The role of river biogeochemical function in the watershed eutrophication cascade

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Eutrophication (proliferation of nuisance and harmful algal blooms) is caused by excess nutrients, phosphorus, P, and nitrogen, N, from agriculture and wastewater. This is a major global source of water-quality impairment, and an urgent and pervasive threat to Canada's water security. Eutrophication costs ~$8.3billion/year in the Canadian Great Lakes basin alone. The long-term goal of this research is to forge novel quantitative understanding of the drivers of freshwater eutrophication, from local to global scales. This research is needed to guide cost-effective water-quality management and to improve aquatic environmental health, which is also increasingly threatened by climate and land-use change. This 5-year research program focuses on understanding the instream processes that control the cycling, transport and cascade of nutrients through watersheds. Instream biogeochemical processes can retain nutrients and function as an important `self-cleansing' service, by regulating downstream delivery of P and N, and reducing eutrophication risk in lakes and other receiving water bodies. However, our understanding of these instream processes is mostly limited to small wadeable streams during low-flow conditions. Larger deeper rivers are predicted to be more efficient at retaining nutrients under higher flows (which is when most watershed nutrient export occurs) and may therefore play an pivotal role in reducing downstream eutrophication risk. However, data to verify this are currently lacking. This program will address this important shortfall, through novel applications of in-situ sensors and high-resolution hydrochemical monitoring (which can be safely undertaken in large rivers and under high flows) to quantify the functional capacity of streams and rivers to retain P and N across the entire flow regime. The program will provide training for two PhD students and two MSc students, combining field and laboratory biogeochemistry, with cutting-edge skills in the use and application of in-situ hydrochemical sensors, along with sophisticated data-analysis techniques. These skillsets are increasingly sought-after by employers in research, environmental agencies and water utilities. The PhD and MSc trainees will use these tools and technologies to explore the role of river biogeochemical function in diminishing or amplifying downstream nutrient flux transmission and eutrophication risk. The program will examine whether wastewater effluent and other `point' sources that discharge into rivers semi-continuously (and can cause chronic baseline river water-quality impairment) degrade river `self-cleansing' capacity. If so, reducing point-source nutrient inputs could have major additional co-benefits by enhancing the `self-cleansing' capacity of rivers to retain nutrients from wider agricultural sources, delivered under high-flows. This would have profound implications for eutrophication management in Canada and internationally.