Sampling of the sediments of the Saint-Maurice River (Québec, Canada) after the construction of two recent Run-of-River dams

Methylmercury (MeHg) is a very toxic organic form of mercury which can bioaccumulate into organisms and biomagnify in the trophic chain. A subsection of the Saint-Maurice River (QC, Canada), has been recently impacted by several landscape perturbations: the recent construction of two Run-of-River dams (RoRs) and artificial wetlands, a forest fire and logging activities. The pondages which are the result of the flooding of soils after the construction of the RoRs could led to anaerobic condition propitious to mercury methylation. In addition, the landscape perturbations can act as indirect factors in mercury methylation by promoting anaerobic conditions and fueling microbial communities with organic matter. These conditions created in this system could have led to the observed increase in MeHg levels in fish of the St-Maurice. In order to assess the impact of these perturbations on the recent contamination, we sampled sediments along a 40 km stretch of the river and performed biogeochemical (Total mercury-THg, MeHg, metals, organic matter-OM) and metagenomic analyses (hgcA, mcrA and dsrB marker gene abundance and diversity of the hgcA-harboring community).