Assessing Monitored Natural Recovery (MNR) for remediating crude oil spills in freshwater environments: The Freshwater Oil Spill Remediation Study (FOReSt) at the Experimental Lakes Area, Canada

Monitored natural recovery (MNR) was assessed as a non-invasive method for limiting residual oil exposure in the aquatic environment following contained spills of Cold Lake Blend diluted bitumen (CLB) and conventional heavy crude (CHV) at the IISD-Experimental Lakes Area in Canada. Oils were applied and left in place for 72h to simulate potential spill cleanup response times. After physical removal of free surface oil, biological response and recovery (microbes, zooplankton communities, emergent insects, and benthic invertebrate) was assessed over 80d and exposure of polycyclic aromatic compounds (PACs) and their alkylated forms (aPACS) in water and sediment were characterized. Embryonic development of fathead minnow eggs exposed to water from each of the enclosures was used to determine potential impacts on fish early life stage development. There were significantly different concentrations of PACs in the enclosures treated with diluted bitumen and CHV immediately after application and attenuation differed between the two products throughout the study period. Water contained primarily 3 ring PACs and aPACs. Microbial taxa with known oil degrading capacity increased in water relative to total community abundance. Emergent insect abundance was significantly lower in both oil treated enclosures relative to reference enclosures, but fish development was not significantly impacted by oil treatments. Monitored natural recovery could be successfully applied to oil spill affected freshwater shorelines, but additional data are required to determine long term recovery trajectories.