Geometric morphology and soil properties of shallow karst fissures in an area of karst rocky desertification in SW China

Abstract

Serious soil erosion and an extremely low rate of soil formation leads to a thin layer of surface soil that makes tree growth difficult in areas of karst. Meanwhile, surface soil, driven by runoff, enters shallow karst fissures (SKFs); these SKFs filled with soil have become the major habitat type in the area. Here, we explore the morphological characteristics of shallow karst fissures as well as the soil physical and chemical properties of the SKFs and comprehensively analyse the factors that influence the soil properties. Three key results are presented. First, a high heterogeneity of morphological characteristics exists for shallow karst fissures. According to the different characteristics of the vertical section, the SKFs can be divided into 5 types. These types are Rectangle-type, Pyramid-type, Funnel-type, Net-type and Diamond-type. In addition, the SKF dip angles were mainly between 60° and 90° (76.39%), the width of the top aperture was mainly between 20 and 40 cm (51.39%), and the trace lengths were mainly between 80 and 160 cm (76.39%). Second, compared with their characteristics of surface soil, the bulk density and fractal dimension of soil particles of the SKFs were both large, and the main composition of the SKF soil was clay. Third, the soil nutrients of the SKFs (the organic matter, total nitrogen and total phosphorus) were lower than the surface soil nutrients but not significantly so. The total potassium (TK) of the SKFs was greater than that observed for the surface and increased as the depth of the SKF increased. The soil nutrients of the SKFs were significantly affected by the fissure morphology. The poorly connected fissures had better soil fertility. When the morphological characteristics and soil properties of the SKFs were comprehensively considered, the vegetation types that were determined to be the best for use in the ecological restoration of areas of karst rocky desertification were deep-rooted plants with especially strong root penetration. The result of this study can supply some reference for future studies of karst rocky desertification control and vegetation restoration in the karst area of Southwest China; in the South Claw Silicon Island in Yogyakarta Province, Indonesia; and in other karst regions with the same ecological background.