Draining of Wetlands

Wetlands are those places in the world where water intergrades with land. They include such diverse areas as swamps and bogs, marshes, mangroves, vernal ponds, and riverside seeps. Although these transitional environments cover only about 6 percent of the earth's surface, they are among the most important of ecosystems. They cleanse polluted waters, help to prevent floods, protect shorelines, recharge groundwater aquifers, and provide habitat for a rich diversity of plants and animals. Yet for all their importance, wetlands have been drained, ditched, and filled over the centuries. In the past 200 years, more than half of the original wetlands in the United States have been destroyed. In some parts of the world, natural wetlands are nearly extinct. This loss has severely harmed wetland-dependent biodiversity.

Humans have directly and drastically altered wetlands for a variety of reasons. An estimated 26 percent of the world's wetlands have been drained and the land converted to agricultural purposes alone. Wetlands have also been filled for development and construction. Many of our major cities located in coastal areas or along rivers have been built on filled wetlands. In addition, people have destroyed wetlands, thinking that they were nothing more than breeding places for disease and vermin. In particular, ditching and draining for mosquito control has altered the hydrology of many wetland systems. The damming of rivers has also changed water flow, damaging wetlands adjacent to the rivers. Interestingly, many of these activities—such as agricultural conversion, irrigation, and dam construction—have been implemented with government support. Indirectly, development of surrounding uplands has also affected wetland quality and function, by introducing pollutants and sedimentation into wetland systems via runoff.

We now know that wetlands are critically important habitats, providing many ecological services for free that would cost billions of dollars to duplicate. Although wetlands are still under threat, today there are many worldwide efforts to protect and restore wetlands. Some countries have established legislation to protect wetlands as natural areas or to enforce the maintenance of water quality. Restoration—that is, the return of a degraded ecosystem to its former, undisturbed chemical, physical, and biological conditions—is also an important conservation tool. To accomplish this, dams are being reopened to restore river flow, which allows the natural cycles of flooding and sediment deposition to function in the adjacent wetlands. Tile drains that had been installed in agricultural fields to drain off water are being removed. Rivers and streams are being cleaned up by reducing point and nonpoint source pollution. (Point source pollution is contamination that originates from one place, such as a sewer pipe; nonpoint pollution comes from many sources, such as road runoff, lawn chemicals, and so forth.)

In addition to habitat restoration, wetland creation and mitigation are two other strategies being used to combat wetland loss. Wetland creation usually entails digging a completely new wetland in a nonwetland site, instead of restoring an existing one. Mitigation is a program whereby for each acre of wetland that is drained or filled another, comparable area is created anew, or restored to offset the loss. In general, wetlands are best protected in situ, where they are hydrologically and ecologically linked to the landscape—either by preventing their destruction in the first place, or by careful restoration.

—Elizabeth A. Johnson

See also: Coastal Wetlands; Dams; Interior Wetlands; Pollution; Rivers and Streams


Mitsch, William J., and James G. Gosselink. 1993. Wetlands. New York: Van Nostrand Reinhold; Moser, Michael, Crawford Prentice, and Scott Frazier. "A Global Overview of Wetlands Loss and Degrada tion." Wetlands International, http://www.ramsar.org; Ramsar Convention on Wetlands, http://www.ram-sar.org; U.S. Environmental Protection Agency, Office of Water, http://www.epa.gov/

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