Diatoms as Bioindicators of Environmental Change in Cape Herschel and Pim Island (Nunavut, Canada) Ponds
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The High Arctic is especially sensitive to climatic change, but typically direct long-term monitoring data are lacking. Instead, paleolimnological approaches are now widely used to reconstruct past environmental changes. In particular, sub-fossil diatoms are well-established paleo-indicators of past limnological conditions. My thesis research is focused on Cape Herschel, east-central Ellesmere Island, as the numerous ponds in this region are well-studied and encompass a spectrum of morphometry, microclimate, and vegetation. This thesis has two separate but related chapters. The first chapter documents recent limnological changes and associated epilithic and surface sediment diatom assemblages from five well-studied Cape Herschel ponds, sampled on a semi-regular basis from 1987-2011. Diatom trends were reconstructed and compared to a suite of water-chemistry variables. Increased species diversity in both epilithic and surface sediments were observed, indicative of warming and associated longer ice-free growing seasons, allowing for the establishment of taxa with more complex lifestyles. These ponds also experienced increases in conductivity, dissolved organic carbon, dissolved inorganic carbon, and pH over the sampling period. Trends in diatom assemblage were more pronounced in epilithic samples (representing year-to year changes), when compared to surface sediments (an integration of multiple years of diatom production). Diatom assemblages from the Cape Herschel ponds were then compared to previously studied and near-by (~10 km away) Pim Island ponds. The latter ponds had a more muted response to recent climate warming, likely due to their colder microclimates linked to their close proximity to near-shore sea ice. The second chapter focused on diatom assemblages from sediment cores recovered from two Pim Island ponds. Diatom assemblages in both sediment cores recorded a recent shift from low diversity benthic fragilarioids to more diverse assemblages dominated by epiphytic taxa, with more complex growth forms. This shift in taxa and diversity reflects a warming environment and longer growing season, but these long-term assemblage changes were more muted when compared to the warmer Cape Herschel ponds. Taken together with previous studies, this research further demonstrates the sensitivity of diatoms to climatic changes.