Variation in Surface Soil Carbon Distribution Across Forested and Grassed Loess Catenas in the Shawnee Hills.

Surface soil carbon, a significant fraction of total soil carbon, is sensitive to environmental changes and land use. This work considers soil carbon volumes as comparators of management and environmental effects. Surface soil (1-7 cm depth) bulk densities and total carbon were measured across landscape positions on three paired (forest and grasslands) zero-order basins as a part of soil landscape study in the Shawnee Hills region of Illinois, Indiana, and Kentucky, located within MLRA 120 (Kentucky and Indiana Sandstone and Shale Hills and Valleys) and a small portion of MLRA 115B (Central Mississippi Valley Wooded Hillslope). The six zero-order basins share parent materials and mutual land use characteristics and objectives, thus creating a unique opportunity to study interactions of pedogenesis, water movement, and landscape position with management practices on a watershed scale. To this end, zero-order basins were delineated based on landscape position, and a minimum of 10 randomly generated points at each landscape position were selected for analysis. Bulk density and total carbon were sampled in duplicate at each point using the core method. Total carbon was determined by dry combustion. Data were checked for normality and homogeneity of variance, and analyzed as a three (thick, intermediate, or thin loess deposit) x two factor (forest or grassland) repeated measures (landscape positions) design with imbalanced data. Distribution of carbon varies with thickness of loess deposit in a complex fashion. Variance of volumetric carbon is heterogeneous, and increases as a monotonic function with decreasing thickness of loess deposit. Management and landscape position effects are evident when loess deposit is thin.