Six Types of Wetlands

Swamps and marshes have mineral soils with sand, silt, or clay. Swamps are dominated by trees or shrubs, whereas marshes are dominated by herbaceous plants such as cattails and reeds. Such wetlands tend to occur along the margins of rivers or lakes, and they often receive fresh layers of sediment during annual spring flooding. Marshes are among the world's most biologically productive ecosystems.

Fens and bogs have organic soils (peat), formed from the accumulation of partially decayed plants. Nutrients such as nitrogen and phosphorus are therefore scarce. Many bog plants are shrubs with small evergreen leaves (sclerophyllous shrubs or ericaceous shrubs). Carnivorous plants obtain nitrogen and phosphorus from the bodies of captured inverte brates. Most peatlands occur at high latitudes in landscapes that were glaciated during the last ice ages. In fens the layer of peat is relatively thin, allowing the longer roots of the plants to reach the mineral soil beneath. In bogs plants are entirely rooted in the peat. As peat becomes deeper (the trend from fens to bogs), plants become increasingly dependent upon nutrients dissolved in rainwater, eventually producing an ombrotrophic bog. Peat has been a traditional fuel in many European countries. The large amounts of organic carbon stored in peatlands help reduce global warming.

Wet meadows occur where land is flooded in some seasons and moist in others, such as along the shores of rivers or lakes. This often creates particularly high plant diversity, often including carnivorous plants and orchids.

Figure 1

Creation of Interior Wetlands by Varying Water Regimes and Nutrient Supplies

PRECIPITATION I SURFACE OR GROUNDWATER DEPENDENT DEPENDENT |

temporary shallow lakes salt flats I floodplains

PRECIPITATION I SURFACE OR GROUNDWATER DEPENDENT DEPENDENT |

temporary shallow lakes salt flats I floodplains

_ wetlands of saline habitats

. grouping acc. to Ruuhijaarvi 1983

approximate degree of peat formation trees bogs I fens

(mainly sphagnum) | poor fen permanent shallow lakes (fresh, saline or alkaline)

_ wetlands of saline habitats

. grouping acc. to Ruuhijaarvi 1983

approximate degree of peat formation trees bogs I fens

(mainly sphagnum) | poor fen permanent shallow lakes (fresh, saline or alkaline)

Nutrient Poor (oligotrophic)

Nutrient Supply

Nutrient Rich (eutrophic)

Source: Gopal, B., J. Kvet, H. Loffler, V. Masing, and B. C. Patten, B. 1990. "Definition and Classification." In Wetlands and Shallow Continental Water Bodies. Vol.1. Natural and Human Relationships. Edited by B. C. Patten. The Hague, The Netherlands: SPB Academic Publishing. p. 14, fig. 4. (Reprinted with permission).

Note: Different kinds of interior wetlands are created by different kinds of environmental conditions. The water regime and nutrient supply (upper left) are the most important factors. The more combinations of environmental conditions in a landscape, the more biological diversity that will occur.

Examples of wet meadows include wet prairies, slacks between sand dunes, and wet pine savannas. Pine savannas may have as many as forty species of plants in a single square meter, and hundreds of species in a hundred hectares.

Aquatic wetlands are covered in water, usually with plants rooted in the sediment but possessing leaves that extend into the atmosphere. Grasses, sedges, and reeds emerge from shallow water, whereas water lilies and pondweeds with floating leaves occur in deeper water. Aquatic wetlands provide important habitat for breeding fish and migratory waterfowl. Animals can create aquatic wetlands: beavers build dams to flood stream valleys, and alligators dig small ponds in marshes or wet meadows.

The two largest interior wetlands (of more than 750,000 square kilometers) are the Amazon River basin and the West Siberian lowland. The Amazon is a tropical lowland with freshwater swamps and marshes containing more kinds of trees and fish than any other region of the world. The West Siberian lowland consists largely of fens and bogs, many of which drain by way of the Ob River north into the Arctic Sea.

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