Soil Organic Carbon Stocks in a Large Eutrophic Floodplain Forest of the Southeastern Atlantic Coastal Plain, USA

Anthropogenic land use has significantly altered sediment and nutrient dynamics at watershed-scales, resulting in significant redeposition within large floodplain ecosystems. Some upland land uses have had documented negative effects on soil carbon (C) stocks, although the specific impacts of these disturbances on soil organic carbon (SOC) dynamics in depositional environments are poorly understood. Assessment of SOC stocks in floodplain environments will allow for more precise estimates of C distribution at watershed and regional scales. In this study, we measured SOC pools to depths of 100 and 200 cm in four distinct floodplain landscapes (natural levee, flats, mineral wetlands, organic wetlands) in a large bottomland forest within Congaree National Park, South Carolina, USA. Mean SOC stocks to a depth of 100 cm were 108-109 Mg C ha(-1) in flats and levees, 193 Mg C ha(-1) in mineral wetlands, and 533 Mg C ha(-1) in organic wetlands. In addition, hydric soils contained significantly more SOC in deep horizons (100-200 cm depths). At a regional scale, similar alluvial soils within large floodplains were estimated to store approximately 0.l Pg of SOC. These results highlight the importance of inclusion of deep SOC storage in alluvial settings when estimating watershed C budgets.