Time-dependent ecosystem model

Figure 33-3 Schematic diagram of the components and biological interactions included in the Hofmann and Ambler (1988) time-dependent ecosystem model. Reproduced with permission from Hofman and Ambler (1988).

The type of model to be used in a given situation depends on the nature of the release and on the properties of the ecosystem. When releases of metals or radionuclides are continuous and steady-state conditions are present, an equilibrium model such as a concentration factor model can be used. In this case,the important parameter needed for the model is the concentration factor, the ratio of the concentration in the animal to that in the water. The concentration in the animal is determined then by multiplying the concentration in the water by the concentration factor. In the case of accidental episodic releases, a dynamic situation exists in which organisms accumulate the material for a relatively short period and then lose it with a characteristic time constant. In this case,the important parameters needed for the model are biological turnover rate constants and concentration factors. 

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