Biogeochemical characterization of a wetland impacted by alkaline mine tailings located in North Cobalt, Ontario

The wetland area studied in the Farr Creek drainage basin in North Cobalt is entirely floored with alkaline mine tailings containing elevated concentration levels of metals including As, Co, Cu, Zn, Pb, and Sb. The results from this study clearly indicate that this wetland is a net sink for metals, with over 75% (by mass) of the metals being retained in the sediments. Also, up to 25 % (by mass) of the metals were retained in the leaves of Typha latfolia. Both oxidizing and reducing bacteria were quantified throughout the wetland and it was found that both types of bacteria were prevalent throughout the wetland at similar population levels. This would suggest that both oxic and anoxic geochemical processes are prevalent throughout this system. It is likely that the presence of localized oxic zones in the vicinity of root zones of Typha latfolia, supported the APB populations observed. The sequentially extracted metals (SEM) results indicated that much of the metals retained in the sediments are associated with the residual and organic matter (OM) fractions. These results have highlighted the geochemical processes prevalent in Alkaline drainage systems which are quite different from those observed in acid drainage systems. These results indicate the importance in considering both the geochemical conditions of the wetland or system being used to treat the mine drainage, as well as to have a detailed understanding of the metals of concern within the mining waste because different metals will have different geochemical interactions based on redox conditions, presence of sulfides, Fe and Mn oxides, and organic matter.