Analysis Of Spatial Differentiation Characteristics Of Soil Elements Based On Environmental Variables

Soil environment is an important topic concerned by Agricultural Environmental Protection Associations and scholars all over the world.Aiming at a series of practical bottlenecks and scientific problems such as the serious lack of soil fine data in China and the urgent need of soil pollution exposure risk assessment,this paper compares five kinds of spatial relations modeling methods which including ordinary kriging（OK）,multiple linear regression（MLR）provision,geographically weighted regression（GWR）,regression kriging（RK）,geographically weighted regression kriging（GWRK）.Based on the optimal model,the spatial differentiation characteristics of soil nutrient elements(including C,C_org,N,P,K₂O,B,Mn,Mo,Se,TFe₂O₃)and heavy metal elements（including As,Cr,Ni,Pb,Zn）and their potential influencing mechanism in western chongqing area were comprehensively analyzed.And the effects of topography and social economy on spatial differentiation are also quantified.On this basis,the author integrates some variables including topography,geomorphology,social and economic environment such as a co-variate,building the typical soil element space differentiation characteristics prediction model to get the data of spatial distribution of soil elements in the region,and makes up for the lack of soil data related,giving accurate data basis and technical support for soil environmental protection.The main research achievements are as follows:（1）Among the soil nutrients of western Chongqing,the spatial variability of a large number of beneficial elements C,N and trace elements B and Mn is strong,and the element content changes relatively（fluctuates）to a large degree and the distribution is concentrated.By comparing the geomorphologic distribution map of the study area,it can be seen from the regional distribution that C,C_org,N,Se and B in the western Chongqing region have high values at the uplifted low mountain of the two folds in the study area.The distribution characteristics of P,K₂O,Mn and TFe₂O₃are opposite to those of the above elements.There is no obvious characteristic phenomenon of Mo,and the distribution of Mo content in soil is mainly high in the northwest and low in the southeast.（2）The variation of Zn in heavy metal elements in western Chongqing was the largest,and the distribution of element content was relatively dispersed,and the relative variation（fluctuation）of element content was the largest.As has the smallest variation,the most concentrated content,and the least relative change（fluctuation）degree of element content.From the perspective of regional distribution,the soil heavy metal elements Cr,Ni and Zn mainly appeared relatively high values in the northwest of the study area,while the relatively low values were distributed in the uplifting low mountains of the two folds in the study area,which was contrary to the spatial distribution of As in the valley and plain below the northern part of the study area,the Pb content at the northern end of the boundary is relatively low,while a small part of the southernmost area is relatively high.（3）Effective covariables ensure the accuracy of soil element content estimation.Among the environmental covariates,DEM,slope and other topographic factors have the greatest influence on the spatial pattern of the content of soil nutrients.In the interaction of all factors,the interaction between town distance and slope was the strongest,and the interaction between DEM and other factors increased significantly compared with the influence of each factor.（4）Among the environmental covariates,the distance between mining areas and towns has the greatest influence on the spatial pattern of soil heavy metal content.In the interaction of all factors,the interaction between town distance and slope is the strongest,and the interaction between mining area distance and other factors is greater than that between each factor itself.It shows that the spatial differentiation of heavy metal elements in soil in western Chongqing is mainly influenced by human factors represented by city and industry.