Recent Environmental Change Inferred from Grain-Size Records in Fuxian Lake,Yunnan Province

210Pb and137Cs were used to analyze for the Fuxian Lake sediment core.210Pb(CRS) dating result showed a little deviation from 137Cs dating,and two reasons were investigated.According to the feature of Fuxian Lake,we analyzed the grain size characteristics and obtained the content of the core,which contained 36% of clay,44% of fine sand and 18% of coarse sand.By calculation,the different grain-size parameters were also obtained,the mean grain diameter() was between 6.48 and 7.92,the standard deviation(So) was between 1.27 and 1.42,and the skewness(SKD) was between-0.18 and 0.04.Based on radionuclide dating and grain-size distribution characteristics in the sediment core,we concluded a sedimentary environment in Fuxian Lake had been greatly changed since 1878,which can be marked off four stages: natural evolution stage,man-made disturbances stage,man-made transformation stage,and recent treatment stage.Human activities of historical period had played a very important role in changing the environment of the Lake.