Kapillesh Balasubramaniam, of the Paleoecological Environmental Assessment and Research Lab (PEARL) at Queen’s University has successfully submitted his MSc thesis, working under supervisors Dr. John Smol and Dr. Andrew Paterson: Have lakes within the Rideau Canal system responded to impacts of recent anthropogenic stressors over the past ~25 years: A diatom-based paleolimnological re-assessment.
His work revisited six lakes in the Rideau Canal system — Big Rideau, Upper Rideau, Lower Rideau, Indian, Lake Opinicon, and Otter Lake — using sediment cores collected in 2019 and 2020 to update paleolimnological studies conducted on the same lakes roughly 25 to 30 years earlier.
The approach relies on diatoms — microscopic, single-celled algae whose silica shells accumulate in lake sediments layer by layer over centuries. Different diatom species thrive under different conditions, making them reliable indicators of how a lake’s ecology has shifted over time. By comparing the diatom communities preserved at different depths in a sediment core, researchers can reconstruct environmental change going back well before any water quality monitoring program existed.
The cores studied captured roughly 150 years of lake history. Across all six lakes, the most dramatic ecological changes were not from the 19th century disruptions of canal construction — flooding, deforestation, major watershed upheaval — but from the past 25 to 30 years. That finding alone is significant.
Three potential explanations were considered and tested. Nutrient enrichment was ruled out: phosphorus levels have actually improved since the 1970s. Zebra mussels, which arrived in the Rideau system around 1990, were also ruled out, because the diatom shifts began before their documented arrival. The remaining explanation — and the one the evidence supports — is climate. Rising air temperatures and declining wind speeds are altering the physical structure of these lakes, producing longer periods of thermal stratification and reduced mixing. Those conditions favour small, buoyant planktonic diatom species and disadvantage heavier species like Aulacoseira that depend on water turbulence to stay suspended. The same conditions are consistent with the emergence of cyanobacterial blooms even as nutrient levels have fallen.
Big Rideau Lake showed an additional signal not seen in the other lakes: a clear increase in epiphytic diatoms — species that grow attached to aquatic plants rather than floating freely — over the past decade. Given the lake’s extensive shallow littoral zone, this may reflect changes in aquatic vegetation that are worth continued monitoring.
The thesis makes clear that the ecological changes now underway in these lakes are not new — they are an acceleration of trends that were already visible in the earlier studies conducted in the 1990s. That continuity is itself an important finding: it suggests these are not short-term fluctuations but sustained, directional shifts driven by a warming climate.
RLEF is proud to have supported this study.
Balasubramaniam, K. (2022). Have lakes within the Rideau Canal system responded to impacts of recent anthropogenic stressors over the past ~25 years: A diatom-based paleolimnological re-assessment. M.Sc. thesis, Queen’s University, Kingston, Ontario. Available via QSpace.