Revegetation of non-Acid-generating, thickened tailings with boreal trees: a greenhouse study

Tree planting presents clear advantages for mine reclamation that is aimed at achieving rapid reclamation of forested landscapes. A greenhouse study was conducted to evaluate the capacity of non-acid-generating, thickened tailings to support six boreal tree species during two growing seasons. One treatment was thickened tailings alone fertilized with inorganic N, P, and K fertilizer or chicken () manure. A thin layer of overburden topsoil was used to cover the tailings and was compared with topsoil alone, where normal tree growth was expected. Two amendments were also tested: overburden topsoil and vermicompost from food wastes. The presence of alkaline thickened tailings under the thin layer of acidic topsoil had a positive effect on tree height and root biomass (broadleaved and jack pine [ Lamb.]) by increasing topsoil pH and available Ca concentrations, which decreased Al, Zn, and Mn phytoavailability to trees; however, root contact with the tailings also increased their Cu concentrations. In thickened tailings that were mixed with topsoil, C/N ratios increased along the experiment from 21 to 40, a value where N immobilization by microorganisms occurred, as suggested by low N concentrations in tree tissues. In consequence, tree height growth (broadleaved) and biomass (conifers) were reduced. Amendment with compost raised the electrical conductivity (3.4 dS cm) to thresholds limiting broadleaved survival, while conifers showed a generalized decrease in biomass production. No trace metal contamination of the trees occurred in the mixtures, probably due to the near-neutral pH conferred by the tailings.