Abstract: Turbulent mixing in coastal environments can influence the distribution of material suspended in the water column and the exchange of water with the coastal ocean, making it a key mechanism controlling water quality. In this talk I will explain how turbulence is accounted for in estuarine physics, how we measure turbulence in the physical environment, and will show results from one case study in Frenchman Bay, Maine, an area known for its complex deglaciated coastline, strong tidal influence, and shellfishing activities that are susceptible to problematic harmful algal blooms (HABs). Measurements of current velocity, density, and turbulence collected over a semidiurnal tidal cycle (~12 h) and a companion numerical model simulation of the study area provide concurrent evidence of counter-rotating sub-mesoscale eddies (2–4 km diameter) that enhance near-surface mixing. The eddies are generated in the wake of several islands in an area with abrupt bathymetric gradients, both legacy conditions partly derived from deglaciation ~15 kya. Increased concentrations of algal cells measured during the 12 h survey follow a trend of elevated turbulent dissipation rates near the water surface due to the eddies. Our findings provide incentive to examine current practices of HAB monitoring and management by linking coastal geomorphology to hydraulic conditions influencing HAB sampling outcomes.



Contact: Chris DiScenza