Vertical organization of freshwater sediment microbial communities: implications for microbial activities and burial processes

Microbial activity in lake sediments plays a key role in the cycling of nutrients and organic matter that continuously sink from water columns. As organic matter accumulates at the sediment surface, upper sediment layers become buried, resulting in a decrease in microbial activity and cell turnover rate with increasing depth. To better understand the structure of freshwater sediment communities and how the burial processes influence it, we quantified the distribution of a broad range of environmental parameters and the community structure of microbial archaea, bacteria, and eukaryotes in the sediments of a clear, temperate lake. Our findings suggest that the two uppermost horizons of the sediment community, which cover approximately the last 70 years, are characterized by a high taxa replacement influenced by “present” environmental parameters. Richness effects became increasingly important in the lowest studied horizon (14-30 cm, age 70-150 a) and could be readily explained by conservative “past” environmental parameters. The lowest horizon is also characterized by a switch in dominance toward archaea, as has been found in marine sediments. Our pioneering study shows that the freshwater lake's community structure, taxa, and vertical arrangement share many features previously observed for marine sediments.