Quality of water in Dabie Lake (North-West Poland) during different seasons (2008-2012)

This paper presents the evaluation of physico-chemical parameters of lake water in Dabie Lake based on the European Union Water Framework Directive.The research was carried out in the years 2008-2012, between April and October. From each of the three measuring stations located in the lake included the study, two separate water samples were taken for chemical analysis. Dabie Lake is located within the administrative borders of the city of Szczecin. It constitutes a large sedimentation basin being a part of hydrographically complex Odra river estuary (the other one is Zalew Szczecinski-the Szczecin Lagoon). The accumulation of allochthonous and autochthonous sediments has taken place in these basins for few thousand years. The studied lake had pH values in the neutral range from 7.65 to 7.87. According to the classification of the European Union Water Framework Directive, all lake were classified as first class. By analyzing the average annual values, one can note that pH, O2diss and NO3– concentration showed a relatively small variation in all the investigated lake. The total suspended solids in Dabie Lake, fell into the II class. The Ptot. concentrations in the surface layer of lake was little differentiated, reaching the levels appropriate for III quality class. The total phosphorus concentration was 0.41-0.69 mgP dm–3. The concentrations of PO43-diss in the tested lake waters varied more significantly corresponding to water quality classes ranging from IV. The concentrations saturation with O2 was 44.8-96.4 %. In case of nitrogen compounds, nitrates and nitrites values for these indicators fell into the I and II class in all the surveyed lake. The indicator which proves high productivity of lake is biochemical oxygen demand (BOD5). The level of this indicator in the studied Lake Dabie was at level III. The highest concentration of oxygen in lake waters was found in Lake Dabie about 8.6 mg O2 dm-3.