Planktonic and Benthic Bacterial Communities of the Largest Central European Shallow Lake, Lake Balaton and Its Main Inflow Zala River

Abstract

Lake Balaton is the largest European shallow lake, which underwent cultural eutrophication in the ‘70–80s. Therefore, strict pollution control measures were introduced and the water quality has become meso-eutrophic since the millennium. Due to the touristic significance and change in trophic levels of the lake, numerous ecological studies were carried out, but none of them was focused on both benthic and planktonic microbial communities at the same time. In our study, an attempt was made to reveal the spatial bacterial heterogeneity of the Lake Balaton and Zala River by 16S rDNA terminal restriction fragment length polymorphism fingerprinting and Illumina amplicon sequencing methods in the summer of 2017. According to the molecular biology results, mostly well-known freshwater microorganisms, adapted to nutrient-poor conditions were found in the pelagic water column. The LD12 subclade member Fonsibacter ubiquis, the cyanobacterial Synechococcus sp. and unknown Verrucomicrobia species were abundant in the less nutrient-dense basins, while the hgcI clade members showed various distribution. In the estuary and in the nutrient-dense western part of the lake, some eutrophic conditions preferring cyanobacteria (filamentous Anabaena and Aphanizomenon species) were also detectable. The benthic microbial community showed higher diversity, according to the observed appearance of microorganisms adapted to the deeper, less aerated layers (e.g. members of Desulfobacteraceae, Nitrosomonadaceae).

Does the Kis-Balaton Water Protection System (KBWPS) Effectively Safeguard Lake Balaton from Toxic Cyanobacterial Blooms?

“…During June 2018, Microcystis aeruginosa and Oscillatoria tenuis were the only two cyanobacterial species detected in the Siófok Basin (Basin 4). This result differs from the observations of Tóth et al [ 53 ] made during August 2018 and Farkas et al [ 40 ] made during June 2017. In the study of Farkas et al [ 40 ], the dominant species in the central and eastern basins (Basins 3 and 4) of Lake Balaton was determined to be the picocyanobacterium Synechococcus sp.…”

“…This result differs from the observations of Tóth et al [ 53 ] made during August 2018 and Farkas et al [ 40 ] made during June 2017. In the study of Farkas et al [ 40 ], the dominant species in the central and eastern basins (Basins 3 and 4) of Lake Balaton was determined to be the picocyanobacterium Synechococcus sp. The study of Tóth et al [ 53 ] further confirms this finding as samples originating from Tihány were dominated by species originating from the order Synechococcales, while there were far fewer cyanobacteria from the order Nostocales.…”

“…Lake Balaton has been a focus of numerous investigations which demonstrated a deterioration and subsequent amelioration of its water quality after several remedial steps were undertaken. Most of these studies have been focused on the water quality and cyanobacterial community of Lake Balaton [ 1 , 6 , 15 , 38 , 39 , 40 ]. Here, for the first time, we have detected the presence of five out of nine tested microcystin congeners in the water of the KBWPS, while no toxins were detected in Lake Balaton.…”

“…The difference in cyanobacteria community composition between the studies most likely originates from the method of determination. In the present study, we used a traditional microscopy-based species determination method, whereas the studies of Tóth et al [ 53 ] and Farkas et al [ 40 ] solely relied on next-generation sequencing. Picocyanobacteria are very small (up to 2 µm in diameter [ 54 ]) and hardly detectable with light microscopy.…”

“…As the KBWPS does not retain 100% of the phytoplankton and a part of the phytoplankton spills over into Lake Balaton, detection of some of these species, especially Aphanizomenon flos-aquae , in Basin 1 (Keszthely Basin) was expected. Indeed, the study of Farkas et al [ 40 ] reports an abundance of Aphanizomenon flos-aquae in Basin 2 (Szigliget Basin), while the study of Tóth et al [ 53 ] demonstrate a predominance of species belonging to order Nostocales in Basin 1. Furthermore, Farkas et al [ 40 ] report the presence of Aphanizomenon , Anabaena and Microcystis genera in the Zala River which completely corresponds with the results of the present study.…”