Abstract

The present study deals with the geochemical stratigraphic evolution of the recent sediments of 26 lakes located throughout the Province of Quebec, Canada. Although there is no major anthropogenic activity within the watersheds of many of these lakes, it is shown that Pb, Zn, Hg, and Cu levels in the most recent sediments of all lakes increased significantly from 1940 onwards. It is suggested that these increases are due to the increased burning of fossil fuels (particularly coal). The heavy-metal increases tend to be relatively high, especially for Pb, Hg, and Zn, in the sediments of lakes from areas close to the U.S.A.–Quebec boundary, while lakes in more remote areas show smaller increases in the strata laid down in the same time periods. Pb contents in the sediments show a sustained increase in all of the upper strata. However, the subsequent reduction in the stratigraphic concentration of Zn and Hg since 1960 in both an acidified system (Lake Tantare) and a non-acidified lake (Lake Laflamme) might be the result of the important decrease of the total particulate emissions to the atmosphere associated with new technology for coal-fired power plants and the use of cleaner energy sources.The increase in Al in the sediments of Lake Tantare since 1950 is attributed to the processes of surface water acidification of this watershed induced by the long-range atmospheric transport of SOx and NOx.Based on the sedimentary anthropogenic enrichment factor (SAEF) values for the remote sites there is no evidence in the present study for associating the origin of certain heavy metals in these lake sediments with alternative anthropogenic sources such as the Ni and Cu smelting complexes located in Sudbury (Ontario) and Rouyn–Noranda (Quebec). The major sources of heavy-metal deposition and acid precipitation are thus associated with the long-range transport of emissions from fossil fuel combustion originating in the heavily industrialized American Midwest region.

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