Storage infiltration of rock-soil interface soil on rock surface flow in the rocky desertification area

Abstract

Rock surface flow, formed from the rock surface of outcrops after receiving rainwater, has become a main form of runoff in rocky desertification ecosystems with frequent regional and seasonal droughts. However, as a main flow path of rock surface flow into the surrounding soil of outcrops, how much the rock-soil interface soil can store and infiltrate the rock surface flow from outcrops is not well known. The goals of this study were to explore the storage-infiltration effect of soil at the rock-soil interface on rock surface flow in rocky desertification areas. Hence, a typical rocky land with large bulk rock outcrops, of which the surrounding soil has experienced five years of rock surface flow, and three special rock surfaces with shapes of convex, straight, and concave with different hydrological paths were selected in a typical rocky desertification county of China. Field investigation, ring knife soaking and infiltration methods were applied to indicate the difference in storage-infiltration between rock-soil interface soil and non-rock-soil interface soil on the rock surface flow in these different rock surface shapes. The results showed that the rock-soil interface soils around outcrops with different rock surface shapes exhibited different storage-infiltration capabilities for rock surface flow. The space of soil carrying water at the rock-soil interface showed the order of the convex shape, the straight shape and the concave shape, in which the non-rock-soil interface soil around the convex shape had greater space, followed by the rock-soil interface soil. The rock-soil interface soil of all three shapes had higher water storage performance than the non-rock-soil interface soil in terms of the field capacity and usable storage, where the rock-soil interface soil at the soil depth of 0–10 cm of the concave shape had lower water storage and lower conservation capacity than the 10–20 cm depth, and this was of positive significance for retaining the rock surface flow. The soil infiltration rate at the rock-soil interface with only the concave shape was greater than that at the non-rock-soil interface, where the concave shape had the greatest soil infiltration rate at the rock-soil interface. The results from this study can be used to understand the influence of outcrops on the soil properties of karst ecosystems.