THE ROLE OF ALLUVIAL LANDFORMS IN STORING SOIL ORGANIC CARBON: A CASE STUDY FROM HUMID-TEMPERATE WESTERN KENTUCKY

The storage of soil organic carbon (SOC) in soils found at depths greater than one meter in river valley bottoms, and those processes that operate on that SOC, are not well understood. This study examines the stock and isotopic composition of SOC along alluvial landforms: floodplains, terraces, and vegetated bars or swales, in the Clarks River National Wildlife Refuge (CRNWR). Preliminary data from three cores along a transect from a terrace to an adjacent channel bar were collected to depths of 1 to 1.5 meters. Bulk density, particle size, and loss-on-ignition were used to estimate stocks of SOC in each landform type. Data were collected for the subsoil and did not include A horizons. Average subsoil-SOC values for each of the landforms decreased along the transect towards the river channel, with the largest value of 1.8 kg/m² ± 0.3 SD found in the terrace and the lowest value of 0.9 kg/m² ± 0.18 SD found in the near-channel bar. The floodplain had an average value of 1.14 kg/m²± 0.3 SD. This is likely due to differences in soil texture, where terraces have greater soil development due to infrequent flooding which allows for clay accumulation, a predictor for SOC storage at depth. Although floodplains and near channel features observe greater flooding and potentially greater deposition and sequestration of SOC, this SOC may be stored temporarily and oxidized with increasing residence time. Additional transects and more direct measurements of SOC via combustion and gas chromatography will be used to test the consistency of these observations.