三峡库区土壤淹水对Cd形态稳定性的影响

Effect of Submerged Condition on Chemical Form of Cd in Soil of Three Gorges Reservoir Area

采用三峡库区紫色土和黄壤作淹水厌氧培养,研究土壤氧化还原过程对吸附于土壤中的外源Cd形态稳定性的影响。结果表明,土壤淹水厌氧培养过程,pH向中性转变,体系Eh降低,土壤从氧化环境转入还原环境,黄壤氧化还原转换趋势更为明显。紫色土CEC含量增加到17.53cmol·kg-1,黄壤为27.94cmol·kg-1。黄壤Fe(II)增加趋势明显,Fe(II)含量达到3 156.30mg·kg-1,紫色土为446.56mg·kg-1。外源Cd进入水土体系后,快速被土壤吸附,至培养结束,99.9%以上Cd被土壤吸附。土壤理化性质的改变与外源Cd在土壤中的形态稳定性具有直接联系,外源Cd被吸附后逐渐达到形态上的稳定,部分Cd由形态稳定性最差的可交换态向更稳定的碳酸盐结合态和铁锰氧化物结合态转变。紫色土中可交换态Cd从5.87 mg·kg-1降低至4.56 mg·kg-1,含量降低22.34%,黄壤从2.87mg·kg-1降低至1.02mg·kg-1,含量降低64.30%,外源Cd在黄壤中形态稳定性好于紫色土。

Purple soil and yellow soil of Three Gorges Reservoir Area were submerged and incubated under a nitrogen atmosphere to study the effect of redox process on chemical form of Cd.It is shown that the pH and Eh decrease in the redox process.With the transition of soil redox condition,the content of CEC increases to 17.53 cmol·kg^-1 for purple soil and 27.94 cmol·kg^-1 for yellow soil,and the content of Fe（II） increases to 3 156.30 mg·kg^-1 for yellow soil and 446.56mg·kg^-1 for purple soil.The soluble Cd concentration declines after submergence for the purple soil and yellow soil,and 99.9% of soluble Cd is absorbed by soils.Chemical form of Cd in soil is significant correlated with the physical-chemical indexes of soil.In the process of redox process,part of Exc-Cd（exchanged fraction） transforms to Carb-Cd（carbonated fraction） and Oxide-Cd（oxide-bound fraction）,and the content of Exc-Cd decreases to 4.56 mg·kg^-1 for purple soil and 1.02 mg·kg^-1 for yellow soil.The stability of Cd in yellow soil is higher than that in purple soil.