Short- and long-term patterns of ¹³7Cs in fish and other aquatic organisms of small forest lakes in southern Finland since the Chernobyl accident.

ABSTRACT

We summarize the patterns of ¹³7Cs activity concentrations and transfer into fish and other biota in four small forest lakes in southern Finland during a twenty-year period following the Chernobyl accident in April 1986. The results from summer 1986 showed fastest accumulation of ¹³7Cs into planktivorous fishes, i.e. along the shortest food chains. Since 1987, the highest annual mean values of ¹³7Cs have been recorded in fish occupying the highest trophic levels, for perch (Perca fluviatilis) 13,600 Bq/kg (ww) and for pike (Esox lucius) 20,700 Bq/kg (ww). At the same time, activity concentrations of ¹³7Cs in crustacean zooplankton and Asellus aquaticus have ranged between 1000 and 19,500 Bq/kg (dw). In 2006, 5-28% of the 1987 ¹³7Cs activity concentration levels were still present in perch and pike. Since 1989 their ¹³7Cs activity concentrations in oligohumic seepage lakes have remained significantly higher than in polyhumic drainage lakes due to the increased transfer of ¹³7Cs into fish in the seepage lakes with lower electrolyte concentrations, longer water retention times and lower sedimentation rate.