Observations of Hypolimnetic Turbulence in Lake Michigan and Implications for Mussel Filtration

Session: 47. - Physical Processes in Lakes

David Cannon, Purdue University, [email protected]
Cary Troy, Purdue University, [email protected]

Abstract

While invasive quagga mussels are known to have dramatic impacts on ecosystem structure and function, their inability to position themselves in the water column means that their potential filtration rates are dependent on hydrodynamic delivery of particles to the bed (i.e. settling and turbulent mixing). Settling is easily prescribed in ecosystem models, but full water column turbulence prescriptions require in-situ measurements for validation, which are lacking in the Laurentian Great Lakes. In this study, we present some of the first direct measurements of hypolimnetic turbulence collected in Lake Michigan’s deep waters, with a combination of high-resolution velocimeters and periodic microstructure profiles used to fully characterize mean flow and turbulence at a 55m site near Milwaukee, WI. Observed turbulent diffusivities, estimated from turbulent kinetic energy (TKE) and TKE dissipation measurements, suggest that hypolimnetic turbulence remains relatively constant despite varied surface conditions, with near-bed diffusivities that follow law-of-the-wall predictions within ~1m of the bed. Estimated hypolimnetic diffusivity rates are an order of magnitude larger than those suggested by oceanic literature, with important implications for mussel filtration models. Turbulence measurements are used in a 1D NPZD-grazers model, with results validated against simultaneous measurements of phosphorous, nitrogen, and zooplankton collected at the sample site.

1. Keyword
Lake Michigan

2. Keyword
modeling

3. Keyword
mussels

4. Additional Keyword
turbulence