Diatoms as Indicators of Environmental and Climatic Change in Peatlands and Lakes Located Across the Boreal Shield and Hudson Bay Lowlands of Canada

Abstract

Long-term monitoring data and paleoecological records are lacking in the Far North of Ontario (~50- 57oN, 79-94oW), a region of ecological and economic significance to Canada. As a landscape covered by extensive peatland complexes, accumulating vegetation (and carbon) since de-glaciation, and tens of thousands of lakes, there is an opportunity to interpret past environmental changes from paleoecological records, and place current climatic and other environmental changes within a longer-term perspective. This thesis addresses this knowledge gap by using archives from peatlands and lakes in the Far North of Ontario to understand environmental changes over the past ~100 to 2000 years. Given that peatlands act as an interface between terrestrial and aquatic environments, finding reliable biotic proxies with well-defined ecological optima is challenging. I use diatoms primarily to track changes in macro-vegetation type, pH and water table position across northern peatlands. Diatom assemblage composition was influenced by both the broader peatland type (i.e., bog, rich and poor fens) and microhabitats within peatland formations (e.g., hummock, hollows). The responsiveness of diatoms to chemical and moisture gradients was used to infer past environmental information archived in peat deposits. Changes in diatom composition from three peat cores reflect hydrosere succession, including past fluctuations in connectivity to the water table and pH. Approximately 600 years ago, synchronous changes in diatoms and testate amoebae infer drying conditions and subsequent microhabitat variations. To understand the response of aquatic biota to climate change over the past ~150 years, and provide detailed baseline ecological information prior to impacts from future mineral extraction and infrastructure development, sedimentary chlorophyll-a, diatom and cladoceran assemblage composition were examined in four lakes across the “Ring of Fire”. Over the past ~150 years, the most notable change was a shift from littoral/benthic dominated assemblages to greater abundances of pelagic Cladocera and planktonic diatom taxa. An increase in planktonic taxa is consistent with warming-induced changes in lake properties including longer ice-free periods and changes in aquatic habitat availability. Collectively, these results help distinguish the ecological response to anthropogenic warming from both natural variation and future resource extraction.