Ecological dynamics of anoxygenic microorganisms in stably redox-stratified waters: Intra and inter-seasonal variability of Lake Cadagno

Abstract

Lake Cadagno (Switzerland) differs from common alpine lakes, as it consists of two stratified layers of water that never vertically mix. This particular environment is a niche for the development of ancient anoxygenic microorganisms similar to those that populated the primordial oceans – which accumulate in the lower part of the chemocline. Yet, linkages between the temporal variation of abiotic factors, controlling stratification, with anoxygenic phototrophic sulfur bacteria community of the bacterial layer (BL) remain unclear. We studied the intra- and inter-seasonal stability of the water column stratification and population dynamics of the BL for three years to address this gap. Analyses of this extended continuous monitoring show the redox-stratified environments of the lake is remarkably stable, with stratification seemingly unaffected by abiotic factors. In contrast, the BL community showed significant intra- and inter-seasonal variability. The distinct weather conditions observed during these three years strongly influenced the composition and development of the BL community. Indeed, especially at the intra-seasonal level, the main populations monitored showed different dynamics each year. The lake's recent history also revealed the same trend. In fact, over the last 35 years, the stability of the meromixis remained unchanged, while the BL community showed considerable variability.