How do belowground bedrock fissures impact soil erosion on karst hillslopes under different rainfall intensity conditions?

In karst regions, bedrock fissures are developed via karstification, which may cause belowground soil erosion (BSE). However, few studies have quantitatively assessed the effect of bedrock fissures on BSE because BSE measurement is difficult on karst hillslopes. The objective of this study was to investigate the differences in runoff and soil erosion at the surface and belowground on karst hillslopes with and without bedrock fissures (hereafter called HS1 and HS2, respectively) under different rainfall intensities (50, 75, and 100 mm hr(-1)). The slope gradient was 5 degrees. In the rainfall process, surface runoff (SR), subsurface runoff (SBR), soil-rock interface flow (SRIF), and underground fissure flow (UFF) data were collected on HS1 and HS2. The results showed that the SR coefficients of HS1 and HS2 were negligible (less than 1%) under rainfall intensities of 50 and 75 mm hr(-1), and UFF (56%-57%) of HS1 and SRIF (40%-44%) of HS2 dominated the runoff pattern. Under a rainfall intensity of 100 mm hr(-1), the SR coefficient increased to approximately 30% under the two treatments, and the coefficients of UFF of HS1 and SRIF of HS2 decreased to 29% and 24%, respectively. Compared to HS2, UFF of HS1 increased by 18%-39%. The SBR coefficient was lower than 10% for all rainfall events. Because SR and SBR were low under rainfall intensities of 50 and 75 mm hr(-1), the soil loss was dominated by UFF (99%-100% of the total sediment) of HS1 and by SRIF (86%-97% of the total sediment) of HS2. Under the 100 mm hr(-1) rainfall intensity, almost all sediment was lost via SR under the two treatments, and the sediment loss of HS2 was 33% higher than that of HS1. Our results indicated that bedrock fissures caused more underground rainwater leakage at the SRI and further decreased surface soil erosion on karst hillslopes.

Automated summary

In karst regions, bedrock fissures contribute significantly to belowground soil erosion. However, quantifying the effect of bedrock fissures on soil erosion is challenging. This study compared runoff and soil erosion between karst hillslopes with and without bedrock fissures under different rainfall intensities. The results showed that bedrock fissures decreased surface runoff and increased underground fissure flow, reducing surface soil erosion.