云南属都湖流域人类活动的湖泊沉积响应

通过对属都湖Esdr1孔沉积物粒度、磁化率等指标研究,利用137Cs建立年代标尺,结合文献和降水数据讨论了人类活动对湖泊沉积环境的影响。结果表明:17~14 cm(1958—1970年)沉积物中粗颗粒的砂含量和磁化率值急剧增加,分析应是20世纪50年代末流域大面积砍伐森林,强烈的水土流失所致;14~8 cm(1970—1988年)沉积物粒径变细,磁化率值降低,指示流域植被逐渐恢复,流域侵蚀减弱;8~0 cm(1988年至今)沉积物黏土含量升高、砂含量降低,应是湖泊出口处修建的水坝改变了湖泊水动力条件所致。

HUMAN ACTIVITIES INDICATED BY LACUSTRINE DEPOSITION IN THE REGION OF SHUDU LAKE

A sediment core Esdr1 from Shudu lake was analyzed for grain size and magnetism.Accurate sediment chronology was established by 137Cs.By comparing the grain-size and magnetism proxies to document and precipitation data,we discussed the influence of disafforestation and dam on depositional environment.Both magnetic susceptibility and grain-size proxies increase remarkably at 17~14 cm(1958-1970) depth.Precipitation data reveal a decrease during this period.But county annals record that there was intense disafforestation from 1958 to 1963.Vegetation cover deterioration will lead to serious erosion in drainage area.More sand and silt transport to lake,which causes grain-size and magnetic susceptibility values to increase.Both precipitation and constructing dam affect lake sediment composition.The precipitation increased from 1988 to 2002.A dam was constructed at the lake outlet in 1988,which enlarged lake area.Finer sediments deposited with streamflow disappearance.Although precipitation slightly increased from 1988 to 2002,it is obvious that dam construction has more influence on lake sediment environment.It may be why grain size in Esdr1 core became finer at 8~0 cm depth(1988-2002).