Remediation of Simulated Heavy Crude Oil Spills in a Boreal Lake Using Enhanced Monitored Natural Recovery (eMNR): Impacts on Phytoplankton and Biofilm Communities.

A lake littoral enclosure study was conducted to evaluate the effects of a minimally invasive secondary remediation method (enhanced Monitored Natural Recovery eMNR) on phytoplankton and biofilm communities following a model heavy crude oil spill. Enclosures (n = 3; ~ 27,000 L) received 1.5 kg of weathered conventional heavy crude and underwent primary remediation by freshwater shoreline flushing and oil recovery using oleophilic sorbent pads, followed by nutrient addition to stimulate microbial degradation (eMNR). Reference enclosures (n = 3) received shoreline flushing only. Phytoplankton chlorophyll-a and biofilm ash-free dry mass were monitored over 400 days, while biofilm community composition was sampled at the end of the study. No statistically significant differences were detected between eMNR and reference enclosures for any measured endpoint. Under the single nutrient-addition regime tested and the specific oligotrophic conditions of this boreal lake, eMNR did not measurably affect primary producer biomass or community structure. However, alternative formulations, nutrient doses, or environmental conditions may yield different outcomes, and caution is warranted when generalizing these results to other systems.