Cesium-137 of Chernobyl origin in lake–river systems of Eastern Fennoscandia: 30 years after the accident

Abstract

Contamination of waters of lake–river systems after many-year migration of ¹³⁷Cs in water bodies was studied. In lakes with the ¹³⁷Cs fallout density lower than 8 kBq m^–2, the radionuclide concentrations in water after 24–29 years did not exceed 2–3 Bq m^–3, and at a fallout level of 37 kBq m^–2 it was in the range 11–34 Bq m^–3. The natural half-clearance time Т of lake waters from ¹³⁷Cs was 6–7 years at the exposure of up to 20 years. The ¹³⁷Cs migration in the lake–river systems that occurred during ~30 years did not lead to structural changes in the water contamination: The initially low ¹³⁷Cs level in lake waters did not become high, and vice versa. Among rivers feeding Lake Ladoga, the ¹³⁷Cs level in the Vuoksa River is ~3 times higher than in waters of the Volkhov and Svir rivers. During the period 1988–2015, 21.3 TBq of ¹³⁷Cs was supplied to Lake Ladoga with Vuoksa waters. The Vuoksa source from the Saima lake system with increased contamination with ¹³⁷Cs of Chernobyl origin leads to long-term supply of this radionuclide to Lake Ladoga.