The geochemistry and sedimentology of the surficial sediments of Lac St-Louis, St. Lawrence River

The particle-size distribution, geochemical composition and concentrations of metals and major elements were determined in radiodated cores collected from Lac St-Louis, St. Lawrence River. Sedimentation rates ranged from 0.5 to 0.8 cm year −1 in the northern part of the basin to as much as 8 cm year −1 in the south. The concentration profiles of the major elements and most of the metals showed a continuous input of geochemically similar material at all the sampling sites. The exceptions (Hg, Zn, Co, Cr) were attributed to input from local sources. Cores from sheltered areas showed a uniform particle-size distribution down the core, indicating continuous and uniform sedimentation; considerable variation in size occurred in one core from a site exposed to current and wave activity. In contrast to Great Lakes' sediments, cores showed no correlation between metal content and grain size, and no surface enrichment in organic carbon and manganese. The thin sediment cover, the coarse grain size of the sediments, and the wave and current energy available for transport suggest that the lake is mainly a conduit for suspended sediment rather than an important sediment sink.