Autor(es):
Marques, J. C. 
; Pardal, M. A. ; Nielsen, S. N. ; Jorgensen, S. E.
Data: 1997
Identificador Persistente: http://hdl.handle.net/10316/13305
Origem: Estudo Geral - Universidade de Coimbra
Assunto(s): Exergy; Biodiversity; Eutrophication
Descrição
Benthic eutrophication often gives origin to qualitative changes in marine and estuarine ecosystems, for example
the shift in primary producers, often followed by changes in species composition and trophic structure at other levels.
Through time such modifications may determine a selected new trophic structure. The development of structural
dynamic models will allow to simulate such changes, using goal functions to guide ecosystem behaviour and
development. The selection of other species and other food web may then be accounted by a continuous optimisation
of model parameters according to an ecological goal function. Exergy has been applied in structural dynamic models
of shallow lakes, and appears to be one of the most promising approaches. Theoretically, exergy is assumed to
become optimised during ecosystems development, and ecosystems are supposed to self organise towards a state of
an optimal configuration of this property. Exergy may then constitute not only a suitable system-oriented character-
istic to express natural tendencies of ecosystems evolution, but also a good ecological indicator of ecosystems health.
Biodiversity is also an important characteristic of ecosystems structure, constituting a powerful and traditional
concept, which was found to be suitable to test the intrinsic ecological significance of exergy. We examined the
properties of exergy (exergy and specific exergy) and biodiversity (species richness and heterogeneity) along an
estuarine gradient of eutrophication, testing the hypothesis that they would follow the same trends in space and time.
This hypothesis was validated in a certain extent, with exergy, specific exergy and species richness decreasing as a
function of increasing eutrophication, but heterogeneity responding differently. Biodiversity measurements and their
interpretation appeared subjective. Exergy and specific exergy may be a suitable alternative, that could be used as goal
functions in ecological models and as holistic ecological indicators of ecosystems integrity. Nevertheless, since exergy
and specific exergy showed to respond differently to ecosystems seasonal dynamics, it is advisable to use both complementary. The method proposed by Jorgensen et al. (1995) to estimate exergy, which takes into account the
biomass of organisms and the thermodynamic information due to genes, appeared to be operational. There is
nevertheless an obvious need for the determination of more accurate (discrete) weighing factors to estimate exergy
from organisms biomass. We propose to explore the assumption that the dimension of active genomes, which are
primarily a function of the required genetic information to build up an organism, are proportional to the relative
contents of DNA in different organisms
