Turbulence and Particle Deposition Under Steady Flow Along a Submerged Seagrass Meadow

Abstract

Seagrass meadows can retain fine particles, improving water clarity and promoting carbon sequestration. Laboratory experiments were conducted to investigate the influence of velocity and meadow density on the retention of fine particles within a meadow. Vertical profiles of velocity and turbulent kinetic energy (TKE) were measured along a model meadow. The net deposition was measured using microscope slides positioned inside and outside the meadow. The deposition was correlated with the evolution of velocity along the meadow. At the leading edge, the net deposition decreased over a distance Lr, relative to the bare bed, which was associated with a region of vertical updraft and elevated TKE. Net deposition increased with the distance from the leading edge, associated with a decrease in vertical velocity and TKE. In some cases, a distinct peak in the deposition was observed at distance Lp from the leading edge, associated with a minimum in TKE. Both Lr and Lp decreased with increasing meadow density. Deposition in the fully developed region of the meadow decreased with decreasing stem density and increasing channel velocity, and for the lowest stem density and highest channel velocity the deposition in the meadow was less than that in the bare channel. Diminished deposition was linked to resuspension driven by stem-generated turbulence. A model for canopy-averaged TKE was validated and used to explore the range of field conditions for which TKE within a meadow would be reduced, relative to the bare bed, which would support the accumulation of fine organic material within the meadow.