Modeling coupling between eelgrass Zostera marina and water flow

Ecological effects caused by submerged aquatic vegetation not only depend on the plants and their morphology but also on the flow and transport patterns of dissolved and suspended constituents near the canopy. Canopy height is a major variable in any quantitative analysis of plant biomass and constituent transport in its vicinity. Height of eelgrass Zostera marina canopies changes due to bending of the blades under varying current regimes. In this paper, I mathematically modeled the coupling between eelgrass blade bending and water flow. Based on the balance of forces of drag, lift, friction, weight and buoyancy on a single blade, the model defined the bending of blades (i.e. height of canopy) and the flow response within and above the canopy. This coupling was tested using laboratory data and indicated that the model performed adequately. Both model results and laboratory data confirmed that the bending of blades, and hence canopy height, was very sensitive to current magnitude and directly influenced current profile. Identifying canopy height is a major factor in defining spatial distribution of grass biomass from optical or acoustic remote sensing devices. The model has direct implications for biological issues related to the plants themselves and to their associated organisms, such as the vertical distribution of photosynthesis within the canopy and the effect of current shear on recruitment of organisms on the blades. It can also be used to study how eelgrass canopies affect horizontal transport of constituents, such as dissolved oxygen, nutrients and organic carbon, and particulate material such as pollen, larvae, plankton and detritus.