| Rocky desertification normally occurs under certain natural conditions. The tropical and subtropical weather provide suitable wet and hot conditions to Karst rocky development。Rocky desertification land is characterized by increasing bare rock area, vegetation degeneration, declining land productivity, and it not only threatened local residency but also restricted domestic economic development. Meanwhile, rocky desertification is ranked one of our nation’s key control programs as it is a hazard to local or even whole region’s eco-environment safety. By studying the soil erosion due to rocky desertification of small watershed, the erosion phases of rocky desertification of Karst area can be discussed. The target region for this study is the small watershed of Xingwen County in Sichuan. First of all to build the rock desertification classification index system, and to analyze rocky desertification in the spatial pattern of the study area; Secondly, to study the soil erosion characteristics of the study rocky desertification region by determine the soil erosion indicators137Cs content and soil physical and chemical indicators; Finally, to study the spatial association of karst rocky desertification and soil erosion and topographic factors by spatial analysis. The main conclusions are:(1) The grading system for rocky desertification in the research region, as well as its spatial grading were established based on former researches and wild field observation. To be specific:The total area of rocky desertification land is100861m2. Moderate rocky desertification land contributed61%of total area, which is61409m2. Slight rocky desertification and severe rocky desertification equally take up the rest39%, with area of19717m2and19735m2respectively.(2) Non-rocky desertification area has higher137Cs content than rocky desertification area. Slight rocky desertification has higher137Cs content than severe rocky desertification area. Moderate rocky desertification area has the lowest137Cs content. Due to the complicated topographic patterns in Karst area and the choices of sampling spots and interpolation methods, the137Cs content may not be very accurate in proving the spatial differentiation pattern. (3) Influenced by chorographic changes and agricultural production, the organic content in soil represent the soil erosion and sedimentation status in varying degree of rocky desertification lands. Mild rocky desertification region has the highest organic matter content comparing to moderate and severe rocky desertification area, while the moderate region is the lowest.(4) The correlation between soil mechanical composition and rocky decortications is reflected by the changes of its sand&clay content. With rocky decortications going severe, sand content declined and clay content and particles increase. This shows the bare rock due to rocky decortications will block the fine soil particles from uphill, which then accumulated in stone cracks and stone pits. And.(5) The tougher slope is, the stronger soil erosion is. However, the erosion slows down and rocky decortications degree declined after the slope exceeds a critical point (30°). The influents of altitude to rocky decortications degree index is mainly between525-700m. and it do not increases with higher altitude.(6) Using wild survey to determine rocky desertification spatial distribution, and prove the distribution of rock desertification land by establishing soil erosion index. It shows there are certain spatial correlation among137Cs content in soil, soil physicochemical property, and topographic factors. However, we need to prove this in wider watershed and to have a long-term track record and monitoring. |
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