Marine habitat recovery in the Saguenay Fiord, Canada: the legacy of environmental contamination

The North Arm basin of the Saguenay Fiord lies at the mouth of the Saguenay River. Severe contamination of benthic habitats in the basin began in 1912. Pb^-210-dated cores reveal a distinctive increase in organic matter (OM) at that time i.e., within one year of the installation of the first large pulp processing machines at a local paper mill situated on the edge of the Saguenay River main channel. The 1912 increase in OM flux to the basin correlates with the first occurrence of distinctly unbioturbated basin sediments suggesting that the deeper parts of the basin had become anoxic throughout the entire year. 1982 and 1988 surveys showed that the historical impact of OM deposition on the benthic foraminifera community was one of reductions in population density and species diversity. Recent observations from a survey carried out in July, 1993, 22 years after Federal regulations curtailed industrial waste discharges into the Saguenay River, indicate significant recolonization by arenaceous foraminifera and polychaetes, marking a return to oxygenated conditions at the sediment/water interface and renewed bioturbation. This environmental setting has the potential to remobilize toxic trace metals such as mercury that were “mineralized” in the sediment during decades of polluted anoxic conditions