Biotic and abiotic characteristics of ecosystems on acid metalliferous mine tailings near Sudbury, Ontario

INCO Ltd., a large mining company near Sudbury, Ont., deposits vast amounts of tailings on its property. These tailings contain elevated levels of Cu, Ni, and sulphides, and to curtail dust and acid drainage, INCO has undertaken a long-term project to cover its tailings with vegetation. Yearly amelioration of fresh tailings with limestone and fertilizer, followed by seeding with various grasses and herbs, transplanted conifers, and the later colonization of volunteer species of plants from adjoining forests, has resulted in the formation of ecosystems of varying age and complexity. To assess the long-term effectiveness of INCO's vegetation techniques, we studied floral diversity, attributes of developing soils, and the accumulation of Cu and Ni in various plant species growing on tailings at different stages of development. Habitat disturbance by tailings deposition, and its subsequent floral recolonizaton, is an example of "anthropogenic succession." Tailings that do not receive amelioration in the form of lime, fertilizer, and seeding remain free of vegetation, other than sparce clumps of the metal-tolerant grass Deschampsia caespitosa (L.) Beauv. Once amelioration begins, various species of grasses and herbs are able to subsist and within 8 years volunteer species begin to colonize. Substrate pH of dried tailings is less than 4 while the pH in upper horizons ranges from 5 to 6, increasing as the sites become more florally diverse; however, pH at lower depths remains less than 4. Substrate organic content in upper horizons at restored sites ranges from 4.5 to 5.0%. Water-soluble concentrations of Cu and Ni in upper horizons ranges from 1 to 5 µg/g dry mass, and 0.5 to 6 µg/g dry mass, respectively, and both metals decrease with increasing floral diversity. Levels of Ni increase at lower depths indicating greater substrate mobility. Levels of Cu and Ni are higher in plants from tailings than in those from control sites; however, concentrations do not decrease in plants from older and more florally diverse tailings sites. Root tissues contain significantly higher concentrations of Cu and Ni than aerial tissues. Monitoring air with moss plates indicates that dispersal of airborne metallic dust remains a problem.Key words: mine tailings, Sudbury, anthropogenic succession, copper, nickel, acid, monitoring.