Environmental Engineering Reference
In-Depth Information
Heterogeneous aquifer, an aquifer with many
impermeable layers or areas where water
cannot flow evenly
Heterotrophy, metabolic energy and growth
from degradation of organic molecules; car-
nivory, detritivory, herbivory, microbial de-
cay, and omnivory
Hind-casting, model is used to predict system
response when the data from the system are
already known
Hochmoor, elevated bog with peaty matter
higher than the rim of the cavity housing
the bog
Holomixis, total circulation or blending as in a
holomictic lake
Homogeneous, of the same or similar kind of
nature
Homogeneous aquifer, an aquifer with evenly
distributed substrata and even ground-
water flows
Homoiothermy, see isothermy
Horst, a depression formed by a fault when
blocks tilt, slide against each other, and cre-
ate a basin; lakes can form in them
HPLC, high-performance liquid chromatogra-
phy; an analytical system in which water
flows through materials that can separate
complex molecules
Humic acids, humic material that is precipi-
tated by acid
Humic compounds, from decomposition of
plant material, includes humic acids, fulvic
acids, and humin
Humin, the fraction of humic compounds that
cannot be extracted by acid or base
Humus, high-molecular-weight organic mole-
cules, polymeric, primarily from decayed
plants; humic acids with the -COOH radi-
cal; humolimnic acids in lake waters and
sediments
Hydraulic conductivity, the ability of a mater-
ial to allow water flow (coefficient of
permeability)
Hydraulic gradient, in groundwater, a line that
will connect the level of water in wells or
that follows the top of the water table; in
streams, the drop in the channel per unit
distance
Hydraulic head, difference in water elevation
between two connected sites
Hydraulic regimes, degree and duration of wa-
ter inundation and depth
Hydric soils, soils with characteristics related
to constant water inundation
Hydrodynamics, temporal and spatial vari-
ations in movement and distribution of
water
Hydrogen bonding, when molecules are polar
(i.e., there is an uneven distribution of
charge across the molecule), the positive and
negative parts of separate molecules are at-
tracted toward each other; particularly im-
portant in water
Hydrograph, plot of discharge as a function of
time for a stream or river
Hydrologic cycle, the fluxes of water across the
landscape
Hydrophyte, an aquatic plant, usually a macro-
scopic, rooted variety; macrophyte
Hydropsammon, interstitial zone in sand be-
low shallow water; sand-dwelling organ-
isms live here
Hydrostatic pressure, the pressure that fluids
exert (density
depth)
Hypereutrophic, extremely productive, with
very high primary producer biomass (also
hypertrophic)
Hypogean, existing underground, subter-
ranean, interstitial, or cave dwelling
Hyporheic zone, a region of groundwater in-
fluenced by a nearby stream or river
Hyporheos, a region of groundwater influenced
by a nearby surface water
Hypolimnion, the bottom layer of a stratified
lake; below the metalimnion
Hypothesis, initial expectation; statement of
cause
Hypsography, mapping and measuring of ele-
vations and contours
Indirect interaction, interaction between two
species mediated by other species
Inertia, resistance of a body to a change in its
state of motion
Infauna, animals that dwell in the substratum
or sediments
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