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Vassova lagoon is a small and shallow lagoon in the area of Nestos River Delta, North Greece, which is used for fisheries. The lagoon is isolated from any freshwater inflow through a peripheral levee. The lack of freshwater input, the shallow depth, and evaporation exceeding precipitation have resulted in an increase of the lagoon salinity, significantly affecting fish productivity. Aiming at partially re- storing the historical freshwater supply to the lagoon, as a part of a LIFE-Environment program, a free-water surface wetland was designed, constructed and is now in operation, receiving agricultural drainage from the surrounding fields for treatment and discharging it into the lagoon. This paper presents the design of this free-water surface constructed wetland, and the results of monitoring its function during the first year of operation. [ABSTRACT FROM AUTHOR]

The contribution of bottom sediments to the trophic status of two adjacent lagoons located in Northern Greece is investigated. The limited water depths (about 1 m) and the depletion of oxygen occurring in the summer suggest that there may be a nutrient release from the bottom sediments to the water column. Temperature, salinity, pH and dissolved oxygen concentration in the water column were measured onsite using suitable portable equipment. Nitrites, nitrates, total phosphorus and chlorophyll-a were determined in water samples, whereas total Kjeldahl nitrogen and total phosphorus in sediment samples. Nutrient concentrations in the water column of Eratino Lagoon increased during the winter (nitrate: from 69 to 76 µg l-1; total phosphorus: from 93 to 116 µg l-1). Nutrient concentrations also increased in Vassova Lagoon. Chlorophyll-a concentration appeared to be nearly stable in both lagoons. Total Kjeldahl nitrogen in the sediment showed increased winter values, especially near the agricultural drainage canal of Eratino Lagoon (10.7 mg l-1). On the contrary, total phosphorus in the bottom sediments decreased by almost one order of magnitude in Eratino Lagoon (from 468 to 26 µg g-1 d.w.), and less in Vassova Lagoon, revealing a phosphorus release from bottom sediments into the water column. Both lagoons were characterized as mesotrophic to hypertrophic. Best management practices have to be implemented in order to improve the water and sediment quality of these two lagoons. [ABSTRACT FROM AUTHOR]

The tidal circulation and the temporal variability of water quality parameters (salinity, nutrients and chlorophyll-a) at the mouth of a coastal lagoon in Northern Greece are described. Vassova is a small and shallow coastal lagoon located at the western bank of Nestos River, in the region of East Macedonia. The lagoon is a closed system (i.e., there is no freshwater input except directly from rainfall and through limited seepage from adjoining agricultural lands). The lagoon has a single entrance canal, which connects its main basin to the open North Aegean Sea (Kavala bay), thus considered as the only water renewal mechanism for this system. Bottom and side friction acting at the entrance channel modifies and distorts the form of the incoming tidal wave. This study is based on an intensive sampling program of physical and chemical parameters obtained at the mouth of Vassova lagoon during 4 separate tidal cycles, aiming at understanding tidal circulation and estimating the instantaneous and residual fluxes of water, salt and nutrients. Field data of hydrographic and water quality parameters were collected under various tidal conditions (neap, intermediate and spring tidal cycles) and under winter and summer circulation, to account for the fortnight and seasonal effects in the lagoon. The analysis showed that the Eulerian residual transport and the Stokes drift are under certain conditions positive in direction, thus pushing water, salt and nutrients inward Vassova lagoon. The water volume entering the lagoon during flood was nearly double that leaving during ebb. Freshwater into the lagoon was found dependent only on precipitation. A near zero return flow factor was calculated showing the important flushing of Vassova lagoon due to the presence of coastal alongshore currents in Kavala Gulf. Lagoon's residence time was found of the order of 4 to 5 days, dependent mostly on the tidal status prevailing in the area. circulation and estimating the instantaneous and residual fluxes of water, salt and nutrients. Field data of hydrographic and water quality parameters were collected under various tidal conditions (neap, intermediate and spring tidal cycles) and under winter and summer circulation, to account for the fortnight and seasonal effects in the lagoon. The analysis showed that the Eulerian residual transport and the Stokes drift are under certain conditions positive in direction, thus pushing water, salt and nutrients inward Vassova lagoon. The water volume entering the lagoon during flood was nearly double that leaving during ebb. Freshwater into the lagoon was found dependent only on precipitation. A near zero return flow factor was calculated showing the important flushing of Vassova lagoon due to the presence of coastal alongshore currents in Kavala Gulf. Lagoon's residence time was found of the order of 4 to 5 days, dependent mostly on the tidal status prevailing in the area. [ABSTRACT FROM AUTHOR]