Pollution of the ecosystem of the Rusalka city lake with heavy metals

In the vegetation season April-October 2010, the value of and the changes in Zntot., Cutot., Cdtot. and Pbtot. concentrations in the water of the Rusalka flow-through lake (with average water retention of ca 30 days) situated in the city centre of Szczecin were determined. Water temperature, pH, concentration of dissolved oxygen (with calculation of water saturation with O2), COD-Cr and BOD5, total hardness, −3HCO concentration (as total alkalinity), Cl–, −24SO, Mntot and Fetot were also determined. The data collected may be used to evaluate the ecological and chemical status of the surface waters under investigation. As far as the ecological status of the Rusalka Lake is concerned, the investigated waters were found, based on the official criteria being in force in Poland in evaluation of the ecological and chemical status of surface waters, to conform to water quality classes I and II considering total zinc and copper concentrations, temperature and dissolved oxygen concentration (except water inflow to the lake in August) as well as BOD5, −24SO and Cl– concentrations and pH value; however, they were always worse than water quality class II while taking the COD-Cr values into account. Regarding the chemical status of the investigated waters, total cadmium and lead concentrations were the levels exceeding the admissible values according to the official criteria in Poland. Changes in the values of indices being investigated along water flow path allowed stating that the equilibriums between the sedimentation and the resuspension and the dissolution processes during the research period were shifted towards sedimentation in case of Zn and Cd only, as well as of the organic matter sedimenting in the form of divalent cation- and divalent anion-sorbing gels. Although three phytoplankton blooms occurred in the body of water, unfortunately weak ones, the dissimilation processes prevailed over assimilation.