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Concentration of heavy metal ions (Zn, Cu, Cd, Pb) and their effect on the survival and respiratory activity of neustonic and planktonic bacteria were studied in film layer, surface microlayer and in subsurface water of estuarine Lake Gardno. Zinc, copper and lead reached their highest concentrations in surface microlayers. Cadmium, in general, was distributed homogeneously in all three studied water layers. Laboratory experiments demonstrated the highest toxicity of cadmium and lead for bacteria inhabiting Lake Gardno. Even low concentrations of those metals in culture media resulted in a rapid decrease in the survival of bacteria. Populations of bacterioneuston and bacterioplankton showed different responses to heavy metals. Neustonic bacteria showed a higher level of tolerance to various concentrations of heavy metals than did planktonic bacteria. The strongest inhibitory effect on the respiration of neustonic and planktonic bacteria was brought about by cadmium and copper.
Key words: heavy metals, bacterioneuston, bacterioplankton, survival, respiratory activity