Glossary - Freshwater Ecology: Concepts and Environmental Applications - page 489

Diapause, part of the normal life cycle that is
stationary, physiologically dormant
Diatoms, one-celled algae with silica shell
(frustule) and golden brown coloring
(Bacillariophyceae)
Diel, 24-h day with a light-dark cycle (as op-
posed to a period of light)
Diffusion boundary layer, the thin layer near a
solid surface where diffusion is dominated
by molecular diffusion; its thickness can
control metabolic rates of microorganisms
Diffusion coefficient, a constant used to de-
scribe diffusion of a compound or heat in-
dependent of distance and concentration
Diffusion flux, the amount of a compound dif-
fusing across an area per unit time
Dimictic, a lake that mixes twice each year
Dinoflagellates, one-celled algae that move by
means of flagella (Pyrrhophyta)
Direct interaction, occurs between two species
and involves no others
Discharge, the volume of a fluid flowing per
unit time
Disproportionation, an anoxic transformation
in which thiosulfate is converted to sulfate
and sulfide yielding energy
Dissimilatory process, a chemical transforma-
tion mediated by organisms that does not
involve assimilation
Dissolved inorganic nitrogen (DIN), the sum of
ammonium, nitrate, and nitrite
Dissolved materials, materials smaller than a
particular size (e.g., 0.45

Drift, the material that washes downstream,
particularly invertebrates
Droop equation, relationship between intracel-
lular nutrient concentrations and growth
dy, sediment of dystrophic lakes, generally with
a high organic content and allochthonous
origin
Dynamic equilibrium model, the idea that re-
sponse of species richness to disturbance is
a function of competition intensity in a
community
Dynamic viscosity, a constant that describes
the intrinsic viscosity of a fluid
Dystrophic, a lake that is not productive be-
cause it has been influenced by factors that
attenuate light or retard photosynthetic or-
ganisms; a lake that is high in tannin and
lignin is dystrophic
Eckman dredge, a dredge that is lowered to the
bottom, with a messenger that is sent down
its line and triggers jaws on the bottom to
shut, taking in sediment
Ecoregion, an area with a geographically dis-
tinct assemblage of communities
Ecosystem, all living and nonliving community
constituents
Ecosystem function, the rate of specific basic
ecosystem processes
Ecotone, transitional zone between two habi-
tats, e.g., where there is a change between
groundwater and surface water organisms
Ectogenic meromixis, meromixis caused by in-
flow of materials from exterior sources (e.g.,
saline water entering a dilute lake)
Edaphic, relating to the ground or soil, par-
ticularly matter influenced by them or
from them
Eddy, current or small whirlpool moving
counter to the main flow
Eddy diffusion, diffusion by transport or
mixing of a diffusing substance or heat;
much faster than molecular diffusion; also
called transport diffusion or advective
transport
Effluent, the water released from a sewage
plant, factory, or other point source
Emergent, growing above the water
Endemic, species having a distribution that is
restricted to a relatively small region

m) that remain

in solution
Dissolved organic carbon (DOC), organic car-
bon compounds dissolved in solution
Dissolved organic nitrogen (DON), organic ni-
trogen able to pass through a 0.45- m filter

Dissolved oxygen (DO), O 2 dissolved in water
Disturbance, an event that disrupts ecosystem,
community, or population structure
Dolina, depression caused by dissolution of
limestone substrata; sink or swallow hole
DOM, see dissolved organic carbon, dissolved
organic matter
Drawdown, lowering a water table by

pumping