Seagrass canopies decrease flow velocity and reduce turbulence, promoting sedimentation and reducing particle resuspension. However, there might be additional mechanisms that cause enhanced sedimentation within seagrass meadows. Recent work revealed that a large proportion of deposited material consists of seston. This points at large fluxes toward seagrass meadows that cannot be explained by hydrodynamics alone. Another mechanism of particle trapping is direct physical interception of particles by the plants themselves within the canopy. Direct retention of particles can be caused by e.g. physical binding to the plants or by loss of energy of the particles upon hitting a leaf and subsequent redirection towards the sediment surface. Flume results of particle retention time and the proportion of direct effects are discussed and conceptionalised with a two dimensional model. We present experimental results on effects of a Posidonia oceanica canopy structure on flow properties and particle retention. Building on these results, we estimate the relative proportion of direct and indirect effects of seagrass meadows on particle retention through model exercises.
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