Climate Simulations in Lentic Ecosystems: A Note on Indirect Effects

Simulations of reservoir ecosystems were carried out by means of the coupled hydrodynamical ecological model SALMO which is vertically resolved. It comprises modules for (i) turbulent diffusion, seiches and the hydrological balance, (ii) advection and sedimentation and (iii) the internal biological/chemical reactions (photosynthesis, grazing, nutrient cycling). Much attention was paid to the meteorological forcing which were determined from large-scale climotological data by specially designed transfer functions. For process analyses and validation, long-term data sets as well as high resolution measurements are available for the reservoirs Saidenbach and Bautzen (Saxony, Germany). The model approach enables not only the variation of nutrient loads and management (water level fluctuations) but also of the meteorological control factors (radiation, air temperature, wind, precipitation). Physical and biological consequences (water temperature, turbulence, stratification, nutrients, plankton, oxygen) can be evaluated in relation to the forcing. Likewise, formerly disregarded but existing feedbacks can be studied due to the direct coupling of the modules (e.g. effect of phytoplankton on light extinction and, thus, on stratification and turbulent mixing). Firstly, the talk presents the main components of the model and the forcing data. Secondly, the applicability for climate impact research of the approach is demonstrated (example Reservoir Saidenbach, 3 years with different winter NAO) with climate scenarios based on the IPCC study. Besides comparing the results with oberved patterns, the role of indirect effects is identified.