Diversity and Structure of the Prokaryotic Community in Tropical Monomictic Reservoir

Bacteria and Archaea are microorganisms that play key roles in the biogeochemical transformations that control water quality in freshwater ecosystems, such as in reservoirs. In this study, we characterize the prokaryotic community of a high-relevance tropical eutrophic reservoir using a 16S rRNA gene survey during a low-water level fluctuation period mainly used for storage, associating the distribution of these microorganisms with the hydrogeochemical conditions of the water column. Our findings revealed that diversity and structure of the prokaryotic community exhibited spatio-temporal variations driven by the annual circulation-stratification hydrodynamic cycle and are significantly correlated with the concentrations of dissolved oxygen (DO), soluble reactive phosphorus (SRP), and dissolved inorganic nitrogen (DIN). During the heterotrophic circulation, the breakdown of thermal gradient leads to a homogeneous distribution of the nutrients, where the presence of DO promotes the dominance of aerobic and facultative heterotrophic bacteria such as Bacteroidota, Actinobacteriota, and Verrucomicrobiota. Also, the autotrophic circulation was characterized by an increase of DO and NO₃^- concentrations, with abundant Cyanobacteria. Finally, during the stratification, the presence of prokaryotes associated with the metabolism of CH₄ was detected, mainly in the hypolimnion, as well as others related to sulfate reduction and nitrification. This study shows the diversity of the prokaryotic community in tropical eutrophic reservoirs, and how the continuous monitoring with metabarcoding techniques can provide critical insights for a deeper understanding of the biogeochemical dynamics and improve the water resource management in the future.