Spatial distribution of heavy metal content in the farmlands of Hainan Island

Abstract

Geographical information system (GIS) combined with Geostatistics was applied to determine the spatial distribution of heavy metal (Hg, Cd, Pb, As and Cr) contents in the farmlands of Hainan Island. The results show that average content of the five heavy metals is below Grade Ⅱ standard of the National Environmental Quality Standard for Soil (GB15618-1995). Theoretical semivariogram models of soil Hg, Cd, Cr and Pb match well with exponential models. Spatial correlation of Hg and Pb is weak, in- dicating that their content is largely affected by soil formation factors. Theoretical semivariogram model of soil As matches well with the Gaussian model. The distributed spatial correlation of Cd, Cr and As is moderate, indicating that their content is affected by ex- ternal inputs. Distribution contour maps of the 5 heavy metals for farmlands in Hainan Island obtained from Kriging in GIS show that heavy metal pollution caused by external inputs from industrial zones are most serious on Hainan Island.