Wednesday, October 22, 2008
ACS Publications: 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.
This summer, the U.S. Geological Survey (USGS) announced that it was launching a $12.3 million project to capture carbon by growing tules (a species of sedge also known as bulrushes) and cattails in wetlands created on abandoned farmland on islands in California’s Sacramento−San Joaquin River Delta. Two months later, the carbon-storing capacity of wetlands headlined 2 days of workshops at the September 16 meeting of the Association of State Wetland Managers in Portland, Ore. The USGS project has captured eye-popping amounts of carbon—an average of 3000 grams of carbon per square meter per year (g-C/m2/yr) over the past 5 years. For comparison, reforested agricultural land, eligible for carbon credits under the Kyoto Protocol on climate change, socks away carbon at a rate much less than 100 g-C/m2/yr, says Gail Chmura, a biogeochemist at McGill University (Canada).
Wetlands capture carbon by incorporating CO2 from the air into new plant growth, explains Roger Fujii, a soil chemist with USGS. When the plant material dies, near-constant water cover keeps oxygen out of the rich mud, slowing decomposition that 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 since farmers drained the delta island marshes 100 years ago, causing the soil to decompose, emit CO2, and subside, Fujii says. A secondary goal is to find out whether the extraordinary carbon storage capacity of the tule and cattail “farms” could be sold as carbon credits on California’s upcoming CO2 cap-and-trade market, he says....
