Beaver ponds increase methylmercury concentrations in Canadian shield streams along vegetation and pond-age gradients.

Beaver impoundments flood forested areas and may be important production sites for methylmercury (MeHg) because of the resulting enhanced microbial activity and oxygen depletion. The influence of 17 beaver impoundments on streamwater chemistry (total mercury (THg), MeHg, nutrients, cations, and anions)] was investigated by sampling sites located along vegetation and pond-age gradients in southwestern Quebec (Canada). Recently inundated beaver ponds (< 10 years old) and those located in coniferous watersheds had the highest MeHg concentrations (range, 0.

Seasonal and inter-annual variations in methyl mercury concentrations in zooplankton from boreal lakes impacted by deforestation or natural forest fires.

We compared the effects of natural and anthropogenic watershed disturbances on methyl mercury (MeHg) concentration in bulk zooplankton from boreal Shield lakes. MeHg in zooplankton was monitored for three years in nine lakes impacted by deforestation, in nine lakes impacted by wildfire, and in twenty lakes with undisturbed catchments. Lakes were sampled during spring, mid- and late summer.

Historical perspective of industrial lead emissions to the atmosphere from a Canadian smelter.

Dated sediment cores from four remote Canadian Shield headwater lakes, where atmospheric deposition has been the only input of anthropogenic Pb, situated along a transect extending 300 km from a nonferrous metal smelter, were analyzed for both lead concentrations and isotopic composition; porewater samples collected at the same sites were analyzed for Pb and other geochemical variables. The depth distributions of stable Pb isotope ratios show the presence of several isotopically distinct Pb types since the preindustrial period. Lead from the smelter emissions had an isotopic signature (e.

Mercury concentrations in fish from forest harvesting and fire-impacted Canadian Boreal lakes compared using stable isotopes of nitrogen.

Total mercury (Hg) concentration was determined in several piscivorous and nonpiscivorous species of fish from 38 drainage lakes with clear-cut, burnt, or undisturbed catchments located in the Canadian Boreal Shield. Mercury concentrations increased with increasing fish trophic position as estimated using stable isotopes of nitrogen (N; r2 = 0.52, 0.