The effects of simulated spills of oil and secondary cleanup methods on macroinvertebrates in a freshwater boreal lake

Abstract

There is significant uncertainty around the impacts of oil spills and subsequent cleanup methods, specifically chemical and biological responses, in freshwater ecosystems. To address these gaps, the multi-year Freshwater Oil Remediation Study (FOReSt) was conducted at the International Institute for Sustainable Development-Experimental Lakes Area (IISD-ELA). The FOReSt initiative consisted of controlled spills contained in littoral enclosures installed in a freshwater lake at the ELA. A 2018 pilot study examined the fate, behaviour, and effects of diluted bitumen (dilbit) and conventional heavy crude (CHV) followed by physical removal of residual oil. The second phase was a full-scale study in 2019 on the behaviour, fate, and effects of dilbit and two secondary cleanup methods, a shoreline washing agent (SWA, Corexit EC9580-A) and a biological cleanup method (enhanced monitored natural recovery or EMNR) on two different substrates (Rock Cobble and Peat Organic). In both studies, the macroinvertebrate communities were monitored pre- and post-experimental spills using insect emergence traps (at multiple points in time) and by standard kick net sampling at the end of the exposure periods, respectfully. In the 2018 pilot study, insect emergence was reduced relative to untreated control enclosures within both dilbit and CHV treatments over the duration of the field season (>50% reduction in total abundance relative to control enclosures). A similar trend was observed in the macrobenthos community, with a >50% reduction in abundance and lesser overall taxa richness relative to untreated control enclosures. In the 2019 study, both SWA and EMNR showed no statistically significant effects on the total abundance or taxa richness for emergent insects and benthic invertebrates in both shoreline types relative to control enclosures. There was a statistically significant decrease in total diversity (Inverse Simpson) for the EMNR for emergent insects in the Peat Organic shoreline relative to control enclosures. Results from the 2018 pilot study indicate that dilbit negatively impacts the macroinvertebrate community, and from the 2019 full scale study, EMNR and SWA additions to a dilbit release did not affect the macroinvertebrate community to the same degree as dilbit alone. Overall, the findings of this thesis can be utilized to better address spill response and cleanup methods for freshwater shorelines.