The Characteristics of Soil Ca and Mg Leakage in a Karst Depression

The soil leakage characteristics of depressions in karst areas should be explored by investigating their soil Ca and Mg contents. As a starting point, in a karst landform typical of Guizhou Huajiang dry valley karst watersheds, we selected surface depression and performed a field investigation, soil profile excavation, and soil sample collection. The soil samples were pretreated and taken to the laboratory for soil physical and chemical analysis. The data were processed, and the Ca and Mg contents of the soils were analyzed to determine the spatial variation characteristics of soil leakage in the depression. We found that in the depression watershed, the Ca and Mg contents in the 0–30 cm soil profile generally increased with increasing soil depth, and the Ca and Mg contents in the 30–150 cm soil profile exhibited more variability with increasing soil depth. The Ca and Mg in the soil surface profiles from the top of the slope, middle of the slope, base of the slope, bottom of the depression, and sinkhole showed obvious characteristics of a sedimentary soil leakage migration path. In combination with analyses of the soil K and N contents, the soil Ca and Mg contents can be used as an index of the likelihood of soil and water leakage in karst depressions.