Characteristics Of Soil And Water Loss In The Slope Land And Technological Effects Of Prevention And Control In Three Gorges Reservoir Areas

Arid mountain slopes land of 66.3%of the total area in Three Gorges reservoir area is a major source of river sediment,in order to control soil and water erosion of Three Gorges reservoir area,a lot of investigation and research of soil erosion of slope land have been taken by the scientific and technical personnel.But the study of soil erosion characteristics and the ecological effects to build under the ecological control pattern also remained at the stage of qualitative description.In this paper,taking several typical control types of Three Gorges reservoir area as the example,the effect factors, characteristics and rules of the soil erosion and its diversification of the soil physical and chemical properties under different vegetation types were studied by large numbers of pilot field survey and positioning observation.And different ecological control types for the ecological benefits were comprehensively evaluated.Observation analysis showed that the sediment loss rules were basically the same as the runoff loss under different vegetation types of the slope land of Three Gorges reservoir area.Soil and water erosion of arable land occurred mainly in a few critical months.The cumulative runoff loss of April,August and September occupied 83.53%of the annual total loss,and sediment loss was 98.55%of the annual total loss.The extent of runoff and sediment loss indicated that:the lightest type was soil and water conservation;the followed was biological fence pattern and ecological forest model;and the most serious one was the bare land.In addition,the typical rainfall played a decisive role to runoff and sediment loss.It showed that 90.28%sediment loss and 63.28%runoff loss in total was accumulated after three times typical rainfall of a year.The change of topsoil particles of before and after the rain showed that the＜0.25mm sand agglomerates and the＜0.001mm clay particle had the enriched characteristics.According to the grey correlation analysis,the impact of runoff and sediment loss of different vegetation types from the factors of rainfall showed that:to the impact of the runoff,rainfall(Y₁) was the largest;followed by 30min largest rainfall intensity(Y₄) and rainfall intensity(Y3);rainfall duration (Y₂) was the minimum impact.In addition,to the impact of the sediment,rainfall duration(Y₂) was the largest;followed by rainfall intensity(Y₃);the impact of the 30min largest rainfall intensity(Y₄) and rainfall(Y₁) were the smallest.On the correlation model analysis between runoff and sediment loss and rainfall erosivity and sub-rainfall of different vegetation types,it showed that there were different functions. The nutrient content of surface soil after rainfall was lower than that before rainfall under different vegetation types.Also the decay extent of available nitrogen,phosphorus and potassium was greater than the total nutrient content.Sediment of 0.05～0.001mm and＜0.001mm in the silt was a major adhesion particles(cartier) for the nutrient loss of the surface soil.Even the nutrient concentrations in sediment were bigger than the topsoil and were far greater than the runoff which was in much lower concentrations.However,the amount of runoff was 20 times more than sediment in the Three Gorges reservoir area due to abundant rainfall.So the nutrients loss of runoff can not be ignored and should be regarded as the nutrient loss with the sediment loss together.The correlation between ground cover and soil erosion was significant negative during the different rainy season under different agricultural systems.According to the average coverage from May to September,that of the two-cropping of wheat-sweet potato was only 50.72%which was the lowest.The average coverage of triple cropping system was more than 70%.So the soil erosion of triple cropping system was significantly less than the loss of the two cropping system.Among different vegetation types,soil characteristics had a positive development trend as the time was changed.It was found that:soil bulk density decreased;and soil porosity increased gradually.Also all of them were better than bare land.The average soil water-holding capacity of different vegetation types was 157.69m³/hm²,which was 2.59 times of that of bare land(60.97m³/hm²).The descending rule of water-holding capacity was that:bamboo＞Tea＞Amorpha fruticosa＞Golden buckwheat＞Chestnut of return farmland＞mixed forest＞pine forest＞chinese chestnut Intercropping.Under different ecological control models,the nutrient content of the surface soil(0～10cm) at different time or during the same period showed some variation rules.The soil particle size changed clearly as well.Comprehensive analysis found that the bamboo played a more important role on improving the physical properties of the soil.And the second of that were mixed forest,pine forest and Amorpha fruticosa.Fuzzy comprehensive evaluation showed that the integrated eco-efficiency of different vegetation types had the following rules:ecological economic forest complex types＞water and soil conservation forest types＞biological fence pattern＞farmland.Even the eco-efficiency of the three ecological control types was three times of slope land.The result indicated that the implementation of the three ecological control models played a essential role in making better the environment of Three Gorges reservoir area.Furthermore,theoretical and applied research should be strengthened in order to provide support for preventing water and soil erosion in the Three Gorges reservoir area.