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Nature Gallery (Global Trends)

Loss of Wetlands

Importance of Wetlands
Wetlands, the transitional zones between land and water environments, are among the most biologically fruitful ecosystems, rivalling tropical rainforests in fertility. Scientists and land-use planners have only recently begun to appreciate the critical role played by marshes, swamps, bogs, lakes, estuaries, deltas, floodplains, and other wetlands in maintaining ecological balance.

Wetlands contribute to flood control, for example, by collecting excess rainfall and releasing it slowly over time rather than in a torrent. Wetland soil and vegetation filter contaminants out of water as it percolates through, returning cleaner water to rivers, lakes, and underground aquifers. In addition, wetlands provide indispensable habitat for hundreds of species of amphibians, birds, mammals, and plants. These areas are also important sources of food, both cultivated and naturally occurring. Rice, a staple crop for half the world, grows primarily in waterlogged paddies, and coastal wetlands are spawning grounds for commercial fish harvests.
Unfortunately, in some parts of the world awareness of these important wetland functions may have come too late. Because they were often perceived as worthless, mosquito-infested swamps, half of the world's wetlands have already been drained for agricultural use or as building sites. New Zealand has lost 90 per cent of its marshy terrain, and more than 70 per cent of European wetlands have disappeared. Even the immense peat bogs of England and Ireland, once thought to be an inexhaustible source of fuel, are 90 per cent depleted.

Draining and Filling Wetlands
A major factor in the decline of wetlands is the concentration of human populations along coastlines. About three-quarters of the world's people live near oceans, rivers, inland seas, and lakes, and many coastal marshes and bogs have been filled in as part of the relentless quest for buildable land. The waste products of human habitation, particularly sewage and highway runoff, contaminate the remaining wetland tracts and endanger wildlife.

In the continental United States, more than half of all native wetlands have been drained, filled, or polluted since colonial times. One estimate puts the rate of wetland loss at 24 hectares per hour (60 acres per hour) since 1780. With the loss of habitat comes a corresponding decline in flora and fauna: one-third of all endangered plants and animals in the US are wetland species, and some bird populations have fallen to 10 per cent of their historic levels.

The most conspicuous degradation in the US is in the Florida Everglades. Less than half of the original 1.6 million hectares (4 million acres) of marshland remains, and most of that is dissected with canals, spillways, and pumping stations. Runoff from sugar cane plantations adjacent to the Everglades has caused eutrophication, a condition in which rising levels of mineral and organic nutrients in the water encourage development of an ecosystem that favours plants over animals. Moreover, in the Everglades and in other US wetlands, acreage that was dried out for agricultural use has lost up to 1.8 metres (6 feet) of topsoil.

Governments around the world have imposed tougher regulations to protect existing wetland terrain. Although there is disagreement among environmental scientists about the extent to which lost wetlands can be reclaimed, many restoration efforts are also under way. In the Netherlands, for example, low-lying fields that had been drained of seawater using dykes and pumps are now being restored as coastal marshes. In the Everglades, attempts are being made to restore the natural flow of water that has been diverted by canals, spillways, and other human-imposed methods. As a result of 1993 floods along the Mississippi River, US federal and state governments are rethinking the use of dykes and levees for flood control. In some areas, natural floodplains will probably be restored, and people who live on or near river banks will be encouraged to move to higher ground.