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Save that swamp!
To create more agricultural land, governments have drained marshes and swamps – thus losing a key element in water recycling and bio-diversity.
Wetlands have often been seen as wastelands, with governments seeking to drain them, whether to eliminate malaria and other water-borne diseases or to create more land for agriculture or development.
But now the world’s swamps, bogs and marshes are coming back into their own as scientists discover the vital role they play in regulating water quality and quantity, providing a critical habitat for plants and animals and influencing the local climate.
Wetlands capture and retain rainfall, and prevent valuable sediments from being washed into lakes and rivers. They add moisture to the atmosphere, which falls as rain and cools the environment.
They can even be used as sewage-treatment plants that require little technology or maintenance.
About half of the world’s wetlands, ranging from the fast-disappearing mangrove swamps in East Asia to the environmentally challenged Jamaica Bay marshes, a few miles from downtown New York, have disappeared in the last 100 years. Many of those that remain have been fragmented with dams, sluices and canals.
Mostly the wetlands have receded under pressure from growing populations and urban sprawl. But sometimes they have been deliberately eradicated as in Iraq, where Saddam Hussein’s regime drained most of the vast marshlands that have stood between the Euphrates and Tigris rivers since the dawn of history, and turned much of its population into refugees.
Patrick Denny, a wetlands scientist at the IHE-Delft Institute for Water Education (Netherlands), has spent much of his career in Uganda, the second country in the world after Canada to grant official protection to its extensive wetlands by constitutional law.
For Professor Denny a good wetland acts both as a sponge and a filter.
“It holds water, and allows a river to be released more slowly,” he says. “It keeps the rivers flowing. In the dry season it keeps the streams trickling. It gives time for the water to recharge the aquifer and keeps the water table up.’’
Without this sponge function, rivers flow faster and carry off valuable nutrients, soil and organic matter from up-stream. Not only is this an economic waste, but the nutrients can damage lakes and kill fish by promoting an explosive growth of algae and reducing the oxygen at deeper levels – a process known as eutrophication.
The effects of neglecting wetlands can be seen in the world’s largest tropical lake, Lake Victoria, which is bordered by Uganda, Tanzania and Kenya, and is a source of livelihood, food and employment for more than 30 million people.
The once astonishing diversity of fish species in the lake has been depleted not only by the introduction of aggressive non-native species but also because of the runoff of pollution and silt from the catchment.
Protection of the lake’s environment was one of the reasons that prompted the Ugandan government to adopt a national wetlands policy and enshrine it in the constitution. Despite a drastic reduction in the nation’s wetlands, swamps still occupy about 13 percent of Uganda’s territory.
“The classic word is that wetlands are wastelands,” says Professor Denny. “I can think of nothing further from the truth. If water and wetland systems are well managed, then health issues are not as serious as one might believe. Disease usually comes from poorly managed systems in which human beings themselves have changed the balance of nature. In a naturally functioning system with good biological diversity, you are not likely to have many mosquitoes because of the amount of fish, insects and birds that eat the larvae.”
Wetlands act as a natural purification. It is also possible to create small artificial wetlands to treat the sewage output of a village or clean the effluent from conventional sewage plants, which in Africa frequently fail to function because of electricity cuts and poor maintenance.
Seeded with fast-growing papyrus, which has many economic applications, the marshes not only filter out the impurities but recycle nutrients as well. This produces food for the invertebrates, which in turn provide nourishment for fish and birds.
“If you have more diversity, there is a greater chance that the people who live in those systems can have a sustainable way of life,” says Professor Denny. “Riparian people can ensure a supply of fish by helping nature by digging ponds where fish collect. The ponds remain flooded in the dry season: the fish are fed on domestic waste and can grow fat.”
Even industrialized nations, he says, are starting to undo some of the hard engineering of rivers and lakes and allow water to occupy natural flood plains with beneficial effects for the people, the environment, for biological diversity and for the aquifers.
Photo © (top) Patrick Denny/IHE, Delft/Dr Kansiime, Makerere University, Kampala: Fishponds on the edge of lake Victoria in Uganda. Fish are trapped during floods to build up stocks during the dry season when the ponds are cut off from the lake.
Photo © (bottom) M.L. Bonsirven-Fontana/UNESCO: Marshes in Iraq. Many of these vital zones have been totally destroyed.
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Author(s) |
Barry James
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Periodical Name |
The new Courier
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