Turbulence, Mixing, and Nutrient Fluxes in Kelp Forests: Effects of Currents, Waves, and Stratification
Abstract
Kelp forests generally develop in shallow-water coastal areas, with the holdfasts cling to the sea bottom while the stipes and blades extend upward to the sea surface by virtue of the buoyance provided by the gas-filled bladders (called pneumatocysts). Providing shelter, food, and protection for many species of fish and marine living creatures, kelp plays a paramount role in preserving biodiversity and ensuring sustainable livelihood in the ocean. Nutrient availability and temperature conditions are major factors affecting the distribution and expansion of kelp forests. Nevertheless, these factors are regulated by flow conditions, which develop in response to the combination of currents, tides, wind, and wave forcing. Better understanding of ecological function provided by kelp requires an in-depth knowledge of relevant hydrodynamic processes within kelp canopies.
The present work uses a fine-scale large eddy simulation method to model turbulent flow and nutrient transport with and without kelp in a shallow-water environment. Kelp is treated as a source of flow resistance and a nutrient sink, and its effects are accounted for by adding a drag force and sink term to the momentum and nutrient transport equations, respectively. The drag coefficient is modeled as current-velocity-dependent considering the fact that kelp fronds bend in response to the flow. The Stokes drift induced by surface waves is imposed in the governing equations to reflect the effects of the wave field since the surface wave motions are not explicitly resolved in our simulations. The suitability of the physical model is first assessed for modeling Langmuir turbulence in shallow water without vegetation, and then applied to simulate kelp environments under different flow regimes (varying wave, current, and stratification conditions).- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS14B..05Y
- Keywords:
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- 4217 Coastal processes;
- OCEANOGRAPHY: GENERAL