Current Threats to Wetlands

Even with a greater sense of the value of wetlands among much of the public, there are still pressures on these habitats. The ability of wetlands to

Wetlands develop wherever there is a depression in the land that brings the water table close to or even above ground.

enzyme a protein that controls a reaction in a cell enzyme a protein that controls a reaction in a cell

community a group of organisms of different species living in a region

community a group of organisms of different species living in a region

GROWTH HABITS OF WETLAND PLANTS

Growth Habit

Examples

Completely submerged

Floating plants, unrooted in substrate Floating leaves, rooted in substrate

Emergent perennials: roots in substrate under water, leaves and stems above water Emergent shrubs Trees: constantly submerged Trees of floodplains: tolerate periodic flooding

Sea grasses, pondweeds, water plantain, water milfoil, elodea Duckweeds, bladderworts, water hyacinth Water lilies, lotus, floating hearts, water chestnut

Cattails, common reed, purple loosestrife, salt marsh grasses, tule, saw grass, wild rice Buttonbush, alders, leather leaf, sweet gale Mangroves, bald cypress, black spruce Cottonwood, willow, silver maple, black ash absorb pollutants is not unlimited. Excessive amounts of pollution entering a wetland over a long period of time is likely to cause long-term changes in the wetland. One of the world's most famous wetlands, the Everglades of southern Florida, has suffered for years from pollution from fertilizers used by farms upstream from it. The pollution has resulted in some major changes in the plant community and suspected declines in the diversity of animals it supports.

Another major threat to wetlands is changes in hydrology (the flow of water). Water is the lifeblood of wetlands. If too much water is removed for human consumption or to irrigate cropland, the wetland may be degraded into a less-valuable habitat or even disappear completely. The Florida Everglades has to compete with the farms and rapidly growing cities of southern Florida for this precious resource and has suffered as a result. Not only is the quantity of water important to maintaining wetlands, but so is the timing. Many wetlands depend on seasonal flooding followed by a dry period. This type of natural cycle may be altered by dams, which may hold back the water during the wet season.

Direct filling of wetlands, although less common than it was twenty years ago, still occurs, particularly with smaller wetlands that may be perceived as less valuable than larger ones. Some small wetland types contain rare species of animals precisely because they are too small and temporary in existence to support fish predators, pointing out that size is not always a good indicator of value.

Finally, many wetlands throughout the world are threatened by invasions of nonnative plant species. Purple loosestrife, a European garden plant, has taken over many freshwater marshes in the northeastern United States. West Coast salt marshes are threatened with being overrun by tall cordgrass, an East Coast salt marsh species. These are only two examples of a very widespread problem. see also Aquatic Ecosystems; Aquatic Plants; Carnivorous Plants; Endangered Plants; Invasive Species; Peat Bogs.

Robert Buchsbaum

Bibliography

Mitsch, William J., and James G. Gosselink. Wetlands, 3rd ed. New York: John Wiley & Sons, 2000.

Niering, William A., and Charles Elliot, eds. Wetlands. National Audubon Society Nature Guides, 1983.

Tiner, Ralph W. In Search of Swampland: A Wetland Sourcebook and Field Guide. New Brunswick, NJ: Rutgers University Press, 1998.

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