"A big issue in wetland science is how carbon sequestration balances against the release of greenhouse gases," Mitsch said. "Methane is a more effective greenhouse gas than is carbon dioxide in terms of how much radiation it absorbs, but it also oxidizes in the atmosphere. Carbon dioxide does not degrade it is an end product. If you take that into account, I think wetlands are very effective systems for sequestering carbon."
Mitsch and Bernal collected soil cores from Old Woman Creek, a freshwater wetland near Lake Erie in northern Ohio, and from a similar flow-through wetland located at EARTH University in northeastern Costa Rica. Old Woman Creek had accumulated between 16 and 18 centimeters (about 7 inches) of sediment since 1964, while the Costa Rican wetland accumulated between 30 and 38 centimeters (12 to 15 inches) of sediment during the same time period.
To determine the age of the sediments, the researchers used radiometric dating with cesium-137. Above-ground nuclear testing in the mid-20th century left behind the cesium-137 compound as a marker in sediments throughout the world. Based on how deep cesium-137 was detected in the soil cores, the researchers were able to date sediment from each wetland that has built up since 1964, the year the concentration of the compound reached its peak.
The tropical wetland sediment was more densely packed with carbon. Its average carbon density was 110 grams of carbon per kilogram of soil (almost 1.8 ounces for every pound of soil), while the Ohio wetland's average carbon density was less than half that, 53 grams of carbon per kilogram of soil (.86 ounces per pound).
Mitsch and Bernal plan to conduct additional comparisons of carbon sequestration in wetlands from different climates to look for patterns that might inform policy
|Contact: William Mitsch|
Ohio State University