Dreissenid mussel distribution in Georgian Bay, Lake Huron is limited by lateral mixing of chemical gradients
There are gradients of conductivity and nutrients in the coastal zone of Eastern Georgian Bay that appear to limit the spatial distribution of mussels. Georgian Bay is located east of the main body of Lake Huron and has a surface area of 15,000 km2, and contains approximately 30,000 islands. Rivers flowing into Georgian Bay from the Canadian shield are relatively low in conductivity compared to the main body of Lake Huron, and so there is an observed gradient of salts reminiscent of a well-mixed estuary near the river mouths. In order to understand the hydrodynamics of these fresh estuaries, we present modelling results using a conceptual one-dimensional model and a more complex three-dimensional hydrodynamic simulation (FVCOM) to show the mechanisms that may be responsible for calcium limitation in the nearshore mussel distribution. Both our simple and complex models show that the mixing length-scale of low conductivity waters from rivers can be described in terms of geometry, eddy diffusivity, and the river volume flux. The mixing scale is in the range of 1-10 km across the seasonally stratified and barotropic coastal waters in the Eastern Georgian Bay. We will present results from tracer release numerical experiments in FVCOM to track transport and dispersion in river waters. In addition to discussing mussel distribution, we will discuss the role of hydrodynamics in setting near-shore nutrient gradients.