Seagrasses Can Store as Much Carbon as Forests

Researchers find that the global carbon pool in seagrass beds is as much as 19.9 billion metric tons

Seagrasses are a vital part of the solution to climate change and, per unit area, seagrass meadows can store up to twice as much carbon as the world's temperate and tropical forests.

So report researchers publishing a paper this week in the journal Nature Geoscience.

The paper, "Seagrass Ecosystems as a Globally Significant Carbon Stock," is the first global analysis of carbon stored in seagrasses.

The results demonstrate that coastal seagrass beds store up to 83,000 metric tons of carbon per square kilometer, mostly in the soils beneath them.

As a comparison, a typical terrestrial forest stores about 30,000 metric tons per square kilometer, most of which is in the form of wood.

The research also estimates that, although seagrass meadows occupy less than 0.2 percent of the world's oceans, they are responsible for more than 10 percent of all carbon buried annually in the sea.

"Seagrasses only take up a small percentage of global coastal area, but this assessment shows that they're a dynamic ecosystem for carbon transformation," said James Fourqurean, the lead author of the paper and a scientist at Florida International University and the National Science Foundation's (NSF) Florida Coastal Everglades Long-Term Ecological Research (LTER) site.

The Florida Coastal Everglades LTER site is one of 26 such NSF LTER sites around the world in ecosystems from forests to tundra, coral reefs to barrier islands.

"Seagrasses have the unique ability to continue to store carbon in their roots and soil in coastal seas," said Fourqurean. "We found places where seagrass beds have been storing carbon for thousands of years."

The research was led by Fourqurean in partnership with scientists at the Spanish High Council for Scientific Investigation, the Oceans Institute at the University of Western Australia, Bangor University in the United Kingdom, the University of Southern Denmark, the Hellenic Center for Marine Research in Greece, Aarhus University in Denmark and the University of Virginia.

Seagrass meadows, the researchers found, store ninety percent of their carbon in the soil--and continue to build on it for centuries.

In the Mediterranean, the geographic region with the greatest concentration of carbon found in the study, seagrass meadows store carbon in deposits many meters deep.

Seagrasses are among the world's most threatened ecosystems. Some 29 percent of all historic seagrass meadows have been destroyed, mainly due to dredging and degradation of water quality. At least 1.5 percent of Earth's seagrass meadows are lost every year.

The study estimates that emissions from destruction of seagrass meadows can potentially emit up to 25 percent as much carbon as those from terrestrial deforestation.

"One remarkable thing about seagrass meadows is that, if restored, they can effectively and rapidly sequester carbon and reestablish lost carbon sinks," said paper co-author Karen McGlathery, a scientist at the University of Virginia and NSF's Virginia Coast Reserve LTER site.

The Virginia Coast Reserve and Florida Coastal Everglades LTER sites are known for their extensive seagrass beds.

Seagrasses have long been recognized for their many ecosystem benefits: they filter sediment from the oceans; protect coastlines against floods and storms; and serve as habitats for fish and other marine life.

The new results, say the scientists, emphasize that conserving and restoring seagrass meadows may reduce greenhouse gas emissions and increase carbon stores--while delivering important "ecosystem services" to coastal communities.

The research is part of the Blue Carbon Initiative, a collaborative effort of Conservation International, the International Union for Conservation of Nature, and the Intergovernmental Oceanographic Commission of UNESCO.

-NSF-

Scientists Unlock Record of Ecosystem Changes Frozen in World's Glaciers

New clues about how Earth's remote ecosystems have been influenced by the industrial revolution have been uncovered. Until now they were locked away, frozen in the ice of glaciers.

So say scientist Aron Stubbins of the Skidaway Institute of Oceanography and colleagues.

They published results of their study in the March, 2012, issue of the journal Nature Geoscience. It shows that everything flows downhill, eventually.

The research was funded by the National Science Foundation (NSF).

The key to the process is carbon-containing dissolved organic matter (DOM) in glacial ice.

Glaciers provide large amounts of carbon to downstream ecosystems. Many scientists believe the source of this carbon lies in ancient forests and peatlands overrun by the glaciers.

However, Stubbins and others think the carbon comes mainly from modern biomass and fossil fuel burning that makes its way onto the glaciers' surfaces.

Once deposited by snow and rain, the DOM moves with the glacier and is eventually delivered downstream where it provides food for microorganisms at the base of the aquatic food web.

"In warmer ecosystems like in the temperate or tropical zones, once this atmospheric organic material makes landfall it is quickly consumed by plants, animals and microbial populations," says Stubbins. "But in cold glacier environments, these carbon 'signals' are preserved."

Remote regions often are perceived as pristine and devoid of human influence.

But glaciers show us that nowhere goes untouched, Stubbins says. Burning fuels has effects on ecosystems far removed from industrial activity.

"Because deposition of combustion products is a global phenomenon, all ecosystems may be receiving this 'subsidy,'" says Matt Kane, program director in NSF's Division of Environmental Biology, which funded the study along with NSF's Divisions of Ocean and Earth Sciences.

"Some aquatic systems previously thought to be pristine have, in fact, been affected by human activities for a century or more."

Glacier ecosystems cover ten percent of the Earth, yet how carbon moves through these ecosystems isn't completely understood.

"More knowledge of glacier biogeochemistry is a priority, as glacier environments are among the most sensitive to climate warming and the effects of industrial pollution," says Stubbins.

Globally, glacier ice loss is accelerating, driven in part by deposits of carbon in the form of soot or "black carbon," which darken glacier surfaces and increase their absorption of light and heat.

Biomass and fossil fuel burning by people around the globe are the major sources of black carbon.

Stubbins and colleagues have conducted much of their research at the Mendenhall Glacier near Juneau, Alaska.

Mendenhall and other glaciers that end their journey in the Gulf of Alaska receive large amounts of rain and snow. This precipitation acts to strip the atmosphere of organic materials, then dumps them on the glaciers.

Consequently, these glaciers are among the most sensitive to global emissions of soot.

The researchers' findings also reveal that the ocean may have changed over past centuries as a result of this process.

The microbes that form the bottom of the food web are sensitive to changes in the quantity and quality of carbon entering the marine system.

The scientists found that the organic matter in glacier outflows stems largely from human activities. This means that the supply of glacial carbon to the coastal waters of the Gulf of Alaska is a modern, post-industrial phenomenon.

"When we look at marine food webs today, we may be seeing a picture that is significantly different from what existed before the late 18th century," says Stubbins.

"It's unknown how this man-made carbon has influenced the coastal food webs of Alaska, for example, and the fisheries they support."

A warming climate will increase the outflow of the glaciers and the accompanying input of dissolved organic material into the coastal ocean.

The effects will be most clear in glacially-dominated coastal regions, such as those off the Gulf of Alaska, Greenland and Patagonia. These areas have the highest rate of glacier ice loss.

"It's not known to what extent organic material deposition has changed, and will continue to alter, glacially-dominated coastal ecosystems or the open ocean," says Stubbins.

"But glaciers will continue to provide a valuable and unique window into the role this deposition of organic material plays in a rapidly-changing environment."

Stubbins' collaborators on the project include Eran Hood and Andrew Vermilyea of the University of Alaska Southeast; Peter Raymond and David Butman of Yale University; George Aiken, Robert Striegl and Paul Schuster of the U.S. Geological Survey; Rachel Sleighter, Hussain Abdulla and Patrick Hatcher of Old Dominion University; Peter Hernes of the University of California-Davis; Durelle Scott of Virginia Polytechnic Institute and State University; and Robert Spencer of the Woods Hole Research Center.

-NSF-