Microbial communities in wetland treating manganese of mine water - Part I: prokaryotes' diversity

Manganese (Mn) removal in passive mine water treatment remains a challenge due to its slow oxidation kinetics, requiring specific biogeochemical conditions to achieve effective removal. This study examines the key biogeochemical factors influencing Mn removal in a full-scale passive mine water treatment plant located in Alès (South-East France). Over one year, monitoring of physicochemical parameters, microbial communities, and Mn speciation in solid phases was conducted every two months. Results highlight seasonal variations in Mn removal efficiency, with two main mechanisms identified: (1) Mn carbonate (MnCO3) precipitation, likely influenced by high carbonate concentrations in mine water, and (2) Mn oxide (?-MnO2) formation, mainly associated with reed rhizosphere, where it accumulates as mineral plaque. In mine water, Mn removal correlates with Fe particle concentrations, suggesting a catalytic effect, as well as with alkalinity, and the abundance of microorganisms affiliated to Alteromonadaceae, indicating a microbial influence. Mn removal appears to be primarily abiotic, driven by favourable pH and alkaline conditions that promote Mn carbonate precipitation and by autocatalytic oxidation reactions occurring on rhizosphere surfaces. However, microbial communities may facilitate certain Mn removal processes depending on environmental conditions. The seasonal dynamics of microbial communities in response to environmental changes are therefore a critical factor influencing Mn removal mechanisms.