典型喀斯特地质高背景区土壤剖面镉的迁移富集机制与形态转化过程研究

Study on mechanisms of migration and speciation transformation of cadmium in soil profiles in a typical karst area

本研究以贵州西北部典型喀斯特地质高背景区土壤剖面为对象,探讨了土壤镉(Cd)含量与形态的纵向分布特征、Cd迁移转化过程及关键影响因素。结果表明,下伏高Cd碳酸盐岩风化成土作用是剖面土壤Cd富集的重要原因,在土壤形成初期,土壤pH较高,地质源Cd淋失较少,土壤Cd含量高;随着土壤发育程度加深,地质源Cd逐渐淋失,Cd含量降低。此外,区域人为源输入可能影响表层土壤Cd的富集。土壤地质源Cd主要以残余态存在,其次为铁锰氧化物结合态,可交换态的占比较低,Cd活性较低。剖面中下层(>60 cm)土壤Cd的赋存形态变化较小,剖面上层(<60 cm)土壤可交换态Cd的占比随土壤深度的降低而逐渐增大,地质源Cd被活化。本研究结果可为理解喀斯特地质高背景区土壤Cd的地球化学行为提供科学参考。

This study investigated the vertical distribution,migration,and chemical speciation changes of cadmium(Cd)in soil profiles collected from a typical high geochemical background karst area and estimated the factors influencing them.The results showed that the natural weathering of the underlying Cd-rich carbonate rocks was the dominant factor for Cd enrichment in local soils.In the early stage of soil formation,the soil pH value was high and the leaching of geogenic Cd was low,resulting in the elevated Cd content in deeper layers of soil profiles.With the increase of soil maturity,geogenic Cd was continuously leached,resulting in the decrease of Cd content in upper layers of soil profiles.In addition,anthropogenic inputs may also affect the Cd content in the surface soil.The sequential extraction experiment showed that most of the geogenic Cd in the soil existed in the residual fraction,followed by the Fe-Mn oxide-bound fraction and then the exchangeable Cd,indicating the low lability of geogenic Cd.The variation of Cd speciation in deeper layers(>60 cm)of the soil profiles was relatively small,whereas the percentage of exchangeable Cd increased gradually from deep to shallow in the upper layers(<60 cm),indicating the mobilization of geogenic Cd.The results of this study are expected to provide a scientific reference for understanding the geochemical behavior of Cd in soils of karst areas with high geochemical background.