Climatic and anthropogenic effects on atmospheric mercury accumulation rates in ombrotrophic bogs from Southern Ontario

Abstract
To quantify the effects of human activities on atmospheric deposition of mercury in eastem Canada, an improved understanding of the natural variations of the concentrations, fluxes and sources of Hg over a long period of time is required. Peat cores from 3 sites in southern Ontario were used to reconstruct changes in atmospheric mercury accumulation rates for the past 10,000 years. The net mercury accumulation rates and excess mercury (mainly anthropogenic) were calculated using the long-terrn average Hg/Br and Hg/Se. The average background mercury accumulation rate during the pre-anthropogenic period was g m ^-2 yr ^-1. An excess of Hg was observed only once during that period, probably reflecting a change in climat. Mercury contamination from anthropogenic sources began about AD 1475 at the Luther Bog, corresponding to extensive biomass burning for agricultural activities by Native North Americans. During the late 17 and 18 centuries, deposition of anthropogenic Hg was at least equal to that of Hg from natural sources. Hg pollution increased again at the beginning of the 19 century. The maximum increase (up to 30 times) compared to "background" occurred during the 1950s, when the anthropogenic component represented up to 85% ofthe total atmospheric mercury deposition.