汉江上游谷地重金属元素变异规律对环境演变的响应

Responses of Heavy Metal Variation Patterns to Environmental Changes in the Upper Reaches of Hanjiang River Valley

以汉江上游谷地一级阶地的上覆黄土—古土壤序列为研究对象,分析包括Ni、Mn、Cu、Zn、As、Ti、V、Pb在内的8种土壤重金属含量及其分布特征,选取铷锶比（Rb/Sr）、磁化率及黏粒含量作辅助指标,研究汉江上游黄土—古土壤序列的成壤强度及所反映的气候演化特征。结果表明：Cu、Ni、Pb、As、Mn、V与成壤强度指标（磁化率、黏粒含量、Rb/Sr值）呈显著相关关系,说明该6种重金属迁移、富集程度受区域气候演变所驱动。依据重金属垂向分布特征,可判断自一级阶地抬升以来,汉江上游谷地共经历了5个气候阶段,其中,全新世中期气候整体温暖湿润,但在6~5 ka B.P.发生了一次干冷气候事件。

Loess-paleosol sequences were recognized as one of the most completed terrestrial records of palemonsoon climate evolution. The chemical parameters and metallic elements were normally used to indicate the soil sources and environmental changes. This study investigated the characteristics of the long-term climate evolution in the upper reaches of the Hanjiang River Valley using the heavy metallic elements variations,which was not commonly adopted by previous researchers. Loess-paleosol soil samples were collected from the first step terrace of the upper reaches of the Hanjiang River Valley. The heavy metallic element contents of Ni、Mn、Cu、Zn、As、Ti、V、Pb in the soil were measured and analyzed as the main climate change indicators. Magnetic susceptibility,Rb / Sr ratio and clay content were selected as the supplement indicators. The results showed that Cu,Ni,As,Pb and Mn contents in the soil were affected by climate changes and the pedogenesis environment and were significantly and positively correlated with the index of Pedogenic（ magnetic susceptibility,Rb / Sr ratio and clay fraction of particlesize）. Strong pedogenesis made some soluble elements migrate to deeper soil layers,leading to relative enrichment of heavy metals in the paleosol. According to the vertical distribution of the heavy metallic elements,the upper reaches of the Hanjang Valley experienced 5 stages of the climatic changes since the lift of the first step terrace. The climate was warm and humid in the Mid-Holocence except a cold and dry event happened at 6- 5 ka B. P.