A Model of Plutonium Dynamics 

 in a Deciduous Forest Ecosystem 



CHARLES T. GARTEN, JR., ROBERT H. GARDNER, and ROGER C. DAHLMAN* 



A linear compartment model with donor-controlled flows between compartments was 

 designed to describe and simulate the behavior of plutonium (^^^'^^^Pu) in a 

 contaminated forest ecosystem at Oak Ridge, Tenn. At steady states predicted by the 

 model, less than 0.25% of the plutonium in the ecosystem resides in biota. Soil is the 

 major repository of plutonium in the forest, and exclianges of plutonium between soil 

 and litter or soil and tree roots were dominant transfers affecting the ecosystem 

 distribution of plutonium. Variation in predicted steady-state amounts of plutonium in 

 the forest, given variability in the model parameters, indicates that our ability to develop 

 models of plutonium transport in ecosystems should improve with greater precision in 

 data from natural environments and a better understanding of sources of variation in 

 plutonium data. 



Systems analysis techniques have been useful in simulating the fate and dynamics of a 

 variety of substances in ecosystems, including radionuclides (Olson, 1965; Wheeler, 

 Smith, and Gallegos, 1977), pesticides (Webb, Schroeder, and Norris, 1975), and stable 

 elements (Shugart et al., 1976). Both descriptive and predictive purposes are considered 

 in the building of these models. Past applications of ecosystem modeling of radionuclide 

 behavior in the environment have included (1) projection of the time-dependent 

 distribution of material within the system and (2) manipulation of the model system to 

 determine the sensitivity of various components to variation in transfer coefficients. The 

 latter exercise allows identification of critical pathways affecting radionuclide distribu- 

 tion in the system. 



This chapter describes an ecosystem model of plutonium (^^^'^^°Pu) behavior in a 

 Tennessee forest. In ecosystem models the complexities of community structure and 

 ecological processes are often simplified to an abstract compartmental system linked by 

 linear differential equations (Hudetz, 1973). The model described was formulated on the 

 basis of data from International Biological Program (IBP) studies on deciduous forests 

 and investigations at a plutonium-contaminated forest in eastern Tennessee. A primary 

 objective of the model was to holistically describe plutonium behavior in the forest. To 

 this end Monte Carlo simulations of the transfer of plutonium from soil to biota and a 

 sensitivity analysis of the model forest were performed. 



*Present address: U. S. Department of Energy, Washington, D. C. 



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