Factors influencing cyanobacteria community structure in Chara-lakes

Abstract

For practical reasons, cyanobacteria attract scientific interest in eutrophicated, often degraded water bodies. Much less attention is paid to blue-greens in less fertilized lakes, including a group of macrophytic lakes with vegetation dominated by charophytes (Chara-lakes). In this study, therefore, two small, mid-forest Chara-lakes with negligible recreational use were compared with two large Chara-lakes subject, along with their drainage basin, to higher human pressure. An attempt was made to find out whether there are any differences in the qualitative and quantitative structure of cyanobacteria and in cyanobacteria functional groups between the studied Chara-lakes. In addition, the lakes ecological status was assessed based on their total phytoplankton and cyanobacteria biomass.Small mid-forest Chara-lakes were distinguished by Chroococcales taxa, while Oscillatoriales and Nostocales preferred large recreationally used water bodies with catchment areas changed by human activity. Aphanothece minutissima, Merismopedia tenuissima, Aphanizomenon gracile, Aphanocapsa holsatica and Cyanodictyon planctonicum differentiated among the studied Chara-lakes.Although cyanobacteria dynamics did not differ Chara-lakes from eutrophic water bodies, the dominance of cyanobacteria was only detected in the two large Chara-lakes characterised by a worse ecological status compared to the small mid-forest ones.Alkalinity, water temperature, colour and, to a lesser extent, TP and TN:TP ratio are postulated to be water properties which, in addition to extensive charophyte meadows, control the development of cyanobacteria in the studied Chara-lakes.