“Methane at Visovac – the role of biogeochemical processes and dynamics of microbial communities – METVIS”

“Methane at Visovac – the role of biogeochemical processes and dynamics of microbial communities – METVIS”
Methane contributes significantly to global warming

After carbon dioxide, it is the second largest cause of global warming caused by direct human activity. The largest biogenic sources of methane are wetlands and other freshwater systems, with an emphasis on bodies of stagnant water.

During 2022 and 2023, the Ruđer Bošković Institute conducted the research project “Methane at Visovac – the role of biogeochemical processes and the dynamics of microbial communities – METVIS”, with the aim of determining the role and importance of microbial communities in the circulation of methane in Visovac Lake.

Physical-chemical parameters were monitored during the period of investigation; the presence of bacteria responsible for the synthesis and/or decomposition of methane in the water column, and the correlation of chemical parameters and methane concentration with the bacterial community. By utilizing the latest methods in investigating the composition of microbial communities (next generation sequencing) and connecting them with physical-chemical parameters, the relationship between the bacteria and methane was investigated at two selected points at Visovac Lake. As an exceptionally large amount of precipitation was recorded during June 2023, which caused mixing of the water column, hence it was not investigated further, but both sampling points had very similar results, and in the future, one sampling point would be sufficient for monitoring the concentration of methane in the lake.

The concentration of oxygen in the water column decreased from spring to autumn, where anoxia was established in the lower  layer, while an increase in sulfate in the lower layer also indicated anoxia. Temperature is the factor that most significantly affects the appearance of anoxia.

Methane was documented in all samples, with an increase in concentration from spring to autumn, but within the limits that have otherwise been established in similar freshwater ecosystems. Each season shaped its own microbial population, but the occurrence of anoxia had the most significant impact on the composition. The most important groups of bacteria responsible for the methane cycle are: Methylococcales and Methanobacteriales/Metanobacterium.

In order to obtain a complete picture of the organic load of the lake system, investigation should include Brljan Lake, in addition to Visovac Lake, and regular sampling should continue. Also, due to the strong interaction of the organic load and methane concentration, it would be necessary in the future to implement monitoring of the organic load of the Krka River ecosystem.