Microbial Community Composition in a Rehabilitated Bauxite Residue Disposal Area: A Case Study for Improving Microbial Community Composition

The chemical composition of rehabilitated Bauxite Residue Disposal Areas (BRDA) remains the primary indicator of rehabilitation success, with little consideration of microbial community development. We investigated links between the chemical and microbial components of rehabilitated residue at the Aughinish Alumina BRDA (Ireland). Rehabilitated was compared to unamended residue and to an analogy reference soil from unmanaged grassland within the refinery boundary. Bauxite residue comprised of areas with 1, 11, and 12 years following rehabilitation establishment, and gypsum applied at 45 and 90 t/ha. The unamended residue was typical of bauxite residues with high pH (10), sodicity (exchangeable sodium percentage [ESP]‐79), exchangeable sodium (19 cmol/kg), salinity (electrical conductivity [EC] 2.6 mS/cm), and low/negligible nutrient content, microbial biomass (71 µg‐C/g), and fungal phospholipid fatty acid (PLF). Microbial biomass increased 10‐fold with only 1 year of rehabilitation. Gypsum application rate had no effect on microbial biomass. Phospholipid fatty acid analysis (PLFA) demonstrated the emergence of distinct microbial community dependent on rehabilitation time and gypsum application rates. Changes of PLFA profiles were correlated (multiple regressions analysis) to shifts in residue chemical properties (sodicity, organic C, total C, total N, salinity, Mg). An increase of the arbuscular mycorrhizal fungi fatty acid (16:1ω5) with reducing pH has implications on rehabilitation practices. The microbial characteristics of the rehabilitated residue were approaching that of a soil from an unmanaged reference site adjacent to the working site. Gypsum affected PLFA properties, and thereby application has implications for rehabilitation success. For successful ecosystem reconstruction, it is critical that rehabilitation practices consider microbial development.