Turbulence from Bio-Mixing by Profundal Mussels in Lake Michigan

Session: Physical Processes in Lakes (2)

Tong Jin, University of Wisconsin-Milwaukee, [email protected]
Qian Liao, University of Wisconsin-Milwaukee, [email protected]
Rae-Ann MacLellan-Hurd, University of Wisconsin-Milwaukee, [email protected]
David Cannon, Purdue University, [email protected]
Harvey Bootsma, University of Wisconsin-Milwaukee, [email protected]
Cary Troy, Purdue University, [email protected]

Abstract

The influence of benthic filter feeders, such as bivalves, on the cycling of plankton and nutrient was considered significant in shallow marine and freshwater systems. Recent indirect evidence showed that the profundal quagga mussels (Dreissena rostriformis bugensis) have fundamentally altered energy flow and dynamics of nutrients and phytoplankton in Lake Michigan and other Great Lakes. To investigate the relation between phytoplankton grazing rate by quagga mussel and their siphon currents induced bio-mixing, an Underwater Particle Image Velocimetry (PIV) was developed to measure the turbulence structure and the turbulent diffusion coefficient immediately above the substrate covered with mussels at a 55-m depth site in Lake Michigan. The system was deployed from July to October 2018, which acquired 500 sets of velocity data, each with 400 snaps of velocity maps. Profiles of turbulent diffusivity were evaluated with several independent approaches by analyzing measured velocity and particle density distributions measured. The study also tested the hypothesis that profundal mussels can maximize the efficiency of grazing by enhancing near bed turbulence which increases the retention time of phytoplankton in the bio-mixing layer.