OXIC METHANE PRODUCTION IN SHALLOW LAKES OF THE PAMPEAN PLAIN (ARGENTINA) AND ITS CONTRIBUTION TO TOTAL LAKE CH4 PRODUCTION

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

Palma de Mallorca

Congreso; ASLO; 2023

ASLO

Methane (CH4) is a potent greenhouse gas that is primarily produced in anoxic sediments by methanogenic archaea. However, several reports suggest that CH4 can also be produced in the oxic water column, known as oxic methane production (OMP). OMP seems to be linked to phytoplankton, either because microalgae might present micro-anoxic niches where methanogenic archaea can survive or also because some phytoplanktonic groups might be able to produce CH4. Regardless of the mechanism involved, the contribution of OMP to total CH4 emissions from lakes remains unclear. In this study, we explored OMP and its contribution to total CH4 emissions in shallow lakes of the Pampean Plain that present different abundance and composition of microalgae. We carried out field experiments in three shallow lakes, where we deployed 4 mesocosms (M) per lake. The M were built with a material that allows the passage of light but not of gases and were closed in the bottom to exclude sediment methanogenesis. We took samples of CH4 dissolved in the M and in the lake at least once a day for five days. Additionally, we took water from the M and the lake to carry out darkness incubations to estimate CH4 oxidation rates and we measured CH4 evasion rates, using static chambers. Preliminary results indicate that the three lakes had OMP, but with differing rates and contribution to total CH4 production, ranging from 4% to 16%. This study sheds light on the role of OMP in CH4 emissions from shallow lakes and highlights the importance of considering OMP in future studies of CH4 emissions from aquatic systems.