The krathis lake, one century of evolution.

A riverbed swamp in the Krathis River, N. Peloponnese, is studied and analyzed geomorphologicaly. Our analysis is also based on sedimentological, geochemical, palaeontological and radiometric dating data which enabled the investigation of the possible relationship between the studied swamp and the 1913 Tsivlos landslide. Sedimentological analysis showed that the current sedimentation is dominated by fine grain material and occasional coarse-grained beds. Micropalaeontological analysis indicated that the deeper layers of the core are barren, while the upper ones contain fresh water ostracods suggesting hydrodynamically a progressively more stable environment. In accordance, radiocarbon C14 and 137Cs dating showed a progressively decreasing sedimentation rate over the last fifty years. The results of this study show that the Tsivlos landslide is not the only cause for the formation of the modern swamp. Tectonic movements in the area seem to play a decisive role causing uplift and subsidence in the area near an active fault.

A sedimentation study of St. Ana Lake (Romania) applying the 210Pb and 137Cs dating methods

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 Băile Tuşnad in Harghita County (Romania)). The concentration of 210Pb was determined 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 excess 210Pb activity values between 4.0±0.5 Bq/kg and 218±20 Bq/kg have been found. As an alternative 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/cm2 year with a mean of value of 0.15±0.02 g/cm2 year. 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.