137Cs AND 210Pb CHRONOLOGY FOR MODERN LAKE SEDIMENT: A CASE STUDY OF CHAOHU LAKE AND TAIBAI LAKE

The distributions of 210Pb and 137Cs in the core sediments of Chaohu Lake and Taibai Lake were determined.It took on typical peaks in 1963 for 137Cs activity in the profile,and the concentration of 210Pbex decreased exponentially along the mass depth,indicating a stable sedimentary environment.The calculated chronology according to the CIC and CRS model was discrepant with the 137Cs age (1963 AD),denoting the influence of land-derived 210Pb from the atmospheric deposition and its discharge from the lake.Therefore,the composite model should be optimal,i.e.different formulae were used for the chronology calculation according to the concentration of 210Pbex for the upper and lower sections of the sediment cores divided by the 137Cs peak depth.The sedimentation rate calculated by the composite model showed that it varied largely in Chaohu Lake and Taibai Lake in the past one hundred years.Regulation capability of the reservoir built in the upper catchment of the inflow rivers of Chaohu Lake and Taibai Lake from late 1950s to early 1960s facilitated silt deposition and reduced the sedimentation rate of the lakes.The increased sedimentation rates for Chaohu Lake and Taibai Lake since late 1970s and mid 1980s should be mainly influenced by the strengthening human activities in the catchment,mainly agriculture development,and the sedimentation rate peaks were correlated with the influence of flood in 1991 and 1998.