Saturation of ecosystems with toxic metals in Sudbury basin, Ontario, Canada.

Mining and resource recovery activities have not been kind to ecosystems in the Sudbury basin, Ontario. The combination of logging, smelting, fires and erosion resulted in an unusual anthropogenic ecosystem of denuded barren land with lifeless lakes, or a micro-desert. Since the 1970s, however, the concerted efforts made to reduce the emissions and rehabilitate parts of the degraded ecosystem have resulted in improvements in water quality, and recoveries in phytoplankton, zooplankton, zoobenthos and fish communities but have had little impact on toxic metal concentrations in many lakes. We show that most of the catchments in the Sudbury basin have become saturated with Cu and Ni, and some with Zn and Pb. It is estimated that mobilization of metals stored in soils and glacial overburden by surface runoff, groundwater drainage and wind re-working of tailings can sustain the high concentrations of Cu and Ni in many lakes for well over 1000 years. Strategies to immobilize the pollutant metals in the watershed rather than further emission controls may be required for dealing with high levels of toxic metals in surface waters of the saturated ecosystems.