Microbial Communities Drive Methane Fluxes From Floodplain Lakes-A Hydrological Gradient Perspective

This study examined the impact of methanotrophic bacteria and methanogenic archaea on CH₄ fluxes from floodplain lakes at various successional stages, analysing their interactions with physicochemical properties of water. Seasonal microbiological and hydrochemical studies of 10 floodplain lakes in the Łyna River floodplain, characterised by varying hydrological connectivity, revealed that methanotrophic bacteria (MOB) and mGen significantly influenced CH₄ and CO₂ emissions. The microbial structure, expressed as the MOB/mGen ratio, was associated with a gradient of CH₄ flux rates specific to each oxbow type. Average CH₄ fluxes from the lakes were 21, 225 and 507 mg m^-2 day^-1 for lotic, semi-lotic and lentic systems, respectively, while corresponding CO₂ fluxes were 0.8, 0.7 and 1.0 g CO₂ m^-2 day^-1, respectively. Statistically significant differences in CH₄ and CO₂ fluxes were observed between lentic and lotic water bodies. The partial least squares model indicated that water temperature significantly stimulated MOB and mGen abundances. Moreover, chlorophyll-a, turbidity and chemical oxygen demand positively correlated with the presence of these microbial groups. Methanotrophs were negatively affected by NH₄-N, while methanogens were affected by NO₃-N. These findings highlight the complex biotic and abiotic interactions driving greenhouse gas emissions in floodplain ecosystems and suggest targeted management strategies to mitigate their climate impacts.