Spatial distribution of sediment archaeal and bacterial communities in the context of hypoxic lake – a case study on Lake Remoray (France). Biogeography of Lake Remoray sediment

Bottom waters hypoxia spreads in many lakes worldwide causing severe consequences on whole lakes trophic network. In this study, we aimed at understanding the origin of the long annual hypoxia events occurring in Lake Remoray (eastern France) and the resulting consequences on the diversity of sediment microbial communities, a major component of lake trophic network functioning. We used a geostatistical approach to map and compare both the variation of organic matter and microbial communities in sediment. Spatialisation of sediment organic matter parameters revealed that Lake Remoray hypoxia mainly results from algal overproduction during summer period which could be related to an excess of nutrient due to close lake-watershed connectivity. Three spatial patterns were observed for sediment microbial communities after the hypoxic event each characterized by specific genetic structure, microbial diversity and composition. The abundance variation of dominant microbial groups across Lake Remoray such as Cyanobacteria, Gammaproteobacteria, Deltaproteobacteria and Chloroflexi provided us important information on the lake areas where hypoxia occurs. Furthermore, presence of methanogenic species in the deeper part of lake suggests important methane production during hypoxia period. Taken together, our results provide well extensive picture on the origin of Lake Remoray hypoxia and their consequences on sediment microbial communities.