Biodiversity of Wetlands


Executive Editor: George Clark; Editor: Paul Malamud
U.S. Department of State Office of International Information Programs

Sea grass in Indonesia. All pictures courtesy of

Wetlands -- marshy areas of land where the soil is saturated with water -- are crucial incubators of species diversity, as important as tropical rain forests and coral reefs. They exist on all continents, save Antarctica, and include salty coastal flats, such as estuaries, and inland systems. Scientists classify wetlands into bogs, swamps, marshes, and other types, depending on geography, soil, and plant life.

Wetlands help filter pollutants and soil runoff from upstream sources, which helps keep rivers, bays, and oceans downstream clean. In this way, healthy wetlands help mitigate the negative effects that human and farm waste, and some byproducts of industrial pollution, have on our Nation's water. Wetlands help control inland flooding and forestall wave erosion along shorelines; they diminish drought damage.

Mangroves in Indonesia

Coastal wetlands protect spawning and feeding grounds for valuable fish and shellfish. Mink, otter, and other mammal species thrive in North American wetlands, as do myriad plants and insects, amphibians, and reptiles. They are vital nesting grounds for birds. According to the U.S. Environmental Protection Agency (EPA), wetlands are essential to the survival of about a third of the endangered animal and plant species in the United States, and about half of these species make use of wetlands at some point in their life.

Unfortunately, especially in this century, the utility of wetlands has been poorly understood. They have been regarded as useless, or worse -- seen solely as breeding grounds for mosquitoes, other insects, or as sources of odors. Vast numbers of wetlands have been drained or destroyed to accommodate agriculture, dams, and human habitation.

Mangroves in Indonesia

It's estimated that over half of the wetlands in the continental United States have been lost since the 18th century; and wetlands elsewhere have fared no better. With the destruction of wetlands has come destruction of biodiversity, both in the wetland areas themselves and downstream. For instance, nitrogen fertilizer runoff from farms has overwhelmed the capacity of some wetlands to filter pollutants, creating "dead zones" in areas such as the Gulf of Mexico, where algae blooms fueled by this and other nutrients have run riot and displaced a once thrivingly diverse ocean ecology.

Wetlands in a sense are a biodiversity laboratory. For one, the diversity of conditions in wetlands set the environmental parameters that allow for, even encourage, the evolution of novel survival strategies. According to the EPA, for example, many bog species have "special adaptations to low nutrient levels, waterlogged conditions, acidic waters, and extreme temperatures." Vernal pools, ponds in winter and mud flats in summer, often include rare species that weather the drought as seeds, eggs, and cysts, and then grow into mature form when the ground is watery again. Mangrove swamps are full of shrubs and trees that have adapted to salty water.

Alaka'i swamp forest in Kauai, Hawaii

Wetlands are important to natural cycles involving water, nitrogen, and sulfur. Their plants and rich soil may provide one buffer against global climate change, by storing carbon instead of releasing it into the atmosphere as carbon dioxide.

In dollar terms, the services wetlands provide are invaluable. According to the EPA, the Congaree Bottomland Hardwood Swamp in South Carolina performs water purification functions equivalent to a five million dollar wastewater treatment plant. Wetlands act like giant sponges, storing, then slowly releasing ground water, melted snow, and floodwater. Because urban buildings and pavements release water runoff quickly, wetlands downstream from urban areas perform valuable flood control services.


In some cases, wetlands have been destroyed to create artificial flood control. Hardwood wetlands along the Mississippi river once stored 60 days' worth of floodwater. Now, due to filling or draining, they store 12 days' worth. Attitudes are changing. In the 1970's, the U.S. Army Corps of Engineers determined that draining 8,500 acres of wetlands near Boston would result in $17 million of flood damage per year - as a result, those wetlands were never drained. Even the finest wetlands, however, will ultimately be degraded or destroyed if too much pollution, silt, and non-native species are sent their way from upstream.


Many familiar animals -- ducks, falcons, bears, deer -- make use of wetlands. Some species of migratory fowl are completely dependent on wetlands. Most commercial fish breed and nurture their young in coastal marshes and estuaries. Such familiar species as striped bass, shrimp, oysters, clams, and crabs can't survive without wetlands. Consequently, wetlands are essential sources of food for burgeoning human populations. Other wetland harvests include blueberries, cranberries, wild rice, and timber, not to mention plants that are sources of medicine. On the Southeastern shore of the United States, almost all commercial fishing depends on healthy estuary wetlands. In 1991, commercial fish and shellfish taken from the state of Louisiana's coastal marshes contributed $244 million to that state's economy. Fur-bearing animals -- muskrat, beaver, and mink -- add millions more. Wetlands are popular with hunters, fishermen, and tourists: nearby towns enjoy economic benefits as a result.

In the United States, the Wetlands provision (1987) of the Clean Water Act established a "no net loss" policy for managing wetlands. In theory, this means that filled-in wetland areas should be offset with restored wetland acreage. In practice, this portion of the law has been slow to be implemented due to the differing interests of communities, environmentalists, and property owners. In addition, the government has offered tax deductions to people who donate or sell wetlands for conservation purposes, and has taken other measures to try to preserve them. Watershed conservation programs that include federal, state, local, and indigenous tribal governments have proved to be useful in managing streams, rivers, and wetlands.

Aerial view of large herd of African buffalo in the Okavango delta

It's difficult to conserve and restore wetlands; the short-term interests of landowners and farmers frequently clash with the long-term benefits of a sustainable natural ecosystem. In the United States, there is particular concern about wetland areas of the Mississippi River, the Missouri River, and the Everglades swamp in Florida. Large parts of these riverine systems have been re-engineered, dammed, and channeled. Previous to this century, 150 species of fish are thought to have cavorted in the lower Mississippi River; now there are 90. Four-fifths of the 8.8 million hectares of wetland forest near the river were cleared. The Lower Mississippi River Conservation Committee is hoping to restore 50 percent of filled-in secondary channels, restore 32,000 hectares of drained wetlands, and reforest 52,000 hectares of wooded wetlands, as a start.

In 1986, the U.S. Congress created the Missouri River Fish and Wildlife Mitigation Project. Over the years, the U.S. Army Corps of Engineers has used funds for this project to buy land from residents and use it to restore natural floodplain habitat.

Governments at all levels are becoming involved in wetlands restoration. The city of Cleveland, Ohio, is planning to spend millions to restore wetlands in the region to compensate for an airport expansion that will destroy a watery area. According to the Associated Press, in Bath, Michigan, "a run-down, garbage-strewn park has been restored as a wetland, home to native Michigan wildlife." In the New Orleans area, efforts are under way to restore wetlands, using aerial photographs from the 1930s and '40s to figure out where the wetlands were before they were destroyed.

Conversion of wetlands for oil palm plantations in Costa Rica

As part of a major effort to restore the Florida Everglades, Florida government officials and scientists are planning to construct five artificial wetlands on 17,200 hectares of land. In July, 2000, according to the Washington Post, "the Senate Environment and Public Works Committee reported out--a bill authorizing the first 10 of 68 planned projects meant not quite to restore the Everglades--that will never happen, but to revive and allow them to flourish once again."

Plans are under way to acquire and restore about 10,000 hectares of wetlands in the Kankakee River Basin of northwest Indiana. The Grand Kankakee Marsh used to extend over 200,000 hectares. About 4 billion (thousand million) dollars has been spent cleaning up Boston Harbor, and more is being done. Scientists are trying to come up with new answers, figuring out, for instance, how farmers could use computers to determine how to farm with the least amount of wetland-disrupting fertilizer.

The Pantanal in Brazil

Efforts in many parts of the world also play a vital role in preserving natural wetlands. The Australasian Wader Studies Group in conjunction with Wetlands International has completed five years of surveying and shorebird counting activities in China during the migration season, a step towards developing information about the importance of inland wetlands in China to bird species. Tasek Bera, the largest natural freshwater body in Malaysia, has been designated a Wetland of International Importance under the Ramsar Convention, raising the profile of an important cradle of many species. Often, the best advocates for wetlands are groups of concerned citizens and scientists willing to do exploration and to inventory declining species, and educators able to train local groups of people to better manage wetlands. Governments are becoming more sensitive to the need to protect wetland areas. A variety of approaches to wetland conservation, undertaken in many parts of the world, are effective in reversing or forestalling damage and in preserving biodiversity.

Caiman in the Pantanal

In the end, however, natural systems are so complex that they are difficult to restore, once highly polluted and degraded. In her book "The Work of Nature," ecologist Yvonne Baskin writes, "Certainly, restoration efforts to return previously damaged lands to ecological service should be encouraged. There are millions [of] hectares of rangelands, forests, and marsh on every continent that might be returned to health and productivity if complex environments could be rebuilt as skillfully as they are being dismantled." She points out, though, that "it would be far less costly to preserve robust natural systems rather than count on being able to piece them back together after they've been torn apart."



Benefits of Biodiversity
Traditional crop varieties and food security
Plant-based medicines
The death of global biodiversity
How to save biodiversity

Coral reefs
Endangered Forests [page 2]
Biodiversity of Wetlands
Arctic Biodiversity