Effect of bedrock permeability on runoff and soil loss in soil-mantled karst slopes under successive rainfall conditions

Soil-mantled karst slopes exhibit rapid surface-belowground hydrological responses to rainfall because thin soil layers cover the bedrock. Bedrock features may play important roles in surface-belowground hydrological processes; however, the underlying mechanisms remain unclear. Herein, the effects of impermeable (no fissures) and permeable (3 % fissure rate) bedrock (BS1 and BS2, respectively) on the surface and belowground runoff and soil loss processes were investigated during three successive rainfall events. During each event, the surface runoff (SR), subsurface runoff (SBR), soil–rock interface flow (SRIF) and bedrock fissure permeation flow (BFPF) were recorded. The results showed that the SR and SBR rates for the BS1 slope were significantly greater than those for the BS2 slope (P < 0.05) under all rainfall events. During rainfall, the SR and SBR accounted for ∼ 19 % and 8 %-12 % of the rainwater on the BS1 slope, respectively, and both were less than 5 % of the rainwater on the BS2 slope. Approximately 40 %-55 % of the rainwater was partitioned into SRIF on BS1 slope, and 54 %-74 % of the rainwater was partitioned into the BFPF on the BS2 slope. Furthermore, the BFPF on the BS2 slope was 33 % greater than the SRIF on the BS1 slope at the 1st rainfall and it increased to 50 % at the 3rd rainfall, suggesting that the successive rainfall increased the difference in rainwater loss from the bedrock surfaces between the slopes with different permeabilities. The surface soil loss rate was very low (< 0.01 g·m²·s⁻¹) due to the low SR, and a significant positive correlation was found between the SR rate and surface soil loss rate (P < 0.01) for both slopes. Compared with that on the BS2 slope, the soil loss on the BS1 slope was greater because of the higher SR rate. The belowground soil loss curves were discontinuous, indicating that the belowground soil loss process was very different from the surface soil loss. Therefore, bedrock permeability has a strong influence on runoff and soil loss in soil-mantled karst slopes, and this effect further increases with successive rainfall events.