Limnology and paleolimnology of adjacent High Arctic lakes with an emphasis on terrestrial-aquatic linkages: Cape Bounty, Melville Island, Nunavut
Stewart, Kailey Amanda
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Our knowledge of how Arctic freshwater ecosystems will respond to continued climate change and variability is fundamentally limited by logistical difficulties of such remote research, resulting in relatively sparse long-term baseline data on these systems. This research applies a unique paired-watershed approach (i.e., two similar, adjacent lakes and catchments) to help address these limitations, which provided an opportunity to identify how broad-scale factors are filtered or modified by site-specific characteristics. My first main objective was to document the seasonal hydrochemical variability of runoff and influences on lake chemistry. Both lakes appear to be relatively insensitive to seasonal hydroclimatic variability, largely because periods of high discharge were also characterized by lower concentrations of dissolved and particulate matter, but also because of the relatively long lake water turnover time that suggests the effects of climatic and environmental changes would be felt later in these systems than in lakes and ponds with smaller lake volumes. My second objective was to investigate spatial and temporal trends in the lake diatom communities in order to refine subsequent paleoenvironmental reconstructions. A critical aspect of this objective was testing how faithfully the whole lake diatom community was represented in deep lake surface sediments where sediment cores are routinely collected. Most differences between the two lakes were largely accounted for with micro-environmental conditions associated with the specific sampling location. Also, both lakes exhibited a degree of disconnection between littoral benthic and profundal zones that manifested as an under-representation of the benthic community in deep lake surface sediments, with implications for paleoenvironmental interpretations. Finally, I present a multi-proxy record of environmental conditions in adjacent lakes spanning the period from pre-industrial times. Biogeochemical records reflected major changes in lake primary productivity and terrestrial organic matter accumulation beginning prior to 1950 in both lakes, pointing to profound environmental changes that culminated with the establishment of an appreciable diatom community in both lakes in the 1980s. Differences in the timing of changes between the two lakes point to differing threshold capacities to external forcings, and suggest that East Lake’s response to post-industrial climate change is advanced compared to West Lake.