FRESHWATER DIATOM PALEOECOLOGY OF BANKS ISLAND, N.W.T., CANADIAN HIGH ARCTIC
LIM, DARLENE S.S.. University of Toronto.
Douglas, Marianne S.V.. University of Toronto.
Smol, John P.. Queen's University.
The Canadian High Arctic is a distinct region of our planet in the way that it supports like, responds to shifts in the climate, and affects the environments of the rest of the globe. With the need to better understand the far reaching effects of high arctic climate change, comes the demand for continued immediate and long-term monitoring of the High Arctic. However, this is a difficult region to monitor on a frequent basis due to financial and logistical constraints (Douglas & Smol 1993), and relatively little ecological baseline data exists for many areas throughout the High Arctic. The situation is slowly being rectified through limnological and paleolimnological investigations that allow for the acquisition of both baseline and historical limnic data from the myriad of lakes (depth>2m) and ponds (depth<2m) that dot the landscape of the High Arctic.
Lake and pond sediments preserve many biological indicators that can serve as proxy indicators of past environmental changes. More specifically, in the oligotrophic lakes and ponds of the High Arctic, diatoms (class Bacillariophyceae) often are a significant part of the algal community (Douglas & Smol 1999). Their fossilized siliceous remains are usually well preserved in stratigraphic deposits, and are used as bioindicators in our investigations of past physical and chemical limnic conditions.
In the High Arctic, surface sediment samples (~ top 1cm) represent an integrated sample of diatom communities, both spatially (i.e. from various habitats) and temporally (i.e. last few years of deposition). A quantitative relationship between the dominant surface sediment diatom assemblages and present-day limnic properties can be established in order to produce environmental reconstruction models. This study focuses on the development of a calibration set for Banks Island, NWT, Canadian High Arctic, and the application of this environmental reconstruction model to a 34cm core taken from lake BK-AH (73º35.57N, 119º35.01W) on Banks Island, which is the southwestern most island of the Canadian Arctic Archipelago. The calibration set construction is currently in progress, however all results to date, including general trends driving species variance amongst the sampled sites, are described in this poster presentation. The completed calibration set will be applied to the core findings from both sites. Core stratigraphies are also presented in this poster.
A total of forty-six lakes and ponds were sampled on foot and via helicopter throughout Banks Island over a three and a half week period. These sites were selected in order to cover as wide an environmental gradient as possible (e.g. proximity to sea, altitude, size, drainage characteristics, etc.). While all sites were sampled for both abiotic and biotic limnological components, only 36 sites of the entire sample set were appropriate for surface sediment diatom collections, and are herein described and analyzed in this poster presentation. Of this subset of sites, nine were lakes, and the remaining 27 were ponds (maximum depth <2m). Although over 250 diatom species were identified from the surface sediments, only those taxa that had a relative abundance of ( 1% in a minimum of three sites were included in the ordination analysis/calibration set construction. The dominant diatom species identified were pennate and benthic, which is typical for high latitude oligotrophic lakes and ponds. Overall, compared to other previously investigated high arctic islands such as Bathurst Island (Lim et al. 2001), the limnology and diatom community composition of the sampled sites on Banks Island are much more diverse, most likely as a result of the varied elevation, vegetation and surficial material across the island. Preliminary Canonical Correspondence Analysis (CCA) results indicate that the first two axes of the ordination captured 28.1% of the cumulative diatom-environment relation, however this value is expected to increase as further analyses are conducted to identify the key limnological drivers for the diatom species distribution. Overall, it appears that Axis 1 of the CCA is most strongly driven by temperature (TEMP), conductivity (COND), DOC/DIC and chlorophyll a (uncorrected) (CHLA-U) concentrations. Axis 2 represents an ionic gradient, driven primarily by Al+, Fe3+ and Zn+. These CCA data will comprise the foundation of the calibration set construction for Banks Island.
Core findings from site BK-AH show a shift in from greater diatom diversity between 0-7cm to a dominance of Fragilaria brevistriata, Fragilaria pinnata, and Fragilaria construens throughout the remainder of the core (7-34cm). Although all three Fragilaria species are present throughout the core, their presence significantly (R=0.84) increases downcore, while overall diatom species diversity decreases from top to bottom. Douglas et al. (1994) and Lim et al. (2001) identified F. pinnata and F. construens as being associated with deeper, colder, more oligotrophic sites, thereby indicating that a potential shift in nutrient and temperature regimes from less to more nutrient rich conditions relative to its past state may have occurred in the Banks Island lake. This hypothesis will be refined once the calibration set is constructed and applied to the core stratigraphy.
Next steps include completing the calibration set and applying it downcore, as well as comparing these findings to additional cores taken from two other sites on Banks Island, and other high arctic sites such as Cape Herschel, Ellesmere Island, Nunavut (Douglas et al. 1994), and the Grinnell Peninsula on Devon Island, Nunavut (Lim et al. in progress).
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