[Researches on the estimate methods and applications of soil environmental geochemical baseline at a regional scale]

Regional soil environmental geochemical baseline is a base tool for studying material changes in the earth surface system at a regional scale as well as for the assessment of natural and human activities impacts on the changes of chemical elemental contents in the soil environment. We choose the Yangtze River Delta (YRD) region and Pearl River Delta (PRD) region as cases to estimate the regional soil environmental geochemical baseline of ten trace elements including As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Zn, Se. Two methods including cumulative distribution frequency (CDF) and average estimation based on weighted soil area were applied to estimate the baseline of different soil categories at a regional scale and the whole region, respectively. A consistent result was obtained based on the two methods, implying the feasibility of the methods for baseline estimation. The estimated baselines were further used to assess the impacts on accumulation and contamination of trace elements caused by geochemical enrichment and human activities in YRD and PRD regions. For the instance of PRD region, Cd level has increased from 0. 035 mg/kg to 0.13-0.22 mg/kg and Hg level has increased from 0.045 mg/kg to 0.15 mg/kg by compared the baselines to soil environmental background levels investigated 20 years ago. Such a change implies a typical trend of heavy metal contamination in soil at a regional scale.