Allowing farmland that's
been reclaimed from the sea to flood and turn back into salt marsh could make
it absorb lots of carbon from the atmosphere, a new study suggests, though the
transformation will take many years to complete.
Scientists looked at one
of the oldest such places in the UK, Tollesbury in Essex. Originally a salt
marsh, the site was claimed for farming in the late 18th century, but
eventually relinquished in 1995 when the bank separating it from the sea was
deliberately breached. Since then it's been reverting to its natural state, though
this is very slow process.
'People want quick results, but these things take time,' says lead author Annette Burden, a wetland biogeochemist based at the Centre for Ecology & Hydrology in Bangor. 'You can't expect a piece of land that's been farmed for a century to turn overnight into something like a saltmarsh that has been there for thousands of years. But the evidence is that this will eventually happen, and this study suggests that the land starts absorbing carbon very quickly after its flood defences are breached.'
In 2010 the researchers
looked at how carbon moves between soil and air at the site, and at the total
amount of carbon accumulated in the soil. They compared the results to nearby
natural saltmarsh and farmland.
Their results show that
the Tollesbury site exchanges carbon with the atmosphere at a similar rate to
the natural marsh, absorbing around 0.92 tonnes of carbon per hectare per year.
But even after 15 years its total carbon content is far smaller and its general
biological functioning is still very different — the authors think it could
take a century or more to catch up.
Known as coastal managed
realignment, the process of turning farmland back into salt marsh involves
breaching sea walls and letting the land revert naturally to how it once was.
It's done for a variety of reasons. At present the main one is to comply with
the EU Habitats Directive, which obliges the UK to replace salt marsh that's
lost to development with new 'biologically equivalent' habitat elsewhere.
Read more at Planet Earth
Online.
