Spatial Predict And Influencing Factors Of Heavy Metal Of Cultivated Soil In The Loess Hilly-Gully Region

Soil heavy metals have the characteristics of strong concealment,easy spread,and great harm,which seriously threaten the farmland ecosystem and human health.As one of China's main agricultural production areas,the loess hilly-gully region of northern Shaanxi has accumulated heavy metals due to long-term farming activities.In order to understand the status of heavy metal pollution of cultivated soil in the region,simulate the spatial differentiation of heavy metal pollution,and identify the influencing factors of heavy metal pollution,this paper takes three typical villages in Gaoqu Township,Mizhi County in the hinterland of the loess hilly-gully region as the research area.Nemerow pollution index and potential ecological risk index were used to evaluate heavy metal pollution in cultivated land.Based on this,the SVM_OK model and MLR_OK model were used to simulate the heavy metal pollution of cultivated land.Finally,a two-level model based on farmers and land plots was constructed to comprehensively characterize the factors affecting soil heavy metal pollution of cultivated soil in the loess hilly-gully region.(1)The average concentrations of heavy metals Pb,As,Cu,Cr,Ni,and Zn in the soil of the study area were 16.00 mg/kg,10.65 mg/kg,29.77 mg/kg,102.07 mg/kg,56.20 mg/kg,and 54.99 mg/kg.Taking the background value of loess soil as the evaluation standard,the average value of the single factor pollution index was: Pb <Zn <As <Cr <Cu <Ni,the extreme values of Nemerow comprehensive index were 1.44 and 1.99,and the average value was 1.71,indicating that the cultivated land was lightly polluted in the study area.The average ranking of the individual potential ecological risk indexes was: Zn <Cr <Pb <Cu <As <Ni,the comprehensive potential ecological risk index was between 32.05-42.19,and the overall level was at a moderate ecological risk level.(2)The SVM_OK model is the best predictor of heavy metal pollution of cultivated soil in the loess hilly-gully region.Its predicted RPD for Nemerow pollution index and potential ecological risk index were 9.034 and 4.807,respectively,reaching excellent levels,which were 284.26% and 17.44% higher than the RPD predicted by MLR_OK,respectively,and 388.89%,645.27% higher than the RPD predicted by OK.Meanwhile,the RMSE,MAE,and MRE values predicted by SVM_OK are smaller.(3)The influencing factors of heavy metal pollution in the soil of different farmer types are different.For the Nemerow index,factors such as the proportion of agricultural income and land elevation of part-time farmers are more significant.The education level,the number of labors,the unit price of crops,and the elevation of the plot of the farming households have significant influence.The age,education level and distance from the road of the self-sufficient peasant household have significant influence.