岷江上游干旱河谷区汶川段岩-土系统元素地球化学特征

    Elemental geochemistry of the rock-soil system in Wenchuan section of the arid valley, Upper Minjiang River

    • 摘要: 地表中元素地球化学特征与基岩有密切的关系, 不同基岩风化形成的土壤元素含量具有显著差异. 本文选择岷江上游干旱河谷区汶川段3类不同成土母岩的岩石-土壤垂向剖面, 采集基岩和土壤样品共18件, 进行常量、微量元素含量测定, 分析其地球化学特征, 据此研究基岩-土壤的元素分布和迁移特征. 结果表明: 研究区3类基岩发育的土壤在CaO和Na2O含量上存在显著差异, 基岩中含量较高的元素在所对应的土壤层中含量也较高; 土壤微量元素平均含量Mn>Zn>Cu>Se, 重金属元素Cr>Pb>As>Cd>Hg, 与基岩中元素含量排序一致; 土壤重金属元素仅Cd、Pb含量略高于农用地土壤污染风险管控标准值. 在岩-土系统中, 以花岗岩为母岩的土壤中Al2O3、K2O、Na2O、SiO2呈现为亏损; 以千枚岩为母岩的土壤中常量元素CaO、Na2O呈现为富集, 微量元素Zn、Cr、Pb呈现为亏损; 以结晶灰岩为母岩的土壤中除Ca表现为迁移淋失, 其余元素在土壤中呈现为富集.

       

      Abstract: The geochemical characteristics of elements in surface environments are closely related to their parent bedrock, leading to significant differences in soil compositions derived from various rock types. This study investigated vertical bedrock-soil profiles with three types of parent rocks in Wenchuan section of the arid valley in the upper reaches of Minjiang River. A total of 18 bedrock and soil samples were collected and analyzed for their major and trace element concentrations to characterize their geochemistry and to examine element distribution and migration between bedrock and soil. The results indicate that soils developed from the three bedrock types differ significantly in CaO and Na2O contents. Elements with higher concentrations in the bedrock generally maintain higher levels in the overlying soil. The average contents of trace elements in soils decrease in the order Mn > Zn > Cu > Se, while the heavy metals follow the sequence Cr > Pb > As > Cd > Hg, consistent with their abundance patterns in the bedrock. Among the heavy metals, only Cd and Pb slightly exceed the risk control standards for agricultural soil pollution. Within the bedrock-soil system, soils derived from granite show depletion of Al2O3, K2O, Na2O, and SiO2; soils from phyllite are enriched in CaO and Na2O but depleted in Zn, Cr, and Pb; and soils from crystalline limestone exhibit enrichment of most elements except for Ca, which undergoes leaching and migration.

       

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