Flow resistance, hydrodynamic tipping points, and the optimal density of aquatic mussels on river beds

Authors: Sean J. Bennett*, University at Buffalo, Brandon J. Sansom, University at Buffalo, Joseph F. Atkinson, University at Buffalo
Topics: Geomorphology, Physical Geography, Water Resources and Hydrology
Keywords: aquatic mussels, turbulent flow, river ecosystems
Session Type: Paper
Day: 4/6/2019
Start / End Time: 3:05 PM / 4:45 PM
Room: Jackson, Marriott, Mezzanine Level
Presentation File: No File Uploaded

Freshwater mussels (Bivalvia: Unionoida) are dominant ecosystem engineers in many streams throughout North America, yet they remain among the world’s most imperiled species. Extensive research has quantified the ecological role of mussels in aquatic habitats, but little is known about the interaction between mussels and their surrounding physical and hydrodynamic environment. To explore these interactions, flume experiments were conducted across a range of densities of model mussels and flow rates where two-dimensional particle image velocimetry was employed to quantify the turbulent flow field. The results show that (1) mussels placed onto the bed in a burrowed position can markedly alter the distributions and magnitudes of time-averaged velocity and Reynolds stress, (2) higher densities of mussels accelerate flow velocity above the mussel canopy, decelerate velocity within the canopy, and shift the maximum Reynolds stress to a position above the canopy, and (3) a hydrodynamic tipping point occurs at a mussel density of 25 mussels per square meter for the models employed here, where wall-bounded rough flow (k-type roughness) is replaced by relatively smoother skimming flow (d-type roughness). These results suggest that when mussel density reaches a critical or optimal threshold in rivers, a fundamental shift in the hydraulic flow regime occurs that clearly increases the stability and resiliency of the mussel-covered bed during higher flow stages. Such information is central to understanding the biophysical interactions between mussels and their environment and to advancing efforts to conserve these important aquatic organisms.

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