Comparison of Microbial Biomass, Biodiversity, and Biogeochemistry in Three Contrasting Gold Mine Tailings Deposits

An interdisciplinary approach was used to assess the biogeochemistry of three deposits of gold mine tailings in Nopiming Provincial Park, Manitoba, Canada. Each depositional site has developed varying levels of natural revegetation over the past 70 years. Although the tailings are the products of processing similar carbonate-hosted quartz-carbonate shear zones by the same methods, the physical, chemical, and hydrogeological conditions varied among sites. The sample from the barren tailings area at the Central Manitoba site was lower in pH (4.87 ± 1.34) and higher in total sulfur (337 ± 166 μmol/g) and copper (44.5 ± 20.9 μ mol/g) than samples from the other two sites. Microbial activities have impacted the biogeochemical distribution of carbon, sulfur (total, sulfide, sulfate), and iron (total, Fe(II)) in the tailings at all three sites. The microbial communities were distributed throughout the tailings, but the biomass and biodiversity were greatest at the surface in the revegetated (Ogama-Rockland) and partially revegetated (Gunner) tailings. In contrast, the most barren set of tailings (Central Manitoba) had the greatest biomass and biodiversity in the middle layer (15 cm depth), which also had the greatest abundance of metals, anions, and carbon. The distribution of fatty acid methyl esters (FAME) in the tailings was dependent on both the depth and the individual characteristics of the site. The biomass and biodiversity correlated with the physicochemical conditions, particularly as affected by water movement and hydrology. The primary determinants limiting natural attenuation of the sites may be insufficient calcite buffering, hydrogeology, and the distribution of microbes, rather than a lack of microbes.