Evaluation of chemical and physico-chemical indicators of water in Miedwie Lake (North-West Poland)

This paper presents the evaluation of physico-chemical parameters of lake water in the Miedwie 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 lakes included the study, two separate water samples were taken for chemical analysis. The studied lakes had pH values in the neutral range 7.61 to 7.88. According to the classification of the European Union Water Framework Directive, all lakes were classified as first class. By analyzing the average annual values, one can note that the pH, O2diss and NO3 – concentration showed a relatively small variation in all the investigated lakes. The total phosphorus concentration was 0.42-0.63 mgP dm–3. The concentrations of PO43-diss in the tested lake waters varied more significantly-corresponding to water quality classes ranging from III through IV. The concentrations saturation with O2 was 50.3-96.8 %. In the case of nitrogen compounds, nitrates and nitrites values for these indicators fell into the I and II class in all the surveyed lakes. The indicator which proves high productivity of the lakes is the biochemical oxygen demand (BOD5). The level of this indicator in the studied Lakes was at level III. The highest concentration of oxygen in the lake waters was found in the Lake Miedwie (about 8.9 mg O2 dm-3).