518 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



50 



I r 



Tree wood 



Ground vegetation 



Tree leaves 



20 



40 



60 80 



TIME, yr 



100 



120 



140 



Fig. 2 Simulated uptake of plutonium from contaminated soil (65 pCi/g) by major 

 biotic components of a deciduous forest. 



0.2 and that the normally distributed model parameters are permitted random excursions 

 about their mean values, what is the variation in predicted amounts of plutonium in the 

 forest at steady state?" 



Coefficients of variation in predicted values for plutonium in the biotic components 

 of the basic and expanded forest model ranged from 0.28 to 0.46 when CV values were 

 set at 0.2 for all transfer coefficients. Considering the basic model (i.e., vegetation only), 

 the predicted amount of plutonium Jn the forest exhibited considerable variation (e.g., 

 the range for Utter was 1300 to 8900 pCi/m^). Similar variation was observed in the 

 expanded model (Table 3). Consequently, even if parameters for plutonium transport in 

 the forest could be measured with CV values approaching 0.2, which is unUkely, the 

 variation in predicted plutonium would be greater than the variation in model transfer 

 coefficients. 



