Circulation and nutrient modeling of Thermaikos Gulf, Greece Nikolaos P. Nikolaidis a, * , Aristomenis P. Karageorgis b,1 , Vasilios Kapsimalis b , Giannis Marconis a , Paraskevi Drakopoulou b , Harilaos Kontoyiannis b , Evangelia Krasakopoulou b , Alexandra Pavlidou b , Kalliopi Pagou b a Department of Environmental Engineering, Technical University of Crete, Hydrogeochemical Engineering and Soil Remediation Laboratory, Polytechnioupolis, 73100 Chania, Greece b Hellenic Centre for Marine Research, Institute of Oceanography, Mavro Lithari, 19013 Anavyssos, Greece Received 24 May 2005; received in revised form 24 October 2005; accepted 29 November 2005 Available online 19 January 2006 Abstract Thermaikos Gulf is considered to be one of the most polluted coastal zones in Greece. It is the final receptor of both municipal and industrial wastewaters from the city of Thessaloniki and of two heavily polluted rivers, Axios and Aliakmon. Nutrient enrichment and consequent eutrophication is the primary water quality issue of Thermaikos. The mathematical model WASP 6.0 was used to simulate the hydrodynamics, nutrient dynamics and phytoplakton evolution in the gulf. The model is a physical-based model that compartmentalizes the water body into high dispersivity, uniform concentration compartments. It then performs mass balances on water quantity and quality. In addition to the hydrodynamics, the model can simulate the carbon, oxygen, nitrogen, phosphorous and plankton concentrations in the water body. Monthly hydrologic and water quality fluxes from 1997 to 1998, inputs to the gulf and seasonal nutrient surveys in the gulf were used to calibrate nutrient dynamics. The gulf was compartmentalized into 12 compartments, six were horizontal and two were vertical. Salinity data were used to calibrate the hydrodynamic variables of the model. Model calibration was conducted by minimizing the root mean square error between field observations and model simulation. The model was able to capture the variation of salinity and nutrient concentrations. The results showed the importance of Thessaloniki effluents to the Thessaloniki Bay and Gulf and the Axios and Aliakmon River loads to the degree of eutrophication of the entire gulf. The model can be used to assess management scenarios to improve the water quality of the gulf. D 2005 Published by Elsevier B.V. Keywords: Nutrients; Modeling; Thermaikos Gulf; Greece 1. Introduction The European Union Water Framework Directive 2000/60/AC (WFD) establishes an integrated and coor- dinated framework for the sustainable management of water (rivers, lakes, estuaries, coastal waters, and groundwater). The WFD stipulates detailed procedures for its implementation including the classification and monitoring of water bodies. Therefore, such a manage- ment approach requires among other things, the esti- mation of nutrient fluxes, the determination of spatial and temporal response and the understanding of bio- geochemical changes in the past, present and future from the entire catchment area to the coastal water body. This integration can be accomplished by the 0924-7963/$ - see front matter D 2005 Published by Elsevier B.V. doi:10.1016/j.jmarsys.2005.11.007 * Corresponding author. Tel.: +30 28210 37106. E-mail addresses: nnikolai@mred.tuc.gr (N.P. Nikolaidis), ak@ath.hcmr.gr (A.P. Karageorgis). 1 Tel.: +30 22910 76369. Journal of Marine Systems 60 (2006) 51 – 62 www.elsevier.com/locate/jmarsys