Salt marsh restoration could bring carbon benefits

Mar 18, 2013 by Tom Marshall
Salt marsh restoration could bring carbon benefits
Breaching the sea defences at Tollesbury in 1995.

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 , the site was claimed for farming in the late , 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 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 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.

But managed realignment offers many other benefits. It can improve biodiversity, since salt marsh hosts many rare and valuable plant and animal species. It can help protect coastlines from flooding by creating a buffer zone between the sea and infrastructure or homes. It can let government bodies save cash on maintaining costly flood defences. And now this study, published in Coastal and Estuarine Science, suggests another possible benefit – absorbing copious carbon dioxide from the atmosphere and locking it up in the soil. This could help limit the impact of our carbon emissions on the climate.

Similar initiatives are afoot around peat bogs, another enormous store of carbon in the UK landscape. Scientists and conservationists are experimenting with blocking drains and other measures aimed at restoring peatlands that were drained in a misguided twentieth-century effort at turning them into .

This is where Burden's background lies. 'I wanted to take what we've learned about peat bogs and apply it to salt marsh,' she says. 'Peatland has had much more attention from scientists, but people are thinking that salt marsh could be just as important as a store of soil carbon.'

She thinks it's possible that per hectare of land, restoring salt marshes could even be more valuable from a carbon-management perspective than restoring peatlands. Re-wetting a peat bog initially makes it emit methane, itself a greenhouse gas; recreating salt marshes has no such drawbacks. But there is much more peatland that could be restored in Britain than salt marsh, so their overall effect is potentially more significant.

Other studies, some of which we've covered on Planet Earth Online (see links to the right) have shown that it takes a very long time for the mix of plants found in a natural salt marsh to return to a deliberately recreated one. The same seems to be true of the soil's carbon content.

She's now carrying out further research looking at a range of sites that stopped being farmed at different times due to breaches in sea defences during storms, some as long as 100 years ago, to get a better sense of how they develop over time. 'The Essex coast is brilliant for this kind of work, because you have so many places that were returned to saltmarsh at different times - it's like a natural experiment,' she says.

Explore further: US delays decision on Keystone pipeline project

Provided by PlanetEarth Online search and more info website

5 /5 (2 votes)
add to favorites email to friend print save as pdf

Related Stories

Salt marsh carbon may play role in slowing climate warming

Sep 26, 2012

A warming climate and rising seas will enable salt marshes to more rapidly capture and remove carbon dioxide from the atmosphere, possibly playing a role in slowing the rate of climate change, according to a new study led ...

Crabs put the pinch on marshlands

Sep 27, 2011

If you take a quick glance at the marsh next to Saquatucket Harbor in Harwich Port, Mass., you will notice right away that some of the grass is missing. The cordgrass there, and all around Cape Cod, has been slowly disappearing ...

Recommended for you

New research on Earth's carbon budget

8 hours ago

(Phys.org) —Results from a research project involving scientists from the Desert Research Institute have generated new findings surrounding some of the unknowns of changes in climate and the degree to which ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

Hev
1 / 5 (3) Mar 18, 2013
It is better to have more arable land. Then we have more to eat. That is why the land was drained in the first place. Salt marsh produces salt. We need something else.
Caliban
5 / 5 (2) Mar 18, 2013

It is better to have more arable land. Then we have more to eat. That is why the land was drained in the first place. Salt marsh produces salt. We need something else.


It is better to have arable land well above sea level.
Salt marshes and peatbogs provide a different, and entirely necessary, class of ecological services and benefits.

More news stories

Magnitude-7.2 earthquake shakes Mexican capital

A powerful magnitude-7.2 earthquake shook central and southern Mexico on Friday, sending panicked people into the streets. Some walls cracked and fell, but there were no reports of major damage or casualties.