乌梁素海湖泊沉积物粒度特征及其环境指示意义

Grain Size Characteristics and Its Environmental Significance of Lacustrine Sediment Recorded in Wuliangsu Lake,Inner Mongolia

结合放射性同位素测年,在对乌梁素海湖泊沉积物粒度的分析基础上,结合黄河以及河套地区相关文献资料,探讨乌梁素海在自然和人类活动共同作用下的演变过程。乌梁素海沉积物中黏土(<4μm)平均含量28.7%、细粉砂(4～16μm)平均含量34.4%、中粉砂(16～32μm)平均含量17.3%、粗粉砂(32～64μm)组分平均含量14.1%、砂质组分(>64μm)含量整体较低,平均含量为5.5%。沉积物不同粒级范围颗粒含量的相关性分析表明,在1965年左右(岩芯深度20 cm)乌梁素海沉积物组分特征发生了明显变化。基于此,结合前期对湖泊沉积物中元素含量特征的分析,利用粒径-标准偏差方法,通过对比黄河泥沙以及流域沉积物的粒度特征,研究了约1965年前后两个时段的沉积物来源。尽管乌梁素海湖泊沉积物主要来源于黄河携带的泥沙以及河套平原灌溉退水携带的大量流域表土侵蚀物质,但同一物源组分在1965年前后这两个不同的演化阶段具有不同的粒级特征。1965年之前,<19.95μm的粒级组分反映了河套平原灌溉退水携带的流域表层侵蚀物质组分特征,而19.95～181.97μm的粗颗粒组分反映了黄河径流携带的泥沙,后者决定了乌梁素海沉积物的粒级特征。1965年以来,这两种不同来源组分的粒级变细,灌溉退水携带的流域表土侵蚀物质(<5.71μm组分)控制了湖泊沉积物的粒度特征,并与总排干入乌梁素海的水量变化、围湖建堤以及扬水站的修建等人类活动强度密切相关。总体来看,上世纪六十年代以来,乌梁素海湖泊沉积物的粒度组成受人类施加的影响已经超越了自然作用的影响。

Based on radiocarbon dating of 210Pb,the grain size of lacustrine sediment in Wuliangsu Lake was analyzed.Comparing with historical documents,the environmental evolution under the combined effects of natural and human activities was studied in Wuliangsu Lake region,Inner Mongolia.The average content for clay（4 μm）,fine silt（4~16 μm）,medium silt（16~32μm）,coarse silt（32~64 μm）,fine sand（64 μm）,is 28.7%,34.4%,17.3%,14.1%,5.5%,respectively.Through the correlation analysis of different grain size contents,the grain size characteristic changed significantly around 1965 AD in Wuliangsu Lake.Based on this result,with the method of grain size vs.standard deviation,the sediment sources were extracted in the two stages before and after 1965AD.The results show that： the sources of lake sediment are composed of materials from Yellow River and topsoil erosion in Hetao irrigation.But in the tow stages,the grain size characteristics of different populations in lake sediment have obvious differences.Before 1965 AD,the fine grain-size populations（19.95 μm） are from the topsoil erosion in Hetao irrigation,and the other coarse grain-size populations（19.95~181.97 μm） are carried by Yellow River,which dominated grain size characteristic of the whole Wuliangsu lake sediment.After 1965 AD,the gain size of the fine and coarse population are 5.71 μm and 5.71~60.56 μm,respectively,but the fine grain size one dominated the lake sediment characteristic,which are consistent with runoff of the main drainage canal in Hetao Plain.Overall,since the 1960s,lake sediments in Wuliangsu were mostly imposed by human influence,which has exceeded the natural role.