Glossary - Freshwater Ecology: Concepts and Environmental Applications - page 497

Polar lake, pond or lake with a surface tem-
perature of 4°C or lower in the warm
season
Polymixis, almost continuous circulation or
many flowing or mixing periods annually
POM, particulate organic matter that is re-
tained by an approximately 0.45-

Psammon, a habitat in interstitial water be-
tween sand grains
Pseudoreplication, replicate samples from one
treatment
Psycrophilic, cold-loving; requires cold temper-
atures to grow or reproduce
Putrifaction, decomposition of organic materi-
als, primarily proteins, resulting in forma-
tion of ammonium (NH 4 ) and sulfide (H 2 S)
Pycnocline, density gradient
Pyrite, a complex of sulfide and metal
Random, by chance
Reach, a series of pools and riffles in a stream
or river
Recharge, water entering an aquifer
Recruitment, the number of fish entering each
size or age class
Redd, area on lake or stream bottom where
salmon or trout spawn; often a round,
cleared depression in gravel
Redfield ratio, algal composition under bal-
anced growth, 106:16:1 C:N:P, by moles
Redox, the relative number of free electrons in
solution; measured as oxidation-reduction
potential
Reedswamp, a wetland dominated by reeds
(Phragmites)
Reflect, to turn, throw, or bend off backwards
at an angle
Regeneration, see remineralization
Remineralization, organisms excreting nutrients
Replication, repeating treatments in an experi-
ment
Reset, the return of a habitat to preceding (in
time) conditions or to conditions upstream
(in a continuum); a flood may “reset” a
stream to earlier conditions
Residence time, amount of time a material
spends in an ecosystem compartment
Retention time, average time materials spend
in an ecosystem compartment
Reynolds number, the ratio of inertia to dy-
namic viscosity; a unitless number that de-
scribes the properties of fluids as related to
spatial scale and movement
Rheocrene, a spring-fed brook

m mem-

brane filter
Pool, a slow-moving portion of a river or
stream
Porosity, the maximum water that can be stored
in a hydrated sediment
Potamodromous, with migratory pattern en-
tirely in freshwater
Potamology, older term for stream biology,
river ecology, and lotic limnology
Potamon, stream or larger water body envi-
ronment (rhithron)
Potential energy, stored energy that can

do work
Pothole, a shallow pond or wetland formed in
glacial till
ppb, parts per billion ( g liter 1 )

PPFD, photosynthetic photon flux density; see
photosynthetically available radiation
ppm, parts per million (mg liter 1 )
ppt, parts per trillion. (ng liter 1 )
P:R, ratio of gross primary production to com-
munity respiration
Prairie pothole, a sizeable, rounded, and often
water-filled depression in grassland habitat;
formed in glacial drift
Precipitation, the deposit on Earth of hail, mist,
fog, rain, sleet, or snow
Predation, one organism eating another
Predator, an organism that feeds on other
organisms
Primary consumer, herbivore
Primary producer, photosynthetic organism
Primary production, net photosynthesis
Probability value, used to express significance
Production, the growth of a population or in-
crease in biomass
Profundal zone, benthic zone in lakes deep
enough that there is not enough light to sup-
port photosynthetic organisms