Grain Size Characteristics And Environmental Indicators Of Lake Sediments In Northern China

Based on the four northern lakes Chagan Lake,lake called Aaron,Wu Liang Suhai,characters as the research object,we obtained the four lake sediment core samples of outdoor.Then we back to the laboratory to determine particle size index and grain size analysis of the features and grain size frequency curves with ~21010 Pb and ~13737 Cs for determination of the lake sediments and the sediment particle size index determination and analysis of characteristics of particle size.The analysis of sediment particle size composition and specific characteristics can predict the climatic conditions and environmental evolution process of the lake over the years.The grain size and distribution of sediments can reflect the deposition process of sediments.Therefore,the analysis of grain size composition and characteristics of the sediments in the four lakes is of great significance to further explore the source and sedimentary environment of pow sediments.(1)The sediments of Chagan Lake,Hulun Lake,Wuliangsuhai Lake and Bosten Lake mainly include clay particles(<4 m),silty sand(4-64 m)and sand(>64 m).The composition of sediment grain size distribution in the vertical profile of different lakes is similar.The proportion of clayey particle size and silty particle size in the environment is obviously greater than that of sandy particle size.Through the transverse comparison of particle sizes of the four lakes,it was found that the lake with the largest mean particle size of the core was Bosten Lake with an average particle size of 43.8?m.The smallest mean particle size was 28.3?m in Chagan Lake.(2)The mechanical composition of lake sediment particle size and its frequency curve can extract environment-sensitive components and analyze the change information of environment-sensitive components,which can well invert the evolution history of the lake.The climatic conditions of the four northern lakes are different and the grain size characteristics of sediments formed by different climatic conditions are different.Chagan Lake is in a semi-arid and semi-humid climate;The Hulun Lake and the Wuliangsu sea are in a semi-arid climate;Bosten Lake is a dry climate;the climatic factors have obvious correlation with the mean particle size of sediment.The comparative analysis of their historical environmental changes.(3)The mechanical composition of sediment particle size varies greatly,but the vertical distribution of sediment particle size generally shows the trend that the grain size changes from thinning to thinning.The grain size parameters reveal the climate change and wind-sand phenomenon of the river basin.According to historical records,from 1940 to 1980,the precipitation in the basin declined on the whole.Sediment core size characteristics also reveal the process of lake development.From 1940 to 1960,the dominant component of lake sediments gradually changed to the dominant component of lake facies.From 1960 to the end of 1980,the composition of lacustrine facies was still more dominant than that of wind facies.Since 1980,lacustrine components have been gradually strengthened,resulting in the formation of typical lacustrine deposits.The analysis of four sensitive components of sedimentary cores shows that precipitation,human activities and wind conditions have a certain influence on lake deposition.Climate and human activities have a great impact,among which human activities mainly affect lake sediments through farming,grazing and the lake needs a long time to recover its stable state.