Examining Model Predictions of Zinc and Copper Aqueous Speciation and Freshwater Ecotoxicity: Case Study of Ross Lake, Flin Flon, Manitoba, Canada

Models of aqueous metal speciation and ecotoxicity have become commonplace due to their ability to estimate metal behaviour. This study evaluated commonly used aqueous geochemical speciation and ecotoxicity models with application to a mine impacted lake in northern Manitoba. The geochemical speciation model Winderemere Humic Aqueous Model (WHAM) was compared with Diffusive Gradients in Thinfilm (DGT) measurements of zinc and copper. DGT measurements in the water column corresponded well with WHAM-estimated Zn2+, Cu2+ was off by up to 100x. Additional metal, either from small organic bound species or dissolution of metal sulphides from resuspended sediment, served to improve model estimates. The single metal Biotic Ligand Model (BLM) predicted acute toxicity to Daphnia magna attributable to copper but not zinc, at low pH (3.55 – 5.5). Comparison of results did not show a significant difference between the single and mixture BLMs, suggesting a non-interactive effect on metal toxicity for measured water chemistry.MAS