Can wetland restoration cool the planet? produce energy, but if they can’t get oxygen, they can use other electron acceptors such as iron oxides, sulfate, and CO2. When they use CO2, they emit methane, he says. Because the tiny traces of methane gas from microbes are hard to measure, very few data are available on methane releases from wetlands, Bridgham says. He recently coauthored a chapter in The First State This summer, the U.S. of the Carbon Cycle Report, Geological Survey (USGS) in which he concluded announced that it was that the climate-warming launching a $12.3 million potential of methane very project to capture carbon likely cancels out the cliby growing tules (a spemate-cooling potential of cies of sedge also known CO2 storage for most as bulrushes) and cattails North American freshwain wetlands created on ter wetlands. In the future, farmers could be paid to grow cattails and abandoned farmland on Because saltwater is tules on this “carbon farm” in the Sacramento-San Joaquin islands in California’s River Delta. high in sulfate, microbes Sacramento-San Joaquin in saltwater marshes don’t River Delta. Two months since farmers drained the delta have to use CO2 as an electron later, the carbon-storing capacity island marshes 100 years ago, acceptor, and therefore they proof wetlands headlined 2 days of causing the soil to decompose, duce negligible amounts of methworkshops at the September 16 emit CO2, and subside, Fujii says. ane, Chmura says. She estimates meeting of the Association of A secondary goal is to find out that North American salt marshes State Wetland Managers in Portwhether the extraordinary carbon sequester an average of 210 g-C/ land, Ore. storage capacity of the tule and m2/yr. These hefty rates, along The USGS project has captured cattail “farms” could be sold as with an ability to accrete carbon eye-popping amounts of carbon credits on California’s upfaster as the sea level rises, make carbonsan average of 3000 grams coming CO2 cap-and-trade marsaltwater marshes ideal sites for of carbon per square meter per ket, he says. restoration and carbon storage, year (g-C/m2/yr) over the past 5 Scientists are excited by the she says. yr. For comparison, reforested agprospect of selling wetland carAlthough the USGS project ricultural land, eligible for carbon bon credits because the sales doesn’t have a reliable estimate of credits under the Kyoto Protocol could provide money and an admethane emissions from the exon climate change, socks away ditional reason for restoring wetperimental plots, initial measurecarbon at a rate much less than lands, says Scott Bridgham, an ments suggest that these 2 100 g-C/m /yr, says Gail Chmura, ecosystem ecologist at Oregon emissions may not cancel out the a biogeochemist at McGill UniverState University. “But if you don’t climate-cooling potential of the sity (Canada). know what the methane emisCO2 storage, says Brian Bergasions are, you can’t assume there Wetlands capture carbon by maschi, a biogeochemist with is a net climate-cooling impact,” incorporating CO2 from the air USGS. He and his colleagues are he says. into new plant growth, explains researching ways to add nutrients The low-oxygen conditions that Roger Fujii, a soil chemist with to the wetlands and to make wapromote carbon storage also proUSGS. When the plant material ter levels fluctuate to maximize mote release of methane, explains dies, near-constant water cover carbon storage while minimizing Ramesh Reddy, a biogeochemist keeps oxygen out of the rich mud, methane emissions. at the University of Florida. Mislowing decomposition that —JANET PELLEY crobes prefer using oxygen to would otherwise emit CO2. Undisturbed wetlands are so effective at accreting carbon that their organic peat soils can be 60 feet deep and 7000-10,000 years old, he says. USGS is now expanding the delta project to see whether it can regain the land elevation lost
8994 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / December 15, 2008
JIM NICKLES/USGS
Wetlands are champions at carbon storage, but they also release methane, a greenhouse gas 20 times more potent than CO2. Scientists are boosting research efforts to determine whether the cooling power of carbon storage outstrips the global warming potential of methane in wetlands. They are finding that the greatest cooling occurs from saltwater marshes.
10.1021/es802790q
2008 American Chemical Society
Published on Web 10/22/2008
