Aquatic Ecosystem Protection Research Division, Environment Canada, Burlington, ON, Canada L7R 4A6, Centre d'e´tudes nordiques, Universite´ Laval, Quebec, QC, Canada GIV 0A6, Canadian Circumpolar Institute, University of Alberta, Edmonton, AB, Canada T6G 1K8, Algal Taxonomy and Ecology, Winnipeg, MB, Canada R3T 2X8, Department of Geography, Queen's University, Kingston, ON, Canada K7L 3N6, SETI Institute, Mountain View, California 94043-2172, United States, and Department of Biology, Queen's University, Kingston, ON, Canada K7L 3N6.
Mercury (Hg) profiles were compared to profiles of climate indicators including microfossil remains and algal-derived or S2 carbon (C) in dated sediment cores from 14 lakes spanning latitudinal and longitudinal gradients across the Canadian high and subarctic. Hg fluxes increased postindustrialization (post-~1850) in 11 of these lakes (postindustrialization Hg fluxes (?HgF(F)) = 2-24 µg m(-2) y(-1)). Correction of HgF(F) for catchment contributions demonstrated that Hg deposition originating from catchment-independent factors, such as atmospheric deposition, increased since industrialization in all 14 lakes. Several of these lakes also showed postindustrial shifts in algal assemblages consistent with climate-induced changes. Eleven lakes showed post-1850s increases in S2F(F), suggesting that lake primary productivity has recently increased in the majority of our sites (?S2F(F) = 0.1-4 g m(-2) y(-1)). Other studies have interpreted significant relationships between Hg:S2 concentrations in Arctic sediment as support for the algal scavenging hypothesis, which postulates that Hg fluxes to Arctic sediments are largely driven by S2. However, in six of our lakes we observed no Hg:S2 relationship, and in one lake a significant negative Hg:S2 relationship was observed due to increased Hg and decreased S2 C deposition during the postindustrialization period. In six of the seven lakes where a significant positive Hg:S2 relationship was observed, algal assemblages either did not change through time or the timing of the shifts did not correspond to changes in Hg deposition. Our results demonstrate that, although Arctic lakes are experiencing a myriad of changes, including increased Hg and S2 deposition or changing algal assemblages, increased lake primary productivity does not appear to be driving changes in Hg fluxes to sediments.