Effects of functional microorganisms and environmental factors on CO2 and CH4 emissions in a typical floodplain lake system.

Lakes are carbon dioxide (CO2) and methane (CH4) emission hotspots, whose associated flux is spatially variable. Many studies have investigated the impact of microorganisms and environmental factors on CO2 and CH4 emissions between different lakes. However, the carbon emissions and their influencing factors of different areas within a single lake remain poorly understood. Accordingly, this study investigates CO2 and CH4 emission heterogeneity in a large floodplain lake system and distribution characteristics of associated functional microorganisms. Findings show that mean CO2 and CH4 flux values in the sub lake area were 62.03 ± 24.21 mg/(m2·day) and 5.97 ± 3.2 µg/(m2·day), which were greater by factors of 1.78 and 2.96 compared to the water channel and the main lake area, respectively. The alpha diversity of methanogens in the sub lake area was lower than that in the main lake and water channel areas. The abundance of methanogens in bottom water layer was higher compared with the middle and surface layers. Conversely, the abundance of methane (CH4)-oxidizing bacteria in the surface layer was higher than that in the bottom layer. Additionally, the composition of methanogen and CH4-oxidizing bacterial community, chlorophyll a (Chl-a), pH, total phosphorus (TP) and dissolved organic carbon (DOC) content constituted the dominate driving factors affecting lake C emissions. Results from this study can be used to improve our understanding of lake spatial heterogeneous of CO2 and CH4 emission and the driving mechanisms within floodplain lakes under the coupling effects of functional C microorganisms and environmental factors.