Glossary - Freshwater Ecology: Concepts and Environmental Applications - page 495

Multivoltine (polyvoltine), producing many
generations annually
Muskeg, a large peatland or bog, particularly
in northern North America
Mutualism, an interspecific interaction in which
both species benefit
15 N, a stable isotope of nitrogen used to trace
nitrogen flux
14 N, the most common stable isotopic form of
N in the environment
Naiad, another term for the larva of an aquatic
insect
Nanoplankton, plankton particles between ap-
proximately 3 and 50

from the landscape, such as that resulting
from cultivation, urban lawn spraying, or
runoff from parking lots
Numerical response, number of predators per
unit prey density
Nutrient, element or chemical compound re-
quired by organisms for growth
Nutrient budget, a quantification of fluxes in a
nutrient cycle
Nutrient cycling, the transformation of nutri-
ents from organic to inorganic forms and
among different oxidation states
Nutrient limitation, control of growth or pro-
duction by a nutrient or nutrients
Nutrient loading, input of nutrients to a system
from river or stream inflow, dry or wet de-
position, and internal sources
Nutrient sinks, compartments that store nutri-
ents over time
Nutrient spiraling, alternate uptake and release
of a nutrient; another term for nutrient cy-
cling, with “spiraling” referring to down-
stream motion between uptake and release
Nymph, another term for the larva of an
aquatic insect
Oligomixis, infrequent circulation of water
masses
Oligotrophic, nutrient-poor system with rela-
tively low primary production
Ombrotrophic, system that receives most of its
water and minerals from precipitation; om-
brotrophic bog; generally nutrient-poor
Optimal foraging, evolution through selection
leads to maximization of energy gain while
foraging
Organism, a complex living structure made up
of a cell or cells
Organotrophy, hetrotrophic nutrition in which
energy is taken from fermenting or oxidiz-
ing organic compounds
ORP, oxygen reduction potential; also
called redox
Orthograde, straight distribution as in a verti-
cal oxygen or temperature profile
Orthophosphate, phosphate—free, as a poly-
mer, or bound to organic compounds
Oxic, with O 2 (aerobic)

m
Natural abundance, amount of a stable isotope
found naturally
Natural experiment, observation of natural
patterns
Nekton, plankton able to control their position
in water columns by swimming
Net photosynthesis, the amount of photosyn-
thesis that is used for growth; in bottle ex-
periments, the O 2 concentration in the light
minus the initial concentration
Net plankton, plankton particles between ap-
proximately 50 and 500 m

Neuston, microorganisms living at the water
surface
New nutrients, nutrients from outside the
system
Nitrate, NO 3 , an oxidized ionic form of in-
organic N in natural waters
Nitrification, microbial processes that convert
nitrate to ammonium, yielding energy
Nitrite, NO 2 , an ionic form of dissolved in-
organic N occasionally found in significant
concentrations in natural waters
Nitrogenase, an enzyme with molybdenum as
a cofactor that reduces N 2 to NH 4 (nitro-

gen fixation); found only in bacteria
Nitrogen fixation, the process of converting N 2
to a form of nitrogen used by organisms (to
combined nitrogen)
N:P, nitrogen to phosphorus ratio; can be ex-
pressed per mole or by weight
Nonpoint source, a diffuse source of pollution