黑色岩系成壤过程中镉和硒的形态转变与迁移特征

Transformation of Chemical Forms and Migration Characteristics of Cadmium and Selenium During Soil Formation in Black Rock Series

[目的]黑色岩系含有高量的镉和硒,为明确其在风化成土过程中,岩石镉和硒的形态转变和释放对周围生态环境产生影响。[方法]在浙西北寒武统荷塘组地层的黑色岩系分布区,通过沿地形不同部位(丘陵上坡、丘陵中坡、丘陵下坡、丘间谷底和河谷阶地)采集土壤剖面分层土样,探讨黑色岩系风化成土及其风化物迁移过程中镉和硒的数量与形态转变规律。[结果]从母岩经母质到土壤,土壤总镉和总硒均呈下降趋势。黑色岩系风化物镉和硒损失随沿丘陵坡地向下迁移搬运距离增加而增加,其中,由坡积物演变为洪积物的过程中,镉和硒的损失大于由残积物演变为坡积物的损失。从风化物中流失的镉和硒以流水扩散方式对下游河流冲积物发育表土镉和硒含量产生影响,但影响程度随距离增加而减小。随着风化物搬运距离增加和土壤的演变,发生碳酸盐结合态镉和残留态镉向水溶性镉、交换性镉、有机质结合态镉、氧化物结合态镉转变,残留态硒逐渐活化转变为交换性硒、有机质结合态硒、氧化物结合态硒。土壤水溶性镉、交换性镉(硒)、有机质结合态镉(硒)呈现向地表增加的趋势;硒的有机富集及表土富集现象比镉更为明显。[结论]黑色岩系风化不仅可通过残留方式直接影响其分布区土壤镉与硒的含量,也可通过流水扩散方式影响周边地区土壤镉和硒的含量。

[Objective]Black rock series contain high amounts of cadmium(Cd)and selenium(Se).During weathering and soil formation on the rocks,the chemical form transformation and release of Cd and Se from the rocks can have an impact on the surrounding ecological environment.[Methods]In this study,a black rock series distribution area of Hetang formation of the Lower Cambrian was selected in northwest Zhejiang.By collecting horizonal soil samples from soil profiles along different parts of the terrain(hill upslope,hill middle slope,hill downslope,inter hill valley bottom and valley terrace),the quantity and chemical form transformation patterns of Cd and Se during the process of weathering soil formation and weathering material migration of the black rock series were discussed.[Results]The results showed that total Cd and total Se in the soil decreased from parent rock to soil.The loss of Cd and Se in the weathered matter of black rock series increased with the increasing of transportation distance along the hilly slope,and the loss of Cd and Se in the process of evolution from slope deposit to diluvium was greater than that from residual to slope deposit.The Cd and Se lost from the weathered materials could affect the contents of Cd and Se in the topsoil derived from the alluvial of the downstream river in the way of water diffusion,but the degree of influence decreased with the increasing of distance.With the increasing of the transportation distance of weathered materials and the evolution of soil,the transformation of carbonate bound Cd and residual Cd to water-soluble Cd,exchangeable Cd,organic matter bound Cd and oxide bound Cd occurred.The residual Se gradually activated and transformed into exchangeable Se,organic matter bound Se and oxide bound Se.The results also showed that soil water-soluble Cd,exchangeable Cd(Se)and organic matter bound Cd(Se)showed an increasing trend toward the surface.The organic enrichment and topsoil enrichment of Se were more obvious than those of Cd.[Conclusion]The results indicated that the weathering of black rock series could not only directly affect the contents of soil Cd and Se in their distribution area through residue,but also affect the contents of soil Cd and Se in the surrounding areas through water diffusion.