By Alister Doyle
OSLO (Reuters) - Man-made salt marshes meant to slow coastal erosion in England are failing to comply with European rules that demand they should be as rich in plant life as natural wetlands, a study showed on Thursday.
The report points to future problems for many nations in protecting coastlines under threat from sea level rise caused by global warming. Salt marshes, or tidal wetlands, are habitats for many plants and creatures from fish to migratory birds.
Artificial salt marshes "were nothing like as good as the natural ones that they are supposed to be replacing," Anthony Davy of the University of East Anglia, a co-author of the study in Thursday's Journal of Applied Ecology, told Reuters.
Both the European Union and the United States say that losses of wetlands should be compensated by the creation of new ones elsewhere. The European Commission says new wetland should have "equivalent biological characteristics."
The 18 artificial salt marshes studied in England were often featureless and typical marsh plants such as sea lavender, sea arrowgrass or sea plantain were under-represented compared to natural marshes, the study said.
The same lack of plant variety was also broadly true of 17 accidentally created salt marshes, some more than a century old. Many of these had formed when old sea walls had collapsed and let in the sea, it said.
The south of England is naturally subsiding into the sea, meaning that it is already experiencing coastal erosion similar to that predicted for many other regions of the world this century because of sea level rise.
"In the face of rising sea levels, managed coastal realignment has become an increasingly important option," the study said. It found that some plants, such as glasswort and seaside alkaligrass, were successful in man-made salt marshes.
Artificial salt marshes in south England are often created by re-locating sea walls inland and breaching the old, outer walls to let the sea to flood in. That creates a marsh as part of a managed retreat of the eroding coastline.
Salt marshes are found around the globe, from the Mississippi delta to the Camargue in the south of France. About half have been lost to causes such as drainage, to create farmland or to destroy breeding grounds for mosquitoes.
Many scientists reckon that sea levels could rise by perhaps a meter this century, up from 17 cms (7 inches) last century, as ice melts and water in the oceans expands because of warming caused by greenhouse gases from the burning of fossil fuels.
Davy said that one problem with artificial marshes was that they often lacked creeks for drainage. Deliberate plantings of a wide range of plant species might help as well as work to create creeks.
The United Nations Environment Programme has urged greater protection for salt marshes, sea grasses, mangroves and seaweeds partly because they soak up greenhouse gases from the atmosphere, helping to slow global warming.
(Reporting By Alister Doyle; Editing by Rosalind Russell)