A numerical study of flow and mass transport processes around active filtering, partially burrowed freshwater mussels

In natural streams freshwater mussels act as “ecological engineers” who create a favorable habitat for themselves and many other aquatic species. They actively filter organic matter from the water column to obtain food and burrow part of their shell into the substrate to prevent being dislocated by the flows. Unfortunately, freshwater mussels are one of the most endangered aquatic species in North America. To stop their population decline, multidisciplinary efforts are needed to restore mussel habitat.

Given that the quality of the mussel habitat depends on the flow conditions around the mussels, the present study focuses on providing information on how the near-bed flow is modified by the presence of active filtering, partially burrowed mussels. High-revolution numerical simulations are performed to investigate the physics of flow in channels containing isolated and large arrays of mussels and the role of large-scale turbulence on flow hydrodynamics, transport processes and the capacity of the flow to erode the bed. The present study also investigates the capacity of the flow to displace mussels from the substrate and to induce channel bed erosion, mixing between the water filtered by mussels and the surrounding water, and how mussel stability varies with the main geometrical and flow parameters. Finally, the present study examines the structure and spatial development of the 2-D turbulent boundary layer forming over a mussel-covered bed. The data from these numerical simulations should help develop strategies to protect freshwater mussels in natural river reaches.