Grant: Discovery Grants Program - Individual

In recent decades, organic carbon (C) concentrations have increased in many lakes across the Northern Hemisphere (i.e., often referred to as "lake browning"), with profound implications for aquatic ecosystem services (e.g., water quality, fishing, and recreation) and the role lakes play in the global C cycle. This browning trend is projected to continue with global climate change, which will be particularly pronounced in northern environments, including the Canadian boreal forest. Long-term data on appropriate spatial and temporal scales are needed to understand the impacts of climate change and other environmental stressors on lakes across this vast and remote landscape. My research program uses physical, chemical, and biological information preserved in lake sediments to understand how lakes and the surrounding landscape change over decades to millennia, and is specifically focused on assessing natural and human-induced impacts on C dynamics between the terrestrial and aquatic environments, and the resulting implications for aquatic ecosystems. Over the next five years, my objectives are to assess how regional and global environmental changes drive long-term C dynamics in eastern Canadian boreal lakes. Theme 1 will use established and newly developed paleoenvironmental techniques to examine long-term trajectories of lake browning (or "re-browning" if lakes are recovering from past impacts) along a 600-km long environmental gradient in NW Quebec. By using a strategically selected lake set along this gradient, my students and I will be able to determine natural variability and baseline conditions prior to significant human disturbances, and to disentangle and identify individual contributions of multiple natural and anthropogenic stressors (e.g., climate change, acid and nutrient deposition) to changing lake-water organic C concentrations over time. Theme 2 will test the hypothesis that climate-driven changes in forest fire regimes co-determine long-term lake browning trends in boreal lakes. By using lakes with known forest fire histories over the past ~50 years, my students and I will examine how forest fire extent, severity (crown vs. surface fires), and frequency define post-fire trends in lake-water organic C. Additionally, we will quantify total and black carbon pools (forest-fire derived C) in lake sediments to provide much needed empirical data regarding the role of northern boreal lakes as long-term C sinks in the global C cycle, and to assess how ongoing environmental changes alter the size of this sink. Organic C dynamics play a key role in the functioning of aquatic ecosystems, and the results of these projects will provide critical data regarding our abilities to assess current and to predict future browning trajectories as well as associated chemical and biological responses in lake ecosystems. Such data will provide key information to policymakers and other stakeholders for effective lake management.