137Cs测年的东北兴凯湖现代沉积速率研究

对兴凯湖我国水域沉积物137Cs比活度及通量空间分布进行了研究,利用137Cs测年法建立年代框架,估算了兴凯湖的沉积速率,结合粒度C-M图分析了湖泊现代沉积环境。兴凯湖我国水域西岸白棱河河口区域137Cs剖面形态区别于典型的137Cs全球大气沉降模式,且137Cs沉积通量高、平均137Cs活度高,中部和东部区域137Cs沉积通量低、平均137Cs活度低；137Cs沉积通量的空间分布主要受流域输入、水动力条件以及沉积物粒径的影响。兴凯湖沉积环境多表现为静水沉积,受特殊的风浪条件和泄洪闸等人类活动的影响,1963—2019年平均沉积速率空间分布上呈现西部高,中、东部低的特点,XKH-1、XKH-2和XKH-3柱样1963—2019年的平均沉积速率分别为0.143 cm/a、0.080 cm/a和0.036 cm/a。

Sedimentation Rate in Lake Xingkai,Northeastern China,Based on 137Cs Dating

Lacustrine sedimentary records are very significant for gaining an understanding of basin erosion, since they reveal regional climatic and environmental changes and the influence of human activities. The 137Cs dating method, which has been widely used since the early 1970s, has greatly promoted high-resolution studies of climate and environmental changes recorded in lake sediments. Based on 137Cs dating and particle-size analysis for Lake Xingkai sediment cores, the distribution of 137Cs was investigated to calculate modern sedimentation rates and the reasons for the different rates. An inventory of 137Cs deposition was compiled for the sediment cores, and the modern sedimentary environment of Lake Xingkai was analyzed using C–M diagrams. The main findings of the study were: （1） The estuary region of the Bailing River west of Xingkai Lake is under the dual influence of terrestrial input and sediment disturbance, causing uniform and higher 137Cs concentrations in the upper part of the vertical profile. This differs from the typical 137Cs global atmospheric precipitation model. In Lake Xingkai the global 137Cs fallout peak （due to atmospheric nuclear weapons testing in other parts of the world in 1963） is smaller than in most lakes in northeastern China, mainly influenced by the grain size of the sediment. （2） The deposition inventory and average activity of 137Cs in the Bailing River estuary region in western Lake Xingkai is higher than in the central area. Deposition in Lake Xingkai is affected by basin input, hydrodynamic conditions and sediment particle size. （3） The average sedimentation rates indicated in cores XKH-1, XKH-2 and XKH-3 are 0.143 cm/a, 0.080 cm/a and 0.036 cm/a, respectively, from 1963 to 2019. Due to the influence of the particular wind/wave conditions and human activities （e.g., release sluices）, the regional sedimentation rate in central and eastern Lake Xingkai is lower than in the west. （4） The particle sizes in all cores from Lake Xingkai indicated by the C-M charts are located either to the left of the III region or beneath it, evidence that mostly still water was the historical sedimentary environment of Lake Xingkai. The cumulative probability curve has two segments due to the two modes of saltation and suspension. The C value of core XKH-1 is relatively dispersed because of the influence of human activities in the upper reaches of the Bailing River. The strong hydrodynamic environment near the second release sluice causes a larger C value for core XKH-3 than for cores XKH-1 and XKH-2, on the whole. （5） The vertical variation of grain size distribution and parameters in core XKH-1 reflects vegetation destruction and soil erosion in the Xingkai Lake Basin since 1963. The mean particle size and sorting coefficient of XKH-2 fluctuate frequently with depth, indicating that the hydrodynamic conditions in the lake bottom varied at different times. The grain size of XKH-3 sediment is coarser at 0~5 cm depths, evidence that the shore of Lake Xingkai has silted up continuously in recent decades. This study provides a theoretical basis and scientific reference for further research. The annual gross accumulation of sediment can be calculated and the internal load of pollutants in lake sediments, lake evolution and environmental changes in the lake basin can be studied further.