Understanding the interaction between the response of a complex ecosystem to climate change and the protection of vulnerable wildlife species is essential for conservation efforts. In the Northwest Territories (Canada), the recent movement of the Mackenzie wood bison herd (Bison bison athabascae) out of their designated territory has been postulated as a response to the loss of essential habitat following regional lake expansion. We show that the proportion of this landscape occupied by water doubled since 1986 and the timing of lake expansion corresponds to bison movements out of the Mackenzie Bison Sanctuary. Historical reconstructions using proxy data in dated sediment cores show that the scale of recent lake expansion is unmatched over at least the last several hundred years. We conclude that recent lake expansion represents a fundamental alteration of the structure and function of this ecosystem and its use by Mackenzie wood bison, in response to climate change.

No abstract

The early settlement history of Canada's National Capital Region, including Ottawa (Ontario) and Gatineau (Québec), was shaped in large part by the towering eastern white pine (Pinus strobus) forests that once covered the Ottawa Valley and fuelled a lucrative lumber export industry spanning the 19 th and much of the 20 th century. Some of the first dwellings and farmsteads of this era are still standing and serve as reminders of this history. A crucial piece of information in the assessment of a structure's heritage value is its date of construction. Unfortunately, this information is not always known and is approximated based on construction styles and other sources of information. In this study, dendroarchaeology methods are applied to constrain the construction dates of six historic structures in the National Capital Region of 19 th century vintage. A multi-century (AD 1670-2009) eastern white pine ring-width chronology was developed for dating the study structures using cross sections from sunken logs recovered from the Ottawa River and cores from live trees from the Petawawa Research Forest. The tree-ring inferred construction dates for the six structures ranged from 1830 to 1878. For most structures, historical records about the property or first inhabitants were available to corroborate the results. The ring-width chronologies of the individual structures were well correlated with the regional chronology (ravg = 0.63, p < 0.01), and this regional coherence clearly demonstrates the value of tree-rings for heritage structure assessments and reconstructing the settlement history of this region.

The inundation of terrestrial vegetation 10 following landscape flooding is an important potential 11 source of mercury to aquatic ecosystems, and may 12 modify mercury cycling, such as through increased 13 methylation. In the Great Slave Lowlands of Canada's 14 Northwest Territories, remarkable landscape flooding 15 has occurred over the recent past, which is the most 16 notable in at least the last several centuries. The 17 potential for this flooding to increase inorganic 18 mercury flux to the lakes of the region has not yet 19 been explored. In this study we used sediment cores 20 from five lakes experiencing a range of recently 21 documented lake expansion to test whether inundation 22 of terrestrial areas has increased the total mercury 23 concentrations in sediments, and resulted in increased 24 total mercury flux. Increases in sedimentary mercury concentrations and fluxes in sediment cores from the expanding lakes were relatively small and within the range of non-expanded systems, suggesting that, to date, flooding has not resulted in major total mercury enrichment, unlike in experimental and natural reservoir impoundments. The potential for increased methylation of existing inorganic mercury following expansion was not explored in this paper because methylmercury is dynamic in sediments and does not preserve well, but is an important consideration for future work.

Spatial and temporal variations in total mercury (Hg), organic matter and lake surface area were assessed to determine if flooding in the Mackenzie Bison Sanctuary (MBS) was influencing Hg inputs to lake sediments. Mercury concentrations in the sediment of all lakes examined are below established guidelines. All lakes demonstrated increased Hg concentration and flux over the past century. Two expanding lakes exhibited maximum total Hg values in surface sediments which correlated with peaks in water surface area and changes in source of organic matter. Reference lakes demonstrated declining total Hg values in recent sediments and no correlation with organic matter or water surface area. This study presents land users and managers with a preliminary assessment of Hg concentrations within MBS lakes. Recommended future work should focus on methyl mercury concentrations and methylation rates in sediments, which often increase after landscapes are flooded, and can pose risks to wildlife species relying on the ecosystem. iii ACKNOWLEDGEMENTS