Experimental observations on sediment resuspension within submerged model canopies under oscillatory flow

Ros, Anna; Colomer, Jordi; Serra, Teresa; Pujol, Dolors; Soler, María Teresa; Casamitjana, Xavier

doi:10.1016/j.csr.2014.10.004

Cited by 56 publications

(54 citation statements)

References 40 publications

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“…Thus, gap size, architectural characteristics and temporal variability must be considered when assessing both the influence of seagrass habitat on wave hydrodynamics and the severity of anthropogenically created gaps in seagrass canopies. Seagrass meadows modify the benthic boundary layer, which manifests in changes in mean velocities, orbital velocities and turbulence (Granata et al 2001, Infantes et al 2012, Ros et al 2014). This modification is generally understood to be moderated by the architectural characteristics of the meadow (both shoot density and number of leaves per shoot) and the plants (shoot biomass, leaf length, leaf width, blade stiffness) (Borg et al 2005, Peralta et al 2008, Paul et al 2012.…”

Section: Discussionmentioning

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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Section: Discussionmentioning

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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“…Although wave‐driven flows are reduced within seagrass canopies (Fonseca and Cahalan ; Manca et al ), they may also induce a mean flow in the direction of wave propagation inside the meadow (Luhar et al ). Despite the presence of these competing mechanisms, observations suggest that seagrasses overall reduce sediment resuspension in wave‐driven flows, especially at higher shoot densities (Ros et al ). While attenuation of both currents and waves by the presence of seagrass typically increases the net sediment deposition, this deposition is likely to be reduced in wave‐driven flows compared with current‐driven flows because mean currents are attenuated by seagrass canopies much more than oscillatory flows (Lowe et al ), and the wave‐driven movement of seagrass blades back and forth increases sediment movement between the seagrass canopy and the overlying water column (Koch and Gust ; Madsen et al ).…”

Section: Overview Of the Seagrass‐sediment‐light Feedbackmentioning

confidence: 99%

Feedback between sediment and light for seagrass: Where is it important?

et al. 2016

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A feedback between seagrass presence, suspended sediment and benthic light can induce bistability between two ecosystem states: one where the presence of seagrass reduces suspended sediment concentrations to increase benthic light availability thereby favoring growth, and another where seagrass absence increases turbidity thereby reducing growth. This literature review identifies (1) how the environmental and seagrass meadow characteristics influence the strength and direction (stabilizing or destabilizing) of the seagrass-sediment-light feedback, and (2) how this feedback has been incorporated in ecosystem models proposed to support environmental decision making. Large, dense seagrass meadows in shallow subtidal, noneutrophic systems, growing in sediments of mixed grain size and subject to higher velocity flows, have the greatest potential to generate bistability via the seagrass-sediment-light feedback. Conversely, seagrass meadows of low density, area and height can enhance turbulent flows that interact with the seabed, causing water clarity to decline. Using a published field experiment as a case study, we show that the seagrass-sedimentlight feedback can induce bistability only if the suspended sediment has sufficient light attenuation properties. The seagrass-sediment-light feedback has been considered in very few ecosystem models. These models have the potential to identify areas where bistability occurs, which is information that can assist in spatial prioritization of conservation and restoration efforts. In areas where seagrass is present and bistability is predicted, recovery may be difficult once this seagrass is lost. Conversely, bare areas where seagrass presence is predicted (without bistability) may be better targets for seagrass restoration than bare areas where bistability is predicted.

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“…The somewhat contradictory results between field and laboratory observations reflect the dual influence of vegetation on wave damping (e.g., Luhar et al, ) and turbulence generation (Zhang et al, ). Stem‐generated turbulence, when present, can locally enhance resuspension (e.g., Ros et al, ; Tinoco & Coco, ), but the damping of waves over the expanse of a meadow can lead to a reduction in resuspension (e.g., Hansen & Reidenbach, ). For weak wave conditions, defined by a small ratio of wave excursion to stem spacing, the presence of flexible vegetation can both reduce turbulence level and inhibit resuspension, relative to bare bed (Ros et al, ).…”

Section: Introductionmentioning

confidence: 99%

Impact of Vegetation‐Generated Turbulence on the Critical, Near‐Bed, Wave‐Velocity for Sediment Resuspension

Tang

Lei

Nepf

2019

Water Resources Research

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Laboratory experiments examined the impact of model vegetation on wave‐driven resuspension. Model canopies were constructed from cylinders with three diameters (d = 0.32, 0.64, and 1.26 cm) and 12 densities (cylinders/m2) up to a solid volume fraction (ϕ) of 10%. The sediment bed consisted of spherical grains with d50 = 85 μm. For each experiment, the wave velocity was gradually adjusted by increasing the amplitude of 2‐s waves in a stepwise fashion. A Nortek Vectrino sampled the velocity at z = 1.3 cm above the bed. The critical wave orbital velocity for resuspension was inferred from records of suspended sediment concentration (measured with optical backscatter) as a function of wave velocity. The critical wave velocity decreased with increasing solid volume fraction. The reduction in critical wave velocity was linked to stem‐generated turbulence, which, for the same wave velocity, increased with increasing solid volume fraction. The measured turbulence was consistent with a wave‐modified version of a stem‐turbulence model. The measurements suggested that a critical value of turbulent kinetic energy was needed to initiate resuspension, and this was used to define the critical wave velocity as a function of solid volume fraction. The model predicted the measured critical wave velocity for stem diameters d = 0.64 to 2 cm. Combining the critical wave velocity with an existing model for wave damping defined the meadow size for which wave damping would be sufficient to suppress wave‐induced sediment suspension within the interior of the meadow.

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Experimental observations on sediment resuspension within submerged model canopies under oscillatory flow

Cited by 56 publications

References 40 publications

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

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

Feedback between sediment and light for seagrass: Where is it important?

Impact of Vegetation‐Generated Turbulence on the Critical, Near‐Bed, Wave‐Velocity for Sediment Resuspension

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