May 13

swamp Photo Credit: Clipart.com

Today in Science

American Wetlands Month

May is American Wetlands Month.

A wetland is an ecosystem that is saturated with water, permanently or seasonally -- which determines the anaerobic soil makeup and the types of plants and animals that live nearby. Wetlands can be freshwater, saltwater, or brackish (which is means the water is saltier than freshwater but less salty than saltwater) and can occur inland, near rivers, or along the coast. They are found on every continent, except for Antarctica.

The four major wetland types are swamps, marshes, bogs, and fens.

A swamp is a wetland where the primary vegetation is water-tolerant trees, such as cypress, or hard-stemmed shrubs, such as mangroves. It serves as home to many animals that do not thrive well elsewhere and offers protection from flood damage. The soil in a swamp is particularly nutrient-rich, which has led to many of them being drained for agricultural uses.

A marsh is a wetland where shallow water covers the ground all or most of the time and comes from surface sources, as well as, sometimes, from groundwater. There are two types -- tidal and non-tidal. Marshes support soft-stemmed plants, like lilies, and a large variety of plants and animals. Marshes serve to replenish groundwater sources and streams, particularly during times of drought; mitigate flood damage; and clean pollutants from water sources.

A bog is a wetland that has a sphagnum moss-covered ground, deposits of peat formed by the decaying moss, and acidic waters that arise from it being fed by rainwater, rather than groundwater or surface water. Bogs are home to plants (and a few animals) unique to its nutrient-poor, acidic ecosystem, such as the pitcher plant. It, too, can help alleviate flooding, as well as serving as a depository for large amounts of carbon, which might otherwise add to global climate change.

A fen also has deposits of peat, but its source is groundwater -- often glacial run-off. This makes it far less acidic and, therefore, far more nutrient-rich. As such, it supports many types of grasses, flowers, and animals and may resemble a meadow to the casual observer. Like the other types of wetlands, it can help moderate flood damage. Because a fen is peat-based, the peat can sometimes build up in a way that cuts the fen off from its groundwater source. If that happens, the fen slowly turns into a bog. A fen is the rarest type of wetland.

Check out these Science NetLinks resources on wetlands:

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