Ecological change in freshwater ecosystems during the Anthropocene: The impacts of legacy pollution and emerging environmental stressors

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Human activities are having a profound impact on aquatic ecosystems degrading water quality and reducing biodiversity. In fact, lakes and rivers are some of the most impacted ecosystems on the planet and there is a growing need to understand how human actions are altering these environments, particularly over longer time scales (decades or longer) where data are scarce. This proposed program will employ both paleoecological techniques and modern sampling to investigate how human actions are altering lake ecosystems, with special focus on the highly biodiverse and productive nearshore environment (littoral zone). Specifically, this program will 1) investigate ecological resilience and recovery (if any) in lake ecosystems contaminated with legacy pollution and 2) determine the transport pathways and fate of microplastics in freshwater environments and assess how microplastics are interacting with littoral habitat (macrophytes, periphytic diatoms). Legacy pollution from historical mining activities is a global environmental problem with hundreds of contaminated sites across Canada. We have shown that many lakes in Cobalt, ON remain highly contaminated with arsenic and other metal(loids) nearly a century after mining has stopped. We have also shown that the response of bioindicators to this legacy contamination at a landscape scale is complex. To address this complexity, we will quantify temporal shifts in diversity in key bioindicator groups (diatoms, chironomids, Cladocera) from dated sediment cores to determine how the multiple stressors of historical contamination and climate change are impacting aquatic biodiversity. We will also examine how metal(loid) concentrations vary spatially within lakes, if macrophyte beds are serving as a sink or source of these metal(loids), and how periphytic diatom abundance and composition is altered over a gradient of arsenic contamination. Although understanding the long-term impacts of legacy pollution remains a priority there is also a need to increase our understanding of the impacts of emerging contaminants such a microplastics on aquatic ecosystems. To address this research priority we will investigate how microplastic concentrations and composition changes with water depth in lakes, varies spatially and temporally within rivers, and use large-diameter dated sediment cores to determine historical trends in microplastic concentration and composition. We will build on this knowledge by also examining how microplastics are interacting with biological components of these systems such as determining if microplastics are part of the periphytic community on macrophytes in lake and river systems. This program will provide important new data on how human activities are altering Canadian freshwater ecosystems across broad spatial and temporal scales and can also be used to set realistic restoration targets for legacy contaminated sites and inform future monitoring programs for emerging contaminants.