泾河上游全新世黄土-古土壤序列微量元素分布特征及环境变化

Distribution of trace elements in Holocene loess-paleosol sequence and environmental change in the upper reaches of Jinghe River

  • 摘要: 在野外考察的基础上, 对泾河上游赵家村全新世黄土-古土壤剖面进行系统采样, 利用X-Ray荧光光谱仪测定了Ba、Zn、Cu、Pb、Cr、Rb、Sr、Co、Th、Zr等10个微量元素的含量及其变化, 并与磁化率、粒度进行了相关性分析, 研究表明大部分微量元素如Ba、Zn、Cu、Rb、Co、Th、Zr在古土壤层(S0)中富集, 而在马兰黄土层(L1)中含量较低; 而Pb、Cr、Sr在古土壤层中含量低于马兰黄土层。同时, 微量元素Ba、Zn、Cu、Rb、Co、Th、Zr与磁化率、黏粒(<0.005 mm)含量呈正相关, 与粗粉沙(0.01~0.05 mm)含量呈负相关; 而元素Pb、Cr、Sr与黏粒、磁化率呈负相关, 与粗粉沙呈正相关关系。在古土壤成壤改造过程中, 由于有机质含量显著增加, 络合-螯合作用增大, 加之黏粒胶体的吸附作用, 导致大多数微量元素在古土壤层的相对富集; 而元素Cr性质稳定, 在整个剖面的波动较小; Sr含量在全新世黄土层(L0)和表土层(TS)中逐渐升高, 主要是由于气候暖干化日趋严重, 表土层碱性增强, CaCO3淋溶作用明显减弱; Pb元素在表土层含量较高的主要原因是工业“三废”排放、金属采矿和冶炼、煤炭和石油的燃烧以及汽车尾气排放等人类活动的干扰。

     

    Abstract: Based on field survey, samples of Holocene loess-paleosol sequence were systematically collected at the Zhaojiacun (ZJC) site in the upper reaches of Jinghe River. The contents of Ba, Zn, Cu, Pb, Cr, Rb, Sr, Co, Th and Zr were then determined by X-Ray fluorescence and compared with magnetic susceptibility and particle-size distribution. It is noted that most of the trace elements including Ba, Zn, Cu, Rb, Co, Th and Zr accumulate in paleosol layer (S0) and drop in Malan loess layer (L1). The correlation coefficients of element content with magnetic susceptibility and clay (<0.005 mm) content are positive, while they are negative with coarse silt (0.01~0.05 mm) content. But the trace elements of Pb, Cr and Sr are high in Malan loess, low in paleosol. They have a negative correlation with magnetic susceptibility and clay content, but are positively related with coarse silt content. During Holocene megathermal epoch, the contents of trace elements are higher in paleosol than in loess because of strong pedogenesis, adsorption and complexity. Cr is largely stable, only weakly fluctuating in the entire sequence. Sr content is high in Holocene loess (L0) layer and the topsoil (TS) because of warming and drying climate, strong topsoil alkalescence and weak CaCO3 eluviation. High Pb content in the topsoil is mainly due to human activity such as “three-waste” discharge, mining and smelting of metals, coal and petroleum combustion, and automobil exhaust emission.

     

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