Sea grass store as much carbon as forests. |
ScienceDaily, September 6, 2012
Destruction of
coastal habitats may release as much as 1 billion tons of carbon into the
atmosphere each year, 10 times higher than previously reported, according to a
new Duke-led study.
Published online
this week in PLoS ONE, the analysis provides the most comprehensive estimate of
global carbon emissions from the loss of these coastal habitats to date: 0.15
to 1.2 billion tons. It suggests there is a high value associated with keeping
these coastal-marine ecosystems intact as the release of their stored carbon
costs roughly $6-$42 billion annually.
"On the high
end of our estimates, emissions are almost as much as the carbon dioxide
emissions produced by the world's fifth-largest emitter, Japan," said
Brian Murray, director for economic analysis at Duke's Nicholas Institute for
Environmental Policy Solutions. "This means we have previously ignored a
source of greenhouse gas emissions that could rival the emissions of many
developed nations."
This carbon,
captured through biological processes and stored in the sediment below
mangroves, sea grasses and salt marshes, is called "blue carbon."
When these wetlands are drained and destroyed, the sediment layers below begin
to oxidize. Once this soil, which can be many feet deep, is exposed to air or
ocean water it releases carbon dioxide over days or years.
"There's so
little data out there on how much carbon might be released when these
ecosystems are disturbed," said Oregon State University's Daniel Donato,
co-lead author of the paper. "With this analysis we tried to reduce some
of that uncertainty by identifying some 'bookends' that represent the lowest
and highest probable emissions, given the information available."
The PLOS ONE study
looked at the potentially massive amount of carbon tucked away from the
atmosphere by the slow accretion, over hundreds to thousands of years, of soils
beneath these habitats. Previous work in the area has focused only on the
amount of carbon stored in these systems and not what happens when these
systems are degraded or destroyed and the stored carbon is released.
"These coastal
ecosystems are a tiny ribbon of land, only 6 percent of the land area covered
by tropical forest, but the emissions from their destruction are nearly
one-fifth of those attributed to deforestation worldwide," said Linwood
Pendleton, the study's co-lead author and director of the Ocean and Coastal
Policy Program at the Nicholas Institute. "One hectare, or roughly two acres
of coastal marsh, can contain the same amount of carbon as 488 cars produce in
a year. Comparatively, destroying a hectare of mangroves could produce as much
greenhouse gas emissions as cutting down three to five hectares of tropical
forest."
The critical role
of these ecosystems for carbon sequestration has been overlooked, the study
said. These coastal habitats could be protected and climate change combated if
a system -- much like what is being done to protect trees through Reducing
Emissions from Deforestation and Forest Degradation (REDD) -- were implemented.
Such a policy would assign credits to carbon stored in these habitats and
provide economic incentive if they are left intact.
"Blue carbon
ecosystems provide a plethora of benefits to humans: they support fisheries,
buffer coasts from floods and storms, and filter coastal waters from
pollutants," said Emily Pidgeon, senior director of Strategic Marine
Initiatives at Conservation International and co-chair of the Blue Carbon
Initiative. "Economic incentives to reverse these losses may help preserve
these benefits and serve as a viable part of global efforts to reduce
greenhouse gases and address climate change."
The work was funded by
Linden Trust for Conservation and Roger and Victoria Sant.
The study was led by
Linwood Pendleton of Duke's Nicholas Institute for Environmental Policy
Solutions and Dan Donato of Oregon State University. Others from Duke's
Nicholas Institute, Conservation International, ESA Phillip Williams &
Associates, U.S. Environmental Protection Agency, School of Public and
Environmental Affairs, Florida International University, Oregon State
University, Mediterranean Institute for Advanced Studies, Smithsonian
Environmental Research Center, International Union for Conservation of Nature
and the Ocean Conservancy contributed as co-authors.
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