Spatial heterogeneity of methane concentration, diffusion, potential production, and methanogen communities’ abundance and diversity in Lake Remoray sediments (France)

Lake ecosystems are significantly contributors of atmospheric methane and their involvement is likely to be of an increasing importance because of the global spreading of hypoxia/anoxia in freshwater ecosystems. In this study, we characterized the spatial variation of potential methane production, methane concentration and both microbial and methanogen communities across Lake Remoray sediment during the summer period, when hypoxic conditions settle in the deepest part of the water column. While methane concentration and production were suspected to be greater in the deeper part of lake, our results showed that some littoral areas exhibited similar or even higher values. From the whole 16S rDNA sequencing datasets, 41 methanogens OTUs were identified and their abundance depended more to the sampling site location than to the sampling depth of collected sediments cores. Co-occurrence network analysis of methanogens revealed the existence of 5 distinct sub-communities suggesting the presence of different methanogen niches across Lake Remoray. Among them, the variation in abundance of the two larger methanogen sub-communities was significantly related to methanogenesis potential and sediment methane concentration across lake. Altogether, our results highlight the need to consider the ecosystem at the whole lake scale when considering methane budgets, and the need to couple spatial and temporal approaches to better estimate lake contribution to atmospheric methane.