Climate change and nutrient enrichment altering sedimentary diatom assemblages since pre-industrial time: evidence from Canada’s most populated ecozone

Abstract

Lakes worldwide are under threat by a myriad of environmental stressors that have been increasing in number and magnitude. These stressors can be regional such as climate change, or local such as nutrient-rich runoff, invasive species, and road salt contamination, to name but a few. To protect lake ecosystems from further deterioration, we need long-term data to define pre-disturbance baselines and to identify stressors that are causing the greatest ecological changes. Paleolimnology is an effective approach to reconstruct limnological history, providing an important window into past changes. Here, we applied paleolimnological tools to explore the pre-industrial and contemporary diatom assemblage changes of 27 lakes located in the most populated ecozone in Canada, the Mixedwood Plains. We also examined a full sediment core for Lac des Chicots (Southern Québec), aiming to disentangle the impacts of natural versus anthropogenic interactions and to assess their relative effects on the lake’s biotic structure. Our ordination analysis suggests that the Mixedwood Plains lakes have experienced varying lake-specific ecological changes over the past ~150 years, with two major trends across most study lakes: (1) a prevalent increase in planktic species, and (2) a rise in mesotrophic/eutrophic taxa in lakes receiving high human impacts. Our case study of Lac des Chicots identifies ecological impacts from both historical natural events and recent human activities, such as cultural eutrophication and climate warming. Overall, our study demonstrates that lakes in the Mixedwood Plains ecozone have experienced marked ecological changes that are mainly associated with human impacts.