Glossary of Freshwater Ecology Terms

Alkalinity

A measure of the availability of the water to resist a change in pH. Water resists changes in PH due to the presence of anions of carbonate, bicarbonates, and hydroxides.

Allochthonous

Material generated outside a particular habitat but brought into that habitat such as debris brought in through a lake by a river.

Andadromous

Refers to an organism that lives in the sea as an adult and returns to freshwater to spawn in the spring.

Aphotic Zone

The portion of a lake where incident light level is less than 1% (total darkness).

Autochthonous

Native substances, generated within a particular habitat, indigenous.

Back eddies

Pools along a stream that are created behind rocks and snags where whirls around but delay its downstream passage.

Basin Characteristics

Features that describe the shape, slope, area, length, number of stream segments, etc in a watershed.

Benthic

Refers to collectively, all those animals and plants living in the bottom of a lake or sea, from the water's edge to the greatest depth (benthos), bottom in pelagic area.

Biomass

The total weight of organisms per unit area at any given moment in time.

Catadromas

Refers to fishes which spend most of their life in freshwater but migrate to salt water to spawn.

Compensation Depth

Depth at which the rate of photosynthesis equals the rate of respiration.

Clinograde Profiles

Oxygen profiles that exhibit 100% saturation in the epilimnion and reduced levels in the hypolimnion.

Cultural Eutrophication

Organic enrichment of a lake induced by human activity.

Deltas

Occur when rivers, streams, tidal inlets enter quiet waters of a lake or ocean and deposit large amounts of sediments; typically triangular in shape and formed at the mouth of a river.

Detritus

Inorganic or organic debris.

Discharge

The volume of water passing through a cross-sectional area of the stream channel per unit of time (Q=Av).

Current Velocity

The downstream water movement in the stream channel.

Hydrographs

Plots of discharge against time.

Mean channel depth

The sum of a channel depth divided by the number of measurements plus one.

Rapids

A part of a stream where the current is moving with greater swiftness than usual and where the water surface is broken by obstructions.

Ephemeral pools

Pools of water that have brief aquatic lives of a few weeks to months; most are less than 1 M deep.

Epilimnion

The warm, oxygen-rich layer of the lake.

Eutrophic

A classification of a lake meaning that the lake is highly enriched.

Eutrophication

The process of organic enrichment of a body of water as a result of the increased nutrient loading and subsequent increase in autotrophic production.

Fetch

The distance that the wind can blow over water without interruption by land.

Groundwater

Water that fills up the pores and hollows within the Earth in a larger and mostly subsurface water table.

Hypolimnion

A lower layer of the lake that lies below the metalimnion.

Impoundment

A body of water which is confined by a dam, ****, floodgate or other barrier; used to collect and store water for future use.

Lacustrine Zone

Refers to lakes or living in lakes.

Lentic

Refers to standing water. Lentic ecosystems include lakes, ponds, puddles and to some extent estuaries.

Littoral Zone

That zone predominated by emergent and floating leaved aquatic plants.

Maximum Fetch

The maximum distance the wind may blow without being interrupted by land.

Mesotrophic

Those lakes that are moderately enriched, between oligotrophy and eutrophy.

Metalimnion

The intermediate layer in lakes between epilimnion and the hypolimnion.

Nekton

The open water community of strong swimmers capable of swimming against strong currents.

Oligotrophic

A classification of lakes having little or few nutrients.

Oligotrophication

The reversal of eutrophication.

Orthograde profiles

Oxygen profiles which exhibit 90-100% saturation at all depths.

Pelagic zone

The open water zone of lakes and oceans referring to the water column away from the bottom.

Periphyton

Algae that grow on a variety of submerged substrates such as rocks, plants or debris in lakes and streams.

Phytoplankton

The plant members of the plankton community, which are suspended or free-floating in the water column.

Plankton

Collectively all those organisms suspended in the water of an aquatic habitat which are not independent of the currents.

Macroplankton

Plankton with the size range of >2000 µS.

Mesoplankton

Plankton with the size range of 200-2000 µS.

Microplankton

Plankton with the size range of 20-200 µS.

Nanoplankton

Plankton with the size range of 2-20 µS.

Picoplankton

Plankton with the size range of 0.2-2 µS.

Profundal Zone

The plantless part of a lake where there is too little light to support the growth of plants.

Riffles

Movements of water in a river characterized by shallow turbulent water passing through or over stones or gravel.

Riparian Zone

The edge adjacent to the stream usually taken as the vegetated area 30 m from the water's edge plus another 30 m to allow for windfallen trees and shrubs.

River Continuum Concept

Physical, chemical and biological attributes of a stream change as a continuum of gradients as stream order size increases.

Shoreline Length

The length of the shoreline perimeter derived from the outline of the lake.

Summer Thermal Stratification

This is part of the annual temperature cycles of lakes when the heating and mixing processes continue and eventually form three thermal layers in the lake.

Thermocline

See metalimnion.

Trophic Status

Enrichment status of a lake. Lakes are classified as either oligotrophic, mesotrophic, or eutrophic.

Trophogenic Zone

The region of a lake where photosynthetic production occurs.

Vernal Pools

Seasonal wetlands.

Watershed

An area of land that intercepts and drains precipitation and collects water for a particular stream or other water body.

Winter Thermal Stratification

This is part of the annual temperature cycle of lakes when low density surface layer (under the ice) at 0° C sits on top of a dense layer near 4°.

Zooplankton

Collectively all those animals suspended in the water of an aquatic habitat which are not independent of currents.