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Modeling vertical diffusion in a shallow eutrophic reservoir

Transport phenomena are important drivers of water quality in natural waters. In lakes and reservoirs, vertical mixing through turbulent diffusion is expected to influence the relative dominance of problematic cyanobacteria to other algal taxa. Our study area is shallow embayments of Jordan Lake (North Carolina), that alternate between stratified and well-mixed conditions depending on wind and surface heat flux. In one embayment, solar-powered circulators were recently tested to determine if enhanced mixing can reduce algal blooms that are dominated by cyanobacteria in summer. To simulate vertical diffusion, a mathematical heat model with meteorological inputs is first constructed to predict time series of water-column temperature profiles. Non-linear optimization is applied to calibrate unknown parameters to within literature-specified bounds based on the fit of the model to in situ thermistor chain records. The model is evaluated using cross validation and through comparison with in situ estimates of diffusion obtained from a temperature microstructure profiler (SCAMP) and dye tests. The model is applied to simulate diffusion over a decadal period, and the impact of enhanced circulation is examined. Finally, we statistically assess potential relationships between diffusion and cyanobacteria dominance.

Yue Han (Primary Presenter/Author), NC State University, ;

Jeremy Smithheart ( Co-Presenter/Co-Author), NC State University,;

Robyn Smyth ( Co-Presenter/Co-Author), Bard College,;

Tarek Aziz ( Co-Presenter/Co-Author), NC State University,;

Daniel Obenour ( Co-Presenter/Co-Author), NC State University,;