Physical measurements and nearshore nested hydrodynamic modeling for Lake Ontario nearshore nutrient study

Application of a well-known hydrodynamic code for the Great Lakes was evaluated for its effectiveness, using a nested modeling approach, to examine nearshore physical processes in connection with the 2008 Lake Ontario Nearshore Nutrient Study (LONNS). The purpose of LONNS was to examine possible causes of nearshore eutrophication, and as a subset the goal of this study was to develop a framework for understanding the role of physical processes in nearshore eutrophication problems (e.g., benthic algae blooms). A relatively fine scale (200. m) nested model was interfaced with a coarser scale (2. km) whole-lake model to allow direct incorporation of processes acting on the whole-lake scale, while also providing spatial detail that better matched available data and the desired resolution for the nearshore. Both models were based on the Princeton Ocean Model. Measurements of temperatures and currents were obtained during 2008 in each of the three regions: Oak Orchard Creek, Rochester Embayment, and Sandy Creek (or Mexico Bay), representing three different regimes of human interaction with the nearshore. The model reproduced general temperatures and flow structures relatively well for the Oak Orchard and Rochester sites, but was less effective for Sandy Creek, where simulation results were possibly adversely affected by the relatively shallow conditions of this site. Results were generally better for summer and fall, while early spring comparisons appeared to be influenced by specified initial conditions, which were found to impact model results well past the one to two month period usually assumed for spin-up time.