Wetlands now cover just over 6 percent of the world’s land area, perhaps half their original extent. Some specialized communities still live in and exploit these ecosystems – for example the Marsh Arabs of Iraq and the 300 000 inhabitants of the Sundarbans of Bangladesh. But for most humans, wetlands have been regarded as disease-ridden wastelands fit only to be drained. Population density is a key determinant of the scale of wetland loss: when land or water are in short supply, wetlands are an obvious source¹.

In the 19th and 20th centuries, wetlands suffered because of the large-scale damming of rivers and pumping of groundwater to meet increasing demand for water. Thus the arid and heavily populated state of California has lost 91 percent of its wetlands in the past 200 years². The United States as a whole has lost 50 million of the 90 million hectares of wetlands it had 500 years ago.

Wetlands along the flood-prone Mississippi once stored 60 days of the river’s floodwater; today they are so reduced that they can only store 12 days’ worth. Those around the edge of Lake Victoria, the world’s second largest freshwater lake, have degraded so much in recent decades that they can no longer filter the nutrients such as nitrates and phosphates that flow into the lake from surrounding land. The result has been eutrophication and an explosive growth of water hyacinth that is clogging the lake.

People have created artificial wetlands for specific purposes such as rice paddies, farm ponds, and reservoirs on dammed rivers, but this has often been at the expense of natural
wetlands. In peninsular Malaysia, 90 percent of freshwater swamps have been drained for rice cultivation.

Conservationists have ensured that more than 800 of the world’s most important wetlands in around a hundred countries are protected as wildlife habitats under the 1971 Ramsar Convention. But there is an increasing realization that they have a large economic value to human society as well. They cleanse water of organic pollutants; soak up floodwaters, so preventing inundation downstream; protect riverbanks and seashores against erosion; recycle nutrients; capture sediment and recharge groundwater.

A study of the large Hadejia-Nguru wetland in arid northern Nigeria found that water in the wetland yielded a profit in fish, firewood, cattle grazing lands and natural crop irrigation that was 30 times greater than the yield of water being diverted from the wetland into a costly irrigation project³. A recent attempt to put a dollar value on the “ecological services” provided by different ecosystems worldwide put wetlands top at almost US$15 000 per hectare per year, seven times that of tropical rainforest⁴. Much of this value comes from flood prevention.

Wetlands store very large amounts of carbon in organic matter. Peat bogs in Siberia, North America and Scandinavia contain a third of all the carbon in the world’s soils. Scottish peat bogs contain more than 90 percent of the carbon in British soils and forests.

Much of the carbon in wetlands is released as methane by natural processes, accounting for roughly half of the methane currently released into the air. Molecule for molecule, this is a much more potent greenhouse gas than carbon dioxide⁵, and much more could be released if climate change warms and dries the northern peatlands, triggering slow destruction or catastrophic burning. Wetland maintenance is therefore significant in helping to moderate global climate change.

The world’s largest wetland restoration project will spend US$700 million over two decades to revive the Florida Everglades. It will include a series of six artificial wetlands known as “storm water treatment areas”, which will receive and clean up excess nutrients that enter the wetland from neighboring farming districts⁶.