Model simulations of the fate of super(14)C added to a Canadian Shield lake

• Published in: Journal of environmental radioactivity 1999-01, Vol.42 (2-3), p.209-223
• Main Authors: Bird, G A, Bergstroem, U, Nordlinder, S, Neal, S L, Smith, G M
• Format: Article
• Language: English
• ISSN: 0265-931X
• DOI: 10.1016/S0265-931X(98)00055-1

Carbon-14 was added to the epilimnion of a small Canadian Shield lake to investigate primary production and carbon dynamics. The nature of the spike and subsequent monitoring allowed the investigation of both short-term and longer-term processes relevant to evaluating impacts of accidental and routine releases and of solid waste disposal. Data from this experiment were used in the BIOMOVS II program as a validation test for modelling the fate of the super(14)C added to the lake. Four models were used: (1) a simple probabilistic mass balance model of a lake; (2) a relatively complex deterministic model; (3) a complex deterministic model; and (4) a more complex probabilistic model. Endpoints were super(14)C concentrations in water, sediment and lake whitefish over a thirteen year period. Each model produced reasonable predictions when compared to the range of the observed data and when uncertainty in model predictions is taken into consideration. The simple lake model did not account for internal recycling of super(14)C and, in this respect, its predictions were not as realistic as those of the more complex models for concentrations in water. However, the simple model predictions for the super(14)C inventory remaining in lake sediment were closest to the observed values. Overall, the more complex probabilistic model was the most accurate in simulating super(14)C concentrations in water and in whitefish but it overestimated super(14)C retention in the lake sediments, as did the other complex models. Choice of parameter values for transfer rate to sediment and gaseous evasion are important in influencing model predictions. Although predicted concentrations of super(14)C in fish of dynamic models were more accurate than those using equilibrium bioconcentration factors typically used in assessments, large variability in observed super(14)C concentrations in whitefish emphasizes the need for a better understanding of the important processes that influence these contaminant concentrations.