Applying microbial indicators of hydrocarbon toxicity to contaminated sites undergoing bioremediation on subantarctic Macquarie Island

Microorganisms are useful biological indicators of toxicity and play a key role in the functioning of healthy soils. In this study, we investigated the residual toxicity of hydrocarbons in aged contaminated soils and determined the extent of microbial community recovery during in-situ bioremediation at subantarctic Macquarie Island. Previously identified microbial indicators of hydrocarbon toxicity were used to understand interactions between hydrocarbon concentrations, soil physicochemical parameters and the microbial community. Despite the complexity of the field sites, which included active fuel storage areas with high levels of soil heterogeneity, multiple spill events and variable fuel sources, we observed consistent microbial community traits associated with exposure to high concentrations of hydrocarbons. These included; reductions in alpha diversity, inhibition of nitrification potential and a reduction in the ratio of oligotrophic to copiotrophic species. These observed responses and the sensitivity of microbial communities in the field, were comparable to sensitivity estimates obtained in a previous lab-based mesocosm study with hydrocarbon spiked soils. This study provides a valuable and often missing link between the quite disparate conditions of controlled lab-based spiking experiments and the complexity presented by ‘real-world’ contaminated field sites. [Display omitted] •HC concentration drives microbial community structural and functional traits.•HC contamination inhibits both bacterial and archaeal ammonium oxidation genes.•HC contamination reduces the ratio of oligotrophic to copiotrophic bacterial species.•Critical Effect Concentrations were comparable between field and lab studies. Hydrocarbon concentration drives microbial community structure and function and inhibits key ecosystem services. Critical Effect Concentrations based on microbial responses were comparable between field and lab studies.