Salt Marsh Carbon May Play Role in Slowing Climate Warming
ScienceDaily (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 by a University of Virginia environmental
scientist and published in the Sept. 27 issue of the journal Nature.
Carbon dioxide is the predominant so-called "greenhouse
gas" that acts as sort of an atmospheric blanket, trapping Earth's heat.
Over time, an abundance of carbon dioxide can change the global climate,
according to generally accepted scientific theory. A warmer climate melts polar
ice, causing sea levels to rise.
Aerial view of a salt marsh at Virginia's Eastern Shore. (Credit: Fariss Samarrai) |
A large portion of the carbon dioxide in the atmosphere is
produced by human activities, primarily the burning of fossil fuels to energize
a rapidly growing world human population. "We predict that marshes will
absorb some of that carbon dioxide, and if other coastal ecosystems -- such as
seagrasses and mangroves -- respond similarly, there might be a little less
warming," said the study's lead author, Matt Kirwan, a research assistant
professor of environmental sciences in the College of Arts & Sciences.
Salt marshes, made up primarily of grasses, are important
coastal ecosystems, helping to protect shorelines from storms and providing
habitat for a diverse range of wildlife, from birds to mammals, shell- and
fin-fishes and mollusks. They also build up coastal elevations by trapping
sediment during floods, and produce new soil from roots and decaying organic
matter.
"One of the cool things about salt marshes is that they
are perhaps the best example of an ecosystem that actually depends on carbon
accumulation to survive climate change: The accumulation of roots in the soil
builds their elevation, keeping the plants above the water," Kirwan said.
Salt marshes store enormous quantities of carbon, essential
to plant productivity, by, in essence, breathing in the atmospheric carbon and
then using it to grow, flourish and increase the height of the soil. Even as
the grasses die, the carbon remains trapped in the sediment. The researchers'
model predicts that under faster sea-level rise rates, salt marshes could bury
up to four times as much carbon as they do now.
"Our work indicates that the value of these ecosystems
in capturing atmospheric carbon might become much more important in the future,
as the climate warms," Kirwan said. But the study also shows that marshes
can survive only moderate rates of sea level rise. If seas rise too quickly,
the marshes could not increase their elevations at a rate rapid enough to stay
above the rising water. And if marshes were to be overcome by fast-rising seas,
they no longer could provide the carbon storage capacity that otherwise would
help slow climate warming and the resulting rising water.
"At fast levels of sea level rise, no realistic amount
of carbon accumulation will help them survive," Kirwan noted.
Kirwan and his co-author, Simon Mudd, a geosciences
researcher at the University of Edinburgh in Scotland, used computer models to
predict salt marsh growth rates under different climate change and sea-level
scenarios.
The United States Geological Survey's Global Change Research
Program supported the research.
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Online at (re-posted from):
Journal Reference:
Matthew L. Kirwan, Simon M. Mudd. Response of salt-marsh carbon accumulation to climate change. Nature, 2012; 489 (7417): 550 DOI: 10.1038/nature11440