Effect of Exposed Bedrock on Soil Water Infiltration in Karst Region

［Objective］ The strong dissolvability of carbonate rock leads to the spatial distribution of karst soil and bedrock, and the outcroppings of bedrock are common, but the mechanism of their influence on hydrological processes is still unclear. In order to investigate the influence of outcropped bedrock on soil water infiltration, the soil infiltration rate at different distances of outcropped bedrock was measured by single-loop infiltration method. ［Methods］ Taking the soil 20 and 100 cm away from the bedrock as the research objects, the characteristics of preferential flow were studied by the bright blue staining and tracing method. ［Results］ The capillary porosity and organic matter content of non-bedrock soil were significantly higher than those of bedrock soil (p<0.05), but the soil bulk density was significantly lower (p<0.05). The infiltration parameters (initial, stable and average infiltration rate) of non-bedrock soil were higher than that of bedrock soil. The area of staining area and preferential flow path increased with the distance from the exposed bedrock. These results indicate that the infiltration capacity and preferential flow frequency of non-bedrock soils are stronger than those of bedrock soils. Rock surface roughness was an important factor affecting soil water infiltration process, and soil infiltration rate increased with the increase of rock surface roughness, and there was a very significant positive correlation between soil roughness and soil infiltration characteristics (p<0.01). Kostiakov Model (R2=0.89), Horton Model (R2=0.80) and Philip Model (R2=0.72) are the best fitting models for soil water infiltration process considering the influence of bedrock outcrop. ［Conclusion］ This study identifies the influence of exposed bedrock on soil infiltration characteristics and emphasizes the controlling role of rock surface roughness.