Carbon sequestration in freshwater wetlands in Costa Rica and Botswana

Tropical wetlands are typically productive ecosystems that can introduce large amounts of carbon into the soil. However, high temperatures and seasonal water availability can hinder the ability of wetland soils to sequester carbon efficiently. We determined the carbon sequestration rate of 12 wetland communities in four different tropical wetlands-an isolated depressional wetland in a rainforest, and a slow flowing rainforest swamp, a riverine flow-through wetland with a marked wet and dry season, a seasonal floodplain of an inland delta-with the intention of finding conditions that favor soil carbon accumulation in tropical wetlands. Triplicate soil cores were extracted in these communities and analyzed for total carbon content to determine the wetland soil carbon pool. We found that the humid tropic wetlands had greater carbon content (P a parts per thousand currency sign 0.05) than the tropical dry ones (96.5 and 34.8 g C kg(-1), respectively). While the dry tropic wetlands had similar sequestration rates (63 +/- A 10 g Cm-2 y(-1) on average), the humid tropic ones differed significantly (P < 0.001), with high rates in a slow-flowing slough (306 +/- A 77 g Cm-2 y(-1)) and low rates in a tropical rain forest depressional wetland (84 +/- A 23 g Cm-2 y(-1)). The carbon accumulating in all of these wetlands was mostly organic (92-100%). These results suggest the importance of differentiating between types of wetland communities and their hydrology when estimating overall rates at which tropical wetlands sequester carbon, and the need to include tropical wetland carbon sequestration in global carbon budgets.