How important is water column dissolved oxygen (O2) for lake methane emissions?
- 1Department of thematic studies, Linkoping University, Linkoping, Sweden (gustav.pajala@liu.se)
- 2Department of Ecology and Environmental Sciences, Umea University, Umea, Sweden (Jan.p.karlsson@umu.se).
Lakes are major global sources of atmospheric methane (CH4), representing an important greenhouse gas. Dissolved molecular Oxygen (DO) in lakes hinders production of CH4 while promoting CH4 oxidation. Consequently, it has been suggested as an important regulator of CH4 emissions from lakes. Presence or absence of DO at the sediment-water interface could therefore influence the extent of CH4 production in top sediment layers, and the amount of CH4 that is stored in the anoxic layer of the water column and potentially emitted during water column mixing events. However, the quantitative importance of DO on CH4 fluxes remains unknown. We studied CH4 fluxes from two lake basins in northern boreal Sweden of which DO was experimentally added to the deep waters in one of the basins (experimental basin) while the other basin was left in a natural state (reference basin). We used spatial and temporally distributed flux chambers to measure CH4 fluxes while the lake basins were stratified (from June to October) and found that there was no significant difference in CH4 fluxes between the two lake basins attributable to the water column experiment. Moreover, we found that the oxygenation of the hypolimnion resulted in a large decrease in CH4 concentration in the experimental basin, in contrast to the reference basin. However, our monthly lake profile measurements indicated that only a small amount of this CH4 may have been emitted during the open-water season. First, the two lake basins were subject to incomplete spring and fall mixing events. Second, our CH4 emission and oxidation model, based on bathymetry, CH4 concentrations, depth distributed 13C/12C measurements, and gas transfer velocities, indicated that 0 – 24 % of the stored CH4 may be emitted on a yearly basis. This shows that the overall impact on CH4 emissions from boreal forest lakes, due to CH4 storage and DO, may be smaller than previously believed. However, Fluxes during the mixing events still represent a large uncertainty for the total yearly lake CH4 emissions.
How to cite: Pajala, G., Sawakuchi, H., Gålfalk, M., Schenk, J., Rudberg, D., Sieczko, A., Karlsson, J., and Bastviken, D.: How important is water column dissolved oxygen (O2) for lake methane emissions?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8863, https://doi.org/10.5194/egusphere-egu22-8863, 2022.
