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 NH4 in waterbodies. My preliminary research suggests that this process may be significant in spring and summer. However, the rate at which DON is converted to NH4 as a function of depth in lakes has not been determined, a necessary step to estimate whole system rates. Therefore, I will measure depth integrated photoammonification in a diverse set of prairie and Precambrian Shield lakes in order to establish the relevance of this pathway. My next objective concerns the measurement of NO3, an important nutrient affecting water quality in lakes. NO3 is usually measured with colorimetric methods. However, colorimetric methods entail many steps and are prone to interferences. The second derivative UV technique for NO3 measurement is emerging as an alternative method; it is rapid, less prone to interferences, and generates less waste. However, this technique has not been tested in more challenging waters typical of prairie regions (e.g., of greater conductivity and higher dissolved organic carbon concentration). My preliminary analyses indicate that both techniques differ greatly in estimating NO3 in such waters. Therefore, I will compare their performance and determine if the second derivative technique is suitable for NO3 measurement in prairie waterbodies. These studies will advance our understanding of biogeochemical processes in lakes and reservoirs, and ultimately aid in the management and protection of inland waters.