Methane production in the oxic water column of shallow lakes from the Pampean Plain with different alternative regimes (Buenos Aires, Argentina)

BALIÑA, SOFÍA; SÁNCHEZ, MARÍA LAURA; BERNAL, CAROLINA; DEL GIORGIO, PAUL

Berlin

Congreso; SIL; 2022

SIL

The traditional paradigm about methanogenesis in freshwater systems is that methane (CH ) is produced in the sediments under anoxic conditions, but a substantial CH production in the oxic water column of lakes has been reported in the last decade. This pelagic methanogenesis appears to be closely linked to algal dynamics, probably because they offer micro-anoxic habitats where methanogenic bacteria can survive, and also because microalgae themselves may be capableof producing CH . In this study we explored pelagic CH production in shallow lakes from the Pampean Plain (Argentina) under different regimes: clear-vegetated and phytoplankton-turbid. We performed field experiments in two turbid and one clear lake, were we allocated 4 enclosures per lake - closed in the bottom to avoid sediment methanogenesis and opened in the surface to allow exchange with the atmosphere and sampling. We measured CH concentrations in each enclosure at least twice a day for four days. We also measured CH evasion rates using floating chambers, estimated CH oxidation rates through incubations and determined phytoplankton structure. Preliminary results indicate pelagic methanogenesis in all three lakes, although its contribution seems to be higher in the turbid lakes. The clear lake had a less abundant but more diverse phytoplanktonic community, including Cryptophyta, Chlorophyta and Cyanobacteria, whereas the turbid lakes presented a much abundant but less diverse phytoplankton community, with one lake dominated by Chlorophyta and the other one by Cyanobacteria. We conclude that CH pelagic production is contributing to the total CH emissions in shallow lakes of the Pampean Plain.