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Glossary of Wetland Terminology

ABIOTIC Those components of an ecosystem which are not living. It is a term often used for chemical and physical influences on organisms.
ABSTRACTION The removal of water from a water body, including aquifers, normally for human use.
ACCRETION  The deposition of clastic and/or organic material. See sedimentation.
ACID(IC) See pH
ACIDIFICATION The process of becoming more acid.
ACIDOPHILOUS Any substance, tissue, or organism having an affinity for acid conditions.
ACROTELM The upper active layer of peat deposits. See peat deposits.
AFFORESTATION Establishment of a new forest by natural regeneration or plantation on non-forested land.
AGEING OF WETLANDS The concept that all wetlands are ephemeral and follow a distinct cycle of ageing. According to this concept, wetlands will tend to be more eutrophic as they age with accretion. Eventually this will lead to to terrestrialization and the disappearance of the wetland. See accretion.
AGUELMANE Berber term meaning lake.
ALGAE Collective name of a large group of chlorophyll-containing plants, comprising the seaweeds and various freshwater forms, ranging in size from single cells to long stems.
ALGAL BLOOM Dramatic increase in algal growth resulting from high levels of nutrients or pollutants.
ALKALI FLAT A plain covered with alkaline salts formed by the evaporation of water in a slight depression.
ALLOCHTHONOUS SEDIMENT Sediment where the main constituents have been formed in situ.
ALLOGENIC A process caused by an external environmental factor e.g.change in the
ALLUVIAL Formed by river flow processes e.g. alluvial plains.
ALLUVIAL CLAY Sediment of the clay grade which has been transported by rivers from the place of its origin, as distinct from that which has originated in situ.
ALLUVIAL CONE An alluvial fan with steep slopes formed of loose material washed down the slopes of mountains by ephemeral streams and deposited as a conical mass of low slope at the mouth of a gorge. Also known as cone delta, cone of detritus, debris cone.
ALLUVIAL DEPOSIT Clay, silt, sand, gravel and other material which has been carried in suspension by river or floods, and is deposited where  the velocity of flow is insufficient to maintain the material in suspension.
ALLUVIAL PLAIN A plain formed from the deposition of alluvium usually adjacent to a river that periodically overflows.
ALLUVIATION Process of alluvial deposit along a shore.
ALLUVIUM Sediment deposited by flowing water.
ANADROMOUS FISH Fish that ascend rivers from the sea at certain seasons for breeding e.g salmon and shad. Compare catadromous fish.
ANAEROBIC (Of organisms) ability to live anoxically i.e. in the absence of free (gaseous or dissolved) oxygen. (Of processes) occurring in the absence of such oxygen.
ANASTOMISING Braiding of channels. The division and subsequent rejoining of
ANNUAL MAXIMUM SERIES A listing in rank order of the largest event each year in an environmental data series. Commonly associated with flood frequency analysis in hydrology. See Recurrence interval
ANTHROPOGENIC Involving the impact of man on nature: induced or altered by  the presence and activities of man.
ANTI – SALT BARRIER A structure, normally a sluiced embankment or low dam, erected in the lowest reaches of a river to prevent the upstream movement of the estuarine salt wedge. The barrier can be opened to allow the discharge of upstream freshwater.
AQUACULTURE Cultivation of natural faunal resources of water, normally freshwater fish, marine fish and shellfish. See mariculture.
AQUATIC FAUNA The animal species which complete their life cycle in the water and which cannot reproduce without the permanent presence of water.
AQUATIC PLANTS (1) Emergent plants, such as sedges, reeds and rushes, rooted in the sediment and protruding above the water surface.(2) Free-floating plants, such as waterlilies, rooted in the sediment with leaves floating on the water surface.(3) Floating-leaved plants, such as waterlilies, rooted in the sediment with leaves floating on the water surface. (4) Submerged plants, such as najas, growing below the water surface.
AQUIFER A permeable body of rock capable of yielding quantities  of groundwater to wells and springs. A subsurface zone that yields economically important amounts of water to wells. See groundwater, pumping test, specific yield, specific retention.
AQUIFER RECHARGE The increase in water storage in the saturated zone as a result of water percolation through the aeration zone.
ARTESIAN Involving, relating to, or supplied by the upward movement of water under hydrostatic pressure in rocks or unconsolidated material beneath the earth’s surface. Where the piezometric surface is above the ground surface, well piercing artesian aquifers will overflow at the surface. See aquifer, hydrogeology, groundwater.
ARTIFICIAL FLOOD A recent concept involving the release of a sufficiently large volume of water from an upstream dam and reservoir to cause beneficial flooding in wetlands downstream. See dam.
ARTIFICIAL MARSH CREATION The simulation of natural wetland features and functions by topographic and hydraulic modification of non-wetland landscapes. Typical objectives of artificial marsh creation include ecosystem replacement or storm water management.
ARTIFICIAL WETLAND (1) Aquaculture/mariculture a.  Aquaculture ponds, including fish ponds and shrimp ponds. (2) Agriculture a. Ponds, including farm ponds, stock ponds and small tanks. b. Irrigated land and irrigation canals, including rice fields, canals and ditches. c. Seasonally flooded arable land.(3) Salt exploitation a. Salt pans and evaporation ponds. (4) Urban/Industrial. a. Excavations, including gravel pits, borrow pits and mining pools. b. wastewater treatment areas, including sewage farms, settling ponds and oxidation basins. (5) Water storage areas a. Reservoirs holding water for irrigation and/or human consumption with a pattern of gradual, seasonal drawdown of water level. b. Hydro-dams with regular fluctuations in water level on a weekly or monthly basis. c. Flood balancing ponds.
ASSIMILATION A general term for all the metabolic processes by which nutrient material is built up and utilized by plants. Removal of dissolved or suspended material from water through biological, chemical or physical processes. Incorporation into the body of an organism of substances which have been synthesized or absorbed by the organism.
ASTATIC Unstable. In Limnology usually refers to water level.
ATHALASSOHALINE Water with ionic proportions quite different from the dissolved salts in sea water (main characteristic of many mediterranean saline wetlands).
ATMOMETER An instrument to measure evaporation rates. The Piche atmometer consists of an upturned water filled tube which keep a circular paper membrane continuously moist. Atmometers tend to give rather higher values for evaporation that exists in surrounding wetlands and they are especially subject to the influence of wind speed.
AUTOGRAPHIC RAIN GAUGE An instrument that records the rate of rainfall continuously. Modern devices use the tipping bucket principle and use electronic logging or telemetering. See rain gauge, precipitation.
BACKWATER An area of relatively still water where drainage is impeded by an obstruction such as a sediment bar across a partial oxbow lake or a sandbar across a coastal lagoon outlet etc.
BANK  (1) Land at the side of water, such as a river or a lake. (2) Long heap of sand, such as a sandbank in shallow water, either in a river or in the sea.
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. Bank stabilization can also be achieved using expensive engineering systems of driven piles, concrete walls and toe-boarding.
BAR Submerged or partially submerged ridges, banks, or mounds of sand, gravel, or other unconsolidated sediment built up by waves or currents within stream channels, at estuary mouths and along coasts.
BARRAGE An artificial dam which increases the depth of water of the river or watercourse, or diverts it into a channel for navigation or irrigation. See dam, barrage.
BASEFLOW That portion of river flow that originates from transfers from the saturated zone. As such it tends to be modest in amount, long continued and subject to little short term variation. See hydrograph.
BATHING WATERS DIRECTIVE The EU Directive 76/160/EEC on Bathing Water.
BEACH An area of sand or shingle sloping down to a sea or lake, esp. the area between the high and low water marks on a sea coast.
BED LOAD That part of the sediment load of a river which moves downstream by bouncing (saltation), rolling or sliding along the bed of the river. See solute, suspended load.
BEDROCK Unbroken solid rock, usually overlaid by rock fragments or soil.
BENTHIC ORGANISM Organism attached to or rooted in the substratum at the bottom of a water body. 
BENTHOS Bottom-dwelling forms of marine life. Also known as bottom fauna.
BENTONITE A particularly impermeable type of clay often used to seal piezometers and wells. See piezometer, well.
BERM A horizonatal terrace, usually underwater, found in streams or in sheltered coastal areas. May be formed by natural processes or constructed by human agency as a means of fostering the growth of emergent plants.
BERM DITCH A channel cut along a berm to drain off excess water.
BIOASSAY A method for quantitatively determining the concentration of a substance by its effect on the growth of a suitable animal, plant, or microorganism under controlled conditions.
BIOCHEMICAL OXYGEN DEMAND (BOD) The amount of dissolved oxygen (in mg per litre) used by micro-organisms feeding on the organic content of water measured over 5 days at 20°C. This is useful measure of organic pollution: <3mg/l indicates clean water, 30mg/l indicates gross pollution. (See also chemical oxygen demand [cod] and permanganate value [pv]). The magnitude of the results obtained is usually PV < BOD < COD.
BIODIVERSITY The variety of all life on earth: the variability amoung living organisims from all sources including terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.
BIOGEOGRAPHICAL A region characterized by distinctive flora and fauna.
BIOLOGICAL CONTROL Control of pests using biological means, with or without the assistance of biotechnology, for example (1) use of another organism (or virus) which can be parasitic to the former (2) use of an organism which is the predator of the former, (3)  massive release of sterilized organisms. Also known as biotic control.
BIOMASS The total quantity of matter (the non-aqueous component frequently being expressed as dry mass) in organisms, commonly those organisms that form a trophic level or population, or inhabit a given region.
BIOME Major regional ecological complex of communities extending over large natural areas and characterized by distinctive vegetation and climate; e.g. grasslands, coral reef, tropical rain forest.
BIOMONITORING Periodic surveillance of aspects of living organisms in order to record the status of an ecosystem. Biological monitoring surveys can span the trophic spectrum from algae and other aquatic plants, to macroinvertebrates and fish species.
BIOSPHERE The part of the earth’s surface and atmosphere inhabited by living organisms.
BIOSPHERE RESERVE One of a global network of reserves coordinated through UNESCO’s ‘Man and the Biosphere’ programme to conserve the diversity and integrity of natural systems; and to provide areas for environmental research and for education and training.
BIOTA Animal and plant life; all living organisms of a certain area. Biota may be considered synonymous to biotic community and distinct from the biotope.
BIOTEST A methodology and set of techniques based on the estimation of environmental quality through the assessment of the condition of living organisms, both plant and animal species. Such an assessment involves an evaluation of morphological, genetic, physiological, biochemical, and immunological parameters that characterize developmental homeostasis in each species. Estimation requires analyses of both indigenous species in situ and test organisms ex situ.
BIOTIC FACTORS Those features of the environments of organisms arising from the activities of other living organisms; as distinct from such abiotic factors as climatic and edaphic influences.
BIOTOPE In strict ecological sense it is the non-living structural part of an ecosystem e.g. climate, soil, water. In a wider sense it is the space in which the organisms of a biotic community live and reproduce. In both cases the biotope is described either by abiotic factors or by geometrical parameters, never by biotic factors. It is therefore an error to say for example, “the reedbeds is the biotope of leeches”.
BIRDS DIRECTIVE Council Directive of the EU (79/409) relating to the conservation of Wild Birds.
BIVALVE Broadly speaking, any animal with a shell in two parts hinged together e.g. oyster, clam, mussel.
BLACK ALKALI A deposit of sodium carbonate that has formed on or near the surface in arid to semiarid areas.
BLUE GREEN ALGAE See cynobacteria
BLUE PLAN A series of planning scenarios for the Mediterranean basin developed under the aegis of the Barcelona Convention.
BOG A plant community that develops and grows in areas with permanently waterlogged peat substrates. Also known as moor; quagmire.
BORROW PIT An excavation dug to provide material (borrow) for a nearby embankment or fill elsewhere.
BRACKISH (1) Slightly salty. (2) Less salty than sea water, but undrinkable. (3) Water with salinity values ranging from approximately 0.50 to 17.00 parts per thousand.
BRAIDED RIVERS Rivers with mid-channel bars, exposed as islands at low flow, with a network of channels between them.
BRANCH (of a water course) A river channel that diverges from the main channel. May rejoin the main channel downstream or disperse itself within the floodplain. 
BROOK Small stream.
BROOKLET See brook
BRYOPHYTES Small phylum of the plant kingdom, including mosses, liverworts, and hornworts, characterized by the lack of true roots, stems, and leaves.
BULK DENSITY OF SOIL The mass per unit volume of soil. The specific gravity is normally reserved for the soil particles themselves. See specific gravity.
CALCAREOUS Resembling, containing, or composed of calcium carbonate.
CALICHE A Castilian term which is also used in the USA. An alkaline salt deposit on the soil surface, usually occurring in arid regions with groundwater close to the surface.
CANAL An artificial water course with controlled water levels for the transport of water or for navigation.
CAPILLARY RISE/FRINGE The area above the upper edge of the zone of saturation which is kept particularly moist by surface tension and adsorptive forces drawing water up the narrow (capillary) openings in the rock or soil. See groundwater, aquifer.
CAPILLARY STREAM Small stream that feeds into a larger stream, or connects two parts of a larger stream.
CARR A swamp area dominated by shrubs, bushes and trees.
CARRYING CAPACITY The maximum biomass that can be continuously present in an area.
CATADROMOUS FISH Fish that live in fresh water and go to the sea to spawn e.g. eel. Compare anadromous fish.
CATCHMENT An area drained by a river and all its tributaries; also referred to as a drainage basin, river basin or, in North America, as watershed. The morphological parameters of the river basin, such as area, shape, slope, perimeter, drainage density, soil permeability etc. may be used to explain observed variations in hydrological phenomena and then employed in predictive equations for sites without formal hydrometric networks.
CATCHMENT APPROACH See watershed scale approach.
CATOTELM The lower “inert” layer of peat deposits. See acrotelm.
CHANNELIZATION Straightening of the meanders in a river system to create more navigable waterways, or when accompanied by channel deepening to provide flood control.
CHANNELS channels in a complex pattern.
CHEMICAL OXYGEN DEMAND (COD) Organic content of waste obtained by measuring the amount of oxygen required for its stabilization. COD uses chemical oxidation employing boiling potassium dichromate and concentrated sulphuric acid. See also biochemical oxygen demand [bod] and permanganate values [pv]). The magnitude of the results obtained is usually PV<BOD<COD.
CHOTTS Large, shallow depressions, found in North Africa, that fill with water from flash floods. Chotts are situated along the northern border of the Sahara and are usually saline. They rarely hold water for longer than 4 months at a time, usually in winter. Permanent vegetation is sparse, though a mass of greenery will appear whenever there is rain. Invertebrates are limited to a handful of species which can cope with the desiccated conditions and rarely there are visits by waterbirds.
CHUTE A conduit for conveying free-flowing materials at high velocity to lower levels. A short channel across a narrow land area which bypasses a bend in a river; formed by the river’s breaking through the land.
CITES Convention on International Trade in Endangered Species of Wild Flora and Fauna (1983)
CLAY A sedimentary rock consisting of aluminium silicates and other minerals which are derived from the weathering of other rocks. Clay particles are smaller than 4.0 µm (0.004mm) diameter.
CLIMAX VEGETATION Mature vegetation in a steady state equilibrium with existing natural environmental conditions.
COAST The zone of land next to the sea or lake.
COASTAL BAR An accretion of sand or silt formed by continental tide movements, and by conflicting or contributory discharges from inflowing rivers.
COASTAL PLAIN An approximately level zone which is between the sea and the nearest hills or mountains.
COASTAL ZONE An imprecisely defined area that includes the inter-tidal zone, the coastal plain, estauries, lower portions of rivers and the shallow offshore zone.
COLORIMETRIC ANALYSIS The chemical analysis of water using reagents which give a coloured response in proportion to the amount of the solute of interest that is present in the sample.
COMMUNITY Ecological term for any naturally occurring group of different organisms inhabiting a common environment, interacting with each other, especially through food relationships, and relatively independent of other groups. Communities may be of varying sizes and larger ones may contain smaller ones.
COMPENSATION See wetland mitigation.
CONE OF DEPRESSION The shape of the depression of the water table around a well that is being actively pumped for water. See well, groundwater, aquifer.
CONFINED AQUIFER An aquifer overlain by an impermeable aquiclude where the water in the aquifer is under hydrostatic pressure as a result of recharge at a higher level. See unconfined aquifer.
CONJUNCTIVE USE The use of surface water bodies and groundwater sources in conjunction so as to derive a greater yield than would be possible by operating the two resources separately. See goundwater, reservoir
CONNATE WATER Water trapped in the interstices of sedimentary rocks at the time of their deposition.
CONSERVATION (1) Protection, preservation, and careful management of natural resources and of the environment. (2) The totality of methods of manipulations which are used by man to ensure continuous and stable high yields from renewable resources and to prevent the wastage of non-renewable ones. (3) The management which succeeds in obtaining the best possible yields while at the same time it succeeds in securing the complete and continuous functioning of the ecosystem (IUCN definition). (4) The totality of protection and management measures aiming at maintaining or restoring the natural habitats and the populations of wild fauna and flora (Directive 92/43/EEC).
COST-BENEFIT ANALYSIS A system of economic analysis involving the determination of the ratio total benefits of a project measured in cash terms: total cash costs of the project. A benefit rato > 1 indicates that the project will produce benefits greater than the costs.
CRATER LAKE A fresh-water lake formed by the accumulation of rain and groundwater in a caldera or crater.
CREST GAUGES An instrument, often of very simple construction, that records the maximum water level reached at a site since the last observation.
CRITICAL LOAD A recently developed concept that derives from acidification studies which describes the maximum loading of a pollutant onto an ecosystem which will not cause significant change to that system.
CULVERT An engineered structure which takes a water course underground through a bridge or for longer distances in urban areas.
CURRENT METER An instrument for measuring the velocity of flow in a channel. Traditionally a propeller where the revolutions have been counted. More modern instruments use an electromagnetic principle.
CYANOBACTERIA Single-cell or filamentous organisms, also known as blue-green algae that are able to convert atmospheric nitrogen into forms that can be utilized for plant growth.
CYCLONIC RAINFALL Rainfall associated with depressions where air rises as a result of frontal activity. The rainfall tends to be low intensity, long duration and very widespread. See convective rainfall, orographic rainfall.
DAM A barrier constructed to obstruct the flow of a watercourse and to impound a reservoir behind the dam.
DARCY’S LAW Defines the relationship between the discharge of a fluid through a porous medium and the gradient of the hydraulic head: v = – K dh/dl  where, v is the velocity, dh/dl is the hydraulic gradient, and K is the hydraulic conductivity.
DAYA Berber term meaning temporary pool or swamp or permanent lake.
DDT Dichlorodiphenyltrichloroethane. A powerful and persistant insecticide, used to control mosquitoes in countries where malaria is a problem. Its use has been discontinued in Europe. It is stored in the bodies of higher animals. It is non-phytotoxic to most plants.
DEEPWATER HABITAT A deepwater habitat is predominantly flooded land lying below the deepwater boundary of  wetlands.
DELTA A gently sloping alluvial deposit, usually triangular in shape, which forms where a river meets the sea (or lake) and consists mainly of silt, sand, and gravel, the coarsest deposits being near the head of the delta and the fine material being in the face of the delta below the level of the sea (or lake). The main channel of the river may break into several channels which may change their course as sediment blocks previous courses.
DENITRIFICATION Process carried out by various facultative and anaerobic soil bacteria, in which nitrate ions act as alternative electron acceptors to oxygen during respiration, resulting in release of gaseous nitrogen. This nitrogen loss accounts in part for  the lack of fertility of constantly wet soils that support nitrate-reducing anaerobes and for lowered soil fertility generally, products of denitrification not being assimilable by higher plants or most organisms. Bacteria such as Pseudomonas, Achromobacter and Bacillus are particularly important. See nitrogen fixation, nitrogen mineralization.
DEOXYGENATION Removal of oxygen (as free or loosely combined oxygen) as  from water, sewage or blood.
DESIGN DROUGHT A precisely defined drought that in extremis could be kept under control by a water resources management scheme. Droughts more severe than the design drought would cause some failure of supply within the water resource system.
DESIGN FLOOD The largest flood discharge which an engineering scheme is designed to accommodate without adverse effects.
DIATOM Microscopic plant abundant in plankton. Diatoms sometimes produce a water “bloom” and give a yellowish or brownish tint to the water. Diatoms are notable for their shells of silica and the siliceous character imparted to bottom deposits by their remains.
DILUTION GAUGING The measurement of river discharge through the assessment of the degree of dilution of a tracer injected into the flow. The injection can either be continuous or slug like.
DIPWELL A shallow (up to around 4m) lined hole in a wetland substrate which allows the measurement of shallow groundwater levels. The lining (usually plastic tubing) is perforated and allows water to enter the dipwell at any level.
DISSOLVED OXYGEN The dissolution of oxygen into water. It is highly dependent upon temperature, the solubility being 14.6 mg/l at 0°C and 7.6 mg/l at 30°C. Since oxygen is consumed in the breakdown of organic pollutants, dissolved oxygen can give a rapid assessment of the level of pollution in a river.
DITCH A narrow channel dug in the earth, usually used for drainage, irrigation or as a boundary marker.
DITCH WATER Water in a ditch which may be flowing, static or about to be desiccated depending upon the season and the water regime
DOWNSTREAM In the direction of flow, as a current or waterway.
DRAINAGE Removal of groundwater, surface water, or water from structures by gravity or pumping.
DRAINAGE BASIN An area in which surface runoff and baseflow contributions from groundwater collects and is carried by a drainage system, as a river and its tributaries. Also known as catchment river basin; watershed; drainage area; water gathering ground; hydrographic basin.
DRAINAGE DITCH An artificial channel to drain away excess water. See ditch.
DRAWDOWN The magnitude of the change in water surface level in a well, reservoir, or natural body of water resulting from the withdrawal of water. See cone of depression.
DREDGING Removing solid matter from the substrate of a waterbody.
DROUGHT A period of water shortage which may be brought about by a number of causes, often interacting. (1) Meteorological drought: low rainfall. (2) Hydrological drought: low river flow and groundwater levels. (3) Agricultural drought: crop productivity reduced by water shortage. (4) Cultural drought: water shortage created by excessive human demand and/or poor water resources management (e.g. excessive leakage from the supply system).
DYKE A wall or embankment of timber, stone, concrete, fascines, or other material, built as training works for a river, to confine the flow rigidly within definite limits.
ECOLOGICAL QUALITY OF WATER DRAFT DIRECTIVE A proposed draft Directive on ecological quality of water presented by the EU Commision on 15th June 1994. It aims to maintain water quality of Community waters where this is already good and ultimately to achieve good water quality elsewhere.
ECOSYSTEM A community of organisms, interacting with one another, plus the environment in which they live and with which they also interact; e.g. a lake, a forest, a grassland. Such a system includes all abiotic components such as mineral ions, organic compounds, and the climatic regime (temperature, rainfall and other physical factors). The biotic components generally include representatives from several trophic levels; primary producers (mainly green plants), macroconsumers (mainly animals) which ingest other organisms or particulate organic matter, microconsumers (mainly bacteria and fungi) which break down complex organic compounds upon death of the above organisms, releasing nutrients to the environment for use again by the primary producers.
ECOSYSTEM- BASED EIA See site-based eia.
ECOTONE A transition zone between two or more diverse communities as between forest and grassland. This zone is often characterized by high species diversity.
ECOTYPE Group of organisms of the same species which has developed special adaptations (physiological and/or morphological) to a certain combination of environmental factors but is able to cross freely with other ecotypes of the same species. Synonymous with habitat form.
EFFECTIVE RAINFALL That portion of a rainstorm that runs off from the catchment to create a flood hydrograph.
EFFLUENT The treated water which emerges from a sewage works or similar purification facility.
ELECTROMAGNETIC GAUGING The measurement of river discharge utilizing the distorting effect that flowing water has on an electromagnetic field. The field is normally generated by a collar around a pipe or by a coil laid under a riverbed.
ELLENBERG’S “MOISTURE VALUE” A semi-objective/semi-qualitative classification of plants on a numerical scale to characterize the wetness of the habitat in which the plant is found to grow naturally. It was developed by the German botanist Ellenberg.
ELVERS Immature eels.
EMBANKMENT See dyke
EMERGENT PLANTS Aquatic plants that are rooted in the sediment, but which leaves are at or above the water surface. These wetland plants provide habitat for wildlife and waterfowl in addition to removing urban pollutants.
EMERGENT VEGETATION Aquatic plants with stems and leaves above the water.
ENDEMIC SPECIES Species that are unique to one region, i.e. they are found nowhere else in the world.
ENDOREIC Drainage basins with no outlet to the sea.
ENVIREG Environmental Regional Programme of DG XVI of the EU Commission.
ENVIRONMENTAL IMPACT ASSESSMENT (EIA) A process designed to ensure that potentially  significant environmental impacts are satisfactorily assessed and taken into account in the planning, design, authorization and implementation of all relevant types of action. Essential steps in an EIA are: (1) Preparation of an EIA study on the potentially significant environmental impacts of the proposed action. (2)Consultation and public participation following the publication of the EIA study. (3) Incorporation of the findings of the EIA study, and of the comments made upon it, into the decision making process for authorizing and implementing that action.
EPHEMERAL WATER BODY Temporary water body.
EPILIMNION In a thermally stratified lake, the turbulent layer of water that extends from the surface to the metalimnion.
EPIPHYTE Plant attached to another plant, not growing parasitically upon it but merely using it for support; e.g. various lichens, mosses, algae, ivy, and orchids, all commonly epiphytes of trees.
EROSION The transportation of weathered debris at the earth’s surface.
ESTUARINE DEPOSITION Sediment deposited in estuaries.
ESTUARINE WETLAND (1) Subtidal a. Estuarine waters: permanent waters of estuaries and estuarine systems of deltas. (2) Intertidal a. Intertidal mud, sand or salt flats, with limited vegetation. b. Intertidal marshes, including salt meadows, tidal brackish and freshwater marshes. c. Intertidal forested wetlands (rare or non-existent in the Mediterranean).
ESTUARY The lowest section of a river where mixing of salt and fresh water occurs under the influence of the tide. See tides.
EURYHALINE Able to tolerate a wide variation of  salinity (osmotic pressure) of environment. Compare stenohaline.
EUTROPHIC (Of lakes) rich in nutrients; highly productive in terms of organic matter produced. In some lakes this enrichment becomes harmful, and light penetration and oxygen production are insufficient to maintain productivity. Compare oligotrophic.
EUTROPHICATION Usually rapid increase in the nutrient status of a body of water, both natural and occuring as a by-product of human activity. May be caused by run-off of artificial fertilizers from agricultural land, or by input of sewage or animal waste. May occur when large flocks of birds collect around watering holes. The biological changes which occur in lakes as a result of eutrophication can be separated into those which are the direct result of raised nutrient influx, such as the stimulation of algal growth (algal bloom), and  those which are the indirect effect, such as changes in the fish community, as a result of reduced oxygen concentration. Artificial eutrophication can be slowed or even reversed by removal of nutrients at source, but may require costly sewage treatment plants. See algal bloom.
EVAPORATION Loss of water from a free water surface or from the soil surface by vaporization.
EVAPORATION PAN An instrument for measuring open water evaporation rates. Consists of a tank of water open to the atmosphere and an associated rain gauge with evaporation being the net change in water level in the tank over the time period. The tank may be sunk into the soil, on the surface or raised on staging above the ground.
EVAPOTRANSPIRATION The prevailing and real rate of evapotranspiration from an area of land. Actual evapotranspiration will equal the potential evapotranspiration rate when the soil is at or near field capacity but will fall below evapotranspiration rate when soil moisture deficits develop. See potential evapotranspiration, penman method, thornwaite method.
EVAPOTRANSPIRATION Combined loss of water from the earth surface by evaporation from open water and soil surfaces and transpiration from the leaves of plants. See potential evapotranspiration, actual evapotranspiration, penman method, thornthwaite method.
EXCLOSURE Fenced area from which grazing animals are excluded for the study of the ecosystem without grazing pressure.
EXOREIC Drainage basin with an outlet to coastal water.
EXOTIC SPECIES. A species introduced to a region or environment where it is not indigenous.
FACULTATIVE WETLAND PLANT SPECIES The plant species which is usually found in places scientifically defined as wetlands (67-99% frequency) while  sometimes it is also found in strictly terrestrial areas. Compare obligate wetland species.
FAN Fan-shaped deposit. An alluvial fan is formed when the flow velocity of streams is suddenly decreased, for example at the mouth of ravines or at the foot of mountains.
FAO Food and Agricultural Organisation of the United Nations. Based in Rome, Italy.
FEN Peatland covered by water, especially in the upper regions of old estuaries and around lakes, that can be drained only artificially.
FERTILIZER Refers most commonly to a chemical substance synthesized by man and applied to the soil in order to maintain or increase soil productivity. The term is sometimes used for material of plant or animal origin (e.g. manure, harvest remnants) or the final product of a sewage treatment plant (deactivated sludge). See eutrophication.
FIELD CAPACITY The maximum amount of water that a soil can hold against the pull of gravity. An addition of water to a soil at field capacity initiates drainage or percolation to groundwater.
FLAGELLATES Microscopic organisms (bacteria or algae) that use whip-like filaments, called flagellae, to locomote.
FLASH FLOOD A sudden local flood of short duration and great volume; usually caused by heavy rainfall in the immediate vicinity.
FLAT See floodplain.
FLOATING MARSH FLOOD Inundation that occurs when water overflows from a river or channel or accumulates because of poor drainage over low-lying areas.
FLOOD BASIN A natural or artificial basin, also a wetland, designated in land use and catchment planning as an area that receives flood water.
FLOOD CONTROL An engineering approach which uses leeves, walls, reservoirs, floodways, and other structures to prevent water overflow and consequent flooding. Such techniques have become both unpopular and uneconomic in recent years and so the modern approach uses source control, zonation of the floodplain, flood basins and wetlands, flood warnings and in the USA, the removal of settlements from the floodplain.
FLOOD FENCING Fencing anchored in such a way that it is either able to withstand the force of floodwaters or hinge over when the water rises significantly.
FLOOD FREQUENCY CURVE The relationship between discharge and flood recurrence interval for a point on a river system. See gumbel distribution, pearson type iii distribution.
FLOOD HYDROGRAPH The rise and subsequent recession of flow in a river as a flood discharge passes downstream. See baseflow, gauging station.
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  nutrient spiraling from upstream to downstream in the river channel; the bulk of the animal biomass in such a system is thought to be derived from production in the floodplain, not from downstream transport of organic matter produced elsewhere in the basin.
FLOOD STORAGE Space used or available for floods. This is one of the major functions of wetlands since they provide a valuable environmental service to human societies that live downstream.
FLOODGATE A sluice that is used to control the flow of water, for instance in a dam when water needs to be released to prevent the reservoir spilling or in a levee when it is necessary to allow controlled flooding of part of the floodplain.
FLOODPLAIN Areas that are periodically inundated (usually annually) either by the lateral overflow of rivers or lakes or by direct precipitation or ground water; the resulting environment causes the biota to respond by morphological, anatomical, physiological, phenological, and/or ethological adaptations, and to produce characteristic community structures. Water will flow down a valley across a floodplain and also be stored in the deposits comprising the floodplain.Overall the floodplain serves to attenuate floodflows in the river and to sustain baseflows after the flood. Typically floodplains appear flat but the micro-relief can lead to great differences in period of immersion. In fact, a floodplain consists of a complex pattern of lagoons, pools, ox-bow lakes, seasonal marshes, etc. According to climate and depth, these different waterbodies are seasonal or more or less permanent. Three main types may be considered:(1) Fringing floodplains:  relatively narrow strips of floodable land lying between the river valley walls e.g. middle Rhone valley.(2) Internal deltas: occur where river systems spread laterally  over very large alluvial plains. The main stream is usually divided into anabranches which join the main channel below the deltaic area. e.g. Oued Djoumine at Ichkeul in Tunisia.(3) Coastal deltaic floodplains: develop where the main channel breaks down into smaller branches and produces the classic fan-shaped delta. These are usually strongly influenced by the sea. e.g. the Rivers Nile (Egypt), Goksu (Turkey), Ebro (Spain).
FLOW CONTROL The management of river flows through dams, barrages, sluices and in some cases groundwater pumping.
FLUME Rectangular or U shaped structure, generally made of concrete, installed in rivers for measuring discharge. See gauging station, rating curve.
FLUVIATILE Influenced or characterized by rivers; or found in or near rivers.
FLYWAY A major route used by migratory birds.
FOOD CHAIN Chain of organisms, existing in any natural community, through which energy is transferred. Each link in the chain feeds on and obtains energy from the one preceding it and in turn is eaten by and provides energy for the one following it. The number of links is usually three or four. At the beginning of the chain are green plants, and organisms whose food is obtained from green plants through the same number of links are described as belonging to the same trophic or energy level. Thus green plants occupy level one (T1), the producer level. All other levels are consumer levels. T2, herbivores, are primary consumers, T3 and T4, smaller and larger carnivores, respectively, are secondary consumers. At each trophic level much of the energy obtained is lost by respiration and thus fewer organisms can be supported at the succeeding one. Bacteria, fungi and some protozoa are consumers that operate in decomposition at all levels. All the food-chains in a community make up the food-cycle or food-web
FOR WETLANDS The time that it takes for the water content of a wetland to be renewed. Normally calculated by dividing the volume of water stored in the wetland by the annual discharge out of the wetland.
FORAMINIFERA Microscopic benthic organisms living in saline conditions.
FOSSIL WATER Water that has been in an aquifer since prehistoric times and is not a part of the hydrological cycle i.e. it is not recharged by rain water.
FRESHWATER MARSH Marsh containing water with no significant amount of salts, such as water derived from rainfall, rivers, freshwater lakes.
FRESHWATER WETLAND See riverine wetland, lacustrine wetland and palustrine wetland.
FROUDE NUMBER The dimensionless ratio of inertial to gravity forces in flowing water: Fr = v / (Ö g d)  where:Fr = v / (Φ g d)  where:v is the velocityg is the gravitational accelerationd is depth.When Fr < 1, flow is subcritical or tranquil, when Fr = 1 flow is critical and when Fr > 1 flow is super critical.
FYKE NET A fish trap consisting of a net suspended over a series of hoops, laid horizontally in the water.
GARAET An Arabic term used in Tunisia for a freshwater wetland environment.
GAUGING STATION An installation (e.g, weir or flume) in a river designed to measure the discharge. Traditionally the river level is measured and transformed to discharge through a stage discharge relationship. See flume, rating curve.
GHYBEN-HERZBERG  
GLACIER A mass of land ice, formed by the further recrystallization of firn, flowing slowly (at present or in the past) from an accumulation area to an area of ablation.
GRAVEL A loose or unconsolidated deposit of rounded pebbles, often within a sandy matrix.
GRAVEL PIT A large opening in the ground from which gravel is extracted.
GREEN ALGAE The common name for members of the plant division Chlorophyta.
GREENHOUSE EFFECT The natural accumulation in the atmosphere of gases, such as carbon dioxide, that trap heat, due to their property that allows the inflow of short wave solar radiation and prevents to a certain extent the outflow of long wave thermal radiation from the earth. The release of industrial chemicals into the atmosphere and the discharge of additional carbon dioxide by the burning of fossil fuels is believed to have enhanced the greenhouse effect.
GROUNDWATER All subsurface water, especially that in the zone of saturation.
GROUNDWATER DISCHARGE The flow of water from the zone of saturation to the surface of the earth as springs, seeps and resurgences within river beds. Groundwater can also discharge indirectly through evaporation and evapotranspiration.
GROUNDWATER RECHARGE The addition of water to the zone  of saturation. This can occur by infiltration of rainwater through a soil at field capacity, direct infiltration through river beds and banks, and infiltration through the substrate in certain wetlands. Water must then percolate through the unsaurated zone of aeration before it reaches the watertable.
GUELTA North African term meaning desert river-bed pools. These are found in mountainous areas, situated either at the foot of former waterfalls or at a site where the river bed was earlier deepened. May be permanent, temporary or spring fed. The term may also be applied to Saharan “kettle holes”. Variants on this term are: glat (plural), gueltet, glertat.
GUMBEL EXTREME VALUE DISTRIBUTION Commonly used flood frequency distribution developed in the USA.
HABITAT Place or environment in which specified organisms live, e.g. sea shore.  Describes the whole complex of flora, fauna, soil and climatic factors to which the organism is adapted.
HABITAT (NATURAL) Definition in the Habitat Directive of the EU: terrestrial or aquatic areas distinguished by geographic, abiotic and biotic features, either entirely natural or semi-natural.
HABITAT DIRECTIVE A Directive of the Council of Ministers of the European Unon (Council Directive 92/43/EEC) relating to the conservation of habitats of Europe-wide importance.
HABITAT OF A SPECIES Definition in the Habitat Directive of the EU: an environment defined by specific biotic and abiotic factors, in which the species lives at any stage of its biological cycle (Habitat Directive 92/43/CEE).
HALOPHYTE Plants that grow in very salty soil typical of shores of tidal river estauries, saltmarshes, or alkali desert flats.
HATCHERY An artificial site where fish hatch eggs.
HEAVY METALS Metals of high specific gravity. The following are all heavy metals: antimony, arsenic, asbestos, beryllium, lead, zinc, cobalt, cadmium, nickel, chromium, mercury, copper, selenium, silver, thallium.
HJάLSTROM CURVE A curve presented by the Swede, Hjόlstrom, to define the threshold flow velocities required to initiate motion of grains of different sizes on a stream bed. See bed load, suspended load.
HUMMOCK A hillock; knoll; a ridge or mound of ice in an ice field.
HUMMOCKY MORAINE Glacial deposits with rounded conical hills and depressions formed under stagnating ice-sheets.
HYDRAULIC CONDUCTIVITY This is K in Darcy’s equation. It reflects the physical properties of both the fluid and the material through which it flows reflecting the ease with which the liquid flows and the ease with which a porous medium permits it to pass through. See permeability, darcy’s law.
HYDRAULIC GRADIENT The slope of water level in a series of piezometers.
HYDRAULIC HEAD The sum of the elevation head and the pressure head in an aquifer. Measured as height above a suitable datum.
HYDRIC OR HYDROMORPHIC SOILS Inadequately drained soil whose profile down to a depth of 45cm or less is saturated with water for a considerable part of the growth period of natural vegetation and which is dominated by reduction phenomena. These soils belong to the Aquic subclasses of the US Soil Taxonomy System
HYDROGEOLOGY The science dealing with the occurrence of groundwater, and its utilization, pollution and management.
HYDROGEOMORPHIC UNIT A small area of land with largely uniform geomorphological and hydrological conditions. The concept is used in the functional analysis of wetlands when it is necessary to identify such units within the landscape.
HYDROGRAPH Discharge at a point in a river recorded over time. See gauging station, rating curve.
HYDROLOGICAL CYCLE The complete cycle through which water passes, from the oceans, through the atmosphere, to the land, and back to the ocean. Also known as water cycle.
HYDROLOGY The study of the cycle of water movement on, over and through the surface of the earth.
HYDROMETRIC NETWORK A series of instruments in an area, usually a catchment, dedicated to recording the stores and transfers of water in the hydrological cycle.
HYDROPHILOUS Inhabiting moist places.
HYDROPHYTE A plant that grows in a moist habitat. A plant requiring large amounts of water for growth. Also known as hygrophyte.
HYDROSERE Collective term for all stages in a succession beginning in water or wet habitats. It refers to a serial progression of plant communities and soils resulting from basin infilling or drying to a terrestrial community.
HYDROSPHERE Part of the earth composed of water i.e. oceans, seas, ice caps, lakes, rivers and underground waters.
HYPERSALINE Containing high concentrations of salt. Hypersaline lakes are saltier than the sea.
HYPOLIMNION In a thermally stratified lake, the layer of water below the thermocline and extending to the bottom of the lake. Water temperature in the hypolimnion is virtually uniform.
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.
ICBP International Council for Bird Preservation based in Cambridge. Superseded by Birdlife International. See birdlife international, rsbp.
ICE SHEET A thick glacier, more than 50,000 square kilometers in area, forming a cover of ice and snow that is continuous over a land surface and moving outward in all directions. Also known as ice mantle or ice cap.
ICHTHYOLOGY A branch of vertebrate zoology that deals with the study of fish.
INFILTRATION The movement of water into the surface of a soil under the influence of gravity and soil suction forces. Infiltration normally follows an exponentially declining rate because as soil suction forces are depleted by the wetting of the soil, infiltration approaches a constant rate dependent only upon gravity drainage into the soil. See percolation.
INLAND WATER An interior body of water not bordered by the sea.
INLET A short, narrow waterway connecting a bay or lagoon with the sea.
INTENSITY-FREQUENCY-DURATION RELATIONSHIPS (RAINFALL) A series of relationships derived from long periods of data from autographic rain gauges that quantify the relationships between rainfall intensity, the duration of that rainfall and the frequency with which is it is likely to recur.
INTER-BASIN TRANSFERS OF WATER The transfer of water by human agency from one river basin to another. Usually involving pipes, canals and pumps. 
INTERCEPTION The trapping of precipitation on the leaves of vegetation. Normally this is rapidly evaporated back to the atmosphere (even as the rainstorm continues). See evapotranspiration.
INTERNATIONAL The global organisation (created from the fusion of IWRB, Asian Wetland Bureau and Wetlands for the Americas) which is dedicated to “sustain and restore wetlands, their resources and biodiversity for future \activities, worldwide”. See iwrb.
INTERTIDAL The area between the high and low water marks which is exposed at low tide
INTERTIDAL MARSH Marsh which is covered at high tide but exposed at low tide.
INTERTIDAL ZONE The part of the littoral zone above low-tide mark and below the high-tide mark.
INVENTORY OF WETLANDS Systematic collection, treatment and presentation of data on the number of wetlands of a geographical region and on the parameters of each wetland such as location, type, area, abiotic and biotic characteristics, functions, values, uses, adverse effects induced by human activities, ownership, legal status etc.
ISOHYTES Lines of equal rainfall amount. See rain gauge.
IUCN The World Conservation Union (formerly the International Union for the Conservation of Nature and Natural Resources). Based in Gland, Switzerland.
IWRB The International Waterfowl and Wetlands Research Bureau (now part of Wetlands International).
JUVENILE WATER Water that originates from the centre of the Earth.
KARST Limestone areas with topographically distinct scenery and a distinct hydrology brought about by the permeability of the rocks, the limited amount of surface water, the occurrence of underground caverns, swallow holes for rivers and strong resurgences.
KARSTIC Typical of karst area. See Karst.
KETTLE A bowl-shaped depression with steep sides in glacial drift deposits that is formed by the melting of glacier ice left behind by the retreating glacier and buried in the drift. Also known as kettle basin; kettle hole.
LACUSTRINE (1) Of, relating to, or formed in lakes (~waters) (~deposits). (2) Growing or living in lakes (~flora) (~fish).
LACUSTRINE WETLAND (1) Permanent a. Permanent freshwater lakes (>8ha), including shores subject to seasonal or irregular inundation. b. Permanent freshwater ponds (<8ha). (2) Seasonal a. Seasonal freshwater lakes (>8ha) including floodplain lakes.
LAG TIME The delay between rainfall and runoff. There are a number of definitions for the calculation of lag time. A common definition is the time delay between 50% of the rainfall occurring to 50% of the quickflow occurring. See flood hydrograph.
LAGOON A small body of normally shallow water isolated from related and normally much larger water bodies by some form of barrier. In the case of coastal lagoons the link to the open sea can be cut by sandbars or coral reefs. Lagoons can be artificial with concrete walls or embankments forming the barriers. More transitory open waters than true lakes.
LAGOONAL DEPOSITION The accumulation of sediment in a shallow arm of the sea, which is cut off from the outer ocean by a barrier which prevents free communication. The strata formed under such conditions constitute a lagoon phase.
LAGOONAL WETLAND Brackish to salty lagoons with one or more relatively narrow connections to the sea.
LAKE An inland body of water, small to moderately large, with its surface water exposed to the atmosphere and which may occasionally be saline.
LAND DRAINAGE The improvement of drainage conditions on a piece of land usually by a combination of means including: embankments to exclude river or sea water, dredging river channels, cutting deep arterial drainage ditches and shallower secondary ditches to feed into them, installation of tile drains and mole drains, planting of certain crops, such as Eucalyptus to increase evapotranspiration and the commissioning of pumps to raise water out of the area at critical locations in the drainage system. This is essentially a process of wetland destruction.
LAND RECLAMATION Gaining land in a wet area, such as a marsh or by the sea, by planting maritime plants to encourage silt deposition, by dumping dredged materials in the area or by the creation of embankments and polders. Activities such as drainage, irrigation, leaching of salts, land grading, land levelling etc. which are performed in order to change the water regime and the soil conditions of an area in such a way as to make it suitable for cultivation or to increase crop yields or both.
LANDSCAPE ECOLOGY An emerging specialization that deals with the patterns and processes of biological systems in spatially and temporally heterogeneous environments.
LEACHING The process whereby salts are washed from soil e.g. marine salts may be leached into drainage ditches after a coastal flood,  nutrients may be washed down through the soil and into the groundwater etc. See percolation, podzol.
LENTIC Of, relating to, or living in still waters (as lakes, ponds, swamps). Compare lotic.
LEVEE Raised bank, either natural or artificial, along a river or riverine floodplain.
LIMNETIC ZONE In ponds and lakes, the open water zone to the depth of effective light penetration.
LIMNOLOGY The study of continental aquatic ecosystems.
LIMNOPHILOUS Organisms that living in marshes, especially fresh water marshes.
LIMNOVOROUS Mud-eating e.g. certain aquatic invertebrates that swallow mud to extract nutrients from it.
LITTORAL Inhabiting the bottom of sea or lake near shore, roughly within a depth to which light and wave action reach.
LITTORAL ZONE The area extending from the high water mark into the water as far as the limit of the zone where photosynthesis exceeds respiration.
LONGSHORE DRIFT The transport of beach material along the coast by oblique wave action.
LOTIC Of, relating to, or living in actively moving water (as in stream currents or waves). Compare lentic.
LYSIMETER A device for measuring the percolation of water through soils and determining the soluble constituents removed in the  drainage.
MACROPHYTE Literally “big plant”, used to describe waterplants other than microscopic algae.
MACROPORE FLOW Relatively rapid flow through an aquifer or soil because of the existence of large fissures, cracks or planes within the medium. See aquifer, darcy’law, hydraulic conductivity.
MANNING’S n The roughness coefficient, n, in the Manning equation to determine flow velocity in an open channel: v = ( R2/3 s1/2 ) / n  where, v is velocity of flow, R is hydraulic radius which is mean depth in wide channel and cross sectional area divided by wetted perimeter in other channels, and s which is the slope of the water surface.
MARICULTURE The cultivation of marine organisms, plant and animal, for human consumption.
MARIGOT Periodically inundated river valley which subsequently develops temporary standing pools and dries out slowly.
MARINE WETLAND (1) Subtidal wetlands a. Permanent unvegetated shallow waters less than 6m deep at low tide, including sea bays and straits. b. Subtidal aquatic vegetation, including sea grasses and tropical marine meadows. c. Coral reefs. (2) Intertidal wetlands a. Rocky marine shores, including cliffs and rocky shores. b. Shores of mobile stones and shingle. c. Intertidal unvegetated mud, sand or saltflats. d. Intertidal vegetated sediments, including mangroves, or sheltered coasts.
MARSH A transitional land-water area, covered at least part of the time by surface water or saturated by groundwater at, or near the surface. Characterized by aquatic and glass-like vegetation, usually without peat accumulation.
MAXIMUM ADMISSABLE CONCENTRATION (MAC) Concept introduced in the EU Drinking Water Directive giving the maximum allowable concentration of any impurity in drinking water.
MEAN ANNUAL FLOOD The average of the maximum annual flood peak discharges in a series. It is equivalent to the flood with a recurrence interval of 2.33 years and it approximates the bankfull discharge in natural alluvial channels. See flood frequency curve, gumbel distribution, pearson type III distribution.
MEANDERING Winding or bending in river beds; usually erosion occurs on the outer bend, while sediment is  deposited on the inner bend. As a result, the meander may be cut off, creating an oxbow lake and causing the river to change its channel.
MEDITERRANEAN ACTION PLAN A plan agreed at UNEP’s first Mediterranean intergovernmental conference in Barcelona in 1975. It called on Mediterranean Governments to draw up and adopt a series of legally binding agreements on environmental concerns.
MEDWET Concerted action for stopping the loss and degradation of wetlands around the Mediterranean basin. Conceived in February 1991 at an international conference in Grado, Italy. Initially implemented in 1992 as an EU initiative with four Mediterranean member states and a number of NGOs. This first phase aimed to analyze the wetland situation around the Mediterranean and to prepare and test methods and tools for the wise use and conservation of wetlands.
MESOTROPHIC See trophic status.
MESOTROPHIC LAKE A lake that is intermediate in nutrient status, having neither a notably high nor notably low total productivity. Compare oligotrophic,  eutrophic.
METALIMNION In a thermally stratified lake, a layer of water between the epilimnion and hypolimnion that is characterized by a sharp change in temperature or density with depth.
METAP Mediterranean Environmental Technical Assistance Programme (of the World Bank).
METEORIC WATER Water in the land phase of the hydrological cycle originating from rainfall
METHANE CH4. A colourless, odourless gas. One of the gases produced by microbiological action, often in large volumes in extremely reduced soils and sediments. Often known as “marsh gas”.
METHANOGENESIS The generation of methane from decomposition.
MICROTOPOGRAPHY The small variations in topography, often measuring only a centimetre or two, important for determining the precise ecological niche for plants and invertebrates in wetlands.
MINERALIZATION The biological transformation of organically combined nitrogen to ammonium nitrogen during organic matter degradation. This can occur under anaerobic and aerobic conditions. See denitrification, nitrogen fixation.
MIRE Wet spongy earth, as of a marsh, swamp, or bog; earth that accumulates peat; a collective term which embraces both bog (moss, in British literature) and fen, differentiated according to rather subtle floristic variations and often containing both communities together. In some cases bogs are genetically related to lakes as a possible final stage of lake development.
MITIGATING ACTIVITY Activity which has the potential to remove or reduce negative impacts on wetland benefits. Mitigation has a much broader meaning than is sometimes assigned to it. It can range from avoiding potential impacts by re-siting the project at the pre-feasibility stage to using technical solutions such as watertight bunds or dikes to prevent drainage of adjacent areas during the construction phase. Includes social and economic measures such as compensation and market intervention.
MONITORING OF WETLANDS The continuous or periodic recording of natural abiotic and biotic parameters of the wetland, and of human induced changes and interferences (e.g. pollutants). A monitoring programme may also include socio-economic parameters.
MONITORING PROCEDURE Method used by the Ramsar Bureau by which solutions are sought to problems concerning internationally important wetland areas.
MONTMORILLONITE A type of clay which is highly reactive and adsorbs many other compounds.
MONTREUX RECORD List of Ramsar sites where changes in ecological character have occurred, are occurring, or are likely to occur.
MOOR A tract of unenclosed ground, usually having peaty soil covered with heather, coarse grass, bracken and moss.
MORASS A tract of swampy low-lying land.
MUD Unindurated mixture of clay and silt with water. It is slimy with a consistency varying from that of a semifluid to that of a soft and plastic sediment.
MUD FLAT A relatively level, muddy coastal strip along a shore or around an island; may be alternately covered and uncovered by the tide or may be covered by shallow water.
MUD PUMPING The removal of liquid and semi-liquid sediments from the bed of lakes and wetlands by suction pumping. Normally undertaken during the restoration of ecosystems which require removal of nutrients that have accumulated and/or the creation of additional active water storage in the system.
NATIVE FISH REINTRODUCTION Phase of a waterbody restoration effort during which fish are reintroduced into the physically restored waterbody system to reestablish the original fish community.
NEAP TIDE Tidal range of a lesser magnitude than spring tides. Neap tides are generated when solar tides tend to cancel the lunar tides.
NEUTRON PROBE An instrument for determining soil moisture content. The instrument consists of a source of fast neutrons and a slow neutron detector and counter unit. The method is based on the principle that fast neutrons emitted into the soil collide with the nuclei of atoms in the soil (notably hydrogen nuclei in soil water) and as a result lose energy and slow down. See soil moisture characteristic curve.
NICHE A particular role (or set of relationships) of organisms in an ecosystem, which may be filled by different species in different geographical  areas. 
NITRATE A nutrient (NO3) created by mineralization of the substrate, decomposition of organic matter or fixation from the atmosphere.
NITRATE DIRECTIVE EU Directive 91/676/EEC on the protection of waters against pollution caused by nitrates from agricultural sources.
NITRATE NITROGEN That portion of nitrate which consists of nitrogen.
NITROGEN FIXATION Incorporation of atmospheric nitrogen (N2) to form nitrogenous organic compounds. This process can be carried out only by certain soil-inhabiting bacteria and certain blue-green algae in the presence of the enzyme nitrogenase. Some N-fixing bacteria live symbiotically with leguminous plants (peas, beans, clover etc.) in nodules on roots, others live independently in soil. By their activity soil is enriched in nitrogen, a fact of considerable practical importance. See denitrification, nitrogen mineralization.
NITROPHILOUS Living in nitrogenous soils.
NON-POINT POLLUTION Pollution which originates from diffuse sources such as agricultural land, urban areas etc. See point source pollution.
NUTRIENT CYCLING The movement of nutrients, notable nitrogen and phosphorus in various forms between the various stores within the wetland ecosystem. Leaf fall, decomposition, sedimentation, plant uptake, grazing, defecation, and denitrification are some of the processes involved.
NUTRIENT LOADING The amount of nutrients available over a period of time.
NUTRIENT SINK Ecosystem store which accumulates nutrients over long or short-term periods. In wetlands, sedimentary deposists, peat and the root tissue of dormant plants are examples of nutrient sinks.
NYMPH Larval stage of exopterygote insect. Resembles adult (e.g. in mouthparts, compound eyes), but is sexually immature. Wings absent or undeveloped.
OASIS A small water body and its surrounding which is fed by perennial springs from groundwater and therefore holds permanent water.
OBLIGATE WETLAND PLANT SPECIES Plant species which is almost always found in places scientifically defined as wetlands. The frequency of presence in wetlands of such a species is 99% or higher. Compare facultative wetland species.
OECD Organisation for Economic Cooperation and Development. Based in Paris.
OLIGOTROPHIC See trophic status.
OLIGOTROPHIC LAKE Lake poorly provided with the basic nutrients required for plant and animal production.
OMBROGENOUS Of plants, able to flourish in wet conditions.
OMBROGENOUS MIRE Peat bog completely dependent upon atmospheric inputs for its water and solute supply
OMBROPHILOUS Of plants, tolerant of wet conditions.
OMBROPHYTE A plant inhabiting rainy places.
OMBROTROPHIC Literally “fed by rain”. The term applies to areas such as bogs that are entirely dependent on rain for their nutrient supply.
OPEN WATER Water less than one tenth of which is covered with floating ice. Water not covered by vegetation.
ORGANIC SOIL Any soil or soil horizon consisting chiefly or containing at least 30% of organic matter e.g.peat soils and muck soils.
ORGANOCHLORINE INSECTICIDES Highly active insecticides which, until recently, have been very widely used. They find their way into the bodies of animals and insects and are stored, principally in the fat. The application of organochlorine insecticides is now widely restricted.
ORNITHOLOGY The scientific study of birds.
OROGRAPHIC PRECIPITATION Precipitation (rain or snow) caused by the forced ascent of air over high ground. In general, precipitation increases with altitude. See convective rainfall, cyclonic rainfall.
OVERLAND FLOW A visible flow of water over the ground surface. A number of hillslope flow processes may be involved: excess rainfall intensity over infiltration capacity; excess rainfall intensity over soil storage capacity and the seepage throughflow particularly in conotur cavities.
OXBOW LAKE OXIDATION Lakes formed in a former riverbed, when a bend in a meandering river is cut off from the main stream.
OXYGENATION BASIN A process which causes a chemical change by reacting with oxygen. A substance undergoes oxidation if it: (1) Gains oxygen. (2) Loses hydrogen. (3) Loses electrons. A basin where oxygenation occurs. Organic waste is broken down by bacterial action. Often oxygen is bubbled though the basin to speed the process.
PALUDIFICATION This occurs when a blanket bog exceeds the basin boundaries and encroaches on formerly dry land. This can be caused by climatic change, geomorphological change, dams created by wildlife, forest clearance and by the natural advancement of a peatland.
PALUSTRINE Living or occurring on or in marshes, swamps or bogs.
PALUSTRINE WETLAND (1) Emergent a. Permanent freshwater marshes and swamps on inorganic soils with emergent vegetation that has its base below the water table for at least most of the growing season. b. Permanent peat-forming freshwater swamps, including tropical upland valley swamps dominated by Papyrus and Typha. c. Seasonal freshwater marshes on inorganic soil, including sloughs, potholes, seasonally flooded meadows and sedge marshes. d. Peatlands, including acidophilous, ombrogenous, or soligenous mires covered by moss, herbs, dwarf shrub vegetation or different types of ferns. e. Alpine and polar wetlands, including seasonally flooded meadows moistened by temporary waters from snowmelt f. Freshwater springs and oases with surrounding vegetation. g. Volcanic fumaroles continually moistened by emerging and condensing water vapour. (2) Forested a. Shrub swamps, including shrub-dominated freshwater marsh on inorganic soils. b. Freshwater swamp forest, including seasonally flooded forest on inorganic soils. c. Forested peatlands, including peat swamp forest.
PAN Depression containing water, mud or mineral salts. Endorheic and not associated with river drainage systems. A shallow oval depression without outlet, but with an impervious substratum. Floods during local rains and dries out seasonally.
PARIS PROTOCOL An amendment to the text of the Ramsar Convention providing an amendment procedure and additional language versions of the Convention.
PARTIAL CONTRIBUTION AREA The area around stream heads which provides the bulk of runoff during floods. The area is variable in size, expanding when substatntial rainfall has occurred and contracting in periods of drought. It is also known as dynamic source area.
PEARSON TYPE III DISTRIBUTION A statistical frequency distribution often used to characterize the variation in flood magnitudes. See gumbel distribution, flood frequency curve.
PEAT A dark-brown or black residuum produced by the partial decomposition and disintegration of mosses, sedges, trees, and other plants that grow in marshes and other wet places.
PEAT BOG Bog formed through the growth of hydrophytes which accumulate in large amounts. Eventually peat forms after partial decay, with up to 50% carbon. Topogenic peat bogs occur in swampy valleys. These depressions may be filled by vegetative accumulations, in which case raised peat bogs or ombrogenic mires may form. These wetlands are colonized by mosses of the genus Sphagnum e.g Dar Fatma in the Atlas mountains of Northern Tunisia.
PEAT SOIL Soil containing more than 50% of non decomposed or slightly decomposed organic matter.
PEATLAND See peat bog.
PENMAN METHOD OF CALCULATING POTENTIAL EVAPOTRANSPIRATION This method, proposed first in 1948, combines the energy balance method with an aerodynamic function. It has become the most widely used method for calculating potential evapotranspiration worldwide. Penman’s formula takes the form:             Ù     Ù   PET = (H + EA) / (+ 1)  where: PET is the potential evapotranspiration (mm/day); H is the energy balance (Joules/cm2/day); EA is the aerodynamic term (mm of water/day), Ù is the slope of the saturation vapour pressure curve at mean air temperature (mb/oC) and t is the psychometric constant (0.67 mb/oC). See thornwaite method.
PERCHED WATERTABLE The upper water surface of underground perched groundwater. This is an isolated body of unconfined groundwater suspended by a discontinuous impervious layer above the main saturated zone and separated from it by unsaturated rock. See aquifer, groundwater.
PERCOLATION The process of essentially vertical water movement downwards through the soil and rock in the unsaturated (or vadose) zone. See infiltration.
PERIPHYTON Plants that grow attached to a solid, non-living substrate, such as rock or plastic.
PERMANGANATE VALUE (PV) Organic content of waste obtained by measuring the amount of oxygen required for its stabilization. See also biochemical oxygen its stabilization. demand [bod] and chemical oxygen demand [cod]). The magnitude of the results obtained is usually PV < BOD < COD.
PERMEABILITY A measure of the ability of rocks or fluids to transmit water. Also called perviousness. See hydraulic conductivity.
PERMEAMETER An instrument for measuring the saturated hydraulic conductivity or K of soils or other sediments. See darcy’s law, hydraulic conductivity.
PERVIOUSNESS See permeability.
pF The log10 of  the negative head of water (in cm) indicating the strength of soil moisture suction at a site. See soil moisture suction.
pH A scale for measuring the acidity or alkalinity of a solution. The lower the value, the more acid the solution. A neutral solution has a pH of 7, an alkaline solution has a pH above 7, an acid solution has a pH value below 7. The ocean has a pH of about 8, an alkaline lake might be about pH 10, an acid bog pH 3.5.
PHOSPHORUS One of the most important chemicals in ecosytems. It is the major limiting nutrient in bogs, freshwater marshes and swamps. Phosphorus is found as soluble and insoluble complexes in both organic and inorganic forms in wetland soils. It occurs in the sedimentary cycle. The principle inorganic form is orthophosphate which encompasses a variety of ions and can be measured approximately as soluble reactive phosphorus. Many forms of phosphorus are unavailable  biologically. This unavailability is fostered by aerobic conditions favouring precipitation of insoluble phosphates of ferric iron, calcium and aluminium; adsorption of phosphorus onto clay particles, organic peat and various hydroxides; and the binding of phosphorus into organic matter in bacteria, algae and vascular plants.
PHREATIC DIVIDE An underground watershed which demarcates the limit from which groundwater moves towards neighbouring rivers.
PHREATOPHYTES All small, living organisms, either animals (zooplankton) or plants (phytoplankton) that drift with the surrounding water, usually vertically.
PHYTOPLANKTON Planktonic plant life.
PIEZOMETER A shallow lined hole in the wetland substrate allowing the measurement of the piezometric surface in a shallow aquifer. The tip of the piezometer is perforated, set in sand and sealed above with bentonite, allowing water to enter the piezometer only at that level. See piezometer nests, aquifer, artesian, confined aquifer.
PIEZOMETRIC SURFACE The theoretical pressure surface to which water would rise from a confined aquifer because of the hydrostatic pressure induced by an overlying impermeable aquiclude.
PLANKTON Small freshwater and marine organisms, a substantial number of which are microscopic.
PODZOL A soil which is characterized by an upper horizon from which aluminium and iron oxides and hydroxides have been leached and a lower horizon where these have accumulated.
POINT BAR An embanked area of land, often reclaimed from the sea or inland lake, where water levels are maintained below their natural levels for the benefit of human activity. Polders may be drained by gravity through sluices or by pumping. Also known as meander bar.
POINT-SOURCE POLLUTION Pollution which emanates from a fixed point such as an efficient outfall pipe, a chimney, a waste dump. See non-point pollution.
POLDER Land reclaimed from the sea or other body of water by the construction of an embankment to restrain the water.
POLLARDING The periodic reduction of trees back to the main trunk so that a mass of new growth exudes from the top. This management technique is frequently applied to willows in wetland areas.
POLYCHAETE Member of the class Polychaeta that comprises chiefly marine annelid worms.
POND This term generally refer to small, shallow waterbodies. They are often defined as lakes of less than 10 ha equivalent to small lakes and can be permanent or temporary.
POOL Pools are generally shallow and small-sized waterbodies. Their origin may either be rainfall (rain pools) or river flooding. Pools are seasonal and dry out in the dry season e.g within the Makhada Marsh between Annaba and El Kala in North Eastern Algeria. In Zaire, the term pool is used to describe expansions of a river system (e.g. Pool Malebo =  Stanley Pool).
POOLS (IN RIVERS) In natural alluvial rivers there are normally sequences of pools and riffles. The pools are zones of deeper water where current velocity is reduced so that silt and other loose materials tend to settle to the bottom, providing conditions unfavourable for surface benthos, but favouring burrowing forms and in some cases plankton. Riffles are the intervening banks of courser sediment where the water is shallower, faster flowing and well oxygenated by the turbulence induced by the riffle.
POROUS ROCK Rock able to absorb water. Note however that a porous rock may not be permeable i.e. allow water to move through it. Clay, for instance, may have a porosity of 60% but it is impermeable.
POTENTIAL EVAPOTRANSPIRATION The rate of evapotranspiration from a short green crop, actively growing, completely shading the ground and never short of water. This specific definition by Penman is often taken to mean the rate of evapotranspiration from an area of land where the soil is at or near field capacity. See actual evapotranspiration.
POTHOLE This is a term that has various applications:(1) A bowl-shaped, cylindrical, or circular hole formed by the grinding action of a stone in the rocky bed of a river or stream. Also known as churn hole; colk; eddy mill; erosion hollow; kettle; pot.(2) A small depression with steep sides in a coastal marsh; contains water at or below low-tide level. Also known as rotten spot.(3) A hole in the ground in karstic (limestone) areas usually with underground chambers and tunnels, into which a stream may flow.
PRECIPITATON The deposition of water from the atmosphere in solid or liquid form.
PRINCIPLE This defines the relationship between fresh and salt water in a coastal aquifer: Zs = (pf/ps-pf)Zw  where: Zs is the depth below sea level to the interface between fresh and salt waters, pf and ps are the densities of fresh and salt water respectively, Zw is the elevation of the water table.
PROBABLE MAXIMUM PRECIPITATION An estimate of the maximum amount of precipitation which is likely to fall in a given time from the atmosphere on a specific place. A statistic used primarily in dam design.
PRODUCTION The difference between gross photosynthetic production and overall respiratory loss of dry matter (kg dry weight/m2/unit time).
PRODUCTIVITY OF AN ECOSYSTEM Primary productivity is the rate at which energy from light is absorbed and utilized with carbon dioxide in the production of organic matter in photosynthesis. Net productivity is given by the amount of organic matter formed in excess of that used in respiration. It represents food potentially available to the consumers of the ecosystem. It can be measured approximately by sampling vegetation at intervals and measuring the dry weight produced per unit area; or on a small scale in appropriate conditions by measuring rate of photosynthesis and respiration of whole plants or small areas of vegetation.
PROFUNDAL ZONE The region below the limnetic zone and extending to the bottom in lakes deep enough to develop temperature stratification.
PROTECTED LANDSCAPE A term used by IUCN to describe an area of land which is of  national ecological and/or cultural importance. The area is inhabited, unlike National Parks (IUCN definition) and used by the  local population. It is protected from unregulated human modifications.
PUBLIC AWARENESS Knowledge, attitudes and opinions which are widely held by members of the public.
PUDDLE (1) A small pool of water, esp. of rain. (2) A worked mixture of wet clay and sand that is impervious to water when dry and is used to line a pond or canal.
PUMPING OF WATER Technique which may involve enhanced land drainage which is detrimental to wetlands. Alternatively this technique may involve raising water onto dessicated wetlands and hence the restoration of wetland conditions.
PUMPING TEST A carefully monitored period of pumping from a well so as to determine the properties of the aquifer penetrated by the well.
QUAGMIRE See Bog.
QUANATS Excavated, sloping galleries, adits and tunnels, which may follow natural occuring fissures and bedding planes in the rocks. These are used in the Middle East to secure a steady flow of groundwater for human consumption and irrigation.
QUICKSAND A highly mobile mass of fine sand consisting of smooth, rounded grains with little tendency to mutual adherence, usually thoroughly saturated with upward-flowing water. Tends to yield under pressure and to readily swallow heavy objects on the surface. Also known as running sand.
RAIN GAUGE An instrument to measure the amount of rainfall. The standard gauges adopted by nations are highly varaiable. An autographic, or recording rain gauge will record the intensity of rainfall through time.
RAINFALL Rainfall from clouds developed in an unstable atmosphere with strong heating of the ground leading to warming and ascent of air from ground level. The rainfall tends to be heavy, short lived and to have large drop sizes.
RAMSAR CONVENTION The Convention on Wetlands of International Importance especially as Waterfowl Habitat commonly referred to as the Ramsar Convention from its place of adoption in Iran in 1971. The first of the modern global intergovernmental treaties on conservation and wise use of natural resources.One of the original motivations for the establishment of the Convention was the concern voiced in the early 1960s about the serious decline in populations of waterfowl (mainly ducks) and the conservation of habitats of migratory waterfowl hence the words ‘especially as Waterfowl Habitat’.More specifically, the Ramsar Convention is the intergovernmental treaty which provides the framework for international cooperation for the conservation and wise use of wetland biomes.The Convention entered into force in 1975 and now has Contracting Parties from all over the world. The United Nations Educational, Scientific and Cultural Organization (UNESCO) serves as Depositary for the Convention.
RAMSAR SITE A wetland included in the List of Wetlands of International Importance.
RAMSAR WETLAND See ramsar site.
RAPID(S) A portion of a stream in swift, disturbed motion, but without cascade or waterfall; usually used in the plural.
RATING CURVE The relationship between water level and river discharge which is used to calibrate traditional river gauging structures. See gauging station, flume, weir.
RATIONAL FORMULA A simple and long used formula to estimate runoff (Q) in terms of a coefficient (C) depending upon the character of the river basin and antecedent conditions, a measure of precipiation intensity (I), and an index of basin area (A). Q = C I A
REAL-TIME FORECASTING The prediction of future events, such as weather or river flow, using models and data gathered up to the time of forecasting.
RECLAMATION (1) The recovery of land or other natural resource that has been abandoned because of fire, water, or other cause. (2) Reclaiming dry land by irrigation, or wetlands by drainage, etc. A process designed to adapt a wild or natural resource to serve a utilitarian human purpose. Often used to refer to processes that destroy native ecosystems and convert them to agricultural or urban uses.
RECURRENCE INTERVAL This is the expected frequency of occurence (in years) of a discharge of a particular magnitude or the expected frequency of occurence of some other hydrological event. See flood frequency curve.
RED TIDE Bloom of red algae in coastal waters as a result of over-enrichment with nutrients from land based sources. See eutrophication.
REDOX POTENTIAL Abbr. reduction potential -oxidation potential. A measure of the electron pressure (or availability) in a solution. Often used to quantify the degree of electrochemical reduction in wetland soils.
REDUCTION A substance undergoes reduction if it: (1) Loses oxygen. (2) Gains hydrogen. (3) Gains electrons.
REED Any tall grass with a slender jointed stem.
REED BED An extensive area which is periodically flooded and is normally dominated by a single species of reed,  commonly Phragmites australis.
REED CUTTING Reeds are cut usually near to the soil, for harvesting as thatch or fibre resources or as a means of removing nutrients from wetland systems.
REEF FLAT A flat expanse of dead reef rock which is partly or entirely dry at low tide; shallow pools, potholes, gullies, and patches of coral debris and sand are features of a reef flat.
REGINA AMENDMENTS Series of amendments to Articles 6 and 7 of the Ramsar Convention, approved by the Conference of the Contracting Parties held at Regina, Canada in May 1987.
REGION  
REHABILITATION OF WETLANDS The enhancement of the remaining functions, and possibly the reintroduction of past functions, to degraded wetlands.
RELATIONSHIP The relationship between the amount of rain that falls and the subsequent volume of (quick) flow that occurs in a river channel. This may be in the form of a summary coefficient expressing the percentage of rain that runs off or a statistical relationship that characterizes the relationship for different rainfall amounts.
RENDZINA SOIL Dark, organic-rich soil horizons developed upon unconsolidated calcareous materials in areas of limestone bedrock.
RESERVOIR A lake constructed for the storage of water, usually by the construction of a dam across a river or an embankment around an area of flat land.
RESIDENCE TIME The length of time between the input of water to a wetland and its outflow. It can be calculated by dividing the volume of water in the wetland by the inflow.
RESILIENCE The ability of a system to return to its original state after a disturbance.
RESISTANCE The ability of a system to resist changes from a disturbance.
RESOURCE SPIRALING Combined process of resource cycling and downslope or downstream transport. A nutrient atom or organic molecule may pass through the same trophic level or chemical state (cycling) during its residence in a stream, but completion of the cycle involves some downstream displacement before the cycle is closed (spiraling). Also used to describe the progressive movement downstream of sediment particles. These may move from one floodplain or channel sediment store to another in each flood. Thus they may take years to exit the basin. This explains why there can be long delays between human impacts on sediment dynamics and changes at the downstream end of the basin.
RESTORATION OF WETLANDS The return of some, or all, pre-existing functions to wetlands that have previously been destroyed and lost. Restoration is different from habitat creation, reclamation and rehabilitation since it is a holistic process not achieved through the isolated manipulation of individual elements. The objective is to emulate a natural self-regulating system that is integrated ecologically with the landscape in which it occurs. Often restoration requires one or more of the following processes: re-establishment of the former hydrology of the site; reconstruction of antecedent physical conditions; chemical adjustment of soil and water; and biological manipulation, including the reintroduction of absent native flora and fauna or of those made non-viable by ecological disturbances.
RETURN PERIOD See recurrence interval.
REYNOLDS NUMBER A dimensionless ratio defining the state of fluid motion as laminar or turbulent according to the relative magnitude of inertial and viscous forces.
RHEOTROPHIC MIRES See soligenous mires.
RHIZOMES The underground stem of some plants.
RHIZOSPHERE Area of  soil which immediately surrounds the root system of plants.
RIFFLES (IN RIVERS) In natural alluvial rivers there are normally sequences of pools and riffles. Riffles are the intervening banks of courser sediment where the water is shallower, faster flowing and well oxygenated by the turbulence induced by the riffle. Pools are zones of deeper water where current velocity is reduced so that silt and other loose materials tend to settle to the bottom, providing conditions unfavourable for surface benthos, but favouring burrowing forms and in some cases, plankton.
RIPARIAN Of, inhabiting, or situated on the bank of a river.
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 regimen.
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 in a riparian zone is generally much shorter, and the timing less predictable than in a river flooplain.
RIVER A large, natural freshwater surface stream having a permanent or seasonal flow and moving towards a sea, lake, or another river in a definite channel.
RIVER CONTINUUM CONCEPT 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 processing of organic matter. Both upstream inefficiency (leakage) and downstream adjustment seem predictable.
RIVER NETWORK A river and all its tributaries.
RIVER REGULATION The control of river flow, usually by dams and sometimes by groundwater pumping, in order to modify the regime to one more suited to human and economic demands.
RIVER ROUTING Mathematical pocedures (e.g. Muskingum-Cunge method) to calculate the attenuation and timing of a flood discharge as it passes down a channel within a river valley.
RIVERINE Situated beside or of a river. (1) Perennial a. Permanent rivers and streams, also waterfalls. b. Inland deltas. (2) Temporary b. Seasonal and irregularly flowing rivers and streams. c. Riverine floodplains, including river flats, flooded river basins and seasonally flooded grasslands.
RIVERINE FOREST Forest which grows along the banks and immediate surroundings of rivers.
RIVERINE WETLAND Wetland systems of less than 0.5 ppt ocean salts, exposed to channelized flow regimes. Riverine wetlands are categorized according to flow regimes such as tidal waters, with well-developed floodplains, fast-moving waters with little floodplain, and intermittent systems.
RIVULET A small stream; a brook.
ROOT CONSTANT A concept introduced by Penman for the amount of water that a particular group of plants can extract from the soil before the moisture stress is such that they can no longer transpire at the potential rate. See actual evapotranspiration, potential evapotranspiration, penman method.
RSPB Royal Society for the Protection of Birds. A British NGO dedicated to the conservation of wild birds and their habitats.
RUDERAL  PLANT Rapidly growing plant which quickly colonise bare soil areas. Commonly known as weed.
RUNOFF The water that moves from the land phase of the hydrological cycle to rivers and in most cases the ocean. It can be by overland flow following intense rainfall or irrigation events or by lateral saturated and unsaturated flow through the upper soil horizons with the reemergence of water at the foot of slopes and in areas of flow convergence. Runoff is often characterised as a coefficient representing the percentage of rainfall that has flowed away down rivers.
SALINA An area, such as a salt flat, in which deposits of crystalline salts are formed or found. A body of water containing high concentrations of salt.
SALINE Of, concerned with, consisting of, or containing common salt (NaCl)
SALINITY The amount of salt in a solution. May be measured (crudely and indirectly) as conductivity or more accurately by measurement of the sodium and chloride concentrations in the solution.
SALINIZATION Increase in salt concentration.
SALT FALT A flat expanse of salt left by the total evaporation of a body of water.
SALT LAKE A confined inland body of water having a high concentration of salts, principally sodium chloride.
SALT MARSH Commonly, a maritime habitat found in temperate regions, but typically associated with tropical and subtropical mangrove swamps, in which excess sodium chloride is the predominant environmental feature. In the Mediterranean it may be found in areas with some tidal influence e.g. Gulf of Gabbes/Iles de Kneiss in Tunisia, in deltas such as the Axios Delta in Northern Greece or in areas with saline ground water such as the sansouires of the Camargue.
SALT MEADOW Land containing high concentration of minerals.
SALT PAN Dry bed of a salt lake after all water has evaporated; also refers to artificial basin created for evaporating sea water to collect salt.
SALT WATER INTRUSION The inflow of salt water into fresh water habitats or aquifers, usually caused by a disruption of natural systems. A common feature is the intrusion of sea water into coastal aquifers as a result of excessive pumping of  fresh groundwater.
SALT WATER WETLAND See marine wetland, estuarine wetland, lagoonal wetland.
SALT WEDGE The relatively dense, saline bottom water which intrudes into estuaries with the rising tide and which can move into rivers if the freshwater flow is diminished for some reason.
SALTING AREA An area of low ground regularly inundated with salt water. Often taken to include its hydrophytic vegetation.
SEA LEVEL RISE The level of the sea relative to the land has changed continuously in geological time and very dramatically in the Quaternary. At present the IPCC has identified a global relative sea level rise caused by thermal expansion of the oceans under the influence of global warming and, to a lesser extent, the melting of terrestrial and polar ice. At a more local level there can be relative changes in sea level compared to the land because of tectonic movement, land subsidence and isostatic change.
SEAGRASS BED Underwater marine vegetated area usually consisting of the plant Posidonia. Also referred to as seagrass meadow.
SEAWALL An earth, concrete, stone, or metal wall or embankment constructed along a shore to reduce wave erosion and encroachment by the sea.
SEBKHAS North African term meaning shallow depressions which typically hold water for a longer time than chotts, usually only drying out at the height of summer although some may remain full for over a year. One of the most important of these for wildlife is Sebkha Sidi El Hani in central Tunisia. It sometimes holds water for more than two years, partly because it is also supplied by an oasis. Sebkhas are also found in northern Tunisia, to the north of the arid chotts zone, and on the plateau to the south of Constantine in Algeria and Mauritania. Vegetated and unvegetated sebkhas have been distinguished in the literature. Often sebkhas imply some form of salt crust (many cms thick at Sidi El Hani) or thin white salt coating (Sebkha El Djem). The notable feature of Sebkha Kelbia is that it is Tunisia’s only Sebkha that does not have any salt crust when it dries out.
SEDIMENT Inorganic solid fragmented material, sometimes augmented with organic material, that comes from weathering of rock and is carried by, suspended in, or dropped by air, water, or ice; or a mass that is accumulated by any other natural agent and that forms in layers on the earth’s surface such as sand, gravel, silt or mud.
SEDIMENT LOAD A characterization of the movement of sediment in a medium, normally a river where it may be expressed as a concentration (e.g. g/l or kg/m3), a flow (e.g. kg/day), or a rate of equivalent erosion (e.g. kg/ha or tons/km2/year)
SEDIMENT RETENTION The deposition of sediments in a wetland or on a floodplain which acknowledges that they may, in the longer term, be remobilized and moved further downstream.
SEDIMENT TRANSPORTERS Aquatic animals which stir up bottom deposits and mix up organic and mineral constituents.
SEDIMENTATION The process of deposition of sediment.
SEEP An area where groundwater moves slowly and steadily up to, and over, the surface without forming very distinct springs or channels. Also known as an ooze.
SEEPAGE The slow movement of water through small openings and spaces in the surface of unsaturated soil into or out of a body of surface or subsurface water.
SERIAL DICONTINUITY 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 take 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.
SETTLING The separation by gravity of heavy from light materials; for example, the settling out of dense solids or heavy liquid droplets from a liquid carrier, or the settling out of heavy solid grains from a mixture of solid grains of different densities.
SETTLING POND A natural or artificial pond for recovering the solids from an effluent.
SEWAGE The fluid discharge from medical, domestic, and industrial sanitary appliances.
SEWAGE FARM An area of land where sewage is spread over the land for treatment by natural processes. The effluent is gathered in drainage channels for discharge to water courses. This is a system suited, nowadays, only to small rural communities.
SEWERS Underground pipes installed to carry water away from urban areas. They can be surface water sewers taking stormwater runoff from rainfall, foul sewers taking waste water from households and industry, or combined sewers which receive both waste water and stormwater.
SHEET-FLOW Overland flow of water across wide areas following intense rainfall onto impermeable or saturated soils. See overland flow.
SHINGLE Pebbles (2 to 64 mm diameter), cobble (64 to 256 mm diameter), and other beach material, occurring typically on the higher parts of a beach.
SHINGLE BANK Bank made of shingle.
SHOAL A normally submerged bank rising from the bed of a shallow body of water and consisting of, or covered by, unconsolidated material which may be exposed at low water.
SHORE The narrow strip of land immediately bordering a body of water.
SILT Sediment (0.004 to 0.0625 mm [4 to 62 microns] diameter) carried or deposited by water.
SILTATION The filling of a wetland, or other water body, with water-borne sediment.
SITE-BASED EIA An EIA study where the impacts on the environment are analyzed from the standpoint of ecosystem components. It initially entails identification of environmental components which may be impacted by any project at the site. It does not exclude the later identification of project activities which will impact on those environmental components.
SLUICE SNOW MELT EQUATION An equation used to calculate the amount of melt water coming from a snow pack under the prevailing weather conditions. Input variables usually include rainfall, air temperature, wind speed, humidity and an index for the degree of exposure of the site. Different countries tend to have their own national equations.
SOIL MOISTURE CHARACTERISTIC CURVE The relationship between soil moisture content and soil moisture suction. The relationship is normally hysteretic. See pF.
SOIL PROFILE The sequence of layers found in most soils. The upper A horizon is normally rich in organics, permeable and well aerated. The lower B horizon is more compact and may be either pale and leached or the site of deposition to create hard pans. The lowest C horizon usually has a low organic content and contains pieces of partially weathered bedrock.
SOLAR RADIATION Short-wave radiation from the sun.
SOLARIMETER Instrument for measuring solar radiation. Traditionally a paper recorder was used on a Campbell-Stokes recorder with a large globe of glass to focus the suns rays. Today, electronic instruments are used. The data is used, amongst other things, for calculating evapotranspiration.
SOLIGENOUS MIRES Primary and secondary peats of valley mires which remain in capillary contact with flowing groundwater. They are less nutrient deficient than ombrotrophic mires. See rheotrophic mires.
SOLUTE Material dissolved in water.
SOLUTE LOAD The amount of dissolved material carried by a river.
SOURCE CONTROL An urban flood control technique which seeks to detain stormwater runoff on the sites where it is generated rather than speeding it to the river immediately. Wetlands can form a multi-functional form of source control.
SPATIAL HETEROGENEITY Variation in the attributes of an environment over space.
SPAWN The collection of eggs deposited by aquatic animals, such as fish.
SPAWNING AREA Area where fish spawn. See spawn.
SPECIES The smallest unit of classification commonly used. In the system of binomial nomenclature, taxa with species status are denoted by Latin binomials, each species being a member of a genus e.g. Homo (genus) sapiens (species). For the great majority of animals and many plants, a species is roughly a group of individuals able to breed amoung themselves (if one disregards geographical separation) but not able to breed with organisms of other groups. As a result no striking differences in genetic composition and in the characters controlled by genes occur within the species, though local differences, which are recognized in classification as a sub-species, may arise through reproductive isolation which is only partial or has recently occurred.
SPECIFIC GRAVITY  (OF SOIL) The ratio of the weight of a given soil particle to the weight of an equivalent volume of water (at 4 oC).
SPECIFIC RETENTION The volume of water which a rock or soil retains against the influence of gravity if it is drained following saturation. Compare specific yield.
SPECIFIC YIELD The volume of water that a water bearing rock or soil releases from storage under the influence of gravity. In an unconfined aquifer, it is expressed as the volume per unit surface area of the aquifer per unit decline in the watertable. Compare  specific retention.
SPIT An elongated point of land extending into open water which commonly consists of sand or gravel and is maintained by a balance new sediment and the erosion of the existing spit.
SPRING A discharge to the surface from groundwater of deep-seated, hot or cold, pure or mineralized water.
SPRING MIRE A peat forming wetland sustained by perennial inflows of groundwater from underlying springs.
SPRING TIDE Exceptionally high high-tides and exceptionally low low-tides created periodically when solar and lunar tides coincide. See tide.
STAGE BOARD A clearly marked board used to read water level above a known datum.
STAGE RECORDER An instrument used to record water level at a gauging station. Traditionally this was a float operated pen and paper mechanism but today it is computerized. See gauging station.
STAGE-DISCHARGE RELATIONSHIP The equation or graph which relates water level to flow for a particular reach of river or gauging structure at a particular time. It is usually derived by current metering at a series of different water levels. See gauging station, flume.
STENOHALINE Organisms that can survive within fairly narrow salinity limits.
STEVENSON SCREEN A shaded enclosure, conventionally a white painted cabinet, used to house thermometers at weather stations.
STILLING WELL A large diameter tube installed at the edge of a river channel, or in a river bank, in order to obtain accurate measurements of river level from still water surface. It is an essential component of traditional river gauging stations. See gauging station, stage recorder.
STOCHASTIC PROCESS A statistical phenomenon in which the evolutionary sequence in time or space follows probabilistic laws.
STOCK POND A natural, or artificial, pond created for the purpose of watering farm stock.
STORM SURGE TIDES Changes in the level of the sea created by extreme weather conditions. Long periods of strong winds in one direction are especially effective in building up the level of the sea at the downwind end of a restricted area of marine waters.
STORMWATER Runoff, usually via surface water sewers, from paved surfaces in urban areas. See source control.
STREAM A body of running water moving under the influence of gravity to lower levels in a narrow, clearly defined natural channel.
STREAM BUFFER A strip of vegetated land of variable width adjacent to a stream preserved from development activity to protect water quality and aquatic and terrestrial habitats.
STREAM FLOW The discharge of water down a stream measured normally in m3/sec.
STREAM FLOW CONTROL Regularization of the flow of water courses, often using reservoirs or groundwater pumping.
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 the watershed and the greater the channel dimensions and discharge.
STREAM RESTORATION The reinstatement of the hydrological, morphological, and ecological features that have been lost in a stream due to urbanization, farming, or other disturbance.
SUBSIDENCE The sinking or caving-in of the ground.
SUBTIDAL The part of the shallow offshore zone which is below the level of the lowest tide.
SUCCESSION vegetation induced by the inflow and deposition of sediment in a pond.
SUSPENDED LOAD Sediment transported by a river in suspension by the upward component of fluid turbulence.
SUSTAINABLE DEVELOPMENT Economic development which meets the needs of the current population without compromising the needs of future generations.
SUSTAINABLE USE OF WETLANDS Human use (of a wetland) so that it may yield the greatest continuous benefit to present generations while maintaining its potential to meet the needs and aspirations of future generations
SWAMP Whilst authorities differ, a swamp may be defined as a vegetated area perennially flooded or saturated with groundwater. It differs from a marsh in that the latter normally has a period of desiccation.
TEMPORARY PAN See pan.
TENSIOMETER An instrument, consisting of a water-filled porous cup inserted into the soil and a pressure gauge, which measures soil moisture suction forces.
TERRESTRIALIZATION The process whereby sedimentation and accretion gradually fill the water storage capacity of a wetland leading to the colonisation of the site by species which are progressively less adapted to an aquatic habitat.
THALWEG The deepest portion of a channel carrying water.
THEIS EQUATION Equation for the computation of non-steady radial flow towards a well in an aquifer. See hydrogeology.
THEISSEN POLYGONS Method of calculating a real rainfall from point measurements at gauges. Involves creating polygons with the perpendicular bisectors of lines joining neighbouring gauges.
THERMOCLINE In thermally stratified lakes, the layer below the epilimnion. It is the stratum in which there is a rapid rate of decrease in temperature with depth (a minimum of one degree centigrade per metre in depth).
THORNTHWAITE METHOD OF CALCULATING POTENTIAL EVAPOTRANSPIRATION A formula developed by C.W. Thornthwaite in the USA in the 1940s for the calculation of monthly potential evapotranspiration rates using only mean air temperature as the input variable.
THROUGHFALL Water from rainfall which passes through the vegetation canopy without being intercepted and reaches the ground.
THROUGHFLOW The lateral downslope movement of water in soil horizons. The convergence of throughflow in hollows can lead to the water flowing over land as first order streams during rainfall events.
TIDAL BASIN A coastal hollow subject to water level changes caused by tides.
TIDAL FLAT Marshy, sandy, or muddy almost horizontal coastal land which is alternately covered and exposed as the tide rises and falls.
TIDAL MARSH Salt or brackish wetland systems subject to tidal flow patterns. Estuarine marshes are subdivided into subtidal (permanently flooded) or intertidal (temporarily flooded) wetland systems.
TIDE The periodic rising and falling of the oceans resulting from lunar and solar tide-producing forces acting upon the rotating earth.
TIDEWATER (1) A body of water, such as a river, affected by tides. (2) Water inundating land at flood tide.
TILE DRAINAGE SYSTEM Pipes, traditionally earthenware but nowadays normally perforated plastic, installed in the sub-soil, perhaps with gravel backfill around them, and inclined so as to discharge to deep ditches surrounding the agricultural land, with the aim of improving the drainage of the land for cultivation. See also underdrainage.
TIPPING BUCKET GAUGE A hydrological instrument consisting of matched containers on a pivot such that an input of water causes the instrument to tip so emptying one container and leaving the other to receive any continuing inflow of water. The flow rate is measured by recording the number and timing of tips. The concept is most commonly used in telemetering rain gauges. See rain gauge.
TORRENT A steep stream with a strong seasonal regime and short periods with high discharges accompanied by high sediment loads including coarse bedload. The usually coarse bed material or rocky substrate creates rapids and white water conditions when flows are high.
TOXIN A poisonous substance produced by certain plant and animal cells, including bacterial toxins, phytotoxins, and zootoxins.
TRANSPIRATION The movement of water through the stomata of plants into the atmosphere. See evapotranspiration.
TROPHIC STATUS The degree to which the ecosystem is fertilized with nutrients. Generally three classes are distinguished but there are no set limits to each class:(1) Eutrophic means nutrient-rich. Usually associated with low oxygen levels since the voluminous plant growth generates large organic deposits that decompose removing much or all of the oxygen from the water.(2) Mesotrophic means medium nutrient availability(3) Oligotrophic systems are nutrient-poor except for oxygen. The trophic status for any one wetland is a condition determined by the surrounding catchment, landform and geology.
TURBIDITY The degree to which turbulent flow maintains suspended sediment in the water giving the water an opaque appearance. Turbidity, in terms of g/l of suspended sediment can be measured by photo-extinction methods.
TURNOVER RATE  
ULTRASONIC GAUGING The assessment of river discharge by measurement of the deflection of ultrasound pulses transmitted across the river at various depth. See gauging station.
UNCONFINED AQUIFER An aquifer without an overlaying impermeable aquiclude. Its watertable is controlled by gravity and the transmissivity of the rocks. Compare confined aquifer.
UNDERDRAINAGE The drainage of agricultural land by the insertion of clay tile or perforated plastic drainage pipes at circa 2m depth. The latter slope to deep ditches which surround the drained field and in which the water level is maintained below the outfall of the pipes. See tile drainage system.
UNDP United Nations Development Programme
UNEP United Nations Environment Programme. Based in Nairobi
UNESCO United Nations Educational, Scientific and Cultural Organisation. Based in Paris.
UNIT HYDROGRAPH A hydrological concept describing for any point on a river the quickflow hydrograph that will result from unit effective rainfall (1 inch in USA, 10 mm in SI units) in unit time (normally 1 hour but time may vary)
URBAN WASTE WATER DIRECTIVE The order of the Council of Ministers of the European Union regarding the installation of primary, secondary and tertiary sewage treatment plants on appropriate inland, estuarine, coastal and, so called, sensitive waters.
VALLI An italian term. One of the most successful and durable systems of traditional fishing used in the 10,000 hectares of lagoons of the Italian Adriatic, including the Po delta and the Venice lagoon. Though practised for many hundreds of years, the valli system comes close to many of the techniques of modern fish farming..
VALUATION OF WETLANDS The assessment of wetland values. Many environmental economists subscribe to the view that the total value of a wetland is found from the summation of (1) Direct use value (e.g. fisheries).(2) Indirect use value (e.g. flood attenuation).(3) Existence value (amount people might be willing to pay for the wetland to continue to exist).(4) Bequest value (the worth of the site when it is passed on to a future generation).
VALUES OF WETLANDS The worth in monetary, cultural and aesthetic terms that wetland functions, products and attributes have to human society.
VAPOUR PRESSURE OF AIR The contribution by water vapour to the total pressure of the atmosphere. Derived from wet-bulb depression and used in the calculation of humidity and evaporation/evapotranspiration rates.
VELOCITY-AREA METHOD The procedure for measuring discharge in a river with a current meter. Measurements are made at several depths at a number of positions across the river, areas of the wetted cross-section are then assigned to each current meter reading and a weighted average for discharge calculated.
WADI An Arabian term. A channel of a watercourse in a semi-arid region that is dry except during periods of rainfall.
WASTE WATER Water based effluent from mining, industrial, and domestic use in an untreated condition and carrying significant amounts of pollutants.
WATER A clear colourless tasteless odourless liquid (chemical formula H2O) essential for plant and animal life and constitutes, in impure form, rain, oceans, rivers, lakes, etc. It is a neutral substance and an effective solvent for many compounds.
WATER BALANCE A hydrological calculation of the water inputs, outputs and changes in storage within a natural system. When appropriately expressed and using complete data without errors, inputs equal outputs plus or minus changes in storage, since water can neither be created nor destroyed in the hydrological cycle.
WATER CYCLE See hydrological cycle.
WATER INDUSTRY A recent term describing all of the organisations, both public and private, that are concerned with water resources exploitation (e.g. water supply companies, sewage works operators, environmental regulators, consulting engineering firms etc).
WATER LEVEL REGIME The pattern of water level change in the wetland which describes both the normal seasonal fluctuations and extreme high (flood) levels and low (drought) conditions. It is such a key feature of the wetland ecosystem functioning that is often known as the “signature of the wetland”. Also known as hydroperiod.
WATER MEADOW A meadow that remains fertile by being periodically flooded by a stream.
WATER REGIME The seasonal and long term balance between precipitation inputs, evapotranspiration and runoff outputs, and storage within the wetland. Closely related to water level regime.
WATER RESOURCE MANAGEMENT The resolution of conflicts over the various uses of water resources which is best undertaken by a suitably empowered body organized on a catchment scale basis.
WATER RESOURCES Often taken to mean simply the bodies of water from which water can be abstracted for human use. More modern usage implies all of the human uses of the hydrological cycle (e.g, water supply, effluent disposal, navigation, fisheries, hydro-power, recreation, maintenance of aquatic ecosystems etc.)
WATER RETENTION CAPACITY OF SOIL This is represented by the soil moisture characteristic curve which relates the moisture content of a soil and the pore water pressure (suction) in the soil. Water content declines as pore pressure decreases. Finer grained soils, such as clays, have a higher water content for a given pore water pressure than coarse grained soils such as sands.. A hysteretic effect normally gives drying soils a higher water content for a given pore water pressure than that found in a wetting soil.
WATER YEAR A hydrological term used to describe the 12 months starting at the end of the dryest season, passing through the wet season(s), and ending with the next dry season. In the Mediterranean the water year runs from September to August. The water year can be important in analyses that require the selection of hydrologically independent events.
WATERCOURSE A channel through which water may run.
WATERFALL A perpendicular or nearly perpendicular descent of water in a stream.
WATERFOWL Aquatic (usually freshwater) birds. Principally the order Anseriformes, including the swans, ducks, geese and screamers. For the purposes of the Ramsar Convention the following groups of species are included; loons or divers (Gaviidea), grebes (Podicipedidae), cormorants (Phalacrocoracidae), pelicans (Pelecanidae), herons, bitterns storks, ibises and spoonbills (Ciconiiformes), swans, geese and ducks (Anatidae). Furthermore wetland related birds of prey, as defined under the Ramsar Convention; Accipitriformes and Falconiformes, cranes (Gruidae), shorebirds or waders (Charadrii) and terns (Sternidae).
WATERLOGGED Ground which is saturated with water; normal soil gases are expelled, so interfering with plant growth and cultivation.
WATERSHED High ground between drainage systems. In US, known as a divide. In US, watershed is used to describe the entire surface drainage area that contributes water to a lake or river.
WATERSHED-SCALE V A consideration of the entire watershed, including the land mass that drains into the aquatic ecosystem and including, for instance, the land and water use and other human activity in the area. Syn. catchment approach.
WATERTABLE The upper surface of saturated conditions. This can be the groundwater level (phreatic watertable) in unconfined aquifers or that level below which the soil is saturated with water. See also piezometric surface.
WATERWAY A channel for the escape or passage of water, usually associated with the navigation function of that water body.
WEIR A structure in a river or water body that restricts discharge to water levels above the crest of the weir. Weirs can be moveable or variable in height. Some weirs are used as fixed structures within gauging stations for measuring river flow.
WET MEADOW Grazing land adjacent to wetlands that is flooded at peak water levels.
WET-BULB DEPRESSION The difference between the temperatures recorded in a Stevenson Screen by normal thermometer and one with its bulb kept moist by a wick placed in distilled water. This wet-bulb depression is used in calculating humidity.
WETLAND Ramsar definition : “Areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static, flowing, fresh, brackish or salt, including areas of marine water, the depth of which at low tide does not exceed six meters”. U.S. EPA definition: “Wetlands are lands inundated or saturated by surface or ground water, at a frequency and duration sufficient to support, and that under normal circumstances do support a prevalence of vegetation, typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas”. See salt water wetland, freshwater wetland, artificial wetland.
WETLAND BENEFITS A term introduced by the Asian Wetland Bureau as an umbrella concept to cover functions, uses, values, attributes, features, goods and services. Wetland benefits are defined as any of these terms which may have a value to people, wildlife, natural systems or natural processes.
WETLAND CLASSIFICATION Classification undertaken to impose boundaries on natural ecosystems for the purposes of inventory, evaluation and management. Involves putting wetlands into categories according to their structural or functional characteristics. The US Fish and Wildlife Service “Classification of Wetlands and Deepwater Habitats of the United States”, published by Cowardin et al. 1979, comprises 5 systems, 11 subsystems, and 54 classes. The classification adopted by the Ramsar Convention at the 1990 Montreux Conference comprises Marine and Coastal Wetlands (11 subtypes), Inland Wetlands (16 subtypes) and Man-Made Wetlands (8 subtypes).
WETLAND DELINEATION The procedure of placing on a map and determining in the field the boundaries of a wetland. The procedure is based on pre-determined criteria pertaining to the definition of the term “wetland” adopted by the persons conducting the delineation.
WETLAND HYDROLOGY The scientific field of hydrology dealing with wetlands. It is characterised by a focus upon storages and water levels in storages rather than water flow which is the main focus of hydrology undertaken in river basins.
WETLAND MITIGATION The implementation of policies, often involving rehabilitation, restoration or creation of wetlands, so that adverse human impacts on one wetland, or one area of a wetland, will not reduce the overall stock of wetlands and wetland functions within the area.
WETLAND TYPE The Ramsar Classification system for “Wetland Type”  includes 11 types of marine and coastal wetland, 16 varieties of inland wetland and 8 man-made wetlands.
WETLANDS Natural or semi-natural stretches of land and/or water which link together wetlands allowing migration and movement of non-flighted species between the sites.
WETLANDS WILTING POINT Soil moisture tension at which plants can extract no further water and therefore they wilt and die. Normally this is around 30 bars.
WISE USE OF WETLANDS Sustainable utilization of wetlands for the benefit of mankind in a way compatible with the maintenance of the natural properties of the ecosystem.
WWF World Wide Fund for Nature. Based in Geneva, Switzerland.
XEROPHYTE Plant adapted to semi-arid habitats.
ZONATION of the floodplain A land use planning technique to ensure the maintenance of a free floodway for the major cross-floodplain discharges, the limitation of development in the floodplain that would reduce storage capacity for floods, and the prevention of development that would be liable to serious damage when a flood occurred.
ZONATION of wetlands and surroundings A widely employed conservation technique. Frequently there are four zones: (1) An inner core zone without human access. (2) A zone where human use may be permitted when it is in sympathy with conservation objectives. (3) A buffer zone, usually outside the reserve, where human activities should not damage the integrity of the reserve. (4) The whole of the rest of the upstream catchment area where strict EIA procedures need to be applied.
ZOOPLANKTON Planktonic animal life.