A relationship between accumulation of heavy metals and microbiological parameters in the surface microlayer and subsurface water of a coastal Baltic lake

Abstract

The present study investigated the relationship between accumulations of heavy metals and the concentration of chlorophyll, as well as the number, secondary production and enzymatic activity of bacteria in the surface microlayer (SML) and subsurface waters of a coastal Baltic lake. Concentration of heavy metals was measured by mass spectrometry, chlorophyll by spectrophotometry, bacteria abundance by DAPI staining, secondary production by 3H-thymidine incorporation into DNA and enzymatic activities using fluorescence-labelled substrate methods. Concentrations of all the analysed heavy metals, chlorophyll, as well as the number of heterotrophic bacteria and the level of enzymatic activity were higher in the SML than in subsurface water. No differences in the total number of bacteria in both the studied layers were noted. The rate of secondary production of planktonic bacteria was found to be higher than that of neustonic bacteria. Seasonal variability was observed in the studied chemical and microbiological parameters. It was found that in SML heavy metal concentrations increased in relation to those in subsurface water. However, this did not reduce the level of chlorophyll, heterotrophic bacteria, or the enzymatic activity. In contrast, increased heavy metal concentrations in SML reduced total number of bacteria and the level of secondary productivity.