| Soil is an important natural resource for human survival,and soil environmental safety is the basis for the sustainable and safe utilization of soil resources.In recent years,with the rapid development of industrialization,urbanization and agricultural intensification in China,industrial and urban waste emissions and agricultural chemical input are increasing,resulting in a continuous increase in the potential risk of soil heavy metal pollution.The enrichment of heavy metals in agricultural soil affects the yield,quality and safety of agricultural products,and then does great harm to human health.it is of great significance to accurately grasp the spatial distribution law and main sources of heavy metals in agricultural soil for the risk control of agricultural soil pollution.This study takes Liuhe District of Nanjing City,which is with rapid economic development in the Yangtze River Delta as a typical study area,and comprehensively uses robust statistics,sequential Gaussian simulation,absolute principal component score-multiple linear regression receptor model and random forest and other methods.through the study of the spatial variation characteristics and spatial distribution of the four most concerned heavy metal elements in the agricultural soil of the study area.The potential pollution risk,distribution characteristics and prediction uncertainty of soil heavy metals in the study area were deeply analyzed,and the sources and influence processes of soil heavy metals were analyzed by quantitative means.The results show that:(1)The average contents of Pb,Cr,Cd and Hg in agricultural soil in the study area were27.81 mg/kg,66.74 mg/kg,0.125 mg/kg and 0.076 mg/kg,respectively.Among them,the spatial autocorrelation of Pb and Cr content is moderate,while the spatial autocorrelation of Cd and Hg is strong.The high value areas of soil Pb and Cr content are mainly distributed in the southeast of the study area along the Yangtze River,the spatial distribution pattern of Cd content shows an obvious increasing trend from northwest to southeast,while the areas with higher soil Hg content are relatively concentrated in agricultural soils in the suburbs of Liuhe.(2)Some of the four heavy metals exceeded the background value,and 19 of the 27 spatial abnormal high values of heavy metals were adjacent to various factories,indicating that the pollution point source had a significant impact on the local anomaly of soil heavy metal content in this area.potential pollution risks should not be ignored.(3)Taking the background value of agricultural soil in Nanjing as the evaluation threshold,the potential pollution risk areas identified with the critical probability of 0.95 are mainly the area proportion of Pb and Hg,is 10.46% and 0.62% respectively,but the spatial uncertainty of the identification result is great,so the potential pollution risk of soil heavy metals is still mainly the risk of point source pollution within the local limited range.(4)The contents of Cd and Cr in agricultural soils in the study area were mainly affected by large-scale natural factors,in which the relative contributions of spatially continuous natural sources to Cd and Cr contents were 77.7% and 97.0%,respectively.Soil Pb and Hg are mainly affected by small-scale spatial continuous processes caused by rapid urbanization,industrialization and soil agricultural utilization,in which the relative contributions of spatially continuous man-made sources to Pb and Hg content are 75.7% and 86.7%,respectively. |
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