云南抚仙湖近现代环境变化的沉积物粒度记录

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

通过对云南抚仙湖沉积物柱芯样品的放射性核素210Pb和137Cs的测试,确定了过去129年的湖泊连续沉积序列。利用210PbCRS计年模式,计算出每个样品深度所对应的年代,与137Cs时标计年法比较存在一定的偏差,分析了两种计年方法存在差异性的原因。根据抚仙湖的湖区特点,对沉积物的粒度特征进行了分析。抚仙湖柱芯的粘土(<4μm)、细粉砂(4～16μm)和粗粉砂(16～63μm)含量分别占约36%,44%和18%。粒度参数根据矩值法求得,平均粒径(值)为6.48～7.92,分选系数So为1.27～1.42,偏度SKD分布范围在-0.18～0.04之间。将整个柱芯的计年结果与粒度特征相结合,自1878年以来,抚仙湖的环境演化大致可以划分为4个阶段:自然演化阶段,人为扰动阶段,人为改造阶段,后期治理阶段。人类活动在特定的历史时期会对湖泊环境变化产生较大的影响。

^210Pb and^137Cs 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（Ф） 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.