Geoscience Reference
In-Depth Information
Feedback -
Relationships between phenomena,
such that a change in one leads to a change
in another, which may be positive (reinforc-
ing) or negative (damping).
Fen -
Waterlogged, spongy ground, containing
alkaline decaying vegetation, characterized
by reeds, sedge, shrub or forest that may
form peat, sometimes occurs in sinkholes of
karst regions. Receives some surface runoff
and/or ground water, which has neutral pH
and moderate to high nutrients.
Floodplain -
Overbank portion of alluvial or
tidal environments that may be l ooded fre-
quently or rarely when water l ows exceed
channel capacity.
Fossil fuel -
Ancient (buried) carbon- and
hydrocarbon-rich sediment (coal, oil shale) or
l uid (oil, natural gas) that may be burned to
provide energy.
Geobotanical -
Refers to mapping and analysis
of landscapes based on vegetation distribu-
tion as a primary indicator of topography,
soils, landforms, sediment, and underlying
bedrock.
Holocene thermal maximum (HTM) -
(see
Altithermal).
Hydraulic conductivity -
One factor that deter-
mines the rate at which ground water is able
to move depending upon the size, shape, and
connections of pore spaces within the sedi-
ment or rock body. Permeability (
k
) of the
sediment or rock.
Hydric soil -
Refers to wetland soils that were
formed under conditions of saturation, l ood-
ing or ponding long enough during the
growing season to develop anaerobic condi-
tions in the upper part (NRCS 2010a).
Hydrograph -
Graphical display of stream dis-
charge or stage versus time. Primary tool for
analyzing stream l ow and l ooding.
Hydroperiod -
Seasonal pattern of water level
in a wetland, as determined by climate and
human management.
Hydrophyte -
Plants that grow only in standing
water or saturated soils, such as moss, sedges,
reeds, cattail and horsetail, mangroves,
cypress, and rice.
Hydroseral succession -
Gradual transition
involving both water and vegetation begin-
ning with open-water habitat and ending
with a raised bog or forest cover.
Hydrosphere -
Liquid water at the Earth's
surface, including the ocean, lakes, rivers, soil
moisture, and shallow ground water.
Hypoxic -
Water bodies that contain
Glossopteris
-
Generic name given to temper-
ate l ora common across Gondwana during
the late Paleozoic.
Gondwana -
Ancient megacontinent consisting
of modern South America, Africa, Arabia,
India, Antarctica and Australia during the
Paleozoic. It made up the southern portion
of Pangaea.
Greenhouse gases -
Gases (CO
2
and CH
4
) that
absorb thermal radiation emitted from the
Earth, thus warming the lower atmosphere.
The atmospheric content of greenhouse
gases is one factor inl uencing the Earth's
climate.
Halophyte -
Plant that tolerates high salt levels
in saline soils or hypersaline water.
Histosol -
Soil order composed largely of
organic materials derived from plant tissues,
including peat and muck soils.
Hoar -
Inland wetland system in Bangladesh
and eastern India that is characterized by
deep, bowl-shaped depressions that contain
water most of the year.
Holocene -
Last 10,000 years of Earth history. The
youngest epoch of the geological time scale.
2 mg/L dis-
solved oxygen, which results in i sh kills and
dead zones, especially in coastal marine waters.
Hypsithermal -
(see Altithermal)
Invasive species -
Exotic or foreign species
whose introduction may cause environmental
or economic harm.
Irrigation -
Diversion or extraction of surface
or ground water for agricultural purposes,
namely watering dry land for growing annual
or perennial crops.
Isostasy -
Density-mass balance within the
crust and lithosphere that determine the
general level (elevation) of the Earth's surface.
Karst -
Landforms created by bedrock solution,
including caves, sinkholes and related
features.
Kavir -
Term for a salt desert, specii cally the
Great Kavir of central Iran. Series of closed
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