DIATOM-INFERRED CHANGES IN EFFECTIVE MOISTURE FROM GALL LAKE, NORTHWESTERN, ONTARIO, OVER THE PAST TWO MILLENNIA
Haig, Heather A.
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The boreal forest of Canada extends across 58% of Canada’s land area providing a large range of ecosystem services including flood control, water filtration, and carbon storage. Despite conservation efforts to protect this ecosystem, the boreal region is still under stress from global stressors including climate change. Anthropogenic climate-change is expected to raise temperatures and decrease precipitation over much of the boreal region increasing the duration and magnitude of droughts. This potential change to a more arid climate could have drastic affects on water levels and stream flows across much of the boreal region. Changes in hydrology, as a consequence of anthropogenic climate change, may result in large changes to aquatic ecosystems. To assess the susceptibility of lakes to climate in northwestern Ontario over the past two millennia, sediment cores from a headwater lake were obtained from near-shore cores to reconstruct changes in drought. The cores were located at a depth where changes in pelagic and benthic diatom assemblages (P: B boundary) were apparent in modern-day sediments because the location has been shown to be susceptible to change. The lake chosen for reconstruction was Gall Lake, a small (surface area = 19 ha, max depth = 18 m, mean depth = 8.5 m), mesotrophic lake (total phosphorus (TP) level of 12.3 μg/L, July 2008), with a gentlysloping eastern basin. This headwater lake in the Winnipeg River Drainage Basin (WRDB) is part of a hydrologically-rich region that is expected to experience increased aridity. Multivariate analysis of diatom assemblages over the past two millennia suggested that the instrumental record does not encompassed the natural variability of this system. The largest decreases in diatom-inferred (DI) depth were synonymous with iii the Medieval Climate Anomaly (MCA), a phenomenon not yet observed this far northeast in North America. The MCA has been proposed as a surrogate for climate change over the next century, therefore the prolonged aridity observed in Gall Lake could aid in the calibration of general circulation models currently used to forecast changes in climate, as well as a scenario that can be used to develop adaptation strategies to future environmental change.