Metal uptake in northern laboratory-scale wetlands treating synthetic mine drainage

Constructed wetlands (CWs) have been employed as passive treatment systems for metal contaminated mine drainage in Canada. However, relatively few CWs have been documented in northern environments and further studies are needed to understand the metal removal mechanisms in wetlands operating under cold climates, with short growing seasons. The goal of this study was to evaluate the performance of laboratory-scale CWs for the removal of Cd, Cu, Se and Zn, as well as to evaluate Cu uptake in two northern plant species (Carex aquatilis and Juncus balticus). Eight laboratory-scale wetlands were constructed using local materials, including locally harvested plant species and microorganisms, and operated under northern summer conditions for ten weeks. The CWs had a three-day retention time and were fed continuously with synthetic influent containing Cd, Cu, Fe, Se, and Zn, at concentrations predicted at mine closure. Average removal efficiencies of 96%, 99%, 79%, and 97% were observed for Cd, Cu, Se, and Zn respectively. There were no significant differences in plant growth between the CW treatments, or any evidence of increasing Cu uptake with increasing availability in either northern plant species. Our study suggests that CWs could operate as successful passive treatment solutions in a northern environment, at least during the summer months. However, further studies are required to examine potential contaminant uptake in a suite of northern plant species and examine the efficacy of CWs under winter conditions.