Structural evolution of soil aggregates in a karst rocky desertification area

Desertification and karst landforms are widespread in the water source area of the middle route project of south-to-north water diversion in China. Soil erosion processes directly influence water quality in the water source area and contribute sediments to the bottom of the water reservoir. This study investigates soil evolution over time by sampling a slope surface and discusses associated changes in soil structure, physical and chemical properties, and mineral associations. Changes in soil aggregate structures with slope surface direction and mineral association evolution are observed. The compositions of the main soil minerals and elements are determined using scanning electron microscopy, and X-ray energy spectrum and X-ray diffraction analyses. The results reveal that (1) the evolution of soil aggregates is consistent with evolutionary trends in soil elements and mineral associations. (2) The ultra-microstructure of soil aggregate indicates the soil development stage and condition, while mineral associations indicate the soil development stage along the soil chronosequence. This study increases the understanding of land surface processes in the study area and the soil development, forming and biogeochemical processes in karst rocky desertification areas.