| Due to the special lithology of red beds and under the humid and rainy climatic conditions,the lithology of red beds soft rock affects ability and rate of anti-erosion and anti-weathering,after losing the surface soil layer.After the red beds soft rock is exposed to the surface,its erosion rate is affected by the factors of sunshine and rainfall.Sunshine and continuous rainfall alternate.The red bed soft rock disintegrates and fragments continuously from its original state,forming the red beds desertification landscape.Desertification is characterized by erosion of surface soil as the initial sign and dense erosion gully(chicken claw gully)as the typical sign.The eroded area of red soil in Jiangxi province ranks third among eight red soil provinces in the south,and the exposed area of red desertification is extensive,which seriously affects ecological stability and sustainable economic development.Yongyang basin,a secondary red bed basin with typical desertification characteristics in Jitai basin,Jiangxi province,was selected as the research object.Based on field geological investigation,image analysis,soil profile survey and physical and chemical characteristics analysis,combining desertification spatial distribution with basin sedimentary facies types,clarify the types and characteristics of erosion gullies in the process of desert evolution in red beds and changes of soil physicochemical properties in different evolution stages,revealing influencing factors of red-bed desertification,to provide scientific basis for desertification control,developing desertification aesthetic value and popular science value into tourism resources,creating desertification as the subject of geo-tourism cultural village,It's conducive to the protection of ecological environment and the maintenance of sustainable economic development.The key results were as follows:(1)Yongyang basin is a basin by continental sedimentary,Cretaceous sandstone,siltstone and mudstone are exposed in the margin of the basin,Quaternary reticulated laterite is exposed in the basin,It mainly develops fluvial alluvial facies and residual-slope facies.Restricted by lithological factors,most of the desertification areas(points)are exposed in the Quaternary alluvial and residual-slope strata with the weakest erosion resistance.(2)The desertification in this area mainly takes four forms on the image: the "maple leaf shape" accumulates and distributes to both sides of the mountain area;in low-lying hills,the trend of expansion is transverse and then longitudinal,and the expansion speed is "flaky";In flat and open terrain,desertification is "star-shaped" with lateral expansion,A "band" appearing on the erodible side of a monoclinic hill.(3)The area of desertification in the study area was calculated by using the image of the study area as the data source through the proposed classification standard of desertification/land degradation.The desertification degree was classified and counted according to field investigation and classification criteria,combining with the data,the desertification in the region is divided into four grades: mild,moderate,severe and extreme.The area of mild desertification becomes the main body,and there is a transition trend from mild to moderate desertification.Desertification of four grades corresponds to four landscape types,and the characteristics of Chicken claw ditch of each landscape type are obviously different.(4)Soil profile structure and physical and chemical analysis show that:with the deepening of desertification and the retrograde succession of vegetation,the thickness of soil layer decreases gradually,the total thickness of the soil layer in the period of extreme desertification is only 40 cm,and the water content of the surface soil layer is only 13.447%~27.16%,which indicates that its water retention capacity is poor.The results of pH values of Cretaceous weathered soils and reticulated laterite weathered soils show that the former has a pH value of 7.08-8.20,and the latter is 4.25-5.39,which is in a superacid state.The physical and chemical analysis of the soil in the desertification area shows that the soil in the study area is sandy soil.Component content is dominated by silt(2-63?m)and fine sand(>125?m),both exceeding 50%,up to 85%,and clay(<2?m)content is precious few.The chroma data and specific gravity data show that the content of soil organic matter decreases with the deepening of soil depth.Soil nitrogen(N)phosphorus(P)potassium(K)content data show that the soil comprehensive nutrients are too low and are classified as grade 3,4 and 5 in the soil nutrient classification table,which are important factors affecting reverse succession of plants.(5)Red beds desertification can be divided into four stages from the beginning to the end,simulating the evolution model of desertification.From a single vegetation type area as the birthplace,under the influence of climate,human activities and the characteristics of Red Beds Soft rock,surface soil emerges sporadically,and weathering erosion accelerates in the mid-to late stages.After that,the bedrock exposes,and in the process of continuous erosion,erosion gullies develop gradually.The direction of erosion changes from planar(horizontal)to downward(vertical)erosion,and then to dense in the later stage.The "chicken claw ditch" presents the existing desert landscape.(6)In view of the characteristics of soil physical and chemical properties(pH value,soil layer thickness,water content,nutrient content,etc.)and topographic gradient in the region,the corresponding suggestions for desertification control in the later stage of the region are put forward.It is proposed that the desertification landscape with aesthetic value and popular science value in the middle and late stages of the region should be exploited as a kind of tourism resource to build a brand of desertification-related geo-tourism cultural village,which can give full play to the value of desertification landscape and improve economic benefits while protecting the ecological environment. |
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