The recent surge in demand for food and biofuel has increased the risks facing the world's wetlands, warn scientists. A declaration by 700 scientists said the habitats faced a growing risk of being converted into farmland.

It also stated that the current knowledge of the extent of the world's wetlands was ""unacceptable"" and called for a global inventory to be set up.
The document was produced at the end of a UN-convened major scientific conference in Cuiaba, Brazil.
In their statement, the scientists highlighted other activities that were degrading the habitats, such as peat extraction and the construction of hydro-electricity dams.
""It is time to recognize the incalculable value of wetlands to all species - including ours,"" said Paulo Teixeira, co-chairman of the 8th Intecol International Wetlands Conference.
""If we don't plan and invest properly now, the cost to recreate artificially the services wetlands provide will dwarf the cost of preserving and protecting them in the first place.""
In their declaration, the scientists called on the 158 countries that were party to the international wetlands agreement, known as the Ramsar Convention, to adhere to the global framework. ""Some countries have high standards for wetlands management, restoration and protection; however, many others are far behind,"" it said.
They also warned against increasing farmland that encroached on the habitat, which caused damage through sediment, fertiliser and pesticide pollution.
""Biofuel production has led to a large loss of wetlands in the U.S. already,"" explained Eugene Turner from Louisiana State University. ""They are now growing as much corn to produce biofuels as they used to export out of the country.""
Professor Turner told BBC News that the surge in demand for the crop had resulted in agreements to conserve areas on the margins of farmland being broken.
""It is more profitable now to farm right up to the edge of a stream, so we are losing wetlands in the U.S. from this alone."" ""Of course, there are knock-on effects,"" he added. ""If you do not grow the corn while the price is high, then somebody else is going to produce it - maybe on a key wetland site.
""This is an example of how interrelationships are not considered when we make decisions.""
Another topic that was high on the conference agenda was the role the landscapes played in the global carbon cycle.
""Although that they may be 3-5% of the terrestrial surface, wetlands store about 20% of all terrestrial carbon, which amounts to 500-700 gigatonnes,"" explained Professor Turner.
""We are releasing, on a net basis, about 3.5 gigatonnes into the atmosphere, so any small change in the carbon from wetlands going into the atmosphere has a big impact.""
He added that the future well-being of wetlands in the Arctic region was of particular concern.
""The places where it is going to proportionally warm the greatest is towards the Arctic; that region has an awful lot of wetlands. ""You put food in a refrigerator at home to keep it cool; if you don't, it begins to rot.
""The same thing applies in the Arctic,"" he explained. ""The carbon is stored under the permafrost, meaning it is permanently frozen. ""The ice is receding, so the carbon that is stored there is going to be released and that is a problem.""
(Source: BBC)