The release of carbon and pollutants from eastern canadian watersheds in response to atmospheric deposition and climate change

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Canada's temperate and boreal landscapes host among the highest amounts and densities of lakes on earth. These lakes, most of them being hundreds to thousands of kilometers away from direct human activities, are experiencing changes in climate and atmospheric deposition of pollutants that disrupt the carbon and contaminant cycles, from their watershed to their water column. Past research has shown that lakes pH and concentrations of dissolved organic carbon (DOC) have been increasing in response to recovery from acidification, following legislation changes in the wake of widespread acid rain issues. These increases, which would in principle represent a return to pre-acidification conditions, have been accompanied by a loss in water transparency and shifts in thermal stratification, an increase in greenhouse gases emissions from aquatic ecosystems, and economic and health issues regarding drinking water treatment. Deposition of nitrogen and mercury have also decreased over the last decades, but the timing and amplitude of this decrease differed, and mercury persistence in watersheds may differ from that of ions and carbon. The cumulative effects of these trends in atmospheric deposition on the carbon and mercury cycles of Canadian temperate and boreal watersheds and lakes thus remain poorly understood. This proposal aims at filling this knowledge gap by building on extensive data available at Environment and Climate Change Canada at different spatial and temporal extents, including 100 lakes that have been sampled yearly since 1984 and 4 watersheds with contrasting climate and tree cover that have been monitored on a weekly basis since for several years in eastern Canada for geochemical properties in the water of lakes, streams, soils, throughfall and precipitation. We will complement these datasets by adding measurements of the composition of DOC as well as the concentrations of nutrients and different forms of total and methylated mercury in the water column of lakes and in key watershed compartments. Doing so, we will be able to better understand how industrial activities affect multiple facets of water quality at different spatial and temporal scales.