A Question of Scale: How Turbulence Around Aerial Roots Shapes the Seabed Morphology in Mangrove Forests of the Mekong Delta

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 under...

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Bibliographic Details
Published in:Oceanography (Washington, D.C.) D.C.), 2017-09, Vol.30 (3), p.34-47
Main Authors: Mullarney, Julia C., Henderson, Stephen M., Norris, Benjamin K., Bryan, Karin R., Fricke, Aaron T., Sandwell, Dean R., Culling, Daniel P.
Format: Article
Language:English
Subjects:
Deltas
Ecosystems
Environmental changes
Environmental effects
Forest canopy
Forest ecosystems
Forests
Fringe
Interactions
Mangrove forests
Mangrove swamps
Mangroves
Mud flats
Ocean floor
Pneumatophores
River deltas
Roots
Sea level
Sea level changes
Sediment
Sediment transport
Sediments
SPECIAL ISSUE ON SEDIMENTARY PROCESSES BUILDING A TROPICAL DELTA YESTERDAY, TODAY, AND TOMORROW: THE MEKONG SYSTEM
Surf zone
Transport
Tropical climate
Turbulence
Vegetation
Water flow
Wave breaking
Waves
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Summary: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.
ISSN:1042-8275
2377-617X
DOI:10.5670/oceanog.2017.312