A sedimentation study of st. ana lake (Romania) applying the 210pb and 137Cs dating methods

Abstract

The biggest problem with most lakes that have no contact with other water sources and are being charged by precipitation is the massive eutrophication. The aim of this work was to determine the sedimentation rate in order to evaluate the progress of eutrophication for St. Ana Lake (Ciomad Mountain near the Baile Tusnad in Harghita County (Romania)). The concentration of 210PB was de-termined by means of high resolution gamma spectrometry as well as derived from 210Po activity which was measured through alpha spectrometry; values obtained are in good agreement. For the ex-cess 210PB activity values between 4.0±0.5 Bq/kg and 218±20 Bq/kg have been found. As an alterna-tive method, the 137Cs dating method was applied as well. Calculated mass sedimentation rates are in the range of 0.06±0.01 to 0.32±0.05 g/cm2year with a mean of value of 0.15±0.02 g/cm2year. Linear sedimentation rates yielded much higher sedimentation values (between 0.5±0.1 and 7.9±0.7 cm/year with a mean of 2.4±0.6 cm/year), due to the predominant organic matter composition and the long suspension time of the sediment. This is an indication for the process of eutrophication which will probably lead to the transformation of the lake into a peat bog. © 2011 Silesian University of Technology.