Ms Jasmine Williams (PhD Student - University of Toronto), Dr Sean C.Thomas (Professor and NSERC Industrial Research Chair - University of Toronto)
Acid-generating mine tailings introduce pronounced challenges to minesite revegetation. Biochar - the carbon-rich product of biomass pyrolysis - has received increasing attention for this application, and is especially appealing to the mining context due to its recalcitrance and potential for heavy metal sorption. Optimizing the use of biochar for mine reclamation relies on understanding whether nutrient, metal, and water sorption behaviors of biochars are substrate-specific and/or dose-specific and whether certain biochars actually reduce contaminant bioavailability. Investigations into relative biochar-tailings compatibility are lacking in current research, as are field trials. Factorial combinations of mine tailings and biochars were examined in multi-species germination and seedling experiments. These tests revealed marked variation in grass and tree seed germination, seedling survivorship, biomass, and photosynthetic performance among biochar-tailings combinations: certain groupings showed increased germination and survivorship for all species, but others showed neutral to negative results. The most successful biochar-tailings combination inspired a large-scale field trial, on acid-generating goldmine tailings in Northern Ontario (48.2°N, 80.4°W), to observe the role of biochar application doses. Native tree growth and survivorship, heavy metal mobility, and erosion prevalence were monitored for one year. Higher biochar doses increased tree survivorship and overall vegetation cover due to increased nutrient and water availability in addition to reduced metals bioavailability. Results suggest that biochar type and dose may be optimized based on a tailings' physical and chemical properties, and hence introduces great potential for revegetation and decontamination of mining terrain.