Spatial Variability And Distribution Pattern Of Heavy Metals In Surface Soil In A Mollisol Watershed Of China

Land is the fundamental guarantee of human production and life,and the basis of the development and progress of human society.In the process of exploitation and utilization of land resources,the contents of heavy metals in soil and their spatial distribution will change in different degrees.With the rapid development of economy and the rapid increase of population pressure forced us to obtain more land resources,in order to ensure production income due to unreasonable input of chemical fertilizer and pesticide caused a series of agricultural cleaner production and environmental safety issues,is the current obstacles to scientific configuration,rational utilization of land resources and regional ecological environment safety and sustainable development of agriculture.It is of great importance and significance to accurately grasp the current status of toxic heavy metal content in soil,its distribution pattern and influence factors to improve the security of grain production and the quality of ecological environment.Based on a mollisol watershed of China as the research area,in order to promote agricultural cleaner production and enhance the ability of agriculture sustainable development,classical statistics and geostatistics in combination with "3S" technology were used to investigate the spatial heterogeneity and distribution pattern and influence factors of toxic heavy metals in soil.The main conclusion are as follows.(1)The average contents of Hg,Pb and Cd in soil were 5.26%,18.20%and 213.13%respectively higher than the soil background values of the Songnen Plain.Among them,the average content of Cd is the highest,which has exceeded the national secondary standard of soil inorganic pollutants.Due to the contents of toxic heavy metals in the watershed soil were in normal distribution,the statistical analysis can be carried out.The variation intensity was Hg>Pb>Cd,and the coefficient of variation was 58.54%,25.65%,13.40%respectively.The coefficient of variation of Hg is the highest,which indicated that the content of Hg was relatively discrete and its difference was larger in all the samples.The coefficient of variation of Pb and Cd were smaller,and the dispersion was relatively smaller,which indicated that the spatial differentiation of them was relatively small,and may be affected by the same external factors,with similar homology.(2)The semi-variance model of Hg,Pb and Cd content in soil corresponded to the Gauss model,the Gauss model and the spherical model,and the corresponding fitting residuals were 1.694E-08,29.8,8.615E-09 and R2 were 0.945,0.732,0.764 respectively,which indicated that these models were fit well,and can effectively reflect the spatial distribution and variation characteristics of the three kinds of toxic heavy metals in soil.The nugget effect revealed the spatial variation was less affected by the structural factors such as topography,soil parent material,and so on,while was more affected by human activities,such as development and utilization,the planting mode and other random factors.(3)Compared with the ordinary kriging interpolation simulation,the prediction accuracy verification error indicators of collaborative kriging interpolation and geographically weighted regression kriging with the help of the terrain and environmental factors as the auxiliary variables were reduced to some extent.Among the three methods,the mean absolute error,average relative error and root mean square error of the predicted values obtained by the geographically weighted regression kriging were smallest.Although the correlation between auxiliary variables leads to the error reduction was not obvious,it still indicated that the geographical weighted regression kriging interpolation could further improve the simulation accuracy of the three toxic heavy metal content in soil and provide an accurate reference for agricultural cleaner production,prevention and control of heavy metal pollution in soil.(4)The physicochemical properties of soil can affect the content of toxic heavy metals in soil,but this effect is relatively limited,and was shown that the content of heavy metals is high and widely distributed in acidic soil.Under the influence of different topography and landform,the toxic heavy metals in soil were concentrated in the area with low and flat terrain.Different land use patterns is the main factors to the difference of spatial distribution of heavy metals in soil,characterized by most of the cultivated land is polluted by heavy metals,and some areas are serious,construction land and residential area come second.The closer to the relevant factors,the spatial distribution of heavy metals in soil is more intensive.(5)The content of Hg,Pb and Cd in soil is mainly caused by the factors of human production and life,which is not a natural phenomenon.And the source of three kinds of toxic heavy metals in the study area is complex,there is a common source,but the source of the degree of difference.In view of the present situation of heavy metal pollution in the study area,the main measures are put forward which is shown that prevent and control the pollution in the area,strengthen the protection of the non polluted area,and control the pollution source.It contributes to quickly control the soil pollution of toxic heavy metal,to prevent the pollution area continues to expand.Reducing the generation of toxic heavy metal pollutants on the source,can effectively inhibit the accumulation of pollutants and reduce the pressure of pollution control and remediation.