EXAMINATION AND OPTIMIZATION OF DIFFERENT EXERGY FORMS IN MACROPHYTE SOCIETIES

The replacement of rooted macrophytes, phanerogames, by non-adhered, d rifting macroalgae have been reported from estuaries and lagoons at va rious geographic positions all over the earth. The observed shift in c omposition in the macrophyte society thus seems to be a general proble m. This paper presents the results of an attempt to simulate the struc tural dynamics of the macrophyte societies in the Danish estuary, Rosk ilde Fjord. The modelling efforts concentrates on the shift between Z. marina and U. lactuca, that has been observed during the recent decad es. The study is a part of a larger cooperation founded by the EU invo lving Italy, study area Lagoons of Venice, and Portugal, study area th e estuary at Figueira da Foz, where other equivalent species and evolu tion of the ecosystems are studied. The results show that it is possib le to simulate the competition between the species and allow spatial c oexistence through time in a very simple model based on growth capacit y, light and temperature characteristics alone. Four types of exergy h ave been proposed in literature to act as goal function to ecosystem d evelopment. In the model the traditional exergy, internal exergy, stru ctural or modern exergy, together with the normalized exergy are exami ned and optimization are carried out. The behaviour of the various exe rgy forms differ considerably in time, which should lead to the hypoth esis that they would act quite different as goal functions. Meanwhile the different exergies behave quite alike when used as goal functions- normalized exergy being the only exception. The consequence of these r esults for optimization strategies in the future is discussed. (C) 199 7 Elsevier Science B.V.