Coupled Aquatic Biogeochemical Cycles in the Anthropocene

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Lakes and rivers provide essential aquatic ecosystem services to Canadians including water to drink, recreational opportunities, inland fisheries, and spiritual fulfilment. However, freshwaters and their biodiversity are under serious threat from agricultural intensification, increased urbanization and climate changes. These pressures contribute an excess of nutrients to aquatic ecosystems and result in eutrophication, which is an over-proliferation of plant life. This can result in the presence of toxic cyanobacteria, habitat degradation, and low oxygen levels in the water. Yet some water bodies can withstand eutrophication better than others because the surrounding landscape has different physical features that influence their ability to process or metabolize what enters them and thereby to maintain a healthy state. However, this relationship remains poorly understood. Developing new knowledge to better quantify the relationships among human-related, physical, and biological features in a watershed is imperative to make evidence-based decisions to manage our freshwaters sustainably. Therefore, the purpose of this program is to characterize the interaction of control points at the watershed scale to understand the metabolic potential of river networks. Control points are areas in the landscape or moments in time that have a disproportionate influence on the biogeochemical stock or flux of elements, in this case carbon, nitrogen, and phosphorus. In a watershed, activities on land represent what the receiving water will `eat'- where excess nutrients from different human activities may act as control points. The first step of the program will be to quantify how humans are altering nutrient fluxes to rivers across Quebec at scales that are relevant to management. In a second step, we will disentangle how rivers with different shapes and configurations are able to process or metabolize what enters them. Why do some rivers remain "healthy" while others do not? What amount of nutrients can a river safely `eat' and for how long? We will answer these questions using long-term data sets, remote sensing, field sampling including the use of high-resolution sensors, and advanced modelling to understand how concentrations of carbon, nutrients, and different biological gases change across rivers with varying shapes and land uses through seasons and under different climates. A diverse group of 11 students will receive multidisciplinary training as ecosystem scientists and in scientific communication through my program. Knowledge generated by their training will inform management by filling in gaps about the dynamic nature of biogeochemical processing in widely used river models, and identifying points of intervention in specific watersheds. Furthermore, new approaches aimed at better characterising watershed development thresholds generated through this program will contribute to the long-term sustainability of aquatic ecosystem services.