| Summary: | Unusually high levels of mercury (Hg) have been detected in several northern Canadian lakes, remote from human industrial activities. At Kusawa Lake, a subalpine glacier-fed mountain lake situated in the Yukon Territory (western Canada), measurements of Hg in caught fish are below, but worryingly close to, the Health Canada guideline for safe fish consumption of 0.5 μg g-1. The sources of the Hg found in the fish of Kusawa Lake (and many other northern lakes) are still unidentified. A suspected pathway for Hg input to freshwater ecosystems is through long-range atmospheric transport and direct or indirect deposition in water and/or snow-covered surfaces, later released to aquatic ecosystems through spring/summer melt and runoff.The objective of this thesis is to estimate the maximal potential contribution of atmospheric Hg released by snow- and ice melt that could enter Kusawa Lake through runoff from snow and glacier ice melt. Hg data previously obtained from the Kusawa Lake catchment were used to estimate the possible range of Hg concentrations in snow and ice. To quantify the input of Hg from snow and ice melt into Kusawa Lake, the total water inflow from these sources first had to be estimated. This was done by using the HBV hydrological model (Hydrologiska Byråns Vattenbalansavdelnings modell), initially developed by the Swedish Meteorological and Hydrological Institute (SMHI), and subsequently modified to include a glacier routine. The HBV model was run using temperature and precipitation data from the nearby city of Whitehorse (~60 km east of Kusawa Lake), and was calibrated using historical hydrometric data from the Kusawa Lake catchment itself.Using these data and the HBV-simulated runoff, the total flux of Hg entering Kusawa Lake trough snow and glacial melt water was estimated to be 550 ± 495 g yr-1 (3.6 ± 3.5 μg m-2 yr-1). This flux comparable in magnitude with model-based estimates of the total atmospheric deposition of Hg in the Yukon region, which range between 4.5 and 7 μg m-2 yr-1. This suggests ...
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