¹³⁷Cs Distribution And Modern Sedimentary Environment Of Lakes In Northeast China

In recent years,with the further study of global change and increasingly outstanding of modern environmental problems such as global warming and shortage of fresh water resources,people begin to pay more attention to the changes of various short time scales closely related to human life.Extracting valuable information from past environmental changes is the basis of evaluating current environmental quality and predicting future environmental changes.Lake sediments contain rich environmental change information with good continuity,high temporal resolution and wide geographical coverage.They record the information of human activities and the evolution of lake ecological environment,and are important habitats for river basin erosion and the transport of environmental pollutants.In this paper,the sediment cores of three lakes（Lake Xingkai,Erlongwan Maar Lake and Lake Wolong）,which located in Northeast China,were taken as the research objects.These three lakes are affected by human activities in different degrees.Based on ¹³⁷Cs dating and particle-size analysis in the sediment cores of three lakes,we calculated the modern sedimentation rates and analysized the evolution of sedimentary environment.It is expected to provide theoretical basis and scientific reference for further research on endogenous pollution load of lakes,estimation of total sediment flux of lakes,and research on the relationship between lake sediments and human activities and environmental climate change.The main conclusions of this study are as follows:（1）Influenced by human activities,watershed landform and sediment moisture content,the sediment flux of lakes with high sedimentation rate is not necessarily high.The average sedimentation rate of the three lakes since 1963 are as follows:Lake Wolong（0.139 cm/a）>Erlongwan Maar Lake（0.116 cm/a）>Lake Xingkai（0.086cm/a）.The sedimentary fluxes of the three lakes are as follows:Lake Wolong（0.089g/（cm²·a））>Xingkai Lake（0.075 g/（cm²·a））>Erlongwan Maar Lake（0.028g/（cm2×a））（2）The deposition inventory of ¹³⁷Cs in Lake Xingkai is affected by basin input,hydrodynamic conditions and sediment particle size.The deposition inventory and average activity of ¹³⁷Cs in the estuary region of Bailing River on the west of Lake Xingkai in China is higher than that in the middle area.The difference of ¹³⁷Cs deposition inventory in Erlongwan Maar Lake mainly related to the offshore distance,which is low in the lake center and high in the offshore.The difference of ¹³⁷Cs deposition inventory in Lake Wolong related to the river input,and the area near the estuary has a high ¹³⁷Cs deposition inventory.The differences of ¹³⁷Cs deposition inventory among the three lake sediments are affected by local wind and wave conditions,organic matter content and precipitation.（3）Due to the influence of provenance,watershed landform and human activities,the grain size of sediments in the three lakes varies greatly.The grain size of sediments in Lake Xingkai is relatively small,and silt is the absolute dominant grain size composition.The silt and clay contents of Lake Xingkai are the highest among three lakes.The grain size of sediments in Erlongwan Maar Lake and Lake Wolong is coarser and the sand content is higher.（4）The accumulation probability curves of sediment cores from Lake Xingkai,Erlongwan Maar Lake and Lake Wolong are consistent with the C-M diagram results.The changes of sedimentary environment of the three lakes closely related to human activities around the lakes.In the past 50 years,the sedimentary environment of Lake Xingkai in history was mostly in still water.The construction of water conservancy projects such as flood sluice had an important influence on the hydrodynamic conditions of the sedimentary environment of Xingkai Lake.The sedimentary environment in Erlongwan Maar Lake is relatively stable in recent 100 years.The vertical changes of the endmembers showed that the establishment of Jilin Longwan National Nature Reserve plays an important role in soil and water conservation.The modern sedimentary environment of Lake Wolong is unstable and hydrodynamic is complex and changeable.