Attenuation of water flow inside seagrass canopies of differing structure

Peterson, Charles H.; Luettich, Richard A.; Micheli, Fiorenza; Skilleter, G. A.

doi:10.3354/meps268081

Cited by 172 publications

(118 citation statements)

References 42 publications

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“…Previous work has shown that the depth-averaged form of Eq. 1 correctly predicts the depth-averaged velocity within an emergent canopy (Peterson et al 2004); we consider the vertical variation in vegetation density in order to resolve the vertical structure in the velocity profile. Because ‫‪x‬ץ/ץ‬ is not a function of vertical position in the water column, the quantity C d au 2 is constant over depth.…”

Section: Analytic Developmentmentioning

confidence: 99%

Prediction of velocity profiles and longitudinal dispersion in salt marsh vegetation

2006

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To predict the behavior of solutes and suspended particles in wetlands, it is necessary to estimate advection and longitudinal dispersion. To better understand these processes, measurements were taken of stem frontal area, velocity, vertical diffusion, and longitudinal dispersion in a Spartina alterniflora salt marsh in the Plum Island Estuary in Rowley, Massachusetts. Vegetation volumetric frontal area peaked at 0.067 Ϯ 0.007 cm Ϫ1 near 10 cm from the bed. If the velocity profile in a dense emergent marsh canopy depends on the local balance between pressure forcing and vegetation drag, the velocity will vary inversely with canopy drag (i.e., velocity is minimum where the frontal area is maximum). In fact, the minimum velocity was observed at 10 cm from the bed. The momentum balance therefore provides a way to predict the velocity profile structure from canopy morphology. The vertical diffusion coefficient also depends on canopy characteristics, such that the vertical diffusion coefficient normalized by the velocity and stem diameter had a constant value of 0.17 Ϯ 0.08 at this study site. The canopy morphology also controls the longitudinal dispersion, observed in this study to be 4 to 27 cm 2 s Ϫ1. However, theoretical considerations show that dispersion coefficients of at least 540 cm 2 s Ϫ1 can occur under typical marsh conditions. Comparisons to other canopies indicate that the prediction of the velocity profile and shear dispersion from canopy morphology can be extended to other emergent canopies and that shear dispersion may vary widely between stands with different physical characteristics.

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Section: Analytic Developmentmentioning

confidence: 99%

Prediction of velocity profiles and longitudinal dispersion in salt marsh vegetation

2006

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“…Granata et al (2001) showed that hydrodynamics may be reduced both under and above the canopies by 10 to 75%. In summary, higher flow attenuation has been observed inside canopies with increasing shoot density (Leonard & Luther 1995, Koch & Gust 1999, Peterson et al 2004, Nepf et al 2007, Hansen & Reidenbach 2012, Pujol et al 2012, 2013a,b) Pujol et al (2013b conducted oscillatory flow experiments in the laboratory using a submerged flexible canopy constructed to simulate P. oceanica properties. They found orbital velocity reductions of 22 and 39% for solid plant fractions (SPF; i.e.…”

Section: Introductionmentioning

confidence: 99%

Impact of anthropogenically created canopy gaps on wave attenuation in a Posidonia oceanica seagrass meadow

Colomer¹,

Soler²,

Serra³

et al. 2017

Mar. Ecol. Prog. Ser.

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Fixed weights moorings, once removed, can create longitudinal gaps in seagrass meadows of different sizes, running perpendicular to the coast. We quantified the interactions between these longitudinal gaps and the hydrodynamic environment of the nearshore environment to determine their potential impact on seagrass meadow ecology. Within the meadow at leaf length distances from the edge, wave attenuation by the lateral vegetation next to the gap was approximately the same as attenuation by fully vegetated areas, and the wave attenuating capacity of the lateral, near-gap vegetation was independent of gap width. Gaps with widths less than twice the leaf length exhibited 8% wave attenuation and 11% turbulent kinetic energy attenuation, confirming that vegetation shelters at least small gaps. Despite similar capacity for wave attenuation, the longitudinal gaps influenced the architectural characteristics of the adjacent (lateral) meadow; lateral shoot density, percent cover and leaf length adjacent to the largest gap were 12, 16, and 20% lower than the fully vegetated site, respectively. Significant differences in the temporal variation of the mean lateral, near-gap seagrass percent cover and the leaf length indicated a strong dependence of the state of the canopy on temporal hydrodynamic conditions, which in turn were impacted by the presence of the gap. Our results quantify the interactions between gaps and lateral meadow vegetation, highlight the structural impact of traditional moorings and support improved management and conservation of seagrass meadows.

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“…Seagrass canopies are known to reduce flow and turbulence (Fonseca et al 1982, Gambi et al 1990, Ackerman & Okubo 1993, Koch 1996, Gacia et al 1999, Koch & Gust 1999, Nepf & Vivoni 2000, Jumars et al 2001, Peterson et al 2004, Koch et al 2006) and attenuate wave action (Fonseca & Cahalan 1992, Koch & Gust 1999, Granata et al 2001, Bouma et al 2005, Koch et al 2006, thereby promoting sedimentation and reducing resuspension within seagrass meadows (Gacia et al 1999, Terrados & Duarte 2000. Examination of the composition of the material deposited within seagrass canopies has revealed the presence of a large (> 50%) contribution of sestonic particles (Gacia et al 2002), pointing to a large pelagic particle flux toward seagrass meadows.…”

Section: Introductionmentioning

confidence: 99%

Experimental assessment and modeling evaluation of the effects of the seagrass Posidonia oceanica on flow and particle trapping

Hendriks¹,

Sintes²,

Bouma³

et al. 2008

Mar. Ecol. Prog. Ser.

249

187

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Retention of particles in seagrass canopies is usually attributed to only the indirect, attenuating effects canopies have on flow, turbulence and wave action, promoting sedimentation and reducing resuspension within seagrass meadows. Yet recent evidence suggests that seagrasses are also able to affect particle flux directly through loss of momentum and increased path length derived from collisions with leaves and binding of particles. We evaluated the role of Posidonia oceanica on flow and associated particle trapping through flume experiments. Our results confirm the existence of 2 dynamically different environments, viz. (1) the below-canopy habitat, with low shear stress and reduced turbulence, and (2) the canopy-water interface region, characterized by high shear stress and turbulence intensity, where vertical transport of momentum is enhanced. At relatively low free stream velocities (i.e. 0.05 and 0.10 m s -1 ) sediment concentration decreased much faster when a Posidonia meadow was present in the flume, indicating major particle trapping in the seagrass canopy. Fluxes to the sediment (as shown by large negative peaks in Reynolds stress inside the Posidonia meadow) indicated 2 to 6 times more sediment transport to the bottom when a meadow is present. However, calculations based on the experimental results point to loss rates an order of magnitude larger in a Posidonia meadow. We hypothesize that direct effects of particle collisions with leaves are responsible for this discrepancy, and we explore possible interactions with a simple model. Using only collisions as a loss factor, the model predicts that the probability a particle is lost from the flow upon a collision is 2 to 3%. Previously observed leaf density and flow velocity effects on particle loss rates were explained by the model. Fitting the model to our experimentally obtained particle disappearance rates in vegetation indicated that around 27% of particle momentum is lost upon each collision with a leaf. We hypothesize that physical filtration by sediment collisions with plant structures plays a role in particle removal in aquatic systems. KEY WORDS: Particle trapping · Physical filtering · SeagrassResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 356: 163-173, 2008 Explaining the full mechanism by which seagrasses enhance particle retention is less clear. Usually, it is assumed that the role of seagrasses is solely indirect, driven by their effects on flow (Fonseca et al. 1983, Ackerman & Okubo 1993, Lopez & Garcia 1998, Granata et al. 2001). Yet recent evidence suggests that once particles are brought near the canopy (through the effects on flow listed above), seagrasses also affect particle flux directly, leading to potentially high particle removal rates (Agawin & Duarte 2002). Possible mechanisms for such direct effects on particle trapping include (1) the loss of momentum and increased path length derived from collisions of the particles with leaves within the dense seagrass canopie...

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Attenuation of water flow inside seagrass canopies of differing structure

Cited by 172 publications

References 42 publications

Prediction of velocity profiles and longitudinal dispersion in salt marsh vegetation

Prediction of velocity profiles and longitudinal dispersion in salt marsh vegetation

Impact of anthropogenically created canopy gaps on wave attenuation in a Posidonia oceanica seagrass meadow

Experimental assessment and modeling evaluation of the effects of the seagrass Posidonia oceanica on flow and particle trapping

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