A Glossary of Wetland Terms
Fact Sheet No. 3
Audubon Society of New Hampshire
3 Silk Farm Road, PO Box 528-B, Concord,
NH 03302-0516. Tel: 603/224-9909. Fax: 603/226-0902
The objective of this glossary is to provide nontechnical definitions of some of the technical terms that are commonly used in wetlands literature. This glossary is not an exhaustive list of all the terminology pertaining to wetlands, but rather focuses on the more frequently used wetland-related terms. You may wish to refer to other texts for definitions of some of the more general terms that are not covered here. We have attempted, as far as possible, to make the glossary recursive - i.e. in the definitions provided below, all words written in italics are defined elsewhere in this glossary (except for the word "wetland"), under the appropriate heading. All definitions marked with an asterisk are wetland classifications as defined in the U.S. Fish & Wildlife Service's Wetland Classification System (Cowardin, 1979).
ANADROMOUS FISH
Fish species which are born in freshwater, spend a large part of their lives in the ocean, and which return to freshwater habitats to spawn, e.g. rivers, brooks, and ponds.
ANAEROBIC
Having an oxygen deficiency. In wetlands, soils are characteristically anaerobic as a result of saturation or inundation with water.
AQUATIC
Plants or animal species living in or near water. Aquatic habitats include ponds, lakes, rivers, and oceans.
AQUATIC BED
An area of open water, such as a pond, that is dominated by floating leaved or submergent plants e.g. pond lillies water milfoil, bladderworts. Aquatic Bed habitats are also found along the shallower portions of deepwater habitats.*
AQUIFER
Geological formations, such as fractured bedrock or permeable layers (e.g. glacial sands or gravels), which can hold water and will allow it to be released in sufficient quantities to be economically viable as a water source, e.g. for domestic or municipal wells. This water is known as ground water.
BEDROCK
Solid rock that underlies both the soil and sub-soil (fragmented rock material).
BOG
A characteristically nutrient poor, acidic wetland that is dominated by a waterlogged, spongy mat of sphagnum moss, ultimately forming a thick layer of acidic peat. There is little or no inflow or outflow of water in bogs, which are fed primarily by rainwater. Bogs are also characterized by a growth of acid-tolerant evergreen trees and shrubs (e.g. black spruce and bog rosemary), and sedges (see also Kettle Hole Bog, Fen).
BUFFER ZONE
A naturally occurring undeveloped area of specified width, bordering a wetland, that serves to lessen the impact of disturbance, e.g. urban development or agricultural use. Buffers around wetlands can provide initial filtration of sediments and pollutants, and can also slow down runoff. The width of a buffer may be defined by a local zoning ordinance.
CORRIDOR
A natural, undisturbed area that allows wildlife to move freely between wetlands, between wetlands and other water bodies, or between one protected tract of land and another.
CREATION OF WETLANDS
The artificial creation of new wetlands, usually in conjunction with the destruction of wetland habitat elsewhere (see also Mitigation).
In-Kind
The construction or replacement of the same kind of wetland as the wetland being impacted.
Out-of-Kind
The construction of a different kind of wetland in replacement for the wetland being impacted.
DEEPWATER HABITAT
Describes aquatic habitats, such as lakes, rivers and oceans, where surface water is permanent and deeper than 6.6 feet most of the year. These habitats are generally lacking in vegetation (deepwater habitats may, however, be bordered by emergent or aquatic bed vegetation in the shallower areas).*
DELINEATION See Wetland Delineation.
DIVERSITY
The variety, number and distribution of species (plant or animal) within a habitat.
ECOLOGY
The study of the interactions between living organisms and their environment.
ECOSYSTEM
A community of plants and animals and the physical environment they inhabit, e.g. rivers, estuaries, wetlands. The ecosystem describes the interactions between soil, climate, vegetation and animal life.
EMERGENT PLANTS
Erect, rooted, herbaceous plants that can tolerate flooded soil conditions, but not extended periods of being completely submerged. Emergent plants include grasses, sedges, rushes, and rooted aquatic species (such as pickerel weed).
Persistent
Emergent plants whose stems remain standing through the winter until the beginning of the next growing season (i.e. they persist), e.g. cattails, or bulrushes.
Nonpersistent
Emergent plants whose stems and leaves break down at the end of the growing season. From late fall until spring, there are no visible traces of these plants above the surface of the water (i.e. they do not persist), e.g. pickerel weed, arrowheads.
EMERGENT WETLAND
A wetland habitat dominated by soft-stemmed herbaceous plants called emergents. Water levels can range from a few inches to a few feet. Emergent wetlands, which can occur in isolation or in association with other water bodies, include deep and shallow marshes and wet meadows. Emergent wetlands are also referred to as marshes (see also Marsh, Freshwater; Marsh, Saltwater).*
EUTROPHICATION
The over-fertilization of the aquatic ecosystem. This may be caused by excessively high concentrations of organic matter and plant nutrients, such as phosphates and nitrates (which are found in fertilizers used in agricultural fields and lawns). This results in excessively high levels of growth ("bloom") and decomposition of plants, e.g. algae and pondweeds. The increased plant growth can lead to a significant depletion of the water's oxygen supply.
FACULTATIVE SPECIES
Plant species that can occur both in wetlands and uplands. There are three subcategories of facultative species: 1) Facultative Wetland Plants (FACW) usually occur in wetlands (estimated probability of occurring in wetlands is 67-99% of the time) but are occasionally found in nonwetlands, 2) Facultative Plants (FAC) are equally likely to occur in wetlands or nonwetlands (estimated probability of occurring in wetlands is 34-66%), and 3) Facultative Upland Plant FACUP) are occasionally found in wetlands, but more often in uplands (estimated probability of occurrence in wetland is 1-33%) (see also Obligate).
FEN
A wetland that often represents a transitional stage between marshes and bogs. Fens are often confused with true bogs. However, unlike true bogs, fens generally receive some drainage from surface runoff and surrounding soils (seepage) in addition to precipitation and are generally characterized by grasses, sedges, and reeds.
FLOATING-LEAVED PLANTS
Plants that have specially adapted leaves that float on the surface of the water. These leaves allow air and water exchange through the top of the leaf, e.g. water lily and spadderdock, thus compensating for the anaerobic environment (see also Hydrophytes).
FLOODPLAIN
The part of a river valley, adjacent to the river channel, over which a river flows in time of flood.
FLOODPLAIN FOREST
Distinct swamps formed along larger rivers in the floodplain area. They are usually characterized by silver maples or willows, and have sandier soils than traditional swamps.
FORESTED WETLAND
A wetland where the soil is saturated and often inundated, and woody plants taller than 20 feet dominate the vegetation, e.g. red maple, tamarack. Water tolerant shrubs and saplings often form a second layer beneath the forest canopy, e.g. red maple saplings, highbush blueberry, with an herbaceous layer below, e.g. cinnamon fern, sensitive fern. Forested wetlands are also referred to as wooded swamps (see also Swamp).
FUNCTIONAL ASSESSMENT
See Wetland Evaluation.
FUNCTIONAL VALUE
The value of a wetland is derived from the functions it performs (e.g. flood control, wildlife habitat, water quality), its physical location, its size, and the human pressures put on it.
FUNCTIONS OF A WETLAND
Functions are the physical "jobs" that a wetland performs, such as retaining floodwater, filtering nutrients and pollutants, stabilizing shorelines, etc. Few wetlands perform all functions. The extent to which a wetland performs a function depends on the biological and physiological nature of that particular wetland.
GROUND WATER
Water that is found below the surface of the ground, usually at or beneath the water table. Ground water usually occurs in the deeper zones of soil and fractured bedrock that are saturated (see also Aquifer).
GROUND WATER DISCHARGE
Ground water that emerges at the land surface in the form of springs or seepage areas. The majority of wetlands are ground water discharge areas. Ground water also discharges into rivers (via bank seepage) and can sustain flows during the drier months.
GROUND WATER RECHARGE
The movement (infiltration) of rain, snowmelt or surface water down through the soil and rock layers to replenish the ground water. In certain instances, wetlands that are hydrologically connected to the ground water system may augment ground water supplies. However, this is the exception rather than the rule. Most wetlands are ground water discharge areas.
HABITAT
The environment in which the requirements (e.g. food and shelter) of a specific animal or plant are met.
HERBACEOUS PLANT (HERB)
A non-woody plant with soft stems, e.g. bulrushes and cattails.
HIS
High Intensity Soil survey. A soil survey that shows the soil patterns in much greater detail than the SCS soil surveys, usually at the scale of a subdivision proposal. HIS maps are intended for actual land use application rather than for broad planning.
HISTOSOL
A term used in soil taxonomy to describe soils that are composed predominantly of decayed organic material (i.e. organic soils, e.g. mucks and peats) rather than mineral material (see also Organic Soil; Mineral Soil.
HYDRIC SOIL
Soil that is saturated, flooded, or ponded long enough during the growing season to develop anaerobic (oxygen lacking) conditions in the upper portion. Hydricsoils are generally classified as "poorlydrained" or "very poorly drained".
Poorly Drained
Water is removed from the soil so slowly that the soil is saturated during the growing season or remains wet for long periods of time (generally referred to as 'Hydric B" soils).
Very Poorly Drained
Water is removed from the soil so slowly that water remains at or on the surface most of the growing season (generally referred to as "Hydric A" soils).
HYDROLOGIC CYCLE
The continuous and indefinite cycle of water between the sea, air and land: water vapor is released into the atmosphere through transpiration (when plants give off water into the air) and evaporation from land and water surfaces. The water vapor condenses and falls to the land as precipitation, which is stored on the surface (in lakes, rivers and wetlands) or at depth as ground water, or is evaporated or transpired to initiate the cycle once more.
HYDROLOGY
The scientific study of properties, circulation and distribution of water as it occurs within the atmosphere and at the earth's surface as streamflow, precipitation, soil moisture and ground water (see also Wetland Hydrology).
HYDROPERIOD
The period during which surface water remains on the wetland. This can range from a few days to several months, and may be seasonal or permanent.
HYDROPHYTES
Plants adapted for life in water, or periodically flooded and/or saturated, anaerobic soils, e.g. air filled root tissues, floating leaves, buttressed roots.
INTERMITTENT STREAM
A stream that only flows periodically, usually after spring thaw or heavy rainfall.
KETTLE HOLE BOG
A bog formed in a depression left by the melting of an isolated glacial iceberg. There is generally minimal water inflow or outflow. The classic kettle hole bog has concentric zones of vegetation around a central pond: open water surrounded by a floating mat of sphagnum moss, sedges, and small shrubs, bordered by taller shrubs and stunted trees and an enclosing bog forest of conifers.
LACUSTRINE SYSTEM
A term used to describe lake environments and sediment deposits in lakes. In the USFWS classification system, the Lacustrine system refers to fresh, deepwater habitats that include lakes, deep ponds and reservoirs.*
MARSH, DEEP
A marsh with an average water depth between approximately six inches and three feet. Emergent vegetation and shrubs usually dominate, with areas of open water present (see also Marsh, Freshwater, Marsh, Salt).
MARSH, FRESHWATER
A type of emergent wetland that is usually seasonally or permanently flooded. Freshwater marshes support growth of emergent plants (e.g. cattails, pickerel weed), floating leaved plants (e.g. waterlilies, pondweeds), and submergents: (e.g. coontail) (see also Marsh, Deep; Marsh, Shallow).
MARSH, SALT
An emergent coastal wetland found along low lying shores or in the sheltered parts of estuaries, and dominated by salt tolerant plants, e.g. spartina (cordgrass) and eelgrass. Fine silts and mud are deposited by the tides in the backwaters, and are often added to by sediments brought down by rivers. Coastal salt marshes are usually tidal and inundated daily by seawater.
MARSH, SHALLOW
A wetland dominated by emergents, and having an average water depth less than approx. 6 inches.
MINERAL SOIL.
Any soil consisting primarily of mineral material (sand, silt, and clay) rather than organic matter.
MITIGATION
The creation of new wetlands, restoration or enhancement of existing wetlands, or permanent protection of undisturbed wetlands as compensation for wetlands impacted by human activity.
NITRIFICATION
The breakdown of ammonia or ammonia compounds by certain bacteria into a useable form of nitrogen for plants.
NON-PERSISTENT PLANTS See definition of Emergent Wetland.
NUTRIENT CYCLING
The mechanism of production, renewal and decomposition of nutrients within an ecosystem.
OBLIGATE (OBL)
A term for plant species that are nearly always found in wetlands, e.g. cattails, pickerel weed, as opposed to plant species that may grow either in wetlands or uplands (the facultative species). It is estimated that obligate species occur in wetlands 99-100% of the time.
OPEN WATER
A wetland class describing areas of open water less than 6.6 feet deep. Submerged or floating-leaved plants often grow in the shallower portions along the edges of the waterbody, e.g. bladderworts, waterlilies, etc. (see also Deepwater Habitat).*
ORGANIC SOIL
A soil that consists primarily of plant and animal residue in various stages of decomposition (see also Histosol).
PALUSTRINE SYSTEM
A term used to describe fresh water wetland environments dominated by trees, shrubs, emergents, mosses or lichens, other than those located along a river or lake (see also Lacustrine and Riverine.)*
PEAT
An acidic, fibrous, spongy soil, generally found in bogs, that develops from the accumulation of dead plant material (especially sphagnum moss), that decays slowly. Decay is slow due to low oxygen levels and the acidic, nutrient poor conditions characteristically found in bogs.
PERENNIAL STREAM
A stream that flows year-round because it is sustained by both ground water discharge and surface runoff.
PERSISTENT PLANTS See definition of Emergent Plants.
PRIME WETLAND DESIGNATION
A legal designation in the state of New Hampshire whereby a municipality votes to identify its "prime", or most outstanding, wetland(s) and submits the wetlands to the state Wetlands Board for consideration for "prime" designation. The designated wetlands are then given special consideration by the NH Wetlands Board when processing applications for projects impacting those wetlands.
RESTORATION
To restore previously degraded, filled, or dredged wetlands back to their original condition.
RIPARIAN
Refers to species and habitats that are located along the edge of a stream or river.
RIVERINE
A term used to describe wetland habitats that occur in and along rivers.*
RUNOFF See Surface Runoff.
SATURATION/SATURATED
A condition in which surface water is seldom present, but all the spaces between the soil particles are filled with water for most of the growing season (you may not see water, but when you walk your feet get wet).
SCRUB-SHRUB WETLAND
A wetland dominated by shrubs, saplings and other woody plants less than 20 feet tall, e.g. alder, buttonbush, red maple saplings. Water levels in scrub-shrub wetlands can range from intermittent to permanent flooding. Scrub-shrub wetlands may also be referred to as swamps (see also Swamp).*
SUBMERGENTS
Plants that grow and reproduce while completely submerged by water, e.g. milfoil and pondweeds. The flowering parts in some species are above water, e.g. bladderworts.
SUBSOIL
The weathered parent material which lies above the bedrock and below the true soil.
SUBSTRATE
That part of the subsoil that lies beneath the topsoil, and that has not been altered by weathering (the disintegration and/or decay of rock). The substrate is thus the surface beneath the wetland in which organisms grow or to which organisms are attached (this includes both plants and animals).
SUCCESSION
The gradual sequence of changes in plant species composition over time and leading to a mature ("climax") community, e.g. an open water body gradually fills in with sediment and decayed material, aquatic bed plants appear, emergents follow, then shrubs and trees, etc.
SURFACE RUNOFF
The movement of water over the land surface resulting from rainfall or snow melt. The percentage of precipitation that becomes runoff varies depending on the slope of an area, the degree of soil saturation, and the amount of vegetation coverage, e.g. on a steeply inclined asphalt surface, runoff will be 100%; on a nearly level vegetated surface, runoff will be substantially less.
SWAMP
A wetland where the soil is saturated and often inundated and the dominant vegetation is woody, including trees, shrubs and saplings, e.g. alder, sweetgale, red maple (see also Forested Wetland; Scrub-Shrub Wetland).
UPLAND
Refers to any area that does not qualify as wetland since the associated hydrology is not sufficiently wet for the development of the vegetation, soils and hydrologic characteristics usually associated with wetlands.
VERNAL POOL
Temporary ponds that fill with water in the spring as result of snowmelt, spring rains, and/or elevated ground water tables, and dry up later in the year. Many species of reptiles, amphibians, insects and invertebrates rely on vernal pools for breeding.
WATERSHED
All the land that surrounds a water body and that contributes water to it, i.e. all the precipitation in that area drains to a single water course.
WATER TABLE
The boundary beneath the ground at which all spaces in the permeable or fractured rock formation (including rock, sands or gravels) are filled with water. The water table may be located at or near the land surface, or at a depth below the land surface. The depth of the water table fluctuates seasonally throughout the year. Wetlands, springs and seepages may occur where the water table intersects the land surface.
WETLANDS
Those areas that are inundated or saturated by surface or ground water, support a prevalence of vegetation adapted for life in saturated soil conditions (i.e. hydrophytes), and are characterized by hydric soils. The term "wetlands" includes bogs, marshes, swamps, wet meadows, and similar areas.
WETLAND DELINEATION
The process of determining the physical boundary between a wetland and the adjacent upland using vegetation, soil samples and signs of wetland hydrology as indicators of "wetlandness". The wetland boundary is generally flagged on-site and drawn to scale on a map. Note: Delineation is a different process from wetland evaluation.
WETLAND EVALUATION
The process of determining the potential and/or actual characteristics, functions and values of a wetland (see also Functional Value; Functions of a wetland).
WETLAND HYDROLOGY
This term describes: 1) the hydrologic pathways (such as precipitation, surface runoff, ground water, tidal fluctuations, and flooding rivers) which transport nutrients to and from wetlands; 2) the water depth; 3) the flooding frequency and duration; and 4) the saturation of soils; in wetlands.
WETLAND INDICATOR STATUS
A term given to plant species which describes the frequency with which they occur in wetlands (see also Facultative Species; Obligate).
WET MEADOW
Seasonally flooded, emergent wetlands that have saturated soils for much of the growing season. Wet meadows are dominated by a variety of sedges, grasses, and rushes, and may often be cultivated or pastured.