EUROPEAN LAGOONS 2D finite element ecological model for the Curonian lagoon Petras Zemlys Æ Ali Ertu ¨rk Æ Artu ¯ ras Razinkovas Ó Springer Science+Business Media B.V. 2008 Abstract The results of application of 2D finite element model SHYFEM to the Curonian lagoon (Baltic Sea) are considered. SHYFEM consist of a physical processes module and an eutrophication module EUTRO adapted for the SHYFEM code from well known modelling system WASP. The SHY- FEM/EUTRO model calibration results were compared with the performance of various biogeo- chemical models analysed in other studies (153 studies published from 1990 to 2002). The perfor- mance of all corresponding state variables— dissolved oxygen, NO 3 , NH 4 , PO 4 , phyto- and zooplankton—was slightly lower than median model performance which could be considered satisfactory given the initial state of model formulation and calibration. Model underestimates phytoplankton autumn blooms, especially for the southern part of the lagoon, where fine sediments dominate and water residence time is high. It can be concluded that, in order to increase model performance, the eutrophi- cation module should be improved to account for the dominance of different phytoplankton groups as well as for the exchanges between the sediments and the water column. The amount and quality of the data available for the model setup and calibration are unsatisfactory and should be improved for the development of the next enhanced model version. Keywords Coastal lagoons Á Curonian lagoon Á Eutrophication Á Ecological modelling Á SHYFEM Introduction The Curonian lagoon (Baltic Sea) is a shallow, large estuarine lagoon with complex interactions between biotic and abiotic components. Effective management of such a complex systems cannot be solely based on observations and measurements. It requires also more sophisticated tools, such as mathematical models, that provide managers with a more holistic view of the physical, chemical and biological processes and their interactions and are suitable as decision support tools. Modelling of large heterogenic ecosystems requires the coupling of biochemical and physical processes. During the recent years, several hydrody- namic models were applied to the Curonian Lagoon (Davulien _ e et al., 2002; Raudsepp & Ko ˜uts, 2002; Guest editors: A. Razinkovas, Z. R. Gasiu ¯nait _ e, J. M. Zaldivar & P. Viaroli European Lagoons and their Watersheds: Function and Biodiversity P. Zemlys (&) Á A. Razinkovas Coastal Research and Planning Institute, Klaip _ eda University, Klaip _ eda, Lithuania e-mail: petras.zemlys@ku.lt A. Ertu ¨rk Faculty of Civil Engineering, Department of Environmental Engineering, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey 123 Hydrobiologia (2008) 611:167–179 DOI 10.1007/s10750-008-9452-7