Microbial distribution and diversity in saturated, high pH, uranium mine tailings, Saskatchewan, Canada

Microbiological analyses were conducted on core samples collected along a vertical profile ( 0-66 m below surface) from the tailings management facility ( TMF) at the Rabbit Lake uranium mine in northern Saskatchewan, Canada. Bacterial numbers in the core materials were similar to surrounding soils and surface waters, regardless of the seemingly unfavorable pH ( mean = 9.9) and temperature (similar to 0 degrees C) in the TMF. The greatest number of viable cells ( 10(5) CFU/g) was detected at the interface between the tailings and overlying standing water, below which cell counts decreased rapidly with depth. Whole-community metabolic profiles for samples from the different depths grouped into 3 clusters; however, these groups could not be positively correlated with sampling depth, temperature, redox potential, pH, or ore-mill feed. Flow-cell studies demonstrated microbial communities in the tailings surface water could develop biofilms and maintain cell activity at both pH 10 and 7, and altering the pH between these 2 values had little effect on biofilm viability. These results demonstrate the resilience and adaptive nature of naturally occurring microbial communities and signify a potential role of microbial activity in the long-term geochemical evolution of the TMF.