青海湖流域表层土壤环境背景值及其影响因素

摘要

为了评价青海湖流域土壤的环境背景值，2008—2009年分别采集流域表层土壤样品共273个，采用X荧光光谱仪分析了29种元素（Na、Mg、Al、Si、K、Ca、Fe、P、Ti、V、Cr、Mn、Co、Ni、Cu、Zn、Ga、As、Rb、Sr、Y、Zr、Nb、Ba、Pb、La、Ce、Nd和 Th）的含量，根据ArcGis的统计工具ESDA模块，确定了表层土壤背景值及其范围。结果表明：总体上青海湖流域表层土壤各元素含量偏低，但Ca元素含量明显偏高，Zn元素含量明显偏低；流域风化程度是初等风化脱Ca、Na阶段向中等风化脱K阶段转变，风化环境处于冷干向暖湿转变，风化的主控因素是母岩和温度；大多数元素含量的变化都与沉积物中粘土（<4µm）含量的变化呈一致性，而与砂（>63µm）的含量变化呈反相关关系，这些元素多赋存在细颗粒物中，少部分元素容易赋存于粗颗粒中；常量元素的活动性的顺序为：K2O > CaO > SiO2> MgO > Na2O > Al2O3> TiO2> P2O5> Fe2O3> MnO；微量元素的活动性的顺序为：Ni > V > Pb > Ba > Sr > Zr > Ce > Rb > Co > Zn > La > Y > Nd > Cu > Th > Nb。%In order to evaluate the soil environmental background values, a total of 273 topsoil samples were collected from Qinghai Lake watershed in 2008—2009, northeast Tibetan Plateau. 29 elements (Na, Mg, Al, Si, K, Ca, Fe, P, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Rb, Sr, Y, Zr, Nb, Ba, Pb, La, Ce, Nd and Th) were determined by the XRF. The environmental background values and its scope were evaluated with Explore Spatial Data Analyst (ESDA) of Geostatistical Analyst in ArcGis 9.3. In contrast to the background levels of trace elements for China topsoil, the contents of each element was low, Ca content was obviously higher and Zn was evidently low. The soil was in a transit stage during the course of chemical weathering, i.e., large amount of leachable Ca2+, Na+ accompanying with deepen dilution trend of K+. The environment of chemical weathering in Qinghai Lake soil was in a stage toward warm and humid climate from cold and dry climate. Bedrock and temperature are main controlling factors for chemical weathering. Variations of the contents of major chemical elements in topsoil were consist with the variation of the percentage of clay fractions (<4 µm) in sediments, but were anti-correlated to those variations of sand fractions (>63 µm). These chemical elements easily existed in ifnd grain particles and little elements in coarse particles. The activity sequence of major elements and trace elements are: K2O > CaO > SiO2 > MgO > Na2O > Al2O3 > TiO2 > P2O5 > Fe2O3 > MnO, Ni > V > Pb > Ba > Sr > Zr > Ce > Rb > Co > Zn > La > Y > Nd > Cu > Th > Nb, respectively.