Downwelling Events in a Coastal Mussel Farming Area, NW Thessaloniki’s Gulf (NW Aegean Sea)
The coastal area of Chalastra (NW Thessaloniki’s Gulf, Northern Greece) features prominent mussel farming activity as well as fishing activity. These activities are closely related to the hydrodynamics of the basin’s seawaters. The prevailing hydrodynamic force for the circulation of coastal waters of Chalastra is wind stresses. The hydrodynamics of this coastal region may be further influenced by three rivers outflowing to the southwestern part of the basin; however, this runoff has dramatically decreased during the last few decades. Concerning the wind forcing regime, this is distinguished by two characteristic regimes. The first one is realized in winter and the other mainly in summer. Systematic field studies were conducted during one year for current and density measurements. Seawater samples were collected and chemically analyzed for dissolved oxygen, chlorophyll α and nutrients. Data revealed some cases of flow currents of opposite direction between the upper and the lower water layer, and a characteristic captured downwelling which seemed to evolve periodically on a diurnal time scale, especially in summer. Furthermore, a two layer mathematical model was developed and applied for the study of the water circulation and the investigation of downwelling processes under specific conditions; the tracing as well as the temporal and spatial evolution of these hydrodynamic processes in the mussels’ culture study area constituted the main aim of the present work. The formation of such events, which were observed mainly during summer periods, may affect the mussels’ development and has to be considered when designing farming practices in the area.
Keywordscoastal downwelling drifters field works hydrodynamics mathematical models mussel farms
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This work is a part of a research program entitled ‘Innovative Practices for a Sustainable and Environmental Friendly Mussel culture’ which is co-financed by the Greek State and the European Union in the context of the Operational Program of Fisheries 2007–2013. We also owe many thanks to Hellenic National Meteorological Service (HNMS) for its generous supply of meteorological data covering a long period of time (1960-2017).
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