Photosynthetic oxygen flux by Macrocystis pyrifera: a mass transfer model with experimental validation

Hansen, Amy T.; Hondzo, Miki; Hurd, Catriona L.

doi:10.3354/meps09196

Cited by 9 publications

(6 citation statements)

References 47 publications

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“…The flow characteristics in the different regimes were determined in the middle of the flume using a field 10 MHz Acoustic Doppler Velocimeter (Sontek, San Diego, CA, USA) before the start of the experiment. These velocities were chosen because they represent speeds at which the DBL can reach maximal and minimal values (Hansen, Hondzo, & Hurd, ), and they are similar to those observed within kelp beds in the field (Gaylord et al., ; Jackson & Winant, ; Kregting et al., ). Individual kelp blades colonized or not by bryozoans were randomly assigned to the different flow treatments.…”

Section: Methodsmentioning

confidence: 99%

“…These velocities were chosen because they represent speeds at which the DBL can reach maximal and minimal values (Hansen, Hondzo, & Hurd, 2011), and they are similar to those observed within kelp beds in the field (Gaylord et al, 2007;Jackson & Winant, 1983;Kregting et al, 2011). Individual kelp blades colonized or not by bryozoans were randomly assigned to the different flow treatments.…”

Section: Experimental Designmentioning

confidence: 99%

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Abiotic and biotic interactions in the diffusive boundary layer of kelp blades create a potential refuge from ocean acidification

Noisette

Hurd

2018

Functional Ecology

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Seaweeds are able to modify the chemical environment at their surface, in a micro‐zone called the diffusive boundary layer (DBL), via their metabolic processes controlled by light intensity. Depending on the thickness of the DBL, sessile invertebrates such as calcifying bryozoans or tube‐forming polychaetes living on the surface of the blades can be affected by the chemical variations occurring in this microlayer. Especially in the context of ocean acidification (OA), these microhabitats might be considered as a refuge from lower pH, because during the day photosynthesis temporarily raises the pH to values higher than in the mainstream seawater. We assessed the thickness and the characteristics of the DBL at two pH levels (today's average surface ocean pH 8.1 and a reduced pH predicted for the end of the century, pH 7.7) and seawater flows (slow, 0.5 and fast, >8 cm/s) on Ecklonia radiata (kelp) blades. Oxygen and pH profiles from the blade surface to the mainstream seawater were measured with O2 and pH microsensors for both bare blades and blades colonized by the bryozoan Membranipora membranacea. The DBL was thicker in slow flow compared with fast flow and the presence of bryozoans increased the DBL thickness and shaped the DBL gradient in dark conditions. Net production was increased in the low pH condition, increasing the amount of oxygen in the DBL in both bare and epiphytized blades. This increase drove the daily pH fluctuations at the blade surface, shifting them towards higher values compared with today's pH. The presence of bryozoans led to lower oxygen concentrations in the DBL and more complex pH fluctuations at the blade surface, particularly at pH 7.7. Overall, this study, based on microprofiles, shows that, in slow flow, DBL microenvironments at the surface of the kelps may constitute a refuge from OA with pH values higher than those of the mainstream seawater. For calcifying organisms, it could also represent training ground for harsh conditions, with broad daily pH and oxygen fluctuations. These chemical microenvironments, biologically shaped by the macrophytes, are of great interest for the resilience of coastal ecosystems in the context of global change. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13067/suppinfo is available for this article.

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Section: Methodsmentioning

confidence: 99%

Section: Experimental Designmentioning

confidence: 99%

Abiotic and biotic interactions in the diffusive boundary layer of kelp blades create a potential refuge from ocean acidification

Noisette

Hurd

2018

Functional Ecology

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“…Similarly, from measurements reported in Hansen et al . [, Table ],

u_{*} \approx 0.07 U

for the kelp Macrocystis pyrifera . For nearly all conditions the turbulent boundary layer model over‐predicted the measured K , and it failed to capture the trend at the higher velocity range (Figure ).…”

Section: Resultsmentioning

confidence: 96%

Impact of current speed on mass flux to a model flexible seagrass blade

Lei

Nepf

2016

JGR Oceans

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Seagrass and other freshwater macrophytes can acquire nutrients from surrounding water through their blades. This flux may depend on the current speed (U), which can influence both the posture of flexible blades (reconfiguration) and the thickness of the flux‐limiting diffusive layer. The impact of current speed (U) on mass flux to flexible blades of model seagrass was studied through a combination of laboratory flume experiments, numerical modeling and theory. Model seagrass blades were constructed from low‐density polyethylene (LDPE), and 1, 2‐dichlorobenzene was used as a tracer chemical. The tracer mass accumulation in the blades was measured at different unidirectional current speeds. A numerical model was used to estimate the transfer velocity (K) by fitting the measured mass uptake to a one‐dimensional diffusion model. The measured transfer velocity was compared to predictions based on laminar and turbulent boundary layers developing over a flat plate parallel to flow, for which K∝U0.5 and ∝U, respectively. The degree of blade reconfiguration depended on the dimensionless Cauchy number, Ca, which is a function of both the blade stiffness and flow velocity. For large Ca, the majority of the blade was parallel to the flow, and the measured transfer velocity agreed with laminar boundary layer theory, K∝U0.5. For small Ca, the model blades remained upright, and the flux to the blade was diminished relative to the flat‐plate model. A meadow‐scale analysis suggests that the mass exchange at the blade scale may control the uptake at the meadow scale.

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“…Previous studies have suggested that Turbulent KE may influence nutrient uptake (Anderson and Charters ; Koch ), and the total energy parameter captures this influence. Specifically, when Turbulent KE is weak, flux is controlled by the time‐mean diffusive sublayer thickness, which is a function of the time‐mean velocity (e.g., Hansen et al ; Rominger and Nepf ; Lei and Nepf ). However, when the Turbulent KE is high, periodic disturbances of the diffusive sublayer by the turbulence can create instantaneously higher concentration gradients at the surface and, thus, higher flux (e.g., Stevens and Hurd ; Huang et al ; Rominger and Nepf ).…”

Section: Discussionmentioning

confidence: 99%

Turbulence‐mediated facilitation of resource uptake in patchy stream macrophytes

Cornacchia

Licci

Nepf

et al. 2018

Limnology & Oceanography

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Many landscapes are characterized by a patchy, rather than homogeneous, distribution of vegetation. Often this patchiness is composed of single‐species patches with contrasting traits, interacting with each other. To date, it is unknown whether patches of different species affect each other's uptake of resources by altering hydrodynamic conditions, and how this depends on their spatial patch configuration. Patches of two contrasting aquatic macrophyte species (i.e., dense canopy‐forming Callitriche and sparse canopy‐forming Groenlandia) were grown together in a racetrack flume and placed in different patch configurations. We measured 15NH4+ uptake rates and hydrodynamic properties along the centerline and the lateral edge of both patches. When the species with a taller, denser canopy (Callitriche) was located upstream of the shorter, sparser species (Groenlandia), it generated turbulence in its wake that enhanced nutrient uptake for the sparser Groenlandia. At the same time, Callitriche benefited from being located at a leading edge where it was exposed to higher mean velocity, as its canopy was too dense for turbulence to penetrate from upstream. Consistent with this, we found that ammonium uptake rates depended on turbulence level for the sparse Groenlandia and on mean flow velocity for the dense Callitriche, but Total Kinetic Energy was the best descriptor of uptake rates for both species. By influencing turbulence, macrophyte species interact with each other through facilitation of resource uptake. Hence, heterogeneity due to multispecific spatial patchiness has crucial implications for both species interactions and aquatic ecosystem functions, such as nitrogen retention.

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Photosynthetic oxygen flux by Macrocystis pyrifera: a mass transfer model with experimental validation

Cited by 9 publications

References 47 publications

Abiotic and biotic interactions in the diffusive boundary layer of kelp blades create a potential refuge from ocean acidification

Abiotic and biotic interactions in the diffusive boundary layer of kelp blades create a potential refuge from ocean acidification

Impact of current speed on mass flux to a model flexible seagrass blade

Turbulence‐mediated facilitation of resource uptake in patchy stream macrophytes

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