Modelling the accumulation of ¹³⁷Cs by age-structured fish population

Scientific & Production Association "Typhoon", 82 Lenin Ave., Kaluga Region, Obninsk 249038, Russia

Abstract

The dynamic model is presented, which enables one to describe difference types of the size effect in the accumulation of ¹³⁷Cs by fish. The fish population is represented by a set of discrete age classes characterized by a specific growth rate, diet and activity of metabolic processes. For validation of the model we used the data of observations on the content of ¹³⁷Cs in fish and other components of the fresh-water ecosystems after Chernobyl accident. The model is applied to the calculation of the dynamics of the ¹³⁷Cs specific activity in the muscles of different age groups of fish in the Chernobyl NPP cooling pond, and other water bodies. It is shown that the decrease in the specific activity of radiocaesium in fish with age in the first few months following the Chernobyl accident was determined by a more intensive feeding and metabolic activity of young fish. An increase in the specific activity of radiocaesium in fish with age in succeeding months was determined by a slower removal of the radionuclide from the organisms of older generations of fish. The age dependence in the accumulation of radiocaesium shows itself more markedly in predatory fish, which is explained by the effect of trophic levels, as well as by the fact that at a certain time the fish change from a non-predatory to predatory type of feeding. The size effect changes sign from negative to positive smoothly, so the distribution of the ¹³⁷Cs activity in fish with ages has a maximum during the second year after the accident.