Novel Biogeochemical Pathways, Patterns and Measurements of Nitrogen and Phosphorus in Lakes and Reservoirs

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This proposal examines the abiotic and biotic factors, including human, that affect biogeochemical processes and water quality in aquatic ecosystems. The factors giving rise to cyanobacterial blooms and their toxins are under intense research. Concern over the loss of ecosystem services (e.g., water quality) has been a major focus. However, only recently has the effect of cyanobacteria on ecosystem function been considered. Cyanobacteria have widespread impacts on food webs through toxin production, resistance to grazing and as poor food quality for grazers. Hence, when lakes are dominated by cyanobacteria their planktonic food webs should be functioning inefficiently. I will test this hypothesis with novel techniques that directly measure food web turnover efficiency. My next objective is to compare two important biogeochemical pathways of P in Lake Diefenbaker (SK). Loading of P from rivers into reservoirs is often a major determinant of water quality. Similarly, planktonic P regeneration is known to be important to maintain productivity. However, the importance of each pathway relative to the other is unknown, despite the potential significance of these processes for lake and reservoir management. Therefore, I propose to measure and compare both pathways in Lake Diefenbaker. My third objective is to determine whole-lake rates of photoammonification. This is a process by which dissolved organic nitrogen (DON) is photodecomposed to the bioavailable nutrient NH