Michelle Cheng MSc Candidate, SMOL LAB Assessing lake ecosystem recovery from acidification and responses to emerging environmental stressors in a suite of lakes from Sudbury, Ontario, Canada Mining and smelting activities have strongly influenced the Sudbury (Ontario, Canada) region since the late 19th century, leading to acidification and metal contamination in many local ecosystems. Regulations on restricting acidic emissions were enacted in the 1970s, after which a considerable volume of paleolimnological work was completed to study the impacts of acidification and metal deposition on Sudbury-region lakes and their subsequent biological recovery. Twenty years after the last regional diatom-based assessment, many lakes have undergone large changes in limnological variables, including increases in pH and dissolved organic carbon concentrations, as well as decreases in metal concentrations. Additionally, these lakes are under the potential impacts of newly emerging environmental stressors such as climate warming and road salt contamination. Here, I revisited a suite of Sudbury-region lakes (n=80) by examining their current water chemistry and diatom assemblages preserved in surface sediments. A canonical correspondence analysis was used to assess the relationships between diatom assemblage composition and environmental variables. Although the pH gradient in my study lakes is shorter than earlier calibration studies conducted in this region by more than one pH unit, lakewater pH was still identified as the strongest environmental variable shaping diatom distributions and so was used to construct a robust inference model (R2boot=0.73; RMSEP=0.32). By assessing ecological changes experienced by Sudbury-region lakes over the past few decades, I identified two major trends: an overall increase in diatom-inferred pH, and a rise in the relative abundance of planktonic taxa. Lastly, several down-core analyses were conducted to assess detailed ecological changes of Sudbury-region lakes over the past ~150 years. Although some lakes are tracking recovery in diatom assemblages, other lakes have less clear ecosystem trajectories.
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