July 5, 2001 (UPI) -- About half of the world's wetlands have disappeared in the past 100 years, gobbled up by agriculture, development, water diversion projects and dredging.

Pollution, water extraction, dam construction and excessive hunting and fishing also contribute to the deteriorating ecological health of these areas.

Wetlands such as marshes, swamps, ponds, bogs and shallow areas in lakes and along river banks are crucial to naturally occurring water purification, flood control and as habitat to tens of thousands of species of plants and animals that cannot survive elsewhere. They also contribute to the recharge of vital water aquifers.

While marshes and swamps used to be seen as places to be drained and filled, it is now understood how critical these areas are to humans as well as plants and animals.

A report from the Organization for Economic Cooperation and Development titled, "Conservation and Sustainable Use of Tropical and Subtropical Wetlands," says there is ample cause for concern. "With the pressure for development increasing, the loss of wetlands has reached alarming proportions, initially in the developed countries over the last century, but also over the last 40 years, in the tropics and sub tropics," the report says.

The OECD, with 30 member nations, estimates agriculture is responsible for about 60 percent of total wetlands loss in Europe and North America, 27 percent in Asia, 6 percent in South America and 2 percent in Africa. The United States and Europe have lost more than half their wetlands.

"One half of the world's wetlands lost over the last century or so is considered a very reliable estimate by scientists," according to Janet Abramovitz, a senior scientist at Worldwatch Institute, a Washington-based organization concerned with developing environmentally sound approaches.

Wetlands are areas not considered to be fully dry land nor completely aquatic. They can range from swamps that may be wet almost permanently to areas that hold water only a few days a year. Soil that is fully saturated with water and specific types of vegetation also are characteristics that help define wetlands.

Because wetlands have the capacity to soak up water like a sponge, they often provide critical absorption capacity to help prevent flooding. Because unique forms of bacterial activity occur in the water-soaked soils, water purification occurs, such as the removal of potentially harmful nitrates. From Botswana to the heart of South America, from the Mississippi to the Mekong, the vital and irreplaceable resource of wetlands is coming under intense pressure as development intensifies around the world at lightning speed.

A good example is a huge ship channel engineering project on the Parana River that flows 2,500 miles (4,000 kilometers) from Brazil, down through Paraguay and Argentina to empty into the Atlantic Ocean. Near the headwaters of the Parana is the largest continuous wetlands in the world, the Pantanal.

The Pantanal wetlands cover 50,000 square miles, (128,000 sq. km.) and provide habitat to more than 600 species of birds, 200 kinds of fish and nearly 100,000 types of plants. Marsh deer, giant otters, anteaters and jaguars inhabit this region of great biodiversity. Additionally, the Pantanal wetlands performs the sponge action, regulating flooding in the region.

Giant industrial concerns and powerful political forces in Brazil, Argentina, Paraguay, Uruguay and Bolivia are pushing to create the Hidrovia, a project that would massively alter the nature of the region by changing the Parana River so that ocean going ships could navigate up river for a thousand more miles than currently allowed.

A coalition of 300 groups, Rios Vivos -- Living Rivers -- is protesting, saying the project is intended to marginally lower the cost of shipping soybeans by boat in order to feed hogs and chickens in Europe. The group says giant conglomerates are attempting to manipulate the process and the negative environmental impacts far exceed the economic benefits.

"Like a lot of river engineering projects, the economic costs have been understated, the returns have been overstated," Abramovitz said.

In Africa, in the Okavango Delta of Botswana, one of the largest inland wetlands in the world is under pressure as water demands for development, which includes agriculture, mining and home use, is threatening this uniquely rich area of plant and animal biodiversity. The Okavango has more than 2,000 species of plants, 65 species of fish and 450 types of birds. It has become the focus of the international attention of conservationists and organizations that want to preserve this unique 5,800-square-mile region.

In Southeast Asia, the 2,600-mile (4200 km) Mekong River runs through a basin shared by large parts of Thailand, Cambodia, Laos, Vietnam and a small portion of China. Wetlands in the Mekong River delta are threatened by massive water diversion projects and large-scale hydroelectric projects upstream.

The fish catch in the Tonle Sap Lake has been reduced to half its previous level. Millions of people in Cambodia and Vietnam depend of the fish for about 80 percent of their protein intake. The threatened Mekong has the second greatest diversity of plants and animals of any river in the world.

Carmen Revenga, a researcher on fresh water systems at the World Resources Institute, told United Press International: "In most of the developing world, the problem is that the wetlands are being drained because of water diversion projects upstream for irrigation. The people growing the crops are not the ones that depend on the wetlands downstream."

Revenga said one idea is to look at an entire watershed and manage it more as a unit rather than piece by piece to see the effects of upstream users on downstream users. Getting international cooperation in a situation in which each country sees its needs as paramount will not be easy.

One of the worst cases of wetlands destruction has been along the Mississippi River. Conversion to agriculture and towns created a situation that fosters flooding and has radically reduced the natural ability of wetlands to remove nitrates from fertilizer-rich agricultural run-off. As a result there is now a large "dead-zone" downstream in the Gulf of Mexico from nitrate contamination.

"Because a lot of the services provided by wetlands are not traded in the marketplace, they don't really have a dollar value, but we've seen examples of how costly it is to restore wetlands and how costly it is to have massive floods," Revenga said. "By preventing deterioration in the wetlands it is possible to avoid a lot of costs later on."

Copyright 2001 by United Press International.