A Paleolimnological Assessment of Cladoceran Assemblage Changes in Two Lakes from Northern Ontario’s “Ring of Fire”
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The Northern Ontario “Ring of Fire” (RoF) contains vast mineral deposits that have sparked considerable interest over the past decade, regarding regional mining and infrastructure development. Little is known about the current limnological or ecological changes occurring in this area prior to industrial development. Paleolimnological techniques were therefore used to assess changes over the past ~150 years in the cladoceran sedimentary assemblages, production and predation regimes of two strategically selected lakes. This study provides historical context on ecological variability in the region, prior to the onset of development. Sediment cores were obtained from Eabamet and McFaulds lakes located near the RoF during the summer of 2012. Significant shifts were present in the cladoceran assemblages of both lakes, with increasing relative abundances of pelagic taxa in the more recent sediments. A cluster analysis of the McFaulds Lake assemblage data detected a primary split around the mid-1990’s, consistent with warming air temperature in the vicinity of Hudson Bay. Trends in production coincide with recent warming, as inferred chlorophyll-a increased in the recent sediments, likely due to a longer ice-free season providing an extended growing period for phytoplankton. Average Bosmina mucro length also increased in the recent sediments. In contrast, the cluster analysis of the cladoceran sedimentary assemblages in Eabamet Lake experienced an earlier change ~1960, prior to the recent warming, and is likely associated with the construction of an upstream dam in the late-1950’s. Finally, a lack of change in the Bosmina size structure of Eabamet Lake suggests a stable predation regime over ~150 years. This investigation provides long-term ecological information to an under-studied region and demonstrates current stressors on aquatic communities in the RoF.