Analysis of the transferability of a biogeochemical lake model to lakes of different trophic state

The transferability of a biogeochemical lake model developed for Lake Zürich was analyzed by confronting it with data from two other lakes. An iterative procedure of: (1) initial simulation, (2) lake-specific calibration, (3) joint calibration for all lakes and (4) sensitivity and identifiability analysis of model parameters was applied with the goal of finding a model with a minimum number of lake-specific parameter values. The application of this procedure led to a revised model structure with recalibrated values of some model parameters. The agreement of the model results with data from all lakes is good. The revised model needs only three parameters with lake-specific values. As the trophic states of the three lakes are significantly different, this demonstrates a remarkably high generality of the model. The main reasons for needing different values of these parameters were identified. They are the coarse spatial resolution of the sediment, the simplified description of mineralization processes in the sediment and the lack of a description of grazing of zooplankton by insect larvae and fish. Conclusions were drawn regarding which model extensions would make the model even more general.