Effect Of Seismic Soil And Water Loss On Soil And Vegetation In Wenchuan Earthquake Area

As an important ecological barrier of the upper Yangtze river, Chengdu Plain, Sichuan Basin, Wenchuan earthquake area which located in the upriver and headstream of Mingjiang river, Fujiang river and Jianglingjiang river etc. has a significant ecosystem services of water conservation or soil and water conservation, which closely related to the water service safety of murtimillion Population of Chengdu Plain even Sichuan Basin. Soil and Water Loss caused by Earthquake made the environment more fragile, and strongly threatened the safety of people’s lives and property. It has became an urgent problem that how to prevent seismic soil and water loss effectively, minimize the harmful influence on environment, keep rivers healthy, ensure residents’life and property safety.With the comprehensive investigation on caopohe small watershed which located in the upriver of Mingjiang river of Wenchuan earthquake area, Four typical fields which were different restoration patterns under earthquake impacts were chosen to study, exposed field, naturally restoration, artificially restoration, comparative field. By means of field investigation along with laboratory analysis, the influence of soil and water loss on soil physical properties, permeability, vegetation variety were discussed, and then soil anti-erodibility evaluation index was established. The strength or weakness of soil anti-erodibility was comprehensively evaluated by using principal component analysis. The research can provide reliable basic data for soil and water conservation research after earthquake and improve help for the corrosion resistance studying of earthquake area, provide technical support implemented step by step for disaster prevention and mitigation, and meet the actual demand of earthquake and its cause disasters and repair of prevention and control for country, provide the scientific basis for nation’s regional sustainable economic and social development. The main results are listed as follows:(1) caopohe watershed is the typical rocky mountain area, the comparative filed contain63.39%of gravel,21.03%of sand,14.42%of silt,3.16%of clay, the proportionment is almost20:7:4:1. the fields that bared, naturally restored or artificially restored are thick, making the gas and water permeability of the Soil badly, the percentage of gravel and sand is almost80%,and the proportionment of gravel and sand is almost1:1. Wenchuan earthquake decreases the mount of aggregate and micro-aggregate, but through naturally restoration or artificially restoration, the field’s amount of aggregate can increased effectively, which can strengthen the Erosion Resistance of soil and also enhance the stability of soil.(2) The soil comparative filed will have nicer gas and water permeability and water retaining capacity when the soil bulk density is about1g·cm-3,the soil porosity is nearly50%, and the non-capillary porosity is almost20%-40%, but the rules of the fields that exposed, naturally restored and artificially restored are change. Water retaining capacity of the comparative field is stronger than the others when considered about maximal water holding capacity and non-capillary water holding capacity. The maximal water holding capacity and non-capillary water holding capacity of artificial cultivated field is better than bare field and naturally restored field, so artificial cultivated vegetation can make soil loose, improve porosity, increase the gas and water permeability, strengthen the function of water holding capacity.(3) The pH of field that exposed, naturally restored and artificially cultivated is higher than comparative land because of exposed carbonate caused by Seismic Soil and Water Loss. The amount of organic matter in different fields is obviously different, separately showing that:comparative field>artificially cultivated field> naturally restored field> exposed field. The soil nutrient such as Total Nitrogen, NH4+-N, NO3-N, total phosphorus, available phosphorus, total potassium, available potassium etc. are all decreased to the level of shortage mainly because of surface runoff, but fertilizing before planting can increase the amount of available Nitrogen and potassium effectively.(4) The beginning infiltration rate, steady infiltration rate, mean infiltration rate, and75min infiltration capacity in different restoration patterns are all show the same law:comparative field>artificially cultivated field> naturally restored field> exposed field. According to soil infiltration rate, the soil infiltration capacity of comparative field is the best and the soil infiltration capacity is shown as follows:comparative field (1.2569)＞artificially cultivated field (-0.2252)> naturally restored field (-0.4578)> exposed field (-0.5738). Effect of soil physical and chemical property on soil infiltration capacity has been studied by means of correlation analysis. The index that significantly associated with soil infiltration rate are soil bulk density, soil porosity, non-capillary porosity, pH value, the amount of humus, total nitrogen, NH4+-N, NO3_N, total phosphorus, available phosphorus, total potassium, available potassium, Those indexes were analysis by principal components, and the results show that the first principal component extracted variance contribution rate is80.22%, the load of total nitrogen, organic matter content, ammonium nitrate nitrogen, phosphorus, the effective capillary porosity and rapidly-available potassium in the first group are more than0.9, soil pH value and load of the soil bulk density are negative values.(5) The disturbed plant association on new soil and water erosion land appeared faultage, the bare land just has herb layers, naturally restored land is short of arbor layers, artificially cultivated field lack shrub layers, but comparative land has significant stratification of arbor layers, shrub layers and herb layers. Through the analysis of community diversity, the diversity index of comparative land are as follows:Margalef abundance index was1.07, Shannon-Wiener index was1.25, Simpson index was0.63, and Pielou index was2.03, which are all higher than the diversity index of the others, the diversity index of the bare land was the lowest, and natural restoration and artificial cultivation can improve the diversity of plant community remarkably.(6) The soil anti-erodibility index system of Wenchuan earthquake area includes:inorganic clay, water stable aggregate, micro-aggregate, soil porosity, organic matter, soil nutrient, soil infiltration capacity, vegetation diversity. We got4principal components by principal component analysis, the contribution of the4principal components is93.598%, and the contribution of the first principal component is60.11%. according to the contribution of principal components, the best index of soil anti-erodibility are as follows:stable infiltration rate,75min total amount of infiltration, the amount of2-0.05mm sand, the amount of0.05-0.002mm silt, fractal dimension of micro-aggregate, soil porosity, total nitrogen, total phosphorus, available phosphorus, available potassium. According to the comprehensive analysis of soil anti-erodibility, the soil anti-erodibility of different field is different, separately show that:comparative field>artificially cultivated field> naturally restored field> exposed field. Along with the results of soil anti-erodibility, we found that at the beginning of vegetation restored phase, classification of soil fertility was firstly taken as the optimized index of soil anti-erodibility, especially total nitrogen, total phosphorus, available potassium, But at the end of vegetation restored phase, characteristics of soil fertility in land are showed by the amount of organic matter and water stable aggregate, which then take as the best index characteristics of soil fertility, instead of classification of soil fertility. In the vegetation restored process, the amount of<0.05mm silt, stable infiltration rate, total infiltration capacity can safely taken as the optimized index.