Life under an oil slick: response of a freshwater food web to simulated spills of diluted bitumen in field mesocosms

Heavy crude oil transportation over land is increasing, yet the ecological impacts of spills, particularly of diluted bitumen, in freshwater environments remain poorly understood. We simulated spills of diluted bitumen in 1400 L land-based mesocosms containing water and sediments from a boreal, oligotrophic lake and monitored the response of natural planktonic communities over 11 days. Most species of phytoplankton (chrysophytes and dinoflagellates) and zooplankton (copepods and cladocerans) were sensitive to oil, exhibiting >70% overall abundance reductions in response to the spills. Declines in nano- and microphytoplankton were short-lived and began to recover after the oil sank, whereas picophytoplankton and zooplankton populations remained depressed at the end of the experiment. In contrast, oil spills stimulated bacteria known to degrade hydrocarbons, especially Alphaproteobacteria, whereas Gammaprotobacteria(a common marine oil spill bacterial class) increased less. This is the first experiment to examine the effects of diluted bitumen in a multitrophic freshwater community. Si le transport terrestre de petrole brut lourd est a la hausse, la comprehension des impacts ecologiques de deversements, particulierement de bitume dilue, dans les milieux d'eau douce demeure limitee. Nous avons simule des deversements de bitume dilue dans des mesocosmes terrestres de 1400 L contenant de l'eau et des sediments d'un lac oligotrophe boreal et surveille les reactions de communautes de plancton naturelles sur une periode de 11 jours. La plupart des especes de phytoplancton (chrysophytes et dinoflagelles) et de zooplancton (copepodes et cladoceres) etaient sensibles a la presence de petrole, presentant des baisses d'abondance globale de >70 % en reaction aux deversements. Les baisses etaient de courte duree en ce qui concerne le nanophytoplancton et le microphytoplancton, et ils commencaient a se remettre une fois le petrole coule au fond, alors que les populations de picophytoplancton et de zooplancton demeuraient reduites a la fin de l'experience. En comparaison, les deversements de petrole stimulaient les bacteries connues pour degrader les hydrocarbures, particulierement les alphaproteobacteries, alors que l'abondance de gammaprotobacteries (une classe repandue de bacteries associees aux deversements de petrole en mer) n'augmentait pas autant. Il s'agit de la premiere experience a examiner les effets du bitume dilue dans une communaute d'eau douce multitrophique. [Traduit par la Redaction]
Introduction Heavy crude oils are complex mixtures of organic components and carry additional contaminants, including sulfur, and metals (vanadium, nickel, iron) (Martinez-Palou et al. 2011; ECCC 2013; Lee et al. [...]