The spatial distributions of the five heavy metals were mapped using the Kriging method on ArcGIS 10.2 . The concentrations of heavy metals were log-transformed to approximate normal distributions prior to the statistical analyses. The correlation analysis on the heavy metal concentrations and soil properties was performed on SPSS 20.0 (SPSS Inc., Chicago, IL, USA). Linear regression models were used to evaluate the temporal trends of the heavy metal concentrations on the OriginPro 8.0