Characterization of the bacterial population and chemistry in the bottom sediment of a laterally subdivided drinking water reservoir system

Sediments in standing waters are complex habitats that are able to provide favorable living conditions for manifold microbial species. The aim of this study was to investigate the spatial and seasonal composition of bacteria in freshwater sediments and the chemical conditions. Four sampling points were investigated at monthly intervals along the flow of water from a pre-reservoir down to the main dam of the Saidenbach reservoir, a drinking water reservoir located in Saxony, Germany. Selected chemical criteria of the sediments were analyzed, as well as the physical conditions of the water body at the chosen sites. Redox-sensitive chemical criteria, such as nitrogen, sulfur, iron and manganese compounds displayed very steep vertical gradients within the sediment. Phylogenetic composition of the communities was investigated utilizing clone libraries and catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH). Up to 90% of the cells that were stained with propidium iodide hybridized with probes for Bacteria and Archaea. This amount decreased with sediment depth. The predominant bacterial groups found in the sediment were α-Proteobacteria, especially at the sampling point with a high content of planktogenic organic material closest to the main dam, as well as β-Proteobacteria and the Cytophaga–Flavobacterium cluster. Clone libraries allowed a more detailed view of the microbial diversity within the detected phylogenetic groups. Despite an observed variation of α-Proteobacteria and bacteria belonging to the Cytophaga–Flavobacterium cluster, a regression analysis showed very weak multiple correlation coefficients between chemical criteria and the analyzed broad phylogenetic bacterial groups.