Long-term cyanobacterial dynamics as related to physicochemical water parameters in a restored urban lake

The aim of this study has been to determine the response of cyanobacteria to the lake protection and restoration measures implemented in the littoral zone of an urban lake called Jeziorak Mały. The first investigations were conducted in 1996 and were resumed in 1997-2003, 2005 and 2013, following the installation of a separator and the creation of stone accumulation sites. Long-term changes in phytoplankton cyanobacterial proportions, abundance and biomass were analyzed in relation to environmental conditions at the sites in the littoral zone (S – separator pipes, K – sites with stones and R – sites with macrophytes). Relationships between cyanobacteria and water chemistry variables were analyzed by calculating the Spearman’s rank correlation coefficient, and then with canonical correspondence analysis (RDA). The results provided evidence that water temperature, total nitrogen and iron concentration (S, R), but also PO43- in spring (S,K) were the principal factors affecting cyanobacterial development. There was a significant decrease in the share, abundance and biomass of cyanobacteria coinciding with a decrease in conductivity and PO43- following the onset of lake restoration efforts. Changes in dominant species from the ones typical in hypertrophic lakes to those typically found in eutrophic lakes took place during the research. The modifications indicated a strong initial response of cynaobacteria to the restoration measures, but the situation stabilized in 2013, when cyanobacteria returned to their previous average levels. This suggests that the introduction of lake restortation measures contributed to the lake’s improved water quality and they should be retained for efficient lake management in the future.