The soil heavy metal content mapping based on Sandwich model

With the rapid development of agriculture and industry, the soil heavy metal pollution is becoming more prominent. It is necessary to know the content and spatial distribution of heavy metal in soil. The soil heavy metal content is not only affected by natural factors such as parent material, climate, biology, topography et al, but also the man-made pollution factors such as pesticide and fertilizer use, sewage irrigation, solid waste accumulation et al. Compared to natural factors, the man-made pollution factors are most often spatially heterogeneous. The Sandwich model proposed by Jingfeng Wang can be used to mapping the distribution of regional variable with spatially stratified heterogeneity. The Sandwich model has three key layers: sampling layer, zooning layer and reporting layer, the information of sampling data is firstly transferred into zooning layer, and then transferred from zoning layer to reporting layer to get estimated mean and related error for each report unit. In this paper, the Sandwich model was used to mapping the spatial distribution of heavy metal (As) content in the soil of South part of Daxing District, Beijing. The sampling data was used as the sampling layer, then the parent material data, and sample clusters were integrated to divide the study area into zones, and the administrative villages were the units of reporting layer. The estimation results show that the average content of As in these villages is about 6mg kg
^-1
, most middle part of whole region is from 4.5 mg kg
^-1
to 7 mg kg
^-1
, and the content of boundary part is less, and individual area has extremely higher content. By comparing with the results obtained by Ordinary Kriging interpolation, Stratified estimation. The mapping result of soil heavy metal content results show that Sandwich Model has better performance than the other two estimation methods.