by Kira Jordun

With an area of approximately 4,848 square kilometers, Lake Nipigon is the largest water body entirely within the borders of the province of Ontario and serves as a major headwater to the Great Lakes-St. Lawrence waterway system. Sometimes referred to as Canada’s “forgotten Great Lake,” Lake Nipigon represents a unique aquatic ecosystem that has been markedly altered by human activities. Pollution associated with large-scale industrial projects, including water diversions for hydroelectric power generation, has contributed to degraded water quality and environmental health. Members of the Biinjitiwaabik Zaaging Anishinaabek (BZA) have raised concerns over these impacts, emphasizing the threat of rising mercury levels to the health of local fish populations, as well as the downstream transport of contaminants originating from mining operations.

Despite its considerable size and ecological significance, the lake has been historically overlooked by Western science, with the most recent intensive limnological study conducted in 1923, prior to the introduction of anthropogenic stressors. Consequently, there is limited understanding of the cumulative effects of industrial developments and the emerging impacts of climate warming, which include changes in water temperature, snow and ice cover, and precipitation regimes. To address these critical knowledge gaps, paleolimnological methods offer a means of assessing how the lake ecosystem has changed over time.

Paleolimnology is a multidisciplinary science that uses physical, chemical, and biological information preserved in sediment profiles to reconstruct past environmental conditions. As sediments settle within a lake basin, a stratigraphic archive develops with the oldest material buried deepest and successive deposits accumulating above. Researchers collect sediment cores from lakebeds and analyze their layered contents to establish a chronological record of ecosystem changes. Such insights are particularly valuable in areas like Lake Nipigon, where direct monitoring data is unavailable.

Under the guidance of Professor Joshua Thienpont, my EUC Undergraduate Research Award endeavored to reconstruct past environmental conditions in Lake Nipigon using chemical indicators – specifically, total mercury (THg), total organic carbon (TOC), and elemental carbon-to-nitrogen ratios (C/N ratio) – to understand climate-driven changes in the ecosystem, with a focus on its southern bays. Sediment cores extracted from the nearshore areas of Shakespeare Island, Wabinosh Bay, and McIntyre Bay were sectioned into 0.5 cm intervals. Approximately 0.1250 g of sediment per interval was weighed into nickel sample boats and analyzed for total mercury concentration using a Milestone DMA-80 Direct Mercury Analyzer. Additional sediment from each interval was pre-treated in concentrated hydrochloric acid for 48 hours to remove inorganic carbon, re-neutralized with distilled water, and freeze-dried. The amount of organic carbon and nitrogen in these samples was subsequently determined using an Elementar UniCube Elemental Analyzer. I used generalized additive models to examine how THg, TOC, and C/N ratios vary with sediment depth, and to detect significant periods of change in these indicators.

Preliminary results revealed significant trends in THg concentrations towards the surface (in more recent time periods) at all study sites, indicating a recent rise in mercury inputs to the lake ecosystem.  Importantly, while all sites demonstrated increasing trends in THg, measured concentrations in all intervals from these southern bays of Lake Nipigon were well below the Canadian interim sediment quality guideline of 0.17 mg/kg for freshwater sediments, suggesting adverse biological effects on aquatic life are unlikely to occur. Mercury concentrations in sediments are typically low when organic carbon concentrations are low, since organic matter plays a critical role in binding and retaining mercury, and thus I will be looking at co-occurring trends with the other elemental indicators I analyzed.

These findings will be incorporated into a broader multi-proxy paleolimnological investigation – conducted in collaboration with BZA and researchers at Lakehead University – that integrates analysis of biological indicators with sediment geochemistry. The objective of the project is to generate a holistic understanding of environmental changes in the Lake Nipigon watershed.

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Kira Jordun is a recipient of EUC’s Undergraduate Research Award (EUCURA) in Summer 2025. She is currently pursuing an Honours Degree in Geography at York University. Her current research involves analyzing lake sediment samples from the southern bays of Lake Nipigon to understand climate-driven changes in the ecosystem, including overall lake productivity. In exploring Lake Nipigon’s environmental history through the EUCURA project, she took part in a collaborative scientific effort to illuminate the cumulative impacts of climate change and human activities on this understudied ecosystem, while gaining invaluable training and mentorship in environmental research practices.