新疆博斯腾湖近现代湖泊沉积物粒度分布特征及其环境记录

Grain-Size Distribution and Its Environmental Records of Modern Lacustrine Sediments from the Bosten Lake in Xinjiang

以新疆博斯腾湖岩芯(41 cm)沉积物粒度为研究对象,结合放射性同位素210Pb测年方法建立了沉积年代序列,利用粒径-标准偏差方法分析了沉积物中环境敏感组分,并重建了过去150 a来的湖泊水位变化历史。博斯腾湖岩芯沉积物中黏土质(<4μm)含量为18%,细粉砂质(4~16μm)含量为40.2%,中粉砂质(16~32μm)含量23.3%,粗粉砂质(32~64μm)含量13.4%,砂质(>64μm)仅有5.1%,不同粒级组分的垂向变化趋势具有较为明显的差异性。通过粒径-标准偏差法对沉积物环境敏感组分的提取表明,组分C2(粒径7.59~22.91μm)的平均粒径变化与中值粒径变化一致(r=0.7,P<0.01),组分C2对博斯腾湖沉积环境变化响应敏感,并由此重建了过去150 a的湖泊水位变化历史。1940年之前,博斯腾湖水位整体处于近150 a来的历史低值期,1910s-1930s低水位期代表了一次较大范围的区域干旱事件;在气候变化和显著增强的人类活动的共同作用下,1980s中后期博斯腾湖水位显著降低。湖泊水位作为沉积粒度变化的影响因子之一,可以通过湖泊沉积物中环境敏感组分的含量重建过去博斯腾湖水位的波动历史,为研究湖泊的历史变化规律及其影响因素提供一种新的途径。

In this study,the 210Pb dating method was used to establish the sedimentary chronology sequence of lacustrine sediments of the Bosten Lake in Xinjiang,China.The purposes of the study were to research the grain size distribution of core sediment(41 cm),analyze the sediment components sensitive to environment by applying the grain size-standard deviation method,and reconstruct the history of lake water level change over the past 150 years.The contents of clay(<4μm),fine silt(4-16μm),medium silt(16-32μm),coarse silt(32-64μm)and the sand(>64μm)in the core sediment of the Bosten Lake were 18%,40.2%,23.3%,13.4%and 5.1%respectively,and the vertical variations of different fractions were obvious.The average grain size of component C2(with particle size of 7.59-22.91μm)was consistent with the median particle size(r=0.7,P<0.01),and the component C2 was very sensitive to the change of sedimentary environment in the Bosten Lake Basin,which could be used to reconstruct the water level of the lake over the past 150 years.Water level of the Bosten Lake was low from the 1910s to the 1930s,which revealed that a large-scale regional drought occurred during this period.Under the joint effect of climate change and human activities,water level of the Bosten Lake was significantly fallen in the midand late-1980s.The change of sensitive components C2 was consistent with the change of lake water level,and the water level fluctuation history of the Bosten Lake could be reconstructed from the sensitive components in lake sediments.