Topographic Gradients in Bulk Soil Properties in Central Kentucky Karst Sinkholes

The Bluegrass physiographic region of Kentucky is underlain by the late Ordovician Lexington Limestone formation. This area has many identifiable karst features, including sinkholes. Karst sinkholes and associated soils coevolve, which may influence the distribution of bulk soil properties and storage of carbon across karst landscapes. Two sinkholes on the University of Kentucky’s C. Oran Little Animal Research Center in Woodford County, central Kentucky, were selected for analysis. We described and sampled nine pedons at the dominant landscape positions (e.g., summit, shoulder, backslope, footslope, and toeslope) within the two sinkholes; we characterized the physical, chemical, and mineralogical soil properties across the hillslope gradient (i.e., toposequence). As a general trend, total carbon content decreased with sampling depth, and the toeslope and footslope positions contained higher carbon stocks relative to other landscape positions. Total carbon and silt tended to accumulate in the base of sinkholes, whereas summit positions exhibited higher clay contents and iron and aluminum oxide concentrations. The relationship between silt and carbon, and negative relationships between carbon and clay content, exchangeable Ca, and dithionite-extractable Fe and Al may suggest that the carbon in the base of these features is less likely to be minerally associated. An estimated 20% of the world’s land surface is underlain by lithologies favorable for karst terrain formation making the characterization of the soil in these landscapes applicable outside of Kentucky’s Inner Bluegrass. Measuring the properties of soils in karst sinkholes will allow for a better understanding of their place in karst landscapes, as well as their role in carbon cycling