Mercury distribution in water and permafrost of the lower Mackenzie Basin, their contribution to the mercury contamination in the Beaufort Sea marine ecosystem, and potential effects of climate variation.

摘要

High levels of mercury (Hg) have recently been found in marine mammals in the Beaufort Sea, causing concerns over the health of the marine ecosystem and of indigenous people who consume marine mammals as part of their traditional diet. As part of a long-term research program aiming to probe the causes of such high Hg contamination, this thesis investigates the distribution and speciation of Hg in water of the lower Mackenzie River and in permafrost along the southern Beaufort Sea, their contribution as Hg sources to the Beaufort Sea, and their potential response to climate warming in the region.; The Mackenzie River is the largest water and sediment source to the Beaufort Sea. Five sampling campaigns were carried out between 2003 and 2005 throughout the lower Mackenzie Basin. Large seasonal and annual variations of Hg were observed, with higher water levels resulting in higher Hg levels. This suggests additional Hg sources at high water levels. For the period of 2003-2005, the Mackenzie River discharged an average of 2.2 +/- 0.9 tonnes of Hg/year, of which approximately 15 kg was in the form of methylmercury (MeHg). The fact that approximately half of the annual Hg discharge occurs during the spring freshet is of concern to marine mammals, as this is the time of the year when marine mammals grow rapidly after a long winter, and hence would bioaccumulate more Hg in doing so. Higher fluxes of Hg and McHg are expected from the Mackenzie River with projected climate warming in the area.; Rates of permafrost melt and coastal erosion along the southern Beaufort Sea coast are high, and likely to increase with climate change. Several permafrost cores were sampled along the Canadian portion of the Beaufort Sea coast showing two distinct types of profiles. Using published estimates of permafrost melt and coastal erosion, it was estimated that approximately 610 kg of Hg are degraded into the Beaufort Sea annually. As increases in temperature, open water season, storms, large waves, and sea level are predicted, it is very likely that permafrost degradation will increase.