| Collapse mound erosion is a serious erosion phenomenon that the weathering crust of hillside soil mass or rock mass decomposes, collapses and accumulates underwater power and gravity, and is a common and special soil erosion in the granite area of South China. The collapse has a big erosion amount, and its rapid development speed can seriously damage land resources, lead to serious floods and ecological deterioration. The research of watershed collapse distribution characteristics and collapse pluvial fan soil properties has special practical significance. This study can enrich collapse erosion theory and provide scientific theory basis for collapse erosion designing and the overall collapse district farmland quality.The study takes collapse group in Tong Cheng County as the research object in southeast Hubei province. Based on field observation, using GIS spatial analysis and Geostatistical Analysis, through the indoor experiment analysis and GPS RTK monitoring, we studied the distribution characteristics of collapses in watershed and the soil distribution spatial variability of its pluvial fan. The main conclusions are as follows:(1)Collapse has the characteristics of multiple, big distribution density and morphological diversity. The distribution density of Yang long watershed collapses is0.57a/hm2. The collapses mainly developed in small and medium size. There are6bar-shaped collapses,6bowl-shaped collapses,3claw-shaped collapses, and1mixed type collapse.(2)Statistics slope that the collapses developed, we found that they all distribute in8°～33°,78%of them distribute in16°～18°, and the collapse in this scope of slope mainly in the activity. Collapse develops along the direction of hill aspect. It can also easily developing in the joint development. Statistics shows the collapse developing direction is relative to aspect and joint. Main gully ratio size affects collapse development. The bigger gully ratio is, the stronger collapse activities.(3)The distribution of collapses in Yang long watershed is affected by valley location. From the upstream to the downstream, the terrain gradually become warming. The collapses concentrate in the upstream, and gradually reduced from the upstream to the downstream. But a single collapse area becomes bigger. The number of collapses on the west side is bigger than east.(4)In the study area, the soil organic matter, available nitrogen, available phosphorus and available potassium content are very low of collapse pluvial fan; the soil pH is medium acidic; the cation exchange capacity is in the middle and lower levers. It shows the study area to protecting fertilizer ability is poor. In this small scale collapse pluvial fan, the variation coefficient of soil pH for weak variability, while other variation coefficient of soil properties values are less than1, for the medium variation.(5) The soil organic matter shows significant correlation with alkali solution nitrogen, rapidly-available potassium, cation exchange capacity, sand, silt and clay. There exit significant positive correlation among The alkali solution nitrogen, rapidly-available potassium, cation exchange capacity in soil., and they has significant correlation among soil particle indexes. Soil pH has no correlation with other soil indexes. Soil available phosphorus has no correlation with organic matter, alkali-hydro nitrogen, rapidly-available potassium, and clay, but shows positive correlation with sand and negative correlation with cation exchange capacity, silt.(6) The trend analysis of soil properties show that soil alkali solution nitrogen increasing from southwest to northeast. The rapidly-available phosphorus has a "U" type change in southwest-northeast direction, both sides low middle high, this shows that the rapidly-available phosphorus have a trend of first and second order at the same time. Organic matter, rapidly-available potassium, cation exchange capacity, silt and clay all weakly decreased then rapidly increased in southwest-northeast direction. But the sand weakly increased then rapidly decreased.(7)The soil variability of the collapse pluvial fan properties is mainly affected by structural factors. There is semi-variance structure in soil variables, but different soil spatial variation characteristics of variables, including available phosphorus expression is isotropic, other variables are characterized by anisotropy. The available phosphorus and available potassium in soil nutrient, cation exchange capacity, soil particle and soil pH all variables are characterized by strong spatial correlation, and the available nitrogen, organic matter in the soil nutrient of medium correlation.(8)The soil variables of the pluvial fan show strong spatial distribution regularity. According to the result of ordinary kriging interpolation, the distribution of available nitrogen, available potassium, organic matter, cation exchange capacity, silt and clay content is consistent, all from top to fan edge increasing convex to the fan edge arc shaped; The distribution of sand content, on the other hand, for from the top to the fan edge decline arc shaped convex to the fan edge; Soil pH changes from top to fan edge decline convex to the top of fan arc shaped; Available phosphorus content of distribution trend is irregular. |
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