Contributions of Subsurface Horizons and Coarse Fragments to Carbon and Nutrient Pools in Forest Soils of the Southern Appalachians.

Forest soils in the southern Appalachians very greatly in soil depth and coarse fragment content. The impact of subsurface horizons and coarse fragments throughout the profile must be determined to accurately estimate soil carbon and nutrient pools. We determined total soil carbon and nutrient pools at seven sites in the southern Appalachians of Virginia and West Virginia. Quantitative soil pits were excavated to a minimum depth of 1 meter to determine surface and subsurface horizon fine fraction carbon and nutrient concentrations. Coarse fragments were also determined in each horizon. Carbon and nutrient content of the fine fraction and coarse fragments were determined. Significant concentrations of carbon and nutrients were found in these coarse fragments derived from shale and sandstone.   Estimates of ecosystem carbon and nutrient pools are significantly underestimated based on concentrations in the fine fraction of the surface mineral soil. In particular, significant quantities of base cations, such as Mg²⁺ and Ca²⁺, are present in coarse fragments in these soils. Spatial variability in soil depth at several of these sites was evaluated using ground penetration radar. Average depth to bedrock and coarse fragment content were estimated from the GPR data collected by developing a method for analyzing the volume occupied by coarse fragments. These data revealed that depth to bedrock varied dramatically over relatively short distances.  To accurately estimate landscape level carbon and nutrient pools in the Appalachians, the contributions subsurface horizons, coarse fragments and spatial variability in these soil properties must be included.