Abstract: In this paper,the spatial distribution characteristics of grain size and its affecting factors were discussed by using the mathematical and statistical methods and analyzing the characteristics of the composition,parameters and frequency curves of grain size of surface sediment in the Bosten Lake region,Xinjiang. The results revealed that the fine silt composition was dominant in surface sediment in the lake region,and its content varied in a range of 19.2%-62.1% with an average of 40.1%. The surface sediment was holistically in a concentric-ring distribution centered on the northwest area,and extended from the northwest area to the southwest and east areas under the effects of the Qingshui River,Huangshui Stream and clockwise or counterclockwise circulating flow. With the increase of distance from the circle center,the content of fine particles increased but that of coarse particles decreased,gradually,and much clay deposited on the south bank. The results of cluster analysis showed that the sediment samples could be divided into two classes,indicating the different deposition environment:① In the broad lake region,the grain size frequency curves of surface sediment were mostly multimodel,but their shape was similar,the high peak was dominated by the particles with moderate diameter of 6-20 μm,and the low peaks were dominated by the particles of 500 μm and about 1 μm respectively,and they were in a negative skewness,showing a hydrostatic and low-energy depositional environment in the suspended transportation of the particle; ② In the estuary area,the grain size frequency curves of surface sediment were multimodel,the high peak was dominated by the particles with diameter of 70-100 μm,and even there was a secondary peak dominated by the particles with diameter of 2-10 μm,suggesting a high-energy deposition environment under the mixing effect of lake wave and river water. Through analyzing the spatial distribution of grain size of surface sediment and its affecting factors,the modern sediment environment and the hydropower conditions in the different lake areas were revealed,and the results could be referred for researching the ecological environment in the lake region.

Key words: surface sediment, grain size composition, spatial distribution, Bosten Lake