生态地球化学评价中建立土壤元素地球化学背景方法研究:以太原盆地潮土中Hg、Cd、Pb、As为例

深层土壤与表层土壤中元素质量分数的差异被一些学者归因于表层土壤受人为污染所致。文中通过解析山西太原盆地深、表层潮土中Hg、Cd、Pb、As的地球化学分布特征,并通过对比研究区与基本保持清洁状态的源区土壤中相应元素质量分数变化特征,论述了成壤过程中元素的自然分异作用是造成深、表层潮土中Hg、Cd、Pb、As质量分数显著差异的主要原因,以及人为污染仅在局部地区造成Hg、Cd、Pb、As在表层潮土中富集的观点。通过求解太原盆地表层潮土中Hg、Cd、Pb、As地球化学背景值的实例,详细介绍了以深层土壤元素的地球化学背景为参照系,运用相关分析和累积频率分析求解表层土壤元素地球化学背景值的方法。

On evaluation of elemental background in topsoil: With Hg, Cd, Pb and As in fluvo-aquic soil of Taiyuan basin as an example

Undeviating the evaluation of the geochemical background of an element in topsoil is very important for the correct assessment of quality of the plough. However, the difference in elemental contents between the topsoil and subsoil in the same place has been ascribed, by some authors, to artificial pollution of the topsoil. The elemental background value of the subsoil has been suggested to be the same as that of the topsoil. Analyzing the distribution characteristics of Hg, Cd, Pb and As in the fluvioaquatic soil profiles of the Taiyuan basin, and on the basis of comparing the elemental contents with that of the least polluted soil in the mountain areas,which is the source of the basin sediments, the difference content of these elements between the topsoil and subsoil in the Taiyuan basin is likely caused by natural differentiations during soil formation. In view of this, a new approach to evaluate elemental background in the topsoil is suggested. The essence of this method is that the background of an element in the topsoil is evaluated by regression analysis and/or cumulative frequency analysis but with the background value of the corresponding element in the subsoil as a reference frame. In this paper, this approach is discussed in detail and the background values of the four relevant elements in the basin topsoil are given. In addition, the elemental background value estimated by the regression analysis coincides well with that estimated by the cumulative frequency analysis.