Path analysis of the effects of hydraulic conditions, soil properties and plant roots on the soil detachment capacity of karst hillslopes

Land use and its transformation significantly affect the soil detachment capacity (Dc) by changing soil properties and altering root characteristics, but few studies have been conducted to quantify the effects of these factors on Dc in karst areas. The objective of this study was to assess the effects of hydrological conditions, soil properties and plant roots on the Dc of karst hillslopes. A total of 270 soil samples were collected from six different land uses and then subjected to flow scouring in a hydraulic flume under nine shear stresses (ranging from 1.61 to 7.04 Pa). The results showed that the mean Dc ranged from 0.0003 kg m−2 s−1 to 0.52 kg m−2 s−1. The variability in soil Dc under different land uses was closely related to hydraulic conditions, soil properties and plant roots but to different extents. The elevated Dc on land affected by greater human activities indicates they are the main disturbance associated with soil erosion on karst hillslopes. Dc was positively correlated with flow velocity, shear stress, stream power and unit stream power, and flow velocity was the optimal hydrodynamic factor for predicting Dc. Dc was positively correlated with soil porosity and saturated hydraulic conductivity and negatively correlated with soil bulk density, water-stable aggregate content, organic matter content, root length density and root mass density. Path analysis showed that water-stable aggregates and root length density were the dominant factors affecting soil detachment. Accordingly, a model was established to estimate Dc based on water-stable aggregates and root length density on karst hillslopes (R2 = 0.88, NSE = 0.87). Therefore, the research results provide theoretical guidance for predicting the Dc of karst hillslopes and a basis for decision-making related to soil erosion control in karst areas.