Retention of Heavy Metals in the Post '96 Flood Sediment Layer Deposited in the Saguenay River, Quebec, Canada

In July 1996 during a 50 year event flood, a new layer of sediments composed of debris, gravel and fine materials was transported and deposited over an ancient, one meter contaminated layer of sediments in the Saguenay River Fjord and Ha! Ha! Bay floors. During the Industrial Revolution years, various metallurgic, plastic, aluminum and pulp and paper production industries discharged their wastes on these waters, resulting in the high contamination of both water and sediments. This contamination limited the exploitation of fish and seafood. Given that the new layer is composed essentially of cleaner material, the zone is presenting important changes in the direction of a healthier environment. The Canadian Government and some of the surrounding industries aim to assess the new potential of the zone and its environmental safety. At present, it represents over a million-dollar study.

This part of the Saguenay project aimed to recognize and evaluate the capacity of the new layer to contain and retain the contaminants left at the bottom layer. Particular interest is given to mercury and to heavy metals such as Pb, Zn, Cd, and Ni and to their geochemical distribution among natural adsorbing materials such as clays, oxides, carbonates and organic matter.

The paper presents the recognition and sampling mission on the Alcide Horth Ship, the contamination profiles given in two dimensions (length and depth), the geochemical distribution of heavy metals on the contaminated layer, transition layer and new layer as well as the evolution of their retention and transfer. Discussion and relations with common sediment characteristics such as grain size, cation exchange capacity and surface area are also given. Sequential selective extraction has been used jointly with scanning electron microscopy (SEM) to study heavy metal species.