Particle capture by seagrass canopies under an oscillatory flow

Abstract

Although seagrass canopies are known to enhance particle sedimentation, there is still limited knowledge about how seagrasses modify the vertical distribution of sediment particles; especially when particles come from allochthonous sources. This study determined the volume of particles trapped by the seagrass leaves, the amount that remains in suspension both within and above the canopy, and the amount deposited onto the seabed. A set of laboratory experiments were conducted in which hydrodynamic conditions and canopy densities were varied to mimic real field conditions. This study demonstrated and quantified previously recorded observations concerning the fate of sediment in seagrass meadows. Seagrass meadows decreased the amount of suspended sediment by capturing the sediment on the blades of the seagrass and by enhancing particle sedimentation on the seabed. However, particles trapped by the blades of seagrass in the whole canopy increased with canopy density and reduced the number of particles in suspension within the canopy. The ecological implications were significant, since a seabed covered by vegetation, when compared to a bare seabed, produced a reduction in the suspended sediment particles within the canopy, improving water clarity. Furthermore, canopies (compared to bare substrates) enhanced seabed sedimentation and the denser the canopy was, the greater the amount of sediment deposited on the seabed.