Use of thermodynamic indices as ecological indicators of the development state of lake ecosystems: Specific dissipation

This paper proposes the ratio between the entropy produced and the exergy stored by the biological component of an ecosystem (which may be called the specific entropy production or the specific dissipation of a community) as a tool for understanding the evolution of ecological systems. Specific dissipation, which may be taken as representing a renewed version of Odum's Schrödinger ratio, is here proposed as an indicator of ecosystems maturity as well as an ecological orientor whose minimisation is expected throughout ecosystem development. After having presented an empirical method for estimating the specific dissipation in lake ecosystems, it has been applied to the characterization of the development state of the communities of a set of shallow lakes which lye from oligotrophic to hyper-eutrophic conditions. The adequacy of the proposed indicator has been tested and discussed along two different ecological series: the seasonal progression of phytoplankton and the trophic gradient. The results confirm that the ratio is an appropriate indicator of ecosystem maturity and support the hypothesis that its minimisation is one of the primary “goals” of ecosystem development.