During the last few decades, the so-called "maximum dissipation principle" has raised a wide debate as a paradigm governing the development of ecological systems. In the present contribution, after having discussed the meaning of the term energy degradation within the framework provided by the entropy and the exergy balance, it is suggested to distinguish three different facets of the phenomenon of the energy degradation, respectively dealing with the overall, system and environmental degradation. In relation with ecological indication, the above classification shows that different types of indicators of energy degradation can be defined, thus emphasising that a clear reference to the specific facet considered should be made in order to avoid ambiguous statements. The behaviour of several thermodynamic indicators, which include previously derived indices and a new set of entropy-based indicators, is examined along the seasonal progression in a lake ecosystem, and the effectiveness of the considered indicators in characterising the development state is evaluated by comparing their responses with the main successional traits of the phytoplankton community. The results show that, although overall degradation and related indices may deserve consideration as indicators of the extent of the degradative (biotic and abiotic) processes acting within an ecosystem, their significance as indicators of development state appears to be limited. On the other hand, indicators related to environmental degradation appear to be more promising as indicators of the development state, provided that some methodological issues dealing with the effect of the abiotic noise are properly addressed. The net radiative entropy exchange shows a significant correlation with phytoplankton successional traits, thus suggesting that the entropy changes in the radiative portion of the entropy budget are the most informative in relation to the development state of aquatic communities. The methodology adopted also lends itself to be used for evaluating the energy quality associated with an energy flow, which is here measured by the energy-to-entropy ratio.
Energy degradation and ecosystem development: theoretical framing, indicators definition and application to a test case study
LUDOVISI, Alessandro
2012
Abstract
During the last few decades, the so-called "maximum dissipation principle" has raised a wide debate as a paradigm governing the development of ecological systems. In the present contribution, after having discussed the meaning of the term energy degradation within the framework provided by the entropy and the exergy balance, it is suggested to distinguish three different facets of the phenomenon of the energy degradation, respectively dealing with the overall, system and environmental degradation. In relation with ecological indication, the above classification shows that different types of indicators of energy degradation can be defined, thus emphasising that a clear reference to the specific facet considered should be made in order to avoid ambiguous statements. The behaviour of several thermodynamic indicators, which include previously derived indices and a new set of entropy-based indicators, is examined along the seasonal progression in a lake ecosystem, and the effectiveness of the considered indicators in characterising the development state is evaluated by comparing their responses with the main successional traits of the phytoplankton community. The results show that, although overall degradation and related indices may deserve consideration as indicators of the extent of the degradative (biotic and abiotic) processes acting within an ecosystem, their significance as indicators of development state appears to be limited. On the other hand, indicators related to environmental degradation appear to be more promising as indicators of the development state, provided that some methodological issues dealing with the effect of the abiotic noise are properly addressed. The net radiative entropy exchange shows a significant correlation with phytoplankton successional traits, thus suggesting that the entropy changes in the radiative portion of the entropy budget are the most informative in relation to the development state of aquatic communities. The methodology adopted also lends itself to be used for evaluating the energy quality associated with an energy flow, which is here measured by the energy-to-entropy ratio.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
