Planktothrix rubescens: a perennial presence and toxicity in Lake Sapanca

Cyanobacteria are expected to adjust to new conditions better than other primary producers since they have a long history of adaptation as one of the first organisms on earth. Their ecophysiological adaptations differ widely among cyanobacterial species. As a stratified species, P. rubescens forms a population in the metalimnion during summer months in lakes with clear water and disperses in the whole water column during the period. However, after a dry season in 2006 and 2007, a prolonged surface bloom in late winter was observed in Lake Sapanca The maximum biomass of P. rubescens reached 13.9 mg L-1 in surface water in February 2007 and microcystin concentrations varied between 0.12 and 8 mu g L-1 MC-LR equiv. in the open water throughout the year. The maximum microcystin value was measured at 79 mu g L-1 when accumulations of filaments were observed on the shoreline. As P. rubescens is a shade-adapted species, lower insolation in February together with stable water conditions and lower water temperature promoted the surface bloom. In conclusion, the presence of toxic P. rubescens throughout the year with changing depths poses severe health hazards to people and also an economic burden to the water treatment facility, since the lake is used as a drinking-water reservoir.