The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Karin R Bryan - One of the best experts on this subject based on the ideXlab platform.
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Deposition gradients across mangrove fringes
Coastal dynamics, 2020Co-Authors: Erik Horstman, Karin R Bryan, Julia C Mullarney, Dean R. SandwellAbstract:Observations in a mangrove in the Whangapoua Harbour, New Zealand, have shown that deposition rates are greatest in the fringing zone between the tidal flats and the mangrove forest, where the vegetation is dominated by a cover of Pneumatophores (i.e. pencil roots). Current speeds and suspended sediment concentrations dropped substantially across this zone. Near-bed turbulence within the fringe was substantially lower where the pneumatophore canopy was denser, facilitating the enhanced deposition in this zone. However, the near-bed conditions were not the primary control on the instantaneous sediment concentrations at this site. The total deposition across the different zones was the combined result of the reduced near-bed turbulence inside the vegetation and the larger-scale dynamics over the spatially variable vegetation cover, along with other confounding factors such as changing sediment inputs.
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are flow vegetation interactions well represented by mimics a case study of mangrove Pneumatophores
Advances in Water Resources, 2018Co-Authors: Erik Horstman, Karin R Bryan, Julia C Mullarney, Conrad A Pilditch, Christopher Andrews EagerAbstract:Abstract Arrays of real mangrove Pneumatophores (i.e. aboveground pencil roots) and artificial dowel mimics were constructed in a laboratory flume to examine differences in canopy flow dynamics. Compared to the uniform-height dowel canopy, the non-uniform height of the Pneumatophores significantly reduced the intensity of the canopy shear, and shifted the turbulence maxima observed directly above the dowels upwards by approximately the standard deviation of the pneumatophore heights. Consequently, bed shear stresses were up to two times greater in the uniform-height dowel canopy than in a pneumatophore canopy of similar density. At the same time, ratios of the within-canopy velocity to the free-stream velocity above the canopies were not significantly altered by the heterogeneous height, shape and spatial distribution of the Pneumatophores. Our results emphasize that uniform dowels are poor proxies of real pneumatophore canopies and may lead to underestimations of sediment-trapping efficiency.
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Spatially varying drag within a wave-exposed mangrove forest and on the adjacent tidal flat
Continental Shelf Research, 2017Co-Authors: Julia C Mullarney, Stephen M. Henderson, J. Reyns, Benjamin K. Norris, Karin R BryanAbstract:Abstract Mangroves have been shown to protect shorelines against damage from the combined hydrodynamic forces of waves and tides, owing to the presence of roots (Pneumatophores) and tree trunks that enhance vegetative drag. However, field measurements within these environments are limited. We present field observations of flows from the seaward coast of Cu Lao Dung Island (Soc Trăng Province) in the Mekong Delta, Vietnam. Measurements were made in two different seasons along a transect that crosses from mudflats to mangrove forest. Flows are also explored using an idealised numerical model. Both the data and model capture the flow transitions from mudflat across the fringing region to the forest interior. We observe a rotation of the obliquely incident flows toward an orientation nearly perpendicular to the vegetated/unvegetated boundary. The momentum balances governing the large-scale flow are assessed and indicate the relative importance of friction, winds and depth-averaged pressure forces. In the forest, drag coefficients were 10–30 times greater than values usually observed for bottom friction, with particularly effective friction in the regions of dense Pneumatophores at the fringe and when water depths were lower than the height of the Pneumatophores. Pressure gradient balances suggest that the drag induced by bottom friction from Pneumatophores was dominant relative to drag from the larger, but sparser, tree trunks.
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A question of scale: How turbulence around aerial roots shapes the seabed morphology in mangrove forests of the Mekong Delta
Oceanography, 2017Co-Authors: Julia C Mullarney, Karin R Bryan, Dean R. Sandwell, Stephen M. Henderson, Benjamin K. Norris, Aaron T. Fricke, Daniel P. CullingAbstract:Mangrove forests are highly productive ecosystems that provide many physical, societal, and ecological services in tropical and subtropical regions. Accurate prediction of the morphological evolution for these areas, in the face of global sea level rise and changes in sediment supply, requires understanding of interactions between vegetation growth, water flows, and sediment transport. Data presented from a wave-exposed mangrove forest in the Mekong Delta, Vietnam, include unique measurements that resolved water flows in and around the aerial mangrove roots (known as Pneumatophores) over scales from a few millimeters to hundreds of meters. Flows were highly turbulent, with turbulence values sometimes as large as those measured in surf zones. These energetic processes appear to stir up sediments, with small scour troughs observed around individual Pneumatophores, and larger-scale scour around clusters of Pneumatophores. The vegetation fringe (the boundary between forest and mudflat) was a particularly dynamic area, with elevated turbulence levels, greater vegetation densities, coarser sediments, and occasional wave breaking. Intense turbulent dissipation at the fringe then reduces the energy of shoreward-propagating waves, sheltering the forest interior. The small-scale processes appear to be linked with forest-wide patterns of sediment transport and deposition. We discuss these links in the context of the biophysical interactions that control the changing shapes of deltas worldwide
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Wave-frequency flows within a near-bed vegetation canopy
Continental Shelf Research, 2017Co-Authors: Stephen M. Henderson, Julia C Mullarney, Benjamin K. Norris, Karin R BryanAbstract:We study water flows and wave dissipation within near-bed pneumatophore canopies at the wave-exposed fringe of a mangrove forest on Cu Lao Dung Island, in the Mekong Delta. To evaluate canopy drag, the three-dimensional geometry of pneumatophore stems growing upward from the buried lateral roots of Sonneratia caseolaris mangroves was reconstructed from photogrammetric surveys. In cases where hydrodynamic measurements were obtained, up to 84 stems per square meter were observed, with stem heights 0.1 Hz), and up to 90 degrees at lower frequencies. A model is developed for wave-induced flows within the vertically variable canopy. Scaling suggests that acceleration-induced forces and vertical mixing were negligible at wave frequencies. Consistent with theory, drag-induced vertical variability in velocity scaled with Λ=Tw/(2πTf), where Tw= wave period, Tf=2/(CDa|u|) is the frictional time scale, CD≈2 is the drag coefficient, and |u| is a typical flow speed. For fixed wave conditions (|u| and Tw), theory predicts increasing dissipation with increasing vegetation density (i.e. increasing a), until a maximum is reached for order-one Λ. For larger Λ, within-canopy flow is so inhibited by drag that further increases in a reduce within-canopy dissipation. For observed cases, Λ⩽0.38 at energetic wave frequencies, so wave dissipation near the forest edge is expected to increase with increasing pneumatophore canopy density. However, under different wave conditions, the most dense canopies may occasionally approach the dissipation maximum (Λ≈1). Predicted dissipation by the pneumatophore canopy was sufficient to attenuate most wave energy over distances slightly less (more) than 100 m into the marsh in 1 m (2 m) water depth.
Majid Bakhtiyari - One of the best experts on this subject based on the ideXlab platform.
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Sediment distribution in shallow estuaries at fine scale: in situ evidence of the effects of three-dimensional structural complexity of mangrove Pneumatophores
Hydrobiologia, 2017Co-Authors: Shafagh Kamal, Jan Warnken, Majid BakhtiyariAbstract:One of the main services offered by mangroves is their capacity for trapping sediment. We investigated how spatial complexity of Pneumatophores of Avicennia marina may influence fine-scale sediment particle size distribution. Using realistic three-dimensional models captured from pneumatophore patches, indices of complexity (the area/volume ratio, the Getis-Ord Gi* statistic) were calculated to quantify mangrove root structural complexity in five 1 × 1 m2 plots. The complexity of Pneumatophores in 16 0.25 × 0.25 m2 subplots in each of the 5 plots was measured and its relationship with the relative abundance of fine sediment particles (clay and silt,
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sediment distribution in shallow estuaries at fine scale in situ evidence of the effects of three dimensional structural complexity of mangrove Pneumatophores
Hydrobiologia, 2017Co-Authors: Shafagh Kamal, Jan Warnken, Majid BakhtiyariAbstract:One of the main services offered by mangroves is their capacity for trapping sediment. We investigated how spatial complexity of Pneumatophores of Avicennia marina may influence fine-scale sediment particle size distribution. Using realistic three-dimensional models captured from pneumatophore patches, indices of complexity (the area/volume ratio, the Getis-Ord Gi* statistic) were calculated to quantify mangrove root structural complexity in five 1 × 1 m2 plots. The complexity of Pneumatophores in 16 0.25 × 0.25 m2 subplots in each of the 5 plots was measured and its relationship with the relative abundance of fine sediment particles (clay and silt, <63 µm) was assessed. Results showed the complexity of the neighbouring subplots in the direction of incoming water was a major factor driving the trapping of suspended silt and clay, thus underpinning the function of mangrove aboveground structures in the distribution of fine particles. This simple low-cost technique to measure the complexity of mangroves demonstrates how further investigations may quantify the relationship between this complexity and their capacity to trap sediment with data derived from actual real-world models rather than based on simplistic, simulated structures. This information will be valuable in guiding future efforts in mangrove rehabilitation and restoration.
Julia C Mullarney - One of the best experts on this subject based on the ideXlab platform.
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Deposition gradients across mangrove fringes
Coastal dynamics, 2020Co-Authors: Erik Horstman, Karin R Bryan, Julia C Mullarney, Dean R. SandwellAbstract:Observations in a mangrove in the Whangapoua Harbour, New Zealand, have shown that deposition rates are greatest in the fringing zone between the tidal flats and the mangrove forest, where the vegetation is dominated by a cover of Pneumatophores (i.e. pencil roots). Current speeds and suspended sediment concentrations dropped substantially across this zone. Near-bed turbulence within the fringe was substantially lower where the pneumatophore canopy was denser, facilitating the enhanced deposition in this zone. However, the near-bed conditions were not the primary control on the instantaneous sediment concentrations at this site. The total deposition across the different zones was the combined result of the reduced near-bed turbulence inside the vegetation and the larger-scale dynamics over the spatially variable vegetation cover, along with other confounding factors such as changing sediment inputs.
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are flow vegetation interactions well represented by mimics a case study of mangrove Pneumatophores
Advances in Water Resources, 2018Co-Authors: Erik Horstman, Karin R Bryan, Julia C Mullarney, Conrad A Pilditch, Christopher Andrews EagerAbstract:Abstract Arrays of real mangrove Pneumatophores (i.e. aboveground pencil roots) and artificial dowel mimics were constructed in a laboratory flume to examine differences in canopy flow dynamics. Compared to the uniform-height dowel canopy, the non-uniform height of the Pneumatophores significantly reduced the intensity of the canopy shear, and shifted the turbulence maxima observed directly above the dowels upwards by approximately the standard deviation of the pneumatophore heights. Consequently, bed shear stresses were up to two times greater in the uniform-height dowel canopy than in a pneumatophore canopy of similar density. At the same time, ratios of the within-canopy velocity to the free-stream velocity above the canopies were not significantly altered by the heterogeneous height, shape and spatial distribution of the Pneumatophores. Our results emphasize that uniform dowels are poor proxies of real pneumatophore canopies and may lead to underestimations of sediment-trapping efficiency.
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Spatially varying drag within a wave-exposed mangrove forest and on the adjacent tidal flat
Continental Shelf Research, 2017Co-Authors: Julia C Mullarney, Stephen M. Henderson, J. Reyns, Benjamin K. Norris, Karin R BryanAbstract:Abstract Mangroves have been shown to protect shorelines against damage from the combined hydrodynamic forces of waves and tides, owing to the presence of roots (Pneumatophores) and tree trunks that enhance vegetative drag. However, field measurements within these environments are limited. We present field observations of flows from the seaward coast of Cu Lao Dung Island (Soc Trăng Province) in the Mekong Delta, Vietnam. Measurements were made in two different seasons along a transect that crosses from mudflats to mangrove forest. Flows are also explored using an idealised numerical model. Both the data and model capture the flow transitions from mudflat across the fringing region to the forest interior. We observe a rotation of the obliquely incident flows toward an orientation nearly perpendicular to the vegetated/unvegetated boundary. The momentum balances governing the large-scale flow are assessed and indicate the relative importance of friction, winds and depth-averaged pressure forces. In the forest, drag coefficients were 10–30 times greater than values usually observed for bottom friction, with particularly effective friction in the regions of dense Pneumatophores at the fringe and when water depths were lower than the height of the Pneumatophores. Pressure gradient balances suggest that the drag induced by bottom friction from Pneumatophores was dominant relative to drag from the larger, but sparser, tree trunks.
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A question of scale: How turbulence around aerial roots shapes the seabed morphology in mangrove forests of the Mekong Delta
Oceanography, 2017Co-Authors: Julia C Mullarney, Karin R Bryan, Dean R. Sandwell, Stephen M. Henderson, Benjamin K. Norris, Aaron T. Fricke, Daniel P. CullingAbstract:Mangrove forests are highly productive ecosystems that provide many physical, societal, and ecological services in tropical and subtropical regions. Accurate prediction of the morphological evolution for these areas, in the face of global sea level rise and changes in sediment supply, requires understanding of interactions between vegetation growth, water flows, and sediment transport. Data presented from a wave-exposed mangrove forest in the Mekong Delta, Vietnam, include unique measurements that resolved water flows in and around the aerial mangrove roots (known as Pneumatophores) over scales from a few millimeters to hundreds of meters. Flows were highly turbulent, with turbulence values sometimes as large as those measured in surf zones. These energetic processes appear to stir up sediments, with small scour troughs observed around individual Pneumatophores, and larger-scale scour around clusters of Pneumatophores. The vegetation fringe (the boundary between forest and mudflat) was a particularly dynamic area, with elevated turbulence levels, greater vegetation densities, coarser sediments, and occasional wave breaking. Intense turbulent dissipation at the fringe then reduces the energy of shoreward-propagating waves, sheltering the forest interior. The small-scale processes appear to be linked with forest-wide patterns of sediment transport and deposition. We discuss these links in the context of the biophysical interactions that control the changing shapes of deltas worldwide
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Wave-frequency flows within a near-bed vegetation canopy
Continental Shelf Research, 2017Co-Authors: Stephen M. Henderson, Julia C Mullarney, Benjamin K. Norris, Karin R BryanAbstract:We study water flows and wave dissipation within near-bed pneumatophore canopies at the wave-exposed fringe of a mangrove forest on Cu Lao Dung Island, in the Mekong Delta. To evaluate canopy drag, the three-dimensional geometry of pneumatophore stems growing upward from the buried lateral roots of Sonneratia caseolaris mangroves was reconstructed from photogrammetric surveys. In cases where hydrodynamic measurements were obtained, up to 84 stems per square meter were observed, with stem heights 0.1 Hz), and up to 90 degrees at lower frequencies. A model is developed for wave-induced flows within the vertically variable canopy. Scaling suggests that acceleration-induced forces and vertical mixing were negligible at wave frequencies. Consistent with theory, drag-induced vertical variability in velocity scaled with Λ=Tw/(2πTf), where Tw= wave period, Tf=2/(CDa|u|) is the frictional time scale, CD≈2 is the drag coefficient, and |u| is a typical flow speed. For fixed wave conditions (|u| and Tw), theory predicts increasing dissipation with increasing vegetation density (i.e. increasing a), until a maximum is reached for order-one Λ. For larger Λ, within-canopy flow is so inhibited by drag that further increases in a reduce within-canopy dissipation. For observed cases, Λ⩽0.38 at energetic wave frequencies, so wave dissipation near the forest edge is expected to increase with increasing pneumatophore canopy density. However, under different wave conditions, the most dense canopies may occasionally approach the dissipation maximum (Λ≈1). Predicted dissipation by the pneumatophore canopy was sufficient to attenuate most wave energy over distances slightly less (more) than 100 m into the marsh in 1 m (2 m) water depth.
Shafagh Kamal - One of the best experts on this subject based on the ideXlab platform.
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Sediment distribution in shallow estuaries at fine scale: in situ evidence of the effects of three-dimensional structural complexity of mangrove Pneumatophores
Hydrobiologia, 2017Co-Authors: Shafagh Kamal, Jan Warnken, Majid BakhtiyariAbstract:One of the main services offered by mangroves is their capacity for trapping sediment. We investigated how spatial complexity of Pneumatophores of Avicennia marina may influence fine-scale sediment particle size distribution. Using realistic three-dimensional models captured from pneumatophore patches, indices of complexity (the area/volume ratio, the Getis-Ord Gi* statistic) were calculated to quantify mangrove root structural complexity in five 1 × 1 m2 plots. The complexity of Pneumatophores in 16 0.25 × 0.25 m2 subplots in each of the 5 plots was measured and its relationship with the relative abundance of fine sediment particles (clay and silt,
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sediment distribution in shallow estuaries at fine scale in situ evidence of the effects of three dimensional structural complexity of mangrove Pneumatophores
Hydrobiologia, 2017Co-Authors: Shafagh Kamal, Jan Warnken, Majid BakhtiyariAbstract:One of the main services offered by mangroves is their capacity for trapping sediment. We investigated how spatial complexity of Pneumatophores of Avicennia marina may influence fine-scale sediment particle size distribution. Using realistic three-dimensional models captured from pneumatophore patches, indices of complexity (the area/volume ratio, the Getis-Ord Gi* statistic) were calculated to quantify mangrove root structural complexity in five 1 × 1 m2 plots. The complexity of Pneumatophores in 16 0.25 × 0.25 m2 subplots in each of the 5 plots was measured and its relationship with the relative abundance of fine sediment particles (clay and silt, <63 µm) was assessed. Results showed the complexity of the neighbouring subplots in the direction of incoming water was a major factor driving the trapping of suspended silt and clay, thus underpinning the function of mangrove aboveground structures in the distribution of fine particles. This simple low-cost technique to measure the complexity of mangroves demonstrates how further investigations may quantify the relationship between this complexity and their capacity to trap sediment with data derived from actual real-world models rather than based on simplistic, simulated structures. This information will be valuable in guiding future efforts in mangrove rehabilitation and restoration.
W G Allaway - One of the best experts on this subject based on the ideXlab platform.
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There is a continuum of gas space in young plants of Avicennia marina
Hydrobiologia, 1995Co-Authors: A. E. Ashford, W G AllawayAbstract:Gas-spaces form a continuum throughout 10-month-old Avicennia marina seedlings. This has direct connection with the atmosphere via the stomata and spongy mesophyll of the leaves, and via the lenticels that occur on all the internodes and the hypocotyl. There is therefore provision for aeration of the root system prior to the development of Pneumatophores. The amount of gas space is greatest in the cortex, and in elongated organs (petiole, root, stem internodes and hypocotyl) it occurs as wide elongated channels that are all interconnected. Continuity is maintained of Pneumatophores. The amount of gas space is greatest in the cortex, and in elongated organs (petiole, root, stem internodes and hypocotyl) it occurs as wide elongated channels that are all interconnected. Continuity is maintained across the nodes by a mass of spongy tissue which connects up with the elongated channels above and below. In all organs the amount of gas space in the pith is much less, but there it also occurs as interconnected elongated channels. The volume of gas space is greatest in the major roots and specialised lignified cells which become collapsed may play a role in supporting the very large gas spaces.
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horizontal structures on Pneumatophores of avicennia marina forsk vierh a new site of oxygen conductance
Annals of Botany, 1994Co-Authors: Mark J Hovenden, W G AllawayAbstract:Abstract Conductance of Pneumatophores of the grey mangrove, Avicennia marina, to oxygen depended on lenticel number up to about 25 functional lenticels per pneumatophore, and probably on cross-sectional area of the gas space in Pneumatophores with over 25. The dependence on lenticel number was far from perfect, because of a substantial non-lenticellular component of conductance. This non-lenticellular conductance was attributed to 'horizontal structures' on the most recently formed part of the pneumatophore. These were thought to result from persistent portions of the root cap which remained attached to the surface of the pneumatophore, and around which breaks in the surface of the periderm developed. Following flooding, the lenticels dried and resumed full conductance within about three minutes. Non-lenticellular conductance imputed to the horizontal structures took about ten times as long to recover after flooding. Nevertheless, these horizontal structures are likely to represent a significant pathway for admission of oxygen, especially in rapidly growing roots where the tip region lacks lenticels. A name, 'subrisules', for these horizontal structures is proposed.