Investigation of microcystin distribution in Manyas Lake

Lake Manyas, also known as a 'bird paradise', is a wetland protected by the RAMSAR convention. The lake, which hosts many migratory bird species, is an ecosystem where bird observations are made intensively and pioneering the understanding of the importance of wetlands in our country. Lake Manyas, which is a shallow lake, is hypereutrophic in terms of water quality due to the high concentrations of nutrients, especially nitrogen and phosphorus. From time to time, with the contribution of the trophic situation and other environmental conditions, excessive increases in cyanobacteria, which are frequently encountered in the world and in our country, and which are capable of producing toxins as secondary metabolites, occur in the lake. Some of these metabolites, called cyanotoxins, have adverse effects on both aquatic life and other living things that come into contact with water. Cyanotoxins have different molecular structures and may have toxic effects depending on the organs they affect. The most common hepatotoxic cyanotoxin in the world is microcystin. In order to detect the presence and variants of microcystin in Lake Manyas, monthly surface water sampling was carried out at four stations between January 2019 and December 2020, and toxin concentrations were determined. In order to reveal the trophic status of the lake, some physicochemical (Temperature, Dissolved Oxygen, pH, Conductivity, Secchi disc depth, Ortho-phosphate, Total phosphorus, Dissolved inorganic nitrogen) and biological (chlorophyll-a concentration) parameters were measured. Carlson Trophic Status Index values were found to be above >62, representing hypereutrophy. As a result of the study, the concentration of microcystin in the lake, varying between 0.07 µg/L and 1.64 µg/L, was measured. Using liquid chromatography high-resolution mass spectrometry (LC-HRMS), 9 variants of microcystin (MC-LR, MC-RR, MC-YR, MC-LY, MC-LW, MC-RR-desmethylated, MC-HiLR, MC-LF, MC-LA) were detected in the lake. The concentration of microcystin in the lake during this study was well below 20 µg/L which is a limit value for bathing waters according to the Regulation on the Management of Bathing Water Quality. However, the year-round presence of presence of microcystins in the lake reveals that monitoring efforts should be carried out regularly for cyanobacteria blooms and the presence of cyanotoxins in Lake Manyas, which is an important wetland.