Types of Wetlands

From Wetland Research

Most people know a wetland when they see one. However, a definition that encompasses all types of wetlands is not easily defined as one may think. There at least 30 definitions for a wetland, dependent on its characteristics.

In the United States, the EPA defines a wetland as follows:

An area that is regularly saturated by surface water or groundwater and is characterized by a prevalence of vegetation 
that is adapted for life in saturated soil conditions (eg, swamps, bogs, fens, marshes, and estuaries). 1994 EPA Definition

For an more in depth look at how the Definition of a Wetland affects policy.

As a general description, a wetland must be continually or partially inundated with water part of all of the year, have Hydric Soil and support vegetation that primarily lives in only wetlands.

One of the ways a wetland can be defined is by examining its vegetation. Although most all wetlands can be defined as either as a swamp, marsh or bog, they have similar characteristics, there are many variations, below are a few of the major types and subtypes and how they are differentiated. They are as follows:

[edit] Swamp

A swamp is easiest to identify visually as it populated with woody vegetation, primarily trees and shrubs. An example of a swamp is the hardwood swamps or bayous of Louisiana. A swamp is the most biologically active of all wetlands.

[edit] Slough

In the US, there are 2 different definitions for a Slough, dependent on geography. In the Eastern and Southeastern United States, a slough is a type of swamp or shallow lake system, typically formed as or by the backwater of a larger waterway. It is similar to a bayou with trees being present (that is, a swamp), and unlike a bog or marsh that lacks trees. It can also refer to the area of deeper water between a sandbar and a beach or between two sandbars.

In the western U.S., a slough is a secondary channel of a river delta or a narrow channel in a shallow salt-water marsh, usually flushed by the tide. While this is in essence the same application of the term as used in the eastern U.S., a singular difference is that there exist no native trees in the west that would grow out into the waterway to form a swamp.

In the northern Great Plains of the U.S. and Canada, a slough is a pond (often alkaline) usually the result of glaciation; also called a pothole, hence the Prairie Pothole Region to describe the area where these sloughs are abundant.

[edit] Marsh

A marsh differs from a swamp in that it contains little woody vegitation, rather it is primarily populated with grasses, such as the commonly found Spartina grasses (spp.Patens and Alterniflora). rushes, reeds, typhas, sedges, and other herbaceous plants in shallow water. A marsh differs from a swamp, which has a greater proportion of open water surface, and is generally deeper than a marsh. The water of a marsh can be fresh, brackish or saline. Coastal marshes may be associated with estuaries and along waterways between coastal barrier islands and the inner coast.

[edit] Bog

A type of wetland found in cold and temperate climates, most frequently found in the northern hemisphere. A bog accumulates peat over time, frequently populated by Sphagnum mosses with minimal or static waterflow. All or a large portion of the water provided for a bog is provided solely by precipitation, with the resultant fewer nutrients found in precipitation as compared to ground water. Also as a result of the minimal in and out flow of water, the bog waters are acidic. Also defined as a Mire.

[edit] Fen

A fen is a type of bog that receives more groundwater flow with dissolved minerals from surrounding areas that can support marsh like vegetation that a true bog would not be able to maintain. A rare type of calciferous fen is found in Minnesota.

[edit] Pocosins

The name pocosin comes from an Algonquin Indian term meaning “swamp on a hill.” Pocosins occur along the Atlantic Coast, particilarly in North Carolina and South Carolina and are dense thickets of shrubs and vines with pine trees, fed by seeps from perched water tables. Like bogs and fens, pocosins soils are acidic, sandy and peaty soils with partially decomposed plant material. Although pocosins are found on hilltops, they are more frequently found on shallow depressions or in valleys. There are two types of pocosins – tall and short. Short pocosins are characterized by minimal plant growth and stunted trees, due to their acidic and nutrient-poor conditions. Tall pocosins, on the other hand, have trees that tend to grow to normal height due to increased waterflow and nutrients.

[edit] Muskeg

[edit] Vernal Pool

A very unique temporary wetland in which it is completely dry at least part of the year. due to the interval in which it is dry, fish are not found in Vernal pools. Vernal pools are important breeding grounds for amphibians and some are protected due to fairy shrimp that are also know to breed exclusively in vernal pool. These pools are frequently found in the North East US as well as California. During the dry season, Vernal Pool locations can be identified by an unvegitated low lying patch of land, that fills with water during the spring and generally dissipating before mid summer.

[edit] Salt Marsh

A salt tolerant coastal grassland frequently inundated by saline tidal water. Populated by halophytic grasses.

[edit] Tidal Freshland Marsh

[edit] Playa

Playas are shallow, isolated, seasonal wetlands. They are typically located at the lowest point in a grassland or open plain, and retain water by virtue of their clay lining. The water found in the playa is most frequent received from rainfall and runoff, and playas are not normally fed by groundwater, hence they are only present at certain times of the year.