcuts, dams) which has a combined effect greater than the
sum of the individual impacts.
Disturbance: an event, such as fire or windstorm, which causes a
rapid change in an ecosystem.
Edge Effects: the conditions which exist along the interface
of two different biological communities (i.e., ancient forest and clearcuts),
which alter the quality of habitat for some species. For instance, humidity
and temperature changes near the edge of a forest.
Ecosystem: the living and nonliving components of an area, and their
Eutrophication: the pollution of a body of water by enrichment with
nutrients, with a consequent increase in the growth of organisms and a
resultant depletion of dissolved oxygen.
Extinction: the loss of a species from an area within its historical
range. Extinction may refer to a population disappearing from a local area
(often termed extirpation) or to global disappearance.
Fossil water: water stored in aquifers which accumulated millennia
ago; considered non-renewable because the recharge rate is very slow even in
terms of geologic age. The Ogallala aquifer is an example, rapidly
diminishing due to irrigating crops on what was once semi-arid prairie.
Fragmentation: The combined effect of disturbances (generally
human-caused) on habitat in an area. For instance, clearcuts and roads not
only radically change habitat in a specific area, but also cause edge
effects and spread of non-native species. All of these effects together are
Ground water: water contained in soil and bedrock; all subsurface
Habitat: the environment in which an organism or species fulfills
some aspect of its biological needs, i.e., food, shelter, breeding.
Hard water: water containing Ca 2+
and/or Mg 2+ ions.
Hydrologic cycle: the cycling of water, in all its forms, on the
Indicator Species: A species of plant or animal, or a community,
whose occurrence serves as evidence that certain environmental conditions
Island Biogeography: the theory that isolated areas of habitat
function similar to islands at sea. Small "islands", and those that are
farther from other islands, support fewer species than large, and/or near
Landscape Ecology: the study of how ecosystems interact within and
between one another (at various scales, such as stands or watersheds) across
Keystone Species: Species that interacts with a large number of
other species in a community. Because of the interactions, the removal of
this species can cause widespread changes to community structure. Compare
with immigrant species, indicator species, and native species.
Minimum Dynamic Area: the smallest size an ecosystem (or reserve)
can be while still maintaining internal recolonization sources under natural
Native: a species which was historically (before human alteration)
present in an area.
pH: a measure of acidity. pH = the minus log of the hydrogen ion
Pollution: the impairment of the quality of some portion of the
environment by the addition of harmful substances.
Re-colonization: a species may reinhabit an area after being extinct
there. Recolonization may occur by individuals moving to the area from
adjacent or nearby habitats where the species had survived whatever event(s)
caused the extinction elsewhere.
Refuge: an area of land dedicated as habitat for native species and
Residence time (for water): the average time that a water molecule
spends in a particular region such as a lake or underground aquifer.
Riparian: the area along the banks of a stream or river which is
influenced (e.g., more moist or sandy soil) by the watercourse. Vegitation
may be very different in riparian areas than in upland areas. Riparian areas
may extend several hundred feet from the water.
Respiration: the process by which plants and animals combine oxygen
with sugar and other organic matter to produce energy and maintain body
function. Carbon dioxide and water are released as by-products.
Runoff: the flow of water toward the ocean through surface and
Saltwater intrusion: the movement of salt water from the ocean to
terrestrial groundwater supplies that occurs when the water table in coastal
areas is reduced.
Shifting Mosaic Steady State: as disturbances effect an area from
year to year, the location of specific ecosystems will change creating a
"shifting mosaic" of ecosystems or habitats. But, even though the actual
locations change, the amount of each habitat over a large area may remain
somewhat constant (steady state).