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 phytoplankton groups, chlorophytes and diatoms, represented the maximum utilisation of system resources indicated by maximum build-up of exergy. Furthermore, it was investigated if the system with the two phytoplankton groups exhibited larger build-up of exergy than if only one of the groups had been present. The study showed that the two phytoplankton groups did perform a larger build-up of exergy than if only one of the groups had been present, and that the calibrated growth parameters for the chlorophytes represented the highest build-up of exergy while the results for the diatoms were less univocal. Based on these results, exergy is proposed as a possible object function for validation and parameter estimation in lake models.