Dynamic variations in soil moisture in an epikarst fissure in the karst rocky desertification area

Abstract

Epikarst fissures filled with soil (EFS) are important factors controlling karst hydrological processes and ecological hydrological functions. The EFS are common in karst rocky desertification areas, and it is important to understand the hydraulic properties and hydrological characteristics of EFS for vegetation restoration. In this study, we analysed the soil moisture content dynamics of surface soil and EFS in a rocky desertification environment to explore the influencing factors of soil moisture variation. A typical epikarst fissure was selected as the sample site in the rocky desertification area of the Karst Plateau Gorge (Beipanjiang catchment, Guizhou Province) in Southwest China, and surface soil was used as the control site. From May 12, 2018 to January 10, 2020, soil moisture content data for the EFS profile (20, 80, 140, 200, and 260 cm) and the surface soil profile (20 and 40 cm) were monitored synchronously at 30-min intervals. Simultaneously, soil samples were collected to measure the physical properties. The results show that the difference in vegetation cover and soil physical properties is the main reason for the difference in soil water dynamics between the shallow EFS and surface soil. The shallow EFS hydraulic connectivity is better, and the mean values of total porosity and saturated hydraulic conductivity of shallow EFS are 15.6% and 69.5% higher than those of the surface soil, respectively. The seasonal variations in soil moisture in the shallow EFS are obvious, the soil moisture rainfall response and dry-wet alternation are fast, the seasonal variations in soil moisture in the surface soil are relatively stable, and the soil water retention time is long. In the EFS profile, the hydraulic connectivity of the shallow soil (0–40 cm) are obviously better than those in the middle and lower layers (40–280 cm), which affected the response speed and retention time of soil water at different depths. In conclusion, the vertical hydraulic connectivity of the EFS profile is quite different and is shown to be significantly different from the surface soil hydrology. These results are helpful for understanding the ecohydrological process of epikarst.