Historical Changes in Acid Precipitation and Heavy Metals Deposition Originating from Fossil Fuel Combustion in Eastern North America as Revealed by Lake Sediment Geochemistry

Abstract

The present study deals with the geochemical stratigraphic evolution of the most recent sediments in lakes of Eastern Canada (Quebec). In particular, the sediments from two representative soft water lakes (Tantare and Laflamme) in “undisturbed” watersheds on the southern edge of the Precambrian Shield were studied. The increase in A1 in the sediments of Lake Tantare since about 1950 is attributed to the processes of surface water acidification of this watershed induced by acid precipitation. The analogous upper strata of the sediments from Lake Laflamme, a non-acidified lake, show no such increase in Al content. Pb, Zn and Hg levels in the sediments increased significantly from 1940 onwards. However, the subsequent reduction in the stratigraphic concentration of Zn since 1960 in both Lake Tantare and Lake Laflamme is, in all probability, the result of the important decrease of the total particulate emissions to the atmosphere from coal-fired plants. The same phenomenon may also explain Hg decrease during the same period. In contrast, Pb shows no such reduction in the more recent strata and the sustained increase of this element in the sediments is attributed to the progression in motor vehicle activity during the past twenty years. Further data from other isolated lakes suggest that the major sources of heavy metal deposition and acid precipitation in the Province of Quebec are the emissions from fossil fuel combustion (coal and/or motor fuel) originating in the heavily industrialized American Midwest and Great-Lakes Regions.