Temporal methane dynamics in the surface waters of a stratified eutrophic lake over four years

Abstract

The occurrence of oxic methane production (OMP) has been reported for numerous aquatic ecosystems. Its seasonal dynamics and contribution to global methane () emissions remains uncertain, however, due to the lack of measurements constraining the spatial and temporal variability of OMP. In this study, we used data collected over 4 yrs with three types of models to estimate the net production/consumption of () in the surface mixed layer of a eutrophic lake. These models allowed us to assess the lateral contribution and the surface fluxes' variability on estimations. All model results show positive rates suggesting that OMP occurs consistently during the stratified period and was often the dominant source of surface diffusive emissions. In years with monthly data, we observed a consistent pattern of high rates at the start of stratification and a decrease towards the end of the stratified season. Along with the trends and in agreement with recent findings, correlations between vs. Secchi depth, chlorophyll a concentrations and light climate suggest that photoautotrophs play a role in production. Finally, using an isotopic mass balance model, we determined that the stable carbon isotopic signature of in this lake was likely between and , which aligns with published work. Clearly, OMP can be a significant component of an aquatic budget of eutrophic systems, but can vary temporally; thus, temporal variability should be considered when assessing the global contribution of OMP to aquatic emissions, particularly in systems experiencing or threatened by eutrophication.