Preferential Flow in Different Soil Architectures of a Small Karst Catchment

Abstract

Core Ideas Macropores and cracks are preferential channels in karst depression and downslope locations Heterogeneity of soil property results in finger flow in karst mid- and upslope locations High Ks and soil layering weaken preferential flow in mid- and upslope locations Preferential flow degree and infiltration rate can be independent in karst regions In karst regions, soil architecture varies along topographical locations, resulting in marked differences in infiltration rates. However, the relationship between soil architecture and preferential flow (PF) is still unclear. In this study, dye tracing was used to investigate PF and the dominant effects of five types of soil architecture in a small karst catchment. These soil architectures included deep clay soil in farmland (CSF) and deep clay soil in shrubland (CSS) in the depression; shallow clay soil with minimally weathered, slanted bedrock on downslope locations (CSWD); shallow sandy loam soil with highly weathered bedrock on midslope locations (SLSM); and sandy loam soil with rock fragments on upslope locations (SLSU). The results showed that macropores and cracks were the major channels that resulted in a high degree of PF in depressions and downslope locations. Preferential flow also continued along the rock–soil interface in the downslope locations. Finger flow mainly appeared in mid- and upslope locations, and cracks mainly appeared in the surface soil layer. However, down- and upslope locations showed lower PF. We observed that PF might not contribute to the different infiltration rates in different topographical locations. Tillage in depressions damages macropores, thereby minimizing vertical percolation. The high saturated hydraulic conductivity (Ks) of the soil matrix covered the development of PF in the mid- and upslope locations, and the decrease in Ks weakened the formation of PF as a result of heterogeneity of soil properties. These findings demonstrate that infiltration-excess runoff may occur in depressions and downslope locations and that saturation-excess runoff may occur in mid- and upslope locations.