¹³⁷Cs migration and pro le in bottom sediments of deep drainage lakes, north-western Russia

Abstract

Modern contamination of global and «Chernobyl» 137Cs in lake-river systems bottom sediments is estimated. Drainage lakes of North-Western Russia were investigated. Kopanskoe Lake, located south of the Gulf of Finland, is on the trail of the «Chernobyl» 137Cs fallout, whereas Ladoga, Sukhodolskoe, Vuoksa, Imandra lakes are located at its periphery, in Karelia and Kola Peninsula. Following parameters are distinguished: lakes bottom 137Cs pollution density (kBq/m2), distribution of 137Cs in the pro le of bottom sediments, 137Cs di usion coe cients ( D ) in bottom sediments and content of the exchange chemical form of the radionuclide. 137Cs contamination of the lakes was formed due to suspended matter sedimentation with 137Cs, 137Cs sorption and di usion in bottom sediments. With sedimentation ≥3 mm/year, the concentration of 137Cs increased from the top to the bottom of the core (lakes Vuoksa, Ekostrovskaya Imandra), re ecting the gradual process of 137Cs migration into the sediments. The opposite trend of 137Cs concentration was observed in the bottom sediments of lakes Ladoga and Sukhodolskoe with sedimentation ≤0.5 mm/year. Here 137Cs di usion with D = (0.5-6.2) ×10-8 cm2/s caused slow radionuclide transfer in the bottom sediments. The main supply of 137Cs was contained in the top layer 0-5 cm. 14.4-20 % of absorbed 137Cs in lake Sukhodolskoye bottom sediments were was in an exchange chemical form, extracted into solution 1 М NH 4 Aс.