Soil invertebrate response to petroleum contaminants in subantarctic soils, and implications for remediation efforts

Subantarctic islands hold scientific and economic importance, but power to support operations in this region is predominantly produced by diesel-fuelled generators, and several leaks and spills have created areas of contaminated soil. This thesis aims to assess the toxicity of highly weathered petroleum contaminants to soil biota on Macquarie Island, in the context of its unique subantarctic climate and biogeography. In the first ever review of petroleum contaminants in subantarctic soils, their effects on endemic biota were found to be extremely variable. Limitations and opportunities for contaminant management were also identified for the sensitive subantarctic environment, and the benefits of management techniques with minimal collateral disturbance were brought into relief. In a field-based experiment, several biotic, environmental and chemical factors were investigated to determine the most important drivers of soil invertebrate assemblages on subantarctic Macquarie Island. Overall, environmental factors that could be linked to physical soil disturbance held greater influence over soil invertebrate assemblages than did petroleum contaminants. In the first of two laboratory-based toxicity tests, well-aged diesel was not found to affect survival at the highest test concentration in either Microscolex macquariensis (an earthworm endemic to Macquarie Island) or Eisenia fetida (a common model test species of earthworm). Sub-lethal endpoints were more sensitive, though in some cases the effect was hormetic. These results suggest that the addition of diesel to a soil may increase its carbon content, thereby stimulating microbial activity and increasing the amount of food available to the worms. Finally, to simplify chemical analyses, a typical weathered diesel profile was synthesised using six hydrocarbon types. The mixture toxicity adhered more closely to a concentration addition joint action scenario than independent action. When tested individually, alkyl napthalenes and cycloalkanes were the most toxic, whereas n-alkanes and branched alkanes were less toxic. Together, these findings will guide the focus of remediation efforts, with implications for how contaminant management techniques are selected for environmentally sensitive sites such as subantarctic islands. In particular, the end goals of contaminant management must be well-defined, and the broader impacts of any works should be taken into consideration.