Mass-transfer-limited nitrate uptake on a coral reef flat, Warraber Island, Torres Strait, Australia

Baird, Mark E.; Roughan, Moninya; Brander, Robert W.; Middleton, Jason H.; Nippard, Greg J.

doi:10.1007/s00338-004-0404-z

Cited by 46 publications

(31 citation statements)

References 20 publications

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“…The number of samples used to estimate the drag coefficient also varies in these studies. Baird et al (2004) use average current and pressure difference measurements over Warraber Island reef for short periods on two successive days to determine C da . The Coronado et al (2007) estimate is based on a sea level difference measurement across Puerto Morelos reef during Hurricane Ivan, assuming a maximum current of 1 m s…”

Section: Synthesis and Comparison To Previous Studiesmentioning

confidence: 99%

Coral Reef Drag Coefficients – Water Depth Dependence

Lentz

Davis

Churchill

et al. 2017

Journal of Physical Oceanography

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A major challenge in modeling the circulation over coral reefs is uncertainty in the drag coefficient because existing estimates span two orders of magnitude. Current and pressure measurements from five coral reefs are used to estimate drag coefficients based on depth-average flow, assuming a balance between the cross-reef pressure gradient and the bottom stress. At two sites wind stress is a significant term in the cross-reef momentum balance and is included in estimating the drag coefficient. For the five coral reef sites and a previous laboratory study, estimated drag coefficients increase as the water depth decreases consistent with open channel flow theory. For example, for a typical coral reef hydrodynamic roughness of 5 cm, observational estimates, and the theory indicate that the drag coefficient decreases from 0.4 in 20 cm of water to 0.005 in 10 m of water. Synthesis of results from the new field observations with estimates from previous field and laboratory studies indicate that coral reef drag coefficients range from 0.2 to 0.005 and hydrodynamic roughnesses generally range from 2 to 8 cm. While coral reef drag coefficients depend on factors such as physical roughness and surface waves, a substantial fraction of the scatter in estimates of coral reef drag coefficients is due to variations in water depth.

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Section: Synthesis and Comparison To Previous Studiesmentioning

confidence: 99%

Coral Reef Drag Coefficients – Water Depth Dependence

Lentz

Davis

Churchill

et al. 2017

Journal of Physical Oceanography

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“…Their empirical result was largely based on laboratory flume experiments with a 20 cm canopy of Porites [Thomas and Atkinson, 1997] 0.06-0.1 u| z=H -0.22 --Acropora palmate [Lugo-Fernandez et al, 1998] 0.06-0.2 u| z=0.6m ----Sand with coral outcrops [Baird et al, 2004] 0.036 et al, 2006] 0.016-0.05 u| z=H 0.45-0.9 --Corals, seagrass, sand [Coronado et al, 2007] 0.015 [Reidenbach et al, 2006] 0.01-0.015 u| z=1m -∼0.01 -Pocillopora sp., Porites sp. [Jones et al, 2008] 0.015 U ---Unknown reef type [Tarya et al, 2010] 0.017-0.027 U ---z 0 Varied, see entry above [Reidenbach et al, 2006] 0. compressa and C D was defined using the bulk flow rate divided by flume cross-sectional area.…”

Section: Introductionmentioning

confidence: 99%

A framework for understanding drag parameterizations for coral reefs

Rosman¹,

Hench²

2011

J. Geophys. Res.

121

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[1] In a hydrodynamic sense, a coral reef is a complex array of obstacles that exerts a net drag force on water moving over the reef. This drag is typically parameterized in ocean circulation models using drag coefficients (C D ) or roughness length scales (z 0 ); however, published C D for coral reefs span two orders of magnitude, posing a challenge to predictive modeling. Here we examine the reasons for the large range in reported C D and assess the limitations of using C D and z 0 to parameterize drag on reefs. Using a formal framework based on the 3-D spatially averaged momentum equations, we show that C D and z 0 are functions of canopy geometry and velocity profile shape. Using an idealized two-layer model, we illustrate that C D can vary by more than an order of magnitude for the same geometry and flow depending on the reference velocity selected and that differences in definition account for much of the range in reported C D values. Roughness length scales z 0 are typically used in 3-D circulation models to adjust C D for reference height, but this relies on spatially averaged near-bottom velocity profiles being logarithmic. Measurements from a shallow backreef indicate that z 0 determined from fits to point measurements of velocity profiles can be very different from z 0 required to parameterize spatially averaged drag. More sophisticated parameterizations for drag and shear stresses are required to simulate 3-D velocity fields over shallow reefs; in the meantime, we urge caution when using published C D and z 0 values for coral reefs.Citation: Rosman, J. H., and J. L. Hench (2011), A framework for understanding drag parameterizations for coral reefs,

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“…When the biochemical demand for a particular metabolite by an organism is high enough, the convective transfer of dissolved metabolites across the concentration boundary layer becomes the rate-limiting step or is ''mass-transfer limited'' (Bilger and Atkinson 1992). Estimates of nutrient fluxes to natural reef communities have been made in the field using principles of convective mass transfer derived from both theory and controlled experimentation (Atkinson 1992; Baird et al 2004;Falter et al 2004). Our ability to make such in situ predictions is essential for understanding how rates of nutrient uptake, photosynthesis, respiration, and other metabolic processes vary within and between reefs.…”

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confidence: 99%

Effects of nonlocal turbulence on the mass transfer of dissolved species to reef corals

Falter¹,

Atkinson²,

Lowe³

et al. 2007

Limnology & Oceanography

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We examined the importance of nonlocal turbulence to the mass transfer of dissolved species from both cylinders and models of reef coral. Solid gypsum cylinders and gypsum-coated model coral were dissolved in an outdoor flume at mean flow speeds of 4.5 and 10 cm s 21 . Three model corals were used: two branched forms of the genera Acropora and Pocillopora, and one lobate form of the genus Platygyra. Turbulence intensities (Tu) were measured as the ratio of the standard deviation of the time-variant flow to the mean. Tu of between 5% and 55% were created independently of the mean flow by pumping water through two vertical arrays of jets. Mass transfer coefficients increased by 10-70% with turbulence intensity for all forms at both mean flow speeds considered (p , 0.05); however, mass transfer coefficients for the branched coral were not as sensitive to changes in turbulence intensity as for the lobate coral. Results for the cylinders were consistent with the engineering literature and indicate that the effects of turbulence intensity on mass transfer become weaker when branch size or flow speed (or both) become very small. Turbulence intensities measured around experimental coral communities and above naturally occurring reef communities typically vary between 15% and 35%. Assuming an average turbulence intensity of around 25%, then ignoring the effects of nonlocal turbulence altogether would result in uncertainties in mass transfer coefficients of at most 610% for the lobate coral form and 65% for the branched coral forms. Measuring external turbulence in bulk flows is not necessary for most evaluations of biogeochemical rates in benthic reef systems.

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Mass-transfer-limited nitrate uptake on a coral reef flat, Warraber Island, Torres Strait, Australia

Cited by 46 publications

References 20 publications

Coral Reef Drag Coefficients – Water Depth Dependence

Coral Reef Drag Coefficients – Water Depth Dependence

A framework for understanding drag parameterizations for coral reefs

Effects of nonlocal turbulence on the mass transfer of dissolved species to reef corals

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