Changes in macroaggregation and associated characteristics in mine tailings amended with humic substances

The mine tailings of a former gold mine in Nopiming Provincial Park, Central Manitoba, Canada, was observed to be highly degraded in soil structure as well as other chemical and biological characteristics. The tailings are highly acidic (pH 3.5), contaminated with copper (2000 mg kg(-1)), have very low organic matter (2.3 g C kg(-1)), and cannot be revegetated by native species. To reclaim the mine tailings, humic substances (HSs) and lime, with or without wheat straw, were incorporated in the tailings and then incubated up to 24 weeks. After incubation, a significant increase of macroaggregates, especially 2- to 20-mm aggregates, was observed in the HS-amended tailings corresponding to the length of incubation and doses of HS. Wheat straw initiated microbial activity in the mine tailings and also showed increase of the macro aggregation. Lime was less effective than HS in the formation of the macroaggregates. The amendments increased organic carbon (OC) in the mine tailings, which remained greater than in the control samples throughout the incubation period. However, the OC in each amended sample decreased over the period of incubation. There was an increase of microbial biomass carbon (MBC) in the straw-amended tailings throughout the incubation period, and the increase was highest at 12 weeks. The HS amendment increased the pH of the mine tailings from 3.5 to 5 as well as the cation exchange capacity (CEC). Macroaggregation of mine tailings was found to be highly correlated with OC and CEC. Significant correlations were also observed between OC and MBC and between OC and CEC.