青海湖布哈河口沉积物粒度特征及其环境意义

以青海湖西北部布哈河口湖泊沉积物为研究对象,用激光粒度仪对其进行粒度分析,并用137Cs定年法测定了该区沉积速率。结果表明:沉积物的粒度特征随着水动力条件的波动呈有规律的变化。QH06和QH08的深度堆积速率分别是0.137 cm·a~(-1)、0.078 cm·a~(-1),质量堆积速率分别是0.105 g·cm~(-2)·a~(-1)、0.030 g·cm~(-2)·a~(-1)。靠近湖岸,137Cs通量较大,沉积速率较大,分选性也较好。结合粒度特征分析得出,青海湖西北部布哈河口气候变化分为3个阶段:1853—1886年,该区气候向干旱方向发展;1886—1940年向湿润方向发展;1940—2013年向干旱方向发展。其中,1978年和1989年粒度特征的明显变化和布哈河水文资料相对应,说明了粒度特征指示该区气候干湿变化的可靠性。布哈河口环境受人类活动的影响较大。

Characteristics of Grain Size and Their Environmental Significance of Sediments at the Buha Estuary of the Qinghai Lake

Lake sediments were sampled from the Buha estuary of the Qinghai Lake.These samples were analyzed using a Malvern2000 Analyzer,and the parameters of grain size were obtained.Sedimentation rates were determined with radioisotope 137 Cs.The results suggested that the parameters of grain size varied regularly with the fluctuation of hydrodynamic conditions.The sedimentary rates of deep sediments were 0.137 and 0.078 cm · a-1,and the mass accumulation rates were 0.105 and 0.030 g · cm-2 · a-1 in cores QH06 and QH08,respectively.Near the lakeshore,137Cs flux was large,the sedimentary rate was high,and the sorting was good.Based on the analysis of the characteristics of grain size,the Buha estuary of the Qinghai Lake experienced the following three environmental evolution stages:it was dry during the period from 1853 to 1886,humid from 1886 to 1940,and dry again from 1940 to 2013,respectively.Significant changes of grain size in 1978 and 1989 corresponded with the hydrological data,they also revealed that grain size could be regarded as a reliable indicator of climate change.The environment change at the estuary may be related to human activities.