Géologie et géochimie du fleuve, de l'estuaire et du golfe Saint-Laurent (Canada)

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Abstract
An outline of conditions of particulate material and sediments in the river, estuarine and gulf sections of the St. Lawrence (Quebec, Canada) is given. The concentration of solids in the river above Lake St. Pierre varies between 4 and 10 mg/l; downstream towards Quebec the concentrations rise to 30-50 mg/l. With the exception of the Sorel delta, this section of the river does not constitute a major sink of sedimentary materials, but the surface sediments of the river are enriched with P, polychlorinated biphenyls, Cu and Pb. The portion immediately upstream from Ile d''Orleans is the interface of riverine water and salt water from the Gulf of St. Lawrence and at this point is a region of high concentrations of suspended solids (up to 300 mg/l). The process of sedimentation in the estuary is complicated by the coagulation of fine particles after contact with salt water. As a result, there is a zone of high sedimentation rates of fine particulates enriched in P, organic matter and polychlorinated biphenyls in the area of Ile d''Orleans, making constant dredging necessary. Downstream from Ile d''Orleans is a decrease from 40-80 mg/l suspended solids to 1-2 mg/l in the Gulf of St. Lawrence.

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