Characterisation of microbial communities within a constructed wetland treating alkaline bauxite residue leachate

Constructed wetlands (CW) have been employed as an effective remediation strategy of mine drainages and alkaline leachates. However, the microbial community in constructed wetlands for alkaline bauxite residue leachates is poorly understood. Soil samples were collected in 2023 along a CW which had been operational since 2015 and analysed using 16S rRNA gene sequencing alongside physico-chemical assessment (pH, EC, trace element content). Sequencing data revealed spatial shifts in microbial community composition and diversity along the wetland, associated with changes in pH, electrical conductivity, and elemental distributions, suggesting microbial zonation and potential roles in carbon cycling, sulfate reduction, and pH neutralisation. Significant differences were found between abundances of three of the top ten phyla: Firmicutes, Bacteroidota and Desulfobacterota at sampling locations along the wetland's length. Firmicutes accounted for around 27% of total abundance in the Top section, decreasing to 7% by the Bottom section, with Halobacterota also decreasing from 24.7% to 18.7%. Several dominant phyla, including Proteobacteria, Chloroflexi, Bacteroidota, Crenarchaeota and Acidobacteriota, generally increased in abundance from inlet to outlet. The identified phyla and families contained genera which are known to carry out functions including: sulfate reducing and organic matter cycling, including acetogens and methanogens which utilise acetate and are also acid producing. Future work is needed to determine how long it takes for the microbial community to colonise/assimilate to a new wetland, to investigate what tolerances are displayed by the microbes present, and whether inoculation of new systems may aid in system commissioning and optimisation.