February 14, 2013
Study Says Wetland Trees Significant Source Of Greenhouse Gas Methane
Lee Rannals for redOrbit.com - Your Universe Online
While wetlands represent an enormous source of atmospheric methane, researchers taking measurements of the gas at ground level in these regions have noticed a significant drop in methane levels compared to what they have measured in the air around tropical areas.
The team of scientists studied both swamps and flooded forests in the tropics. After taking ground-based measurements of methane, they found that levels of the simple organic gas have fallen short of the quantities detected in tropical air by satellites.
During the study, the team spent several weeks in a forested peat swamp in Borneo, trying to determine whether soil methane might be scaling to the atmosphere through an alternative route.
"Methane emissions are normally measured by putting sealed chambers on the ground to capture gas seeping or bubbling from the soil," said Sunitha Pangala, a PhD student at The Open University who worked on the study. "We also enclosed tree stems in chambers and the results were surprising. About 80 per cent of all methane emissions was venting through the trees."
Tree roots need oxygen in order to survive, and one strategy they depend on in order to cope with waterlogged soils is to enlarge porous structures in their stems to allow air to enter and diffuse to their roots.
From their research, the team was able to show that these adaptations made by wetland trees serve as two-way conduits that also allow soil gas to escape to the atmosphere.
"This work challenges current models of how forested wetlands exchange methane with the atmosphere," said Dr Vincent Gauci of The Open University, who led the study. "Ground-based estimates of methane flux in the tropics may be coming up short because tree emissions are never included in field campaigns."
The trees that the team investigated for the study are considered common in tropical regions like the Amazon Basin. Determining whether tree-mediated emissions of methane are ubiquitous in tropical wetlands was the focus of a new three-year Natural Environment Research Council (NERC) grant that the team received. Work on this study will begin later on this year.
Methane gas is known to have a greater ability to trap heat in the atmosphere than carbon dioxide and is considered one of the most important greenhouse gases. Recent research revealed that greenhouse gas emissions from beef cattle have a carbon footprint of 23.5 to 49.8 pounds of carbon dioxide equivalent per pound of carcass.