Microbiological changes in the environment caused by deep dredging. A case study: post-dredging pit Ku nica II (Puck Bay)

In this study psychrophilic, mesophilic and denitrifying bacterial abundances were studied seasonally (summer, autumn, winter and spring) in the water column and surface sediment layer (0-5 cm) in the post dredging pit Ku nica II and natural areas of Puck Bay. The research was conducted between VI 2001 and III 2003. In the pit area an increase in mesophilic bacteria and a decrease in denitrifying bacteria numbers were observed, when compared to the natural areas. In the case of the mesophilic bacteria, the increase was visible in the near-bottom waters and surficial sediments during the period of well developed vegetation - in summer and autumn. In the case of denitrifying bacteria, the decrease of number concerned the sediments. Numbers of psychrophilic bacteria in both the natural and dredged areas did not differ significantly over the course of the study. These results suggest that deep dredging can cause the self-purification potential of the ecosystem to be diminished and induce strong bacteriological pollution.