Phytostabilization of acidic mine tailings with biochar, biosolids, lime, and locally-effective microbes: Do amendment mixtures influence plant growth, tailing chemistry, and microbial composition?

Abandoned mine lands present persistent environmental challenges to ecosystems and economies; reclamation an important step for overcoming these challenges. Phytostabilization is an elegant and cost-effective reclamation strategy, however, establishing plants on severely degraded soils is problematic, often requiring soil amendment additions. We evaluated whether amendment mixtures composed of lime, biochar, biosolids, and locally effective microbes (LEM) could alleviate the constraints that hinder phytostabilization success. We hypothesized that 1) plants grown in tailings amended with lime, biochar, and biosolids (LBB) would establish faster and grow larger than plants grown in tailings amended with lime only, and 2) the LEM source would influence microbial community function and structure in amended mine tailings. We conducted a greenhouse study that simulated in situ conditions to measure the influence of LBB-LEM amendment blends on plant growth, plant nutrients, metal concentrations, microbial function, and microbial community structure. Blue wildrye [Elymus glaucus Buckley ssp. Jepsonii (Burtt Davy) Gould] was grown in tailings collected from the Formosa mine site amended with various combinations of LBB-LEM. The above and below ground biomass of plants grown in mine tailings amended with LBB was 3 to 4 times larger than the biomass of plants grown in tailings amended only with lime. Although the LEM addition did not influence immediate plant growth, it did affect nutrient content and altered the rhizosphere community membership. As such, it is not yet clear if LEM-driven alterations in microbial membership will advance mine reclamation strategies by improving long-term growth.

Microbial response to designer biochar and compost treatments for mining impacted soils.

The Oronogo-Duenweg mining belt is a designated United States Environmental Protection Agency Superfund site due to lead-contaminated soil and groundwater by former mining and smelting operations. Sites that have undergone remediation - in which the O, A, and B horizons have been removed alongside the lead contamination - have an exposed C horizon and are incalcitrant to revegetation efforts. Soils also continue to contain quantifiable Cd and Zn concentrations. In order to improve soil conditions and encourage successful site revegetation, our study employed three biochars, sourced from different feedstocks (poultry litter, beef lot manure, and lodge pole pine), at two rates of application (2.5%, and 5%), coupled with compost (0%, 2.5% and 5% application rates). Two plant species - switchgrass (Panicum virgatum) and buffalograss (Bouteloua dactyloides) - were grown in the amended soils. Amendment of soils with poultry litter biochar applied at 5% resulted in the greatest reduction of soil bioavailable Cd and Zn. Above ground biomass yields were greatest with beef lot manure biochar applied at 2.5% with 5% compost, or with 5% biochar at 2.5% and 5% compost rates. Maximal microbial biomass was achieved with 5% poultry litter biochar and 5% compost, and microbial communities in soils amended with poultry litter biochar distinctly clustered away from all other soil treatments. Additionally, poultry litter biochar amended soils had the highest enzyme activity rates for ß-glucosidase, N-acetyl-ß-D-glucosaminidase, and esterase. These results suggest that soil reclamation using biochar and compost can improve mine-impacted soil biogeophysical characteristics, and potentially improve future remediation efforts.