Modeling coupling between eelgrass Zostera marina and water flow

Abstract

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.

Does the canopy mixing layer model apply to highly flexible aquatic vegetation? Insights from numerical modelling

“…This model is suitable for modelling highly flexible 'tensile' vegetation (Ca ) 1, B ) O(1)) with low rigidity and localised bending. Similar models have previously been applied to seagrasses [19,69]. Full details concerning the two biomechanical models are reported by Marjoribanks et al [20].…”

Strong and weak, unsteady reconfiguration and its impact on turbulence structure within plant canopies

“…31 We propose that the mean reconfiguration model can be used to infer the impact of instantaneous reconfiguration associated with the arrival of individual turbulent events. It is important to note that, for aquatic plants, buoyancy, in addition to rigidity and drag, can influence plant posture in flow, because the material density of many aquatic plants is below that of water (e.g., seagrass blade density is 700 kg m −3 ), 41 compared to typical coastal water densities of 1015 kg m −3 (Atlas of the Oceans, NOAA). In addition, aquatic plants often have small gas filled chambers, used to enhance buoyancy and maintain upright postures.…”

High-resolution numerical modelling of flow—vegetation interactions

“…Li and Xie (2011) extended this modelling approach to account for highly flexible vegetation, however the spatial resolution of the model was sufficiently low that stems were not explicitly resolved and thus the model relied upon a priori assumptions regarding plant-flow interaction. Abdelrhman (2007) developed a model for highly flexible stems, based on an Npendula model to represent plant motion (see Section 3.4). However, this model had several limitations.…”