Spatial Variability Properties Of Surface Soil Physiochemical In The Landslide Area Of Beichuan County,Southwestern China,after 5.12 Wenchuan Earthquake

After 5.12 Wenchuan earthquake.mountainous ecosystems in the Leigu town Mountains were seriously destructed.Based on the landslide of Fenghuang Mountain in the Leigu town. Beichuan County, landslide plot(?)?transition plot(?) and un-destructed plot(?) were selected as the contrast.Combined with the grid sampling and laboratory analysis,classical statistics method, geo-statistics statistics method and GIS were used to analyze the characteristics of soil physical structure and soil nutrient. The results were as followed.(1) Under the dry sieve processing, the>5mm dry aggregates content in plot I was the lowest, followed by plot ? and plot ?. Under the wet sieve processing, the>2mm soil water stable aggregate were the major fraction for all plots.It generally presented that the aggregate contents increased with the decreasing of aggregate size. Under the dry and wet sieve processing, the mean weight diameter (MWD) and geometric mean diameter (GMD) values presented as ?<?<?. The change rule of aggregate fractal dimension values contrary to MWD and GMD. The values of stability parameters had no significant difference in ? and ?. but ? and ??? had significant difference. In the sample ? (except the aggregate value D). the stability parameter values were increased with increasing of altitude, but that had no obvious change rule with increasing of altitude.In conclusion, the sample soil stability presented as ?<?<?.(2) Under the dry and wet sieve processing, the semi-variance model of aggregates stability parameters and soil particle composition had a high fitting degree. The MWD of wet sieve aggregates showed moderate spatial autocorrelation, and all other aggregate parameters showed strong spatial autocorrelation; The ratios of nugget to sill of clay was 45.9% and showed the moderate spatial autocorrelation, while silt(0.1%) and sand (8%) suggested strong spatial autocorrelation. The MWD and GMD values of dry and wet aggregates were increased gradually from left(?) to right (?) in the study area, but the distribution of aggregate fractal dimension was contrary to that distribution rule:In the study area, the sand content decreased gradually but the content of clay increased from left to right. Also, the sand contents were the dominant fraction at all three sample plots, and sand content was significant higher than content of clay and silt, so there was sandy soil. The soil particle composition quality fractal dimension values had high negative correlation with sand content, and had close positive correlation with clay and slit contents, but the correlation of slit content was relatively weak.(3) The soil nutrient content in the study area at lower level in general, variation degree was larger, the soil available phosphorus (AP) was high strength variation, and all the other soil nutrients were moderate intensity variation. Soil nutrients had no significant variation with the increase of altitude, but gradually increased from ? to ?. The total and available phosphorus contents of the ? area decreased by 10.3% and 79.7% compared to that of the ? area, respectively. The soil nutrient contents in the II area accounted for 31.1%-87.2% of that of the ? area, with the least and largest reduction in total and available phosphorus contents, respectively. The soil TP had a poor fit of semi-variance function model, but the other soil nutrients semi-variance function model fitting were good. The ratios of nugget to sill of soil AP and organic carbon (SOC) were 27.9% and 28.8%, respectively, and ratios of nugget to sill of all the other soil nutrients were showed a strong spatial autocorrelation.(4) The correlation between soil nutrients contents and soil aggregates was not obvious. It showed mainly that soil nutrient contents had positive correlation with>5mm dry aggregates and>2mm water stable aggregates, but had negative correlation with<0.25mm dry and water stable aggregates. The soil aggregate parameters had no significant correlation with the soil TP and AP, but all the other soil nutrients had extremely significant or significant correlation with the parameters of soil aggregate. Mostly soil nutrients contents had extremely significant or significant positive correlation with clay and silt, while had extremely significant or significant negative correlation with sand contents. There were no significant correlation existed between the fractal dimension of soil particle composition and soil nutrients contents, but except for the soil TP and AP.The vegetation were destroyed seriously on the landslide, where soil texture?soil aggregates?soil nutrients and corresponding stability parameters showed a declining trend. Moreover, seismic landslides disturbance was the main factor for the spatial variation of soil properties.