Abrasion: the process of wearing down or rubbing away by means of friction

Acid neutralizing capacity: ANC; the property of water that reacts with an acid; recently replacing alkalinity.

Adfluvial: descriptive of migration pattern of fish species that spawn in a freshwater stream then migrate to a freshwater lake for growth.

Aerobic: said of an organism, such as a bacterium, that can only live or function in the presence of free oxygen; also said of processes or conditions that can only occur in the presence of free oxygen

Aggregation: a collection of material at a given place

Alga (pl. Algae): any of various primitive, chiefly aquatic, one-celled or multicellular plants that lack true stems, roots, and leaves but usually contain the green pigment called chlorophyll

Alkalinity: property of water containing alkaline substances, mainly bicarbonate in natural water, expressed as parts per million (ppm); see acid neutralizing capacity.

Allochthonous: describing organic matter that is produced on land and then is moved to the stream, compare autochthonous.

Allochthony: study of production, transport, and use of allochthonous matter in a stream.

Allopatric: not existing in the same stream; compare sympatric.

Alluvial: Of or pertaining to material deposited by a stream or flowing water.

Anadromous: descriptive of fish that spawn in a stream and migrate to the Ocean for major growth; compare adfluvial.

Anadromy: form of fish life history with spawning in a stream and major growth in the ocean.

Anaerobic: said of an organism, such as a bacterium, that does not require free oxygen to live or function; also said of processes or conditions that do not require oxygen

ANC: acid neutralizing capacity; see alkalinity.

Angiospermae: any of a class of plants that is identified by having their seeds enclosed in an ovary

Anthropogenic: caused through human activity; usually applied to sediment or other pollutant.

Aquifer: layer of groundwater beneath land surface.

Artesian: spring or well arising from pressure in deep aquifer.

Autochthonous: term applied to organic matter produced by aquatic plants within the stream; compare allochthonous.

Autochthony: study of organic matter production within a stream; compare photosynthesis, primary production.

Autotroph: green plant, "self-feeding;" compare heterotroph.

Autotrophy: study of production by green plants; compare heterotrophy.

Backwater: water held or pushed back by or as if by a dam or current; especially a body of stagnant or still water thus formed

Bank Stabilization: Methods of supporting the structural integrity of earthen stream channel banks with structural supports to prevent bank slumping and undercutting of riparian tress, as well as overall erosion. Recommended bank stabilizing techniques include the use of willow stakes, overlapping riprap, or brush bundles.

Bar: anything that impedes or prevents; an obstacle, such as a sandbar in a river that impedes the flow of water

Base flow: flow of a stream when it is composed entirely of groundwater from springs.

Baseline discharge: base flow.

Bedload: soil, rocks, and other debris rolled along the bottom of a stream by moving water, in contrast to siltload, which is carried in suspension

Bedrock: the solid rock that underlies soil, sand, clay, gravel, and loose material on the earth's surface

Benthic: referring to the bottom of streams, takes, and oceans; see benthos.

Benthos: assemblage of organisms inhabiting the bottoms of streams, lakes, and oceans.

Bigeminus: daily pattern of stream invertebrate drift with two peaks a major one at full darkness and a lesser one before dawn; compare alternans.

Biodiversity: property of a community of organisms varying in number of species, in their relative abundance, and life histories.

Biofilm: accumulation of biological matter on the surface of stone and wood, consisting mainly of algae, bacteria, and fungi; see periphyton, epilithon.

Biogeographic region: Any region delineated by its biological and geographic characteristics.

Biomass: the combined weight of all living organisms in a given area

Biospeleology: study of biological communities in caves.

Biota: assemblages of living organisms.

Biotic: composed of plants and animals

Bivoltines: having two generations, or cohorts, per year.

Borer: a functional group of organisms that feed by boring into wood.

Brackish: containing some salt; briny

Buffer strip: a strip of vegetation that is left along the margins of a stream or a river to reduce the impact of logging activities on that stream or river

Buffering capacity: ability of water to resist change in its chemical property when receiving a toxicant.

Calcareous: composed of, containing, or characteristic of calcium carbonate, calcium, or limestone; chalky

Calcium carbonate: a colorless or white crystalline compound that occurs naturally in chalk, limestone, marble, and other forms

Calorie: amount of heat energy required to raise one cubic centimeter of pure water one degree Celsius.

Capture net: fine-meshed net made of silk by some caddisfly species to filter fine particles of organic matter from water currents for food.

Carapace: hard covering of the head and thorax of some aquatic insects and crustaceans.

Carbon: a naturally abundant nonmetallic element that occurs in many inorganic and in all organic compounds

Carrying capacity: maximum level to which the biomass of an animal population can reach in accordance with the quality of its environment.

Cascade: a waterfall or a series of small waterfalls over steep rocks

Catadromous: descriptive of fish species that spawn in the ocean and migrate to freshwater for growth, the eel is the best known species; compare anadromous.

Catadromy: the type of life history exhibited by catadromous species; compare anadromy.

Catchment: total area drained by a stream or river, older usage: watershed.

Catchnet: net made by some species of caddisfly larvae to filter food particles from water currents; see capture net.

Cellulose: an amorphous carbohydrate polymer, the main constituent of all plant tissues and fibers, that is used in the manufacture of many fibrous products, including paper, textiles, and explosives

Channel: the bed of a stream or river (active channel ~ the lower limit of terrestrial plants)

Channelization: Straightening of the meanders in a river systerm to create more navigable waterways, or when accompanied by channel deepening to provide flood control.

Chitin: a semitransparent, horny substance that forms the principal component of the shells of crustaceans, the exoskeletons of insects, and the cell walls of certain fungi

Circadian: approximately 24 hours, descriptive of some rhythmic animal behaviors.

Clay: a very fine-grained sediment that becomes plastic and acts like a lubricant when wet; consists primarily of hydrated silicates of aluminum and is widely used in making bricks, tiles, and pottery

Climatic cycle: the cyclic changes in weather patterns in a geographical area over time

Coarse particulate organic matter: CPOM; particles of organic matter ranging from about 1/32 inch (one millimeter) up to a fallen tree; compare FPOM.

Cohort production interval: CPI; period of time that a cohort is alive and growing; not in egg, pupa, or other quiescent stage.

Cohort: group of animals or plants hatched, born, or established at the same time; a generation.

Coldwater: descriptive of salmonid fishes; implies they need cold water.

Colluvial deposits: any loose, heterogeneous mass of soil materials or rock fragments deposited along the base of  hillslopes or more gentle slopes by rainwash, sheetwash (debris flows) or slow, continuous downslope creep. 

Colonization: the process or act of establishing a colony or colonies; see also Colony

Colony: a group of the same kind of plants or animals living together

Community: a group of one or more populations of plants and/or animals using a common area; an ecological term used in a broad sense to include groups of plants and animals of various sizes and degrees of integration

Conditioning (of organic matter): transforming fresh organic matter into form more palatable to invertebrate consumers; accomplished primarily by bacteria and fungi.

Conduit spring: freshwater spring where water has flowed through large subsurface openings; compare diffuse spring.

Confined aquifer: subsurface layer of water under pressure from impermeable rock strata above and below the aquifer, compare unconfined aquifer.

Conifer: the most important order of the Gymnospennae, comprising a wide range of trees, mostly evergreens that bear cones and have needle- shaped or scale-like leaves; its timber is commercially identified as softwood

Coniferous: of or pertaining to conifers

Conservation tillage: suite of agricultural practices aimed at reducing erosion and retaining precipitation on land.

Continuum: a continuous extent, succession, or whole, no part of which can be distinguished from neighboring parts except by arbitrary division

Copepod: any of numerous small marine and freshwater crustaceans of the order Copepoda

Cosmopolitan: found throughout the world.

CPOM: see coarse particulate organic matter. 

Creep: very slow downslope movement of soil resulting from deformation of soil under the influence of gravity; rate of speed is fractions of an inch per year

Crenon: area of headwater springs.

Crown: the upper part of a tree or other woody plant that carries the main branching system and foliage and that surmounts at the crown's base a more or less clean stern

Crustacean: any of various predominantly aquatic arthropods of the class Crustacea, including lobsters, crabs, shrimps, and barnacles, characteristically having a segmented body, a chitinous exoskeleton, and paired, jointed limbs

Cyanobacteria: blue-green algae; believed to be the first oxygen- producing organisms with fossils estimated at 2.3 billion years old.

Debris flow: very fast movement of water-charged soil and vegetation, both dead and alive, down stream channels; rate of speed is in feet per second

Debris slide: very fast movement of soil, commonly containing a high concentration of water, down hillslopes under the influence of gravity; the initial sliding surface is generally 3 to 12 feet below the surface of the ground,

Debris torrent: a slurry of debris, soil, and water that occurs where a landslide enters a steep channel and moves downstream during conditions of severe flooding

Decapitated. River that does not conform to the original RCC in that it does not begin in a wooded area.

Decay: to decompose; to rot; in wood, the decomposition by fungi or other microorganisms results in softening, progressive loss of strength and weight, and changes in texture and color

Deciduous: pertaining to any plant organ, such as a leaf, that is shed naturally; also referring to perennial plants that shed their leaves and are therefore leafless for some time during the year

Decomposers: organisms that accomplish the decomposition of organic matter, such as bacteria and fungi.

Delta: the usually triangular deposit of alluvial material at the mouth of a river

Denitrification: process of transforming nitrate in stream water back into atmospheric nitrogen.

Denitrifying bacteria: organisms responsible for denitrification.

Detritus: any disintegrating organic material or debris

Detritus pool: total accumulation of nonliving organic matter in streams.

Detritivore: an organism that feeds on decaying organic materials

Diapause: temporary cessation of metabolism in some insects, usually to survive severe environmental conditions.

Diatom: any of various minute, one celled or colonial algae of the class

Dichotomous: stream tributary pattern, branching by twos.

Diel periodicity: 24-hour pattern of behavior in plants and animals; involved with many species of stream invertebrates subject to drift.

Diffuse spring: freshwater spring fed by groundwater that arrives at the spring through many small interstices in rock and soil.

Dioecious: possessing male and female flowers on separate, unisexual plants; compare monoecious.

Discharge: flow of water in a stream, measured in units of cubic feet per second (cfs) or cubic meters per second (cms),

Discharge area: that part of a catchment where groundwater exits the surface as springs; compete recharge area.

Discontinuity- obstacle to the stream continuum; see reset.

Dissolved organic matter: DOM; organic matter in dimension smaller than 0.45 micron (about 1/50,000 inch).

Diversity: the relative degree of abundance of species of plants and animals, functions, communities, habitats, or habitat features per unit of area

Dom. Dissolved organic matter.

Drainage basin: watershed, catchment.

Duckweed: floating plants with tiny leaves and roots; genus Lemna dynamics: processes and functions expressed as rates.

Dynamic: characterized by or tending to produce continuous change

Ecological integrity: Maintenance of the structure and functional attributes characteristic of a particular locale, including normal variability.

Ecological niche: functional position of an organism in a community.

Ecological: referring to a relationship between living organisms and their non-living, physical environment

Ecology: scientific discipline treating the relationships among living organisms and their environment.

Ecoregions: Ecological regions that have broad similarities with respect to soil, relief, and dominant vegetation.

Ecosystem: spatial area inhabited by organisms living together in an orderly manner, interdependent among their cohabitants and with their environment.

Ecotone: transition zone between different biological communities; example is riparian zone.

Eddy (pl. Eddies): a current, as of water or air, moving contrary to the direction of the main current, especially in a circular motion

Effluent stream: stream flowing below the water table and receiving water from the groundwater; compare influent stream.

El Nino: a regional or global oceanic-atmospheric disturbance whose manifestations range from increased sea surface temperature in the tropical east Pacific to aberrant rainfall patterns

Emergent plants: Aquatic plants that are rooted in the sediment, but whose leaves are at or above the water surface. These wetland plants provide habitat for wildlife and waterfowl in addition to removing urban pollutants.

Energy- calories needed by a biological system to function or do work.

Engulfer: functional group of predators who take in the whole prey animal in their feeding; compare piercer.

Epigean: above ground habitats; open streams, forests; compare hypogean

Epilimnion: a thermally stratified lake, the turbulent layer of water that extends from the surface to the metalimnion.

Epilithon: surface film on stones, consisting of algae, bacteria, fungi, and other organisms and organic matter.

Erosion: the group of processes, including weathering, dissolution, abrasion, corrosion, and transportation, by which earthy or rock material is removed from any part of the earth's surface

Estuary: the wide, lower course of a river where its current is met and influenced by the tides; it also is defined as an arm of the sea that extends inland to meet the mouth of a river

Eurythermic: preferring a wide range of temperature; characteristic of warmwater fish species.

Eutrophic: overly rich and productive; descriptive of a water body that is over-fertilized, as with organic pollution

Eutrophication: the state of being eutrophic; generally a perjorative term.

Evapotranspiration: water loss from a plant or tree; combination of evaporation and transpiration.

Exoskeleton: hard exterior covering of insects and crustaceans, giving support to the body.

Fauna: assemblage of animals.

Feeding guild: group of animals using a common type of food.

Ferric oxide: insoluble compound of iron and oxygen, found where ferrous compounds in groundwater reach an oxygen-containing atmosphere.

Ferrous: descriptive of iron compounds in dissolved form.

Filterer: functional group that filters fine particles of organic matter from stream currents; many caddishly and black fly larvae; a subdivision of collectors.

Fine particulate organic matter: FPOM; nonliving organic matter ranging from 1/50,000 inch (0.45 micron) to 1/32 inch (one millimeter); compare CPOM.

First-order stream: see Stream order

Flood pulse concept: The idea that the pulsing of river discharge, the flood pulse, is the major force controlling biota in river-floodplain systems. Lateral exchange between the floodplain and river channel, and nutrient cycling within the floodplain, are postulated to have a more direct impact on biota than does nutrient spiraling from upstream to downstream in the river channel; the bulk of the animal biomass in such a system is believed to be derived from production in the floodplain, not from downstream transport of organic matter produced elsewhere in the basin.

Floodplain: Defined by hydrologists as the area flooded at a recurrence interval of once in 100 years. Ecologists define floodplains as areas that are periodically inundated (usually annually) by the lateral overflow of rivers or lakes, or by direct precipitation or ground water; the resulting physicochemical environment causes the biota to respond by morphological, anatomical, physiological, phenological, and/or ethological adaptations, and to produce characteristic community structures.

Fluvial: Of or pertaining to a river or rivers (produced by the action of stream or river)

Food chain: progression of feeding from prey to predators; compete food web.

Food web: feeding pattern of predators and prey in a complex web of different forms.

Forage: vegetation used for food by wildlife, particularly wild ungulates, such as deer and elk

Forb: any herbaceous species of plant other than grasses, sedges, or rushes; fleshy-leaved plants

FPOM: fine particulate organic matter.

Freestone stream: softwater stream usually with igneous rock and cobble substrate.

Freshet: the sudden overflow of a stream or river resulting from a heavy rain, or thaw, or both

Fry: early life history stage of fish after complete absorption of the yolk sac.

Function: the natural or proper action for which an organism, habitat, or behavior has evolved

Functional group: a group of organisms having the same function.

Fungus (pl. Fungi): mushrooms, truffles, molds, yeasts, rusts, etc.; simply organized plants, unicellular or made of cellular filaments or strands called hyphae, lacking chlorophyll; fungi reproduce asexually and sexually with the formation of spores

Gallery forest: woodlands along the sides of a stream, often referring to forest downstream from headwaters.

Gatherer: functional group that forages for food particles on the streambed; a subdivision of collectors.

Genus: the first word in a binomial or scientific name

Geomorphology: the geological study of the configuration and evolution of land forms

Germinate: to begin to grow, to sprout

Gouger: functional group that feeds on woody debris by gouging the conditioned wood surface.

Gradient: a rate of inclination, a slope; an ascending or descending part; an incline

Grazer: functional group that forages on periphyton, especially algae.

Groundwater outcrop: where groundwater exits the land surface as a spring.

Groundwater: water existing below the land surface.

Habitat: the sum total of environmental conditions of a specific place occupied by a plant or animal, or a population of such species

Hardness: property of water rich in calcium and magnesium and that is difficult to make suds with soap.

Hardwood: the wood of broad-leaved trees, and the trees themselves, belonging to the botanical group Angiosperinae; distinguished from softwoods by the presence of vessels

Headland: a point of land, usually high and with a sheer drop, extending out into a body of water; a promontory

Hemimetabolous: life history trait where change in form from immature insect to adult is incomplete, or "half-changed"; compare holometabolous.

Herbivorous: descriptive of feeding behavior on plants.

Hermaphroditic: descriptive of plant or animal having both male and female reproductive organs.

Heterotroph: organism that depends on tissue produced by other organisms; animals, fungi, bacteria.

Holistic: treating a subject in its entirety.

Holometabolous: life history trait of immature insects that change to adults with complete transformation of form; compare hemimetabolous.

Home range: area used by an animal for all its needs, such as feeding, reproduction, refuge from predators.

Hydraulic complexity: the system of variations in the velocity of the water and the water-operated physical processes in a stream as governed by the physical obstructions within the stream's channel

Hydraulic: of, involving, moved, or operated by a fluid, especially water.

Hydrologic cycle: cycle of major events involving water of precipitation, runoff to the ocean, evaporation, and again to precipitation over land.

Hydrology: science of natural water, its form, transport, and transformatiom on land and in the atmosphere.

Hydrolysis: decomposition of a chemical compound by reaction with water

Hypha (pl. Hyphae): filament or strand of a fungus thallus (non-reproductive vegetative body) that is composed of one or more cylindrical cells; increases by growth at its tip; gives rise to new hyphae by lateral branching

Hypogean: below ground habitats, such as caves, hyporheic zone; compare epigean.

Hyporheic: Pertaining to the hyporheos.

Hyporheos: The saturated zone beneath a river or stream consisting of substrate, such as sand, gravel, and rock, with water-filled interstitial pore. The zone often extends beyond the width of the stream channel and is typically used by certain aquatic organisms during their normal life cycle and as a refuge.

Impervious: incapable of being penetrated

Influent stream: stream flowing above the water table and losing water into it.

Inorganic: involving neither organic life nor the products of organic life; not composed of organic matter, especially minerals; contrast Organic

Integrity: the state of being unimpaired; soundness; completeness; unity

Interflow: subsurface flow of groundwater between catchments.

Intermittent: starting and stopping at intervals, such as a stream whose flow is periodically interrupted

Interstices: tiny spaces within streambed sediments.

Invertebrate: an animal lacking a backbone or spinal column

Isopod: any of numerous crustaceans of the order Isopoda, which includes the sow bugs and gribbles and shrimp.

Iteroparous: descriptive of an animal or plant that reproduces more than once annually, or having more than one brood in its lifetime.

Jam: to block, congest, or clog, such as with fallen trees and other woody debris.

Karst topography: landscape resulting from erosion of limestone bedrock, such as caves, springs, sinkholes, and underground rivers.

Katharobic: descriptive of a group of protozoans found in springs and small streams with oxygen-rich water.

Kilocalorie: 1,000 calories; calories on food packaging, etc. are actually kilocalories.           
Knickpoint: sharp irregularity in a stream-channel profile (commonly bedrock intrusions)

Lacustrine: referring to lakes.

Landscape ecology: An emerging specialty that deals with the patterns and processes of biological systems in spatially and temporally heterogeneous environments.

Landscape perspective: A way to view interactive parts of a watershed not necessarily all within one watershed.

Landslide: the dislodging and fall of a mass of earth and rock; see also Debris flow; Earthflow

Large Woody Debris (LWD): wood > 10cm in diameter and > 1m in length                          
Larva (pl. Larvae): the general term for the newly hatched, earliest stage of any of various animals that undergo metamorphosis, such as insects, frogs, and salamanders, and differ markedly in form and appearance from the adult

Leachate: solution of dissolved organic matter from material such as leaves, wood, and other nonliving matter.

Leaf pack: accumulation of leaves on streambed structures.

Lentic: pertaining to still water, lakes and ponds; compare lotic.

Lichen: a plant that is actually two plants in one; the outer plant is a fungus that houses the inner plant, an alga

Life history: series of ecological events during major stages of life cycle.

Lignin: the chief non-carbohydrate constituent of wood; a polymer that functions as a natural binder and support for the cellulose fibers of woody plants

Limestone stream: hardwater stream with streambed particles of sedimentary origin; productive of invertebrates and fish; compare freestone stream.

Limnocrene: spring pool.

Lithologic: referring to sedimentary rock.

Litter (forest): the uppermost layer of organic debris on the floor of a forest; essentially the freshly fallen or slightly decomposed vegetable material, mainly foliate or leaf litter, but also twigs, wood, fragments of bark, flowers, and fruits

Litter fall: the fall of litter to the floor of the forest

Longitudinal profile: graphical representation of stream decrease in elevation.

Lotic: pertaining to streams and rivers; flowing water; compare lentic.

Macroinvertebrate: stream invertebrate large enough to be seen easily

Macrophyte: large plant usually rooted in the streambed.

Marine: pertaining to the ocean.

Meander: to follow a winding and turning course, such as streams that flow through level land; also said of a bend in a stream that has been cut off from the main channel by the stream having shifted its course

Meiofanna: small animals of the streambed, ranging from 1.5 to 40 thousandths of an inch.

Membrane: a thin, pliable layer of tissue that covers surfaces, or separates, or connects regions, structures, or organs of an animal or plant

Mesotrophic: middle range of productivity; between oligotrophic and eutrophic.

Metabolism: the complex of physical and chemical processes involved in the maintenance of life

Metabolite: any of various organic compounds produced by metabolism Metamorphic: of or relating to metamorphosis; in geology, a rock that has been changed by metamorphism

Metamorphosis: change is size or form at molting of an insect or crustacean

Microcrustaceans: small crustaceans, consisting of ostracods, copepods, and cladocerans.

Microfauna: assemblage of very small animals.

Microinvertebrate: very small invertebrate too tiny to see without magnification (See also meiofauna)

Micron: one-millionth of a meter, about 1/25,000 of an inch.

Microtopography: the features of a small place or region, such as one square foot, as opposed to the features of a large place or region, such as one square mile

Mineral soil: soil composed mainly of inorganic materials and with a relatively low amount of organic material

Mineralization: breakdown of a chemical compound into lesser compounds or elements.

Mollusk: any member of the phylum Mollusca, of largely marine invertebrates, including the edible shellfish, such as clams, and some 100,000 other species

Monoecious: term applied to a plant having both male and female reproductive organs; see hermaphroditic.

Montane: moist, cool upland slopes (below timberline) dominated by coniferous trees.         
Multilayered: a forest canopy with two or more distinct layers of trees

Multivoltine: having several generations per year.

Mycelium (pl. Mycelia): the vegetative part of a fungus, consisting of a mass of branching threadlike filaments or strands called hyphae

Mycorrhiza: the symbiotic relationship of a fungus with the roots of certain plants

Naiad: older use for the immature stage in certain insect orders; now: nymph.

Natural history: science of distribution, behavior, and taxonomy of organisms; see ecology.

Nauplius: juvenile form of copepods.

Nekton: group of aquatic organisms capable of swimming; compare plankton.

Neuston: group of aquatic animals occurring in the surface film of water; see nekton, plankton.

Nitrification: process of transforming ammonium nitrogen into nitrate.

Nitrogen fixation: the conversion of elemental nitrogen (N) from the atmosphere to organic combinations or to forms readily usable in biological processes

Nitrogen-fixing bacteria: bacteria that can take nitrogen gas out of the air and transform it into an organic compound that plants can use

Nocturnal: to be active during the hours of darkness

Null point: that point in an estuary where the velocity of the downstream flow of less dense, less saline water near the surface of the channel and the upstream flow of more dense, more saline water near the bottom of the channel meet and effectively cancel one another out

Nutrient spiraling: pattern of nutrient movement downstream, into and out of various forms.

Nymph: immature stage of hemimetabolous insects.

Obligate: an organism that is able to survive only in a specific type of environment or only in a specific type of relationship within a variety of environments

Oligotrophic: referring to low level of productivity.

Organic: of, pertaining to, or derived from living organisms; of or designating compounds containing the element carbon; contrast Inorganic Organic combinations: mixtures of organic substances

Overflow channel: a channel that is created and used by a stream when it is overflowing its banks during a flood

Oviposition: act of laying eggs, usually referring to insects.

Ovoviviparous: term applied to animals wherein the females produce eggs, retain them unto hatching, and then release the living young; compare viviparous.

P:B: production/biomass ratio.

Patch of an ecosystem: The term patch dynamics is used regularly in the newly developing fields of landscape ecology and conservation biology, but it has been used previously as a standard ecological term. Use of the term patch recognizes that most eco- systems are not homogeneous, but rather a group of patches or ecological islands that are recognizably different from the parts of the ecosystem that surround them but nevertheless interact with them.

Periphyton: form of algae and other organisms on stones and other substrates on the streambed, the principal food of many benthic insects and other invertebrates.

Phytoplankton: plant organisms, generally microscopic, that float or drift in great numbers in fresh or salt water

Piercer: functional group whose members are equipped with a piercing organ used to penetrate the tissues of other organisms for feeding; some herbivorous, some predaceous.  
Piezometer: shallow-well for measuring groundwater-surface water interactions.

Piling: a log driven into the bottom of a stream, river, or estuary to support a structure or to use as a mooring for such things as rafts of logs

Plankton: plant and animal organisms, generally microscopic, that float or drift in great numbers in fresh or salt water

Plastron: envelope of air that some air-breathing insects use for respiration under water.

Polytypic species: species of animal with many genetic types or stocks, known for many salmonids.

Potamodromous: referring to fish species that migrate solely between portions of streams.

Potamodromy: life history feature of migrating for spawning only in rivers.

Potamon: lower section of rivers where currents are slow, water temperatures high, and the fish fauna of warmwater species; compare rhithron.

Predator: any animal that kills and feeds on other animals

Primary production: process of elaborating plant tissue; see photosynthesis.

Production: biomass ratio: P:B; the relationship between production rate and biomass; turnover ratio.

Progradation: the process of building upward and outward of land through the deposition of sediments that result from disturbances to the stability of the upslope water catchments, which increases the amount of sediments that are carried down the streams and rivers and thereby increases the amount of sediments that are deposited in a given locale in the lowlands

Pupa (pl. Pupae): the stage between the larva and the adult in insects with complete metamorphosis; it is a non-feeding and usually outwardly inactive stage

Pupate: to transform to a pupa

Rapid: an extremely fast-moving part of a river, caused by a steep descent in the riverbed

RCC: river continuum concept.

Reach of stream: a stretch of water that is geomorphically defined, such as between bends in a stream, river, or channel or between the start of a meadow or canyon

Recharge area: part of a catchment where precipitation filters into the ground; compare discharge area.

Recruitment: juvenile individuals of a given species entering a population for the first time

Redd: spawning nest of trout and salmon.

Refractory: resistant to decomposition.

Reset: return to downstream succession below a dam.

Retreat: chamber constructed of small stones and sand by members of the caddisfly family Hydropsychidae, in which the larva lives and gleans food particles from its capture net.

Rheogenesis: origin of a stream or river.

Rhithron: upper portion of a stream where currents are swift, water temperatures are low, streambeds are composed of stones and gravel, and the fish fauna often includes salmonids; compare potamon.

Riffle: a stretch of choppy water caused by a shoal or sandbar lying just below the surface of a waterway

Riparian forest: forest stands that extend laterally from the active channel to include the active floodplain, adjacent wetlands, etc. that contribute organic matter, LWD on floodplain and channel surfaces.                                                                                                     
Riparian vegetation: Hydrophytic vegetation growing in the immediate vicinity of a lake or river close enough so that its annual evapotranspiration represents a factor in the lake or river regime.

Riparian zone: The border or banks of a stream. Although this term is sometimes used interchangeably with floodplain, the riparian zone is generally regarded as relatively narrow compared to a floodplain. The duration of flooding is generally much shorter, and the timing less predictable, in a riparian zone than in a river floodplain.

River Continuum Concept (RCC): The idea that a continuous gradient of physical conditions exists from headwaters to mouths of rivers, and that structural and functional characteristics of biological communities are adapted to conform to the most probable position or mean state of the physical system. Producer and consumer communities establish themselves in harmony with the dynamic physical conditions of a given reach, and downstream communities are fashioned to capitalize on the inefficiencies of upstream procession of organic matter. Both upstream inefficiency (leakage) and downstream adjustment seem predictable.

Riverine wetlands: Wetland systems of less than 0.5 ppm ocean salts, exposed to channelized flow regimes. Riverine wetlands are categorized according to flow regimes such as tidal waters, slow-moving waters with well-developed floodplains, fast-moving waters with little floodplain, and intermittent systems.

Riverine: of the river

Runoff: water from precipitation as it flows over land toward a stream.

Salmonid: a fish of the family salmonidae, which includes trout and salmon

Salter: anadromous brook trout that spawns in freshwater streams and migrates to the ocean for growth.

Saprophyte: a plant that lives on and derives its nourishment from dead or decaying organic matter

Scraper: functional group equipped with an organ to scrape surfaces for periphyton or biofilm; see grazer.

Second-order stream: see Stream order

Sediment: inorganic particles deposited on the streambed, ranging in size from clay to boulders.

Semelparous: reproducing only once during a life cycle.

Semiaquatic: adapted for living or growing in or near water; not entirely aquatic

Semiterrestrial: adapted for living or growing on or near land; not entirely terrestrial

Semivoltine: one generation living for two or three years.

Serial discontinuity concept: The idea that dams shift the physical and biological characteristics of streams and rivers away from the pattern predicted by the river continuum concept. A dam may make conditions more like those of the headwaters (an upstream shift) or more like those downstream, or it may have a negligible effect. Multiple dams create multiple discontinuities in the expected or natural pattern of streams and rivers.

Seston: small particles of drifting organic matter.

Shredder: functional group of invertebrates that chew up pieces of CPOM.

Side channel: a channel that extends off the main channel of a stream but remains connected to it, such as the backwater of an overflow channel or of a cut-off meander

Silt: a sedimentary material consisting of fine mineral particles intermediate in size between sand and clay

Slash: a collective term used for the roots, branches, tops of the trees, and other unmerchantable fragments that are left on the site after the trees have been cut down and the desirable pieces/logs have been removed

Slope: the incline of the land surface measured in degrees from the horizontal; also characterized by the compass direction it faces

Slough: a stagnant swamp, marsh, bog, or pond, especially as part of a backwater, inlet, or bayou

Smolt: life cycle stage of migratory fish, particularly salmonids, when they approach leaving their natal stream for the ocean.

Snag habitat: twigs, branches, and trunks of trees and bushes that fall into a stream, providing habitat for insects that cling to the structures.

Spatial heterogeneity: Variation in the attributes of an environment over space.

Splake: hybrid between lake trout and brook (speckled) trout.

Splash dam: a small, wooden dam that temporarily retains water that can be released at will to raise the level of the water in a stream's channel to float logs to a larger river

Spring wood: young, usually soft, fast-growing wood with large cells that lies directly beneath the bark and develops in early spring when there is ample moisture; spring wood can be seen in the stump of a tree as the lighter, larger rings in the wood, as opposed to the summer wood, which is represented by the smaller, darker rings in the wood

Standing stock: see biomass.

Stem: the principal axis of a plant from which buds and shoots develop; with woody species, the term applies to principal axes, or trunks, of all ages and thicknesses

Stenothermic: term applied to fish and other animals that prefer a narrow range of temperatures, often salmonids; compare eurythermic.

Stream buffer: A variable-width strip of vegetated land adjacent to a stream that is preserved from development activity to protect water quality and aquatic and terrestrial habitats.

Stream order: Rivers and streams are classified by order. The order of a river or stream is a dimensionless number that indicates how many tributaries it has. The smallest unbranched tributary in a watershed is designated order 1. A channel formed by the confluence of two such tributaries is designated order 2. Where 2 order tributaries join, a channel segment of order 3 is formed, and so on. In general, the higher the order number, the larger is the watershed, and the greater are the channel dimensions and discharge.

Structure: objects on the streambed that support periphyton and biofilms, cover, and attachment sites for invertebrates, such as stones, woody debris, and macrophytes.

Subimago: life cycle stage of mayflies, a flying, immature form preceding the flying adult.

Succession: sequential changes in vegetation, invertebrates, and fish downstream through the course of a stream.

Summer wood: wood that develops during the latter part of the growing season when the supply of water is not so ample as in spring and therefore has smaller cells, which in turn makes it darker, harder, and less porous than spring wood; summer wood can be seen in the stump of a tree as the darker, smaller rings in the wood, as opposed to the spring wood, which is represented by the larger, lighter rings in the wood

Suspended sediments: sediments that are suspended in and by the water in which they are carried and in which they may be kept from settling out by the motion or velocity of the water in which they are suspended

Sympatry: when populations of two species occur together.

Synchrony: referring to the occurrence of each of a species' life cycle events occurring over a short period of time.

Tannin (tannic acid): any of various chemically different substances capable of promoting the tanning of leather

Taxon: unit of taxonomy, such as phylum, order, species, etc.

Terrace: a raised bank of earth that has vertical or sloping sides and a flat top; a flat, narrow stretch of ground that has a steep slope facing a river

Terrestrial: associated with the land

Third-order stream: see Stream order

Trivoltine: with three generations, or cohorts, per year.

Trophic level: group of organisms with common feeding behavior.

Trophic pyramid: graphic representation of pyramid-shaped structure of successive trophic levels.

Unconfined aquifer: aquifer located only above an impermeable rock stratum.

Underfit river: small river flowing through a large valley.

Univoltine: with one cohort per year.

Upwelling: the movement of cold water up from the bottom to mix with the warmer water at the surface

Vascular plant: any plant that contains vessels 

Vertebrate: an animal with a backbone                                                                              
Vertical Height Gradient (VHG): measure for quantifying hyporheic exchange (unitless value; if positive = upwelling, if negative = downwelling)

Voltinism: expressing number of cohorts per year.

Warmwater: term roughly defining stream with warmwater fish species.

Water catchment: a drainage basin that catches water; either rain, snow, or both, and stores it in a slow-motion downward flow as it merges with ever-larger water catchments until it is finally accepted into the sea

Water column: the vertical space of water that exists between the bottom and the surface of a body of water, such as a stream or lake

Water table: the surface in a permeable body of rock of a zone saturated with water

Watershed scale approach: A consideration of, the entire watershed, including the land mass that drains into the aquatic ecosystem.

Watershed: The entire surface drainage area that contributes water to a lake or river.

Wetlands: Term for a broad group of wet habitats. Wetlands are lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. Wetlands include features that are permanently wet, or intermittently water covered, such as swamps, marshes, bogs, muskegs, potholes, swales, glades, slashes, and overflow land of river valleys. According to the 1989 federal wetlands delineation manual, wetlands include lands saturated for at least 7 days to a depth of 12 inches. A newly proposed definition by the Bush Administration would be lands that have 15 days of standing water and 21 days of surface saturation.

Xylophage: organism feeding on wood.

Xylophagid: the vernacular for the generic name Xylophaga

Year class: cohort of fish, named by year of hatching.

Zero Order: headwater region of stream consisting of small spring seeps; that is, above First Order.