A mathematical model of a shallow and eutrophic lake (the Keszthely Basin,Lake Balaton) and simulation of restorative manipulations

Concern about the overall management of lakes has been growing, and a lake ecological model provides the guidelines necessary for such management. In this study, an ecological model describing the ecosystem of the Keszthely B asin, Lake Balaton, Hungary, one of the typical shallow and eutrophic lakes , was proposed. This model includes three types of zooplankton and two type s of fish as well as two types of algae and nutrients. Parameters concernin g the algae and fish were estimated based on observations in the basin betw een 1991 and 1995. The other parameters and the structure of the model were determined by our previous study. The parameters of the model were calibra ted with the Monte Carlo technique, and its predictability was confirmed. T he effects on the basin's ecosystem of three restorative manipulations, nam ely a biomanipulation, reduction of loading phosphorus, and dredging the se diment, were assessed by simulation studies using the proposed model. The s imulation results indicated that a biomanipulation that removed 90% of the bream should suppress the growth of algae temporarily through bottom-up reg ulation; however, this effect seemed to not be perpetuated in this basin. T he reduction of loading phosphorus seemed to be the most effective means to suppress algal growth, while dredging of sediment seemed to be the most de sirable restoration method from the standpoint of the overall management of the lake, because it was expected to accelerate the growth of fish populat ion as well as to suppress algal growth. Furthermore, the algal growth supp resion mechanism of the dredging was disccused on the basis of the model ca lculations. (C) 2001 Elsevier Science Ltd. Ail rights reserved.