Study: Tropical wetlands hold more carbon than temperate marshes

COLUMBUS, Ohio – In one of the first comparisons of its kind, researchers have demonstrated that wetlands in tropical areas are able to absorb and hold onto about 80 percent more carbon than can wetlands in temperate zones.

The scientists extracted soil cores from wetlands in Costa Rica and in Ohio and analyzed the contents of the sediment from the past 40 years. Based on their analysis, they estimated that the tropical wetland accumulated a little over 1 ton of carbon per acre per year, and the temperate wetland accumulated .6 tons of carbon per acre per year.

The temperate Ohio wetland in the study covers almost 140 acres, meaning it sequesters 80 tons of carbon per year. The tropical wetland covers nearly 290 acres and stores 300 tons of carbon each year.

"Finding out how much carbon has accumulated over a specific time period gives us an indication of the average rate of carbon sequestration, telling us how valuable each wetland is as a carbon sink," said William Mitsch, senior author of the study and an environment and natural resources professor at Ohio State University. "We already know wetlands are outstanding coastal protection systems, and yet wetlands continue to be destroyed around the planet. Showing that wetlands are gigantic carbon sequestration machines might end up being the most convincing reason yet to preserve them."

Mitsch, also director of the Wilma H. Schiermeier Olentangy River Wetland Research Park at Ohio State, conducted the study with graduate student Blanca Bernal, who presented a poster on this research Wednesday (10/8) at the Geological Society of America joint meeting in Houston.

Often called the "kidneys" of the environment, wetlands act as buffer zones between land and waterways. In addition to absorbing carbon and holding onto it for years, wetlands filter out chemicals in water that runs off from farm fields, roads, parking lots and other surfaces.

But wetlands are also a natural source of methane, and bacteria present during the decay of organic material cause wetlands to release this greenhouse gas into the atmosphere.