Spatial structure and distribution characteristics of heavy metals in the soil in Chengde

Based on the combination of geo-statistics and GIS, this paper analyzed the normal distribution characteristics, dominant distribution trends and interaction regulations of heavy metals including As, Cd, Cr, Cu, Hg, Ni, Pb, Zn, and trace elements Se in the topsoil in whole area of Chengde. Both the most suitable geo-statistics interpolation model and spatial distribution law for these elements were determined. The results showed that the average contents of As, Cd, Cr, Cu, Hg, Ni and Pb, were respectively 8.28,0.200, 60.85, 24.37, 0.034, 27.76, 26.65, 77.1 mg/kg. The coefficients of variation of Cd, Cu, Hg, and Pb were respectively 385%, 143%, 350%, and 118%, which indicated the level of dispersion was great. The average value of Zn contents was significantly affected by soil types. While the average value of Cr, Cu, Ni contents was significantly affected by land use types. After comprehensively comparing the interpolation errors of order elements of different trends, the following results were obtained that non-trend parameters were suitable for As, Cr, Pb, Zn, Ni, and Se, first-order trend parameters were suitable for both Hg and Cu, while second-order trend parameters were suitable for Cd. The theoretical model of As was an exponential model, which was mainly affected by structural factors. The theoretical models of Cd, Cr, Cu, Hg, Ni, Pb, Zn, and Se were linear models, which were mainly affected by random factors. According to the Kriging method, it could be seen that the 9 elements in the area presented a characteristic of low level in the north and high in the south. And a relatively wide Pb high-value band was formed in the central area, similar to Cd. According to the characteristics of contents distribution, the high-value spatial distribution areas between Cr and Ni, Cu and Hg, Zn and Pb, Se and Cd were similar, and the sources were also the same, and only As was significantly different from them. The analysis results were partially consistent with the traditional statistical results.