USE OF A LAKE MODEL TO EXAMINE EXERGY RESPONSE TO CHANGES IN PHYTOPLANKTON GROWTH-PARAMETERS AND SPECIES COMPOSITION

In a model for a natural lake ecosystem, exergy was used as a measure of build-up of biological structure. It was examined if the calibrated parameters for maximum growth of the two naturally present phytoplank ton groups, chlorophytes and diatoms, represented the maximum utilisat ion of system resources indicated by maximum build-up of exergy. Furth ermore, it was investigated if the system with the two phytoplankton g roups exhibited larger build-up of exergy than if only one of the grou ps had been present. The study showed that the two phytoplankton group s did perform a larger build-up of exergy than if only one of the grou ps had been present, and that the calibrated growth parameters for the chlorophytes represented the highest build-up of exergy while the res ults for the diatoms were less univocal. Based on these results, exerg y is proposed as a possible object function for validation and paramet er estimation in lake models.