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

Abstract

Lake ecosystems contribute significantly to atmospheric methane and are likely to become even bigger methane emitters with the global spread of hypoxia/anoxia in freshwater ecosystems. Here we characterized the spatial heterogeneity of methane production potential, methane concentration, archaeal and bacterial and methanogen communities across Lake Remoray sediment during the summer period, when hypoxic conditions settle in the deepest part of the water column. It was hypothesized that methane concentration and production would be higher in the deeper part of lake, our results showed that some littoral areas exhibited similar or higher values than the deepest area. The full 16S rRNA gene sequencing dataset counted 41 methanogen OTUs in abundances that depended more on sampling-site location than on the water depth gradient. The methanogen co-occurrence network revealed the existence of 5 distinct sub communities, suggesting the presence of different methanogen niches across Lake Remoray. The variation in abundance of the two larger methanogen sub communities was significantly related to methanogenesis potential and sediment methane concentration across-lake. Taken together, our results highlight the need to consider the ecosystem at whole-lake scale when calculating methane budgets, and the need to couple spatial and temporal approaches in order to better estimate lake ecosystems contribution to atmospheric methane.