Limnological and paleolimnological investigations of environmental change in three distinct ecosystem types, Canadian High Arctic
Keatley, Bronwyn Elizabeth
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The biological remains preserved in the sediments of Arctic lakes and ponds in the Canadian High Arctic are important indicators of environmental change, especially as long-term instrumental data are often lacking. Although recent studies have underscored variability amongst these aquatic ecosystems, data are lacking from several key ecosystems. This thesis addresses some of these critical knowledge gaps in the Canadian high Arctic, using diatom-based limnological and paleolimnological techniques. First, I explore the limnology and diatom ecology along a gradient of bioclimatic zones on Melville Island in the western High Arctic. Lakes and ponds located in the most lushly vegetated zone were significantly different from those elsewhere on the island, both in terms of measured limnological variables and in terms of diatom assemblage composition. Diatom species distributions from Melville Island can best be explained by differences in pH and related variables. Secondly, ponds and lakes located in a High Arctic oasis on northern Ellesmere Island, recorded significantly higher specific conductivity, nutrients, and dissolved organic carbon than freshwater bodies from the surrounding polar desert. In Chapter 5, I provide an examination of long-term environmental change from Melville Island, a region of the High Arctic for which no paleolimnological data exist. The timing of diatom shifts in a dated sediment core from a small pond is consistent with the onset of climate warming in the early 20th century. Differences in ice cover have often been invoked to explain differences in the timing and magnitude of diatom shifts in the Arctic, but this hypothesis has not been explicitly tested. In Chapter 6, I compare two adjacent lakes with similar physical characteristics but different ice cover regimes from northern Ellesmere Island. I provide strong evidence that extended ice cover dampens diatom community responses to environmental change. In the final chapters, I determine that marine-derived nutrients significantly affect the limnology of ponds on Cape Vera, Devon Island, and are related to the degree of seabird influence. Although a portion of diatom species distributions can be linked to seabird influence, the most abundant taxa show little relation to the nutrient gradient. In a paleolimnological context, diatoms are not robust indicators of seabirds in High Arctic ponds.