The effects of a simulated spill of diluted bitumen on invertebrates in a boreal lake environment

To bring bitumen from Canada's Oil Sands to market requires transportation over sensitive boreal environments via rail, truck, and pipeline. With proposed expansion of pipeline infrastructure, there is a need for whole-ecosystem research evaluating fate and toxicity of oil spills specific to freshwater environments; the Boreal Lake Oil Release Experiment by Additions to Limnocorrals (BOREAL) aimed to address this. The BOREAL study was conducted in an oligotrophic lake (Lake 260) at the IISD-Experimental Lakes Area in Summer 2018. Nine 10-metre diameter, ~ 100-m3, limnocorrals were deployed, with seven treated with different volumes of a diluted bitumen product in a regression design accompanied by two reference limnocorrals. Dilbit volumes ranged from 1.5 L to 180 L, which is representative of historical oil:water ratios for pipeline spills in North America between the 50th and 99th centile (2008-2018). Zooplankton, emerging insects, and benthic invertebrates were monitored pre- and post-spill for abundance and community composition. By 13 days post-spill, zooplankton abundance had decreased in all limnocorrals and did not recover to pre-treatment values, with rotifers becoming the dominant phylum. No discernable impact based on treatment to zooplankton community diversity was observed. No impact was observed to resident benthic invertebrate communities relative to control limnocorrals; however, a concentration-response decline was observed in total insect emergence. Emergence rate declines were confounded by benthic impacts and presence of submerged oil and will require further work to elucidate drivers of long-term impacts. The physical component of oil was observed to be the likely driver of pleuston (water striders) immobility and mortality.