SRA

In 1999 a wetland close to Ste. Croix de Lotibiniere (Quebec, Eastern Canada) and located along the St. Lawrence River was the site of a simulated oil spill. Test plots were set up, contaminated with crude oil and subsequently used to test natural attenuation, nutrient amendment or vegetation cropping as remediation treatments. In 2020, this study revisited the former test plots to investigate any lingering effects of the original Ste. Croix study. Test plot sediments and control sediments featured detectable quantities (75 - 165 g/kg) of mid-chain n-alkanes (C10-C36), but no other kinds of hydrocarbons. Differences in hydrocarbon, total organic carbon, nitrogen and phosphorous content were not significantly different between test plot sediments and control sediments. A microbial analysis did not detect significant differences in microbial load, microbial diversity or microbial community composition between test plot sediments and control sediments. Key genes for the aerobic and anaerobic degradation of n-alkanes as well as for the aerobic degradation of polycyclic aromatic hydrocarbons were detected in all sediment samples. Abundances of these genes did not differ significantly between formerly oil-contaminated sediments and control sediments. This study shows that after 21 years, previously oil-contaminated sediments of the Ste. Croix wetland can be considered completely remediated irrespective of the performed remediation treatment.