Abstract
Suspended sediment collected by vegetation in marshes and wetlands contributes to vertical accretion, which can buffer against rising sea levels. Effective capture efficiency (ECE), a parameter quantifying the fraction of incoming suspended particles directly captured by underwater vegetation surfaces, plays a key role in determining the significance of direct interception in morphodynamic models. The ways in which physical characteristics of collectors and transitionally turbulent flows affect ECE are not yet thoroughly understood. We conducted a set of 12 experiments at three flow velocities and three stem densities (plus equivalent zero-collector control experiments), plus four experiments where biofilm was allowed to accumulate. We determined that ECE decreases with increasing collector Reynolds number (study range: 66 to 200; p < 0.05 for two of three treatments) and increasing collector density (solid volume fraction: 0.22% to 1.17%; p < 0.05 for two of three treatments). Adding biofilm increased ECE in all cases, by a multiplicative factor ranging from 1.53 to 7.15 at different collector densities and biofilm growth durations. In some cases, the impact of biofilm on ECE far outweighed that of collector Reynolds number and density. By combining our data with those of one similar study, we present a preliminary model quantitatively assessing the effect of collector density on ECE.
Highlights
Models predict that vegetation will play an important role in determining the vertical accretion rate of these same habitats, which factors into their degree of adaptability to sea level rise [3,4]
In order to better predict sedimentation rates, as well as other properties that are related to sediment transport such as water quality [5] and ecological productivity [6], researchers and modelers require empirical estimates of the magnitudes of different interactions between aquatic vegetation and suspended sediment
ECE decreased with increasing Rec and φc throughout our parameter space, with one exception (Figure 4). This exception occurred at the minimum collector density, where the intermediate Rec treatment (Rec = 134) had lower ECE than both the minimum and maximum Rec treatments
Summary
Models predict that vegetation will play an important role in determining the vertical accretion rate of these same habitats, which factors into their degree of adaptability to sea level rise [3,4]. Leaves, and other plant surfaces intercept suspended sediment [7,8,9] via direct capture, diffusional deposition, and inertial impaction [10,11,12] (Figure 1). Direct capture describes the mechanism whereby particles moving along flow streamlines in close proximity to the surface of a collector (e.g., stem) contact and are retained on that surface (Figure 2).
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