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The Laurentian Great Lakes region of North America contains substantial aquatic resources and mercury-contaminated landscapes, fish, and wildlife. This special issue emanated from a bi-national synthesis of data from monitoring programs and case studies of mercury in the region, here defined as including the Great Lakes, the eight U.S. states bordering the Great Lakes, the province of Ontario, and Lake Champlain. We provide a retrospective overview of the regional mercury problem and summarize new findings from the synthesis papers and case studies that follow. Papers in this issue examine the chronology of mercury accumulation in lakes, the importance of wet and dry atmospheric deposition and evasion to regional mercury budgets, the influence of land–water linkages on mercury contamination of surface waters, the bioaccumulation of methylmercury in aquatic foods webs; and ecological and health risks associated with methylmercury in a regionally important prey fish. [Copyright &y& Elsevier]

Water-covered lands comprise approximately 30% of the total area of the world’s boreal forest biome. Most of these lands are peatlands (i.e., bogs and fens), which store over half of the total carbon in the biome. Because climate warming threatens to alter the carbon stocks of peatlands, much attention has been devoted to understanding the climatic and hydrologic conditions that affect peatland biogeochemistry. However, there are other aquatic systems that are widespread in the boreal forest that also process and store carbon, including lakes and ponds. Although non-peatland aquatic systems cover a much smaller portion of the boreal landscape, they still contain approximately 15% of the total carbon pool for the biome, much of it stored as either profundal or littoral sediments. Further, the carbon dynamics of boreal lakes are dynamically coupled to watershed processes. Excepting major disturbances to boreal catchments, such as forest fires and forest harvest, surface waters are the only locations of net loss of carbon to the atmosphere. Our objectives are to review what is known about factors that affect lake ecosystem carbon dynamics in the boreal forest and to identify areas of study that we deem to be profitable for forecasting the impacts of climate change on carbon pools and flux rates. We primarily focus on the boreal forest of North America, but recognize that our findings may also be relevant for boreal areas of Fennoscandia and Russia. The following research priorities are identified: (i) estimation of carbon pools in profundal and littoral sediments across the boreal forest, (ii) warming experiments that include quantification of ecosystem carbon dynamics in addition to measuring changes to aquatic food web structure, (iii) whole system experiments to understand the hydrologic and biogeochemical conditions by which allochthonous carbon is integrated into aquatic food webs, especially in the context of increased nutrient concentrations associated with a warmer, and possibly drier, climate, as forecast for the southern boreal forest, (iv) watershed-scale assessment of carbon budgets for lakes that straddle transitional zones between the boreal forest and prairie-parkland, temperate forest or tundra, to detect evidence of ecosystem migration, and (v) integration of lacustrine carbon pools and flux rates into carbon budgets at scales that range from local watersheds to the boreal forest biome. [ABSTRACT FROM AUTHOR]