Particle Retention in a Submerged Meadow and Its Variation Near the Leading Edge

Abstract

The retention of particles within meadows of submerged aquatic vegetation impacts the fate of organic matter, pollen, and larvae. Because flow conditions near the leading edge differ from those over the bulk of the canopy, particle retention is likely to differ as well. In particular, near the leading edge of a wide meadow, flow deceleration generates a vertical updraft, which impacts particle fate. In the fully developed region of the meadow, shear layer vortices at the top of the meadow may also influence particle fate. In this study, the retention of particles was measured along the length of a 10-m model meadow (height h = 0.1 m) and was connected to the evolving flow field. Two particle sizes, with settling velocity w _s50 = 0.00075 , 0.018 m s⁻¹, were released at two heights within the model meadow $\left(\frac{Z_{rel}}{h}=0.31,0.81\right).$ The retention of particles was measured using microscope slides distributed along the flume bed. Retention increased with distance from the leading edge, associated with the decrease in vertical updraft. Retention was also greater for the particles with higher settling velocity. In the fully developed region of the meadow, particle retention was lower for particles influenced by the shear layer vortices at the top of the meadow ($\frac{Z_{rel}}{h}=0.81$).