吉林省西部月亮湖沉积物的^(210)Pb和^(137)Cs测年及沉积速率

^(210)Pb and ^(137)Cs Dating of the Sediment Core and Its Recent Accumulation Rates in Yueliang Lake in West Jilin Province

在吉林省西部月亮湖沉积柱中137 Cs和210Pb比活度测定的基础上,进行了沉积柱137 Cs和210Pb测年和现代沉积速率研究。月亮湖沉积柱在18cm和32cm处存在2个明显的137 Cs峰值,所对应的时标分别为1986年和1963年,据此时标计算的1963 2006年月亮湖的平均沉积速率为0.74cm/a,19862006年平均沉积速率为0.90cm/a。对比了CIC、CRS和CFCS模式的210Pb计年结果,其中:CIC模式的计年结果明显偏离137 Cs时标;64cm以浅沉积物的CRS、CFCS模式计年结果接近,并与137 Cs时标基本一致;但当沉积物的深度大于64cm时,CRS、CFCS模式计年结果具一定差别,鉴于此深度以下CFCS模式计年的指数方程的相关系数较低,其计年结果的代表性较差,因此,此深度以下采用CRS模式计年。根据CRS模式计年结果计算的月亮湖沉积速率为:1835 1898年平均为0.33cm/a,1898 1920年平均为1.09cm/a,1920 1961年平均为2.21cm/a,1961 2006年平均为0.94cm/a。沉积速率的年际变化反映了月亮湖及其流域内自然环境变化和人类活动的影响程度。

210Pb and 137 Cs dating of sediment core and its recent accumulation rates of the Yueliang Lake in the western Jilin Province are investigated on the base of determination of their specific activities. Two distinct 137Cs peaks at position of 18 cm and 32 cm were recognized along the sediment core from the lake, both peaks are corresponding to the years of 1986 and 1963, respectively. The calculated mean sedimentation rates of Yueliang Lake during 1963 -2006 and 1986 -2006 are 0.74 cm/a and 0.90 cm/a. The dating results using CIC,CRS and CFCS models of 210Pb are compared, among them the results with CIC model are distinct with those of 137 Cs time marks the dating results with CRS, CFCS models for the sediment with depths of beneath 64 cm are similar, both are in agreement with those of 137 Cs time marks; while the dating results with CFCS model shows somewhat different to those with CRS model for the sediment with depths of more than 64 cm. The CRS model is adopted for dating the sediment below the depth of 64 cm because of the poor representatives by using CFCS model to date sediment under this depth due to low correlation coefficient of formula fitted by an exponential function for dating. The average sedimentation rates of Yueliang Lake calculated by dated result of CRS model in years of 1835 - 1898, 1898 = 1920, 1920 - 1961 and 1961 - 2006 are 0.33 cm/a, 1.09 cm/a, 2.21 cm/a and 0. 94 cm/a, respectively. The yearly variations of sedimentation rates reflect the natural environmental changes and the influence of human activities around Yueliang Lake and its watershed.