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

Abstract

Lake Balaton is the largest shallow lake in Central Europe. Its water quality is affected by its biggest inflow, the Zala River. During late 20th century, a wetland area named the Kis-Balaton Water Protection System (KBWPS) was constructed in the hopes that it would act as a filter zone and thus ameliorate the water quality of Lake Balaton. The aim of the present study was to test whether the KBWPS effectively safeguards Lake Balaton against toxic cyanobacterial blooms. During April, May, July and September 2018, severe cyanobacterial blooming was observed in the KBWPS with numbers reaching up to 13 million cells/mL at the peak of the bloom (July 2018). MC- and STX-coding genes were detected in the cyanobacterial biomass. Five out of nine tested microcystin congeners were detected at the peak of the bloom with the concentrations of MC-LR reaching 1.29 µg/L; however, accumulation of MCs was not detected in fish tissues. Histopathological analyses displayed severe hepatopancreas, kidney and gill alterations in fish obtained throughout the investigated period. In Lake Balaton, on the other hand, cyanobacterial numbers were much lower; more than 400-fold fewer cells/mL were detected during June 2018 and cyanotoxins were not detected in the water. Hepatic, kidney and gill tissue displayed few alterations and resembled the structure of control fish. We can conclude that the KBWPS acts as a significant buffering zone, thus protecting the water quality of Lake Balaton. However, as MC- and STX-coding genes in the cyanobacterial biomass were detected at both sites, regular monitoring of this valuable ecosystem for the presence of cyanobacteria and cyanotoxins is of paramount importance.

Cyanobacteria, cyanotoxins, and their histopathological effects on fish tissues in Fehérvárcsurgó reservoir, Hungary

“…The investigation consisted of qualitative and quantitative analyses of cyanobacterial presence, detection of cyanotoxin encoding genes within the cyanobacterial biomass, detection of cyanotoxins in water and fish tissues, and histopathological studies of fish tissues. Similar studies were conducted in the neighboring country, Serbia, on commercial fishponds and lake Ludaš, by the same group of authors (Drobac et al, 2016;Tokodi et al, 2018Tokodi et al, , 2020, and recently in Hungary on Lake Balaton and Kis-Balaton Water Protection System (KBWPS) (Marinović et al, 2021). The data arising from this type of research and monitoring at the local, regional, and global scale contribute to assessing the risks and consequences cyanobacteria and cyanotoxins can have on human beings and the environment.…”

“…Page 3 of 14 554 23 μm) at a depth of 0.3 m (Marinović et al, 2021;Tokodi et al, 2020). All samples were immediately preserved in 10% neutral-buffered formalin (NBF).…”

“…About 1.5 to 2 L of reservoir water was collected for cyanotoxin analyses during the investigation in July and September of the same year and frozen until the start of the analysis. Fish sampling was carried out in the center of the reservoir with a standard electrofishing device (Marinović et al, 2021;Tokodi et al, 2020). The fish were sampled during all four sampling surveys and consisted of common bream -Abramis brama (Linnaeus 1758) and Prussian carp -Carassius gibelio (Bloch 1782) (Table 1) of which the latter was sampled only in July.…”

“…Qualitative and quantitative analyses of cyanobacteria Cyanobacterial taxa were identified at 100 ×, 400 × magnification in accordance with several taxonomic keys (Komárek, 2013;Komárek & Anagnostidis, 1998 under the Motic BA310 light microscope equipped with a digital camera (Bresser 9 MP) and Micro Cam Lab software. The quantitative analysis of phytoplankton was made with a Motic AE 2000 inverted microscope using the Utermöhl method (Utermöhl, 1958), expressing data as number of cells per ml (Marinović et al, 2021;Tokodi et al, 2020).…”

“…As a part of the same project, cyanotoxin encoding gene analyses were conducted as previously described in Tokodi et al (2020) and Marinović et al (2021). A short description of the procedure is presented below.…”