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Fig. 7.14. The specific mean exergy as a function of the total amount of matter (a), and the rate of nutrient uptake by phytoplankton (b).

delineated. Finally, we can say that the dynamic reaction of the considered ecosystem is weaker in relation to the thermal pollution than to the enrichment.

Note, finally, that very similar results were obtained by J0rgensen (1995a) when he studied numerically two models of eutrophications with two and three trophic levels, respectively. These models also have complex dynamic behaviours (cycles and pre-stochasticity regime), and the behaviour of exergy, which is defined analogously, is very similar to that considered above. The only difference is that the maximum rate of zooplankton growth, ^max, is considered as a bifurcation parameter.

7.9. Embodied energy (emergy)

In Section 7.8 we demonstrated that the weighing of biomasses in relation to exergy has allowed us to obtain interesting results. Generally speaking, the idea lies on the surface: the problem is how to select reasonable and ecologically meaningful weighing coefficients. One concept of this type was introduced by Odum (1983a,b) and attempts to account for the energy required in the formation of organisms in different trophic levels. The idea is to correct energy flows for their quality. Energies of different types are converted into equivalents of the same type by multiplying by the energy transformation ratio. For example, fish, zooplankton and phytoplankton can be compared by multiplying

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