Long-term trends and variation in super(137)Cs activity concentrations in brown trout (Salmo trutta) from Oevre Heimdalsvatn, a Norwegian subalpine lake

The Norwegian mountain lake, Oevre Heimdalsvatn, received major fallout from the Chernobyl accident in the spring of 1986. Activity concentrations of super(137)Cs have been monitored annually in the brown trout (Salmo trutta) population of the lake over a 22-year period since 1986. The activity concentrations of super(137)Cs in brown trout have declined over the period, although in recent years there has been little or no reduction in activity concentrations. Throughout the period, there has been considerable individual variation in super(137)Cs activity concentrations. Within a single year, fish weight was the most significant factor affecting activity concentrations of super(137)Cs in individual fish, although sex and age.weight were significant explanatory variables. The "size effect" was not significant during the initial period after fallout and in some recent years. During the first years after fallout, the ecological half-life of super(137)Cs in brown trout was 3-4years, but during the last decade this has increased significantly and has approached the physical half-life of 30years for super(137)Cs, suggesting a dynamic equilibrium between catchments inputs, possible remobilisation from lake sediments and lake outputs of super(137)Cs.