Glossary - Freshwater Ecology: Concepts and Environmental Applications - page 500

T 50 , the amount of time necessary for 50% of
original dry leaf mass to break down in de-
composition studies
Tannins, derivatives of multimeric gallic acid
that leach from bark and leaf litter with prop-
erties similar to those of humic substances
Taxis, movement toward stimuli
Tarn, a small mountain lake (often in a cirque)
Tectonic basin, a basin formed by movement
of the earth's crust
Thalassohaline, having ionic proportions simi-
lar to seawater
Thalweg, the part of a stream channel through
which the main or most rapid flow travels
Thermal bar, vertical or horizontal mass of wa-
ter separating two areas of less dense water
Thermocline, see metalimnion
Thermophilic, hot-temperature-loving; requires
warm temperatures to grow or reproduce
Throughfall,

Trophic basis of production, the individual
food sources responsible for production of
each species
Trophic cascade, influence of consumer organ-
isms on those lower in the food web with
alternating effects at each trophic level (top-
down control)
Trophic level, position in a food web
Trophic state, ecosystem productivity
Trophogenic zone, area of photosynthetic

production
Tropholytic zone, area of decomposition
Turbidity, the amount of suspended particles in
water (TSS) or absorption of light by those
particles
Turbulent flow, flow with swirls and eddies not
in the direction of the main flow
Turnover, calculation of residence time of wa-
ter in a lake given volume and amounts of
water entering and leaving; can also be the
rate of flux of any material through a com-
partment (e.g., in nutrient budgets)
Ultraoligotrophic, exceptionally unproductive
system
Unconfined groundwater,

precipitation falling through

vegetation
Thymidine uptake, a method using [ 3 H]thymi-
dine incorporation into DNA to assess bac-
terial growth rate
Time series, temporal replication in experiments
Top-down control, regulation of biomass by
organisms higher in the food web
Total dissolved solids (TDS), total mass of ma-
terial left after a filtered water sample is dried
Total suspended solids (TSS), total weight of
particulate material per unit volume of water
Tracer, a dye, isotope, or ion used to trace the
movement of water or chemicals through
the environment
Trait-mediated interactions, interactions evi-
denced by evolved traits
Transmit, to cause or allow to spread (partic-
ularly transmission of light in water)
Transport diffusion,

water not con-

strained from above
Unit hydrograph, the hydrograph resulting
from a single storm event
Univoltine, producing one generation annually
Unsaturated zone, vadose zone
Uptake, nutrients taken into cells from the wa-
ter surrounding them
Uptake length, the distance a nutrient travels
in the water column before being taken up
Urea, a nitrogen-containing organic compound
that can be excreted by organisms
V, volume of a body of water
Vadose zone, above the water table; below the
surface soil (also called unsaturated zone )
Van Dorn bottle, a tube that can be lowered to
a specific depth on a rope; when a messen-
ger is sent down the rope, it triggers two
ends to snap onto the tube, trapping the
sampled water
Vaporization, evaporation
Vernal pond, shallow pool dry for part of the
year (usually wet during spring)

diffusion with water

movement
Treatment, method to remove contaminants
from water
Troglobitic, obligatory cave-dwelling or hy-
pogean organisms
Troglophilic, facultative cave-dwelling or hy-
pogean organisms