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Sediments
Mercury Concentrations in Sediments in the Great Lakes and the St. Lawrence River
Overview of the Situation
Between 1968 and 2004, research scientists at Environment Canada, the Department of Fisheries and Oceans Canada, and the United States Environmental Protection Agency collected many hundreds of samples of surface sediments and countless sediment core samples for all of the Great Lakes and the St. Lawrence up to the Upper Estuary. These samples were analysed to understand the current status of mercury contamination and to determine how it has evolved since the late 1960s. Overall, mercury concentrations vary considerably throughout the system, depending on local sources and the sedimentary dynamics of the area.
Mercury concentrations in Great Lakes
and St. Lawrence River sediments
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The concentrations of mercury in sediments in the Upper Estuary can be attributed exclusively to the St. Lawrence River. Surface sediments contained an average Hg concentration of 0.097 µg/g in 1989. The Lower Estuary and Gulf of St. Lawrence were long subjected to inputs of mercury from the industrial sector of Saguenay–Lac-Saint-Jean. Mercury concentrations measured in a dozen sediment cores distributed between the mouth of the Saguenay and the Gulf (Smith and Schafer, 1999) show that concentrations peaked at close to 0.6 µg/g, only to fall to less than 0.3 µg/g.
Mercury concentrations in sediments
in the Great Lakes–St. Lawrence Basin
Lake Ontario–St. Lawrence River Water-level Regulation |
Lake Ontario’s water level has been regulated since 1960 to facilitate increasing demand for shipping and hydroelectric power. Unfortunately, what is good for shipping is not so good for shoreline wetlands. Natural water-level variability has diminished, thereby reducing the biological diversity of these shoreline wetlands, which depend on variability to maintain their plant communities. Developing criteria to guide water-level and flow regulation in Lake Ontario and the St. Lawrence River is a challenge being addressed by a binational study launched in 2001 by the International Joint Commission (IJC). The five-year IJC study provides a major opportunity to improve the understanding of the impacts of past water regulation on shoreline wetlands. The new knowledge will be used to develop and recommend water-level regulation criteria for the benefit of all interests, including the specific objective of maintaining shoreline wetland diversity and health. |
Date modified: 2008/05/01 – Important Notices
