Diffusive Boundary Layer Thickness Research Articles

Chronopotentiometric study of a Nafion membrane in presence of glucose

Chronopotentiometric and swelling experiments have been conducted to characterize the behavior of a Nafion membrane in NaCl and KCl aqueous solutions without and with glucose. A mixture solution with similar composition to the cerebrospinal fluid and blood plasma has also been studied. From the chronotentiograms, current-voltage curves have been obtained, and the values of the limiting current density, diffusion boundary layer thickness, difference between counter-ion transport number in membrane and free solution, and transition times have been determined for the investigated membrane systems. The obtained results indicate that the presence of glucose affects the ion transport through the membrane depending on the electrolyte and glucose concentrations. At low electrolyte concentration, experimental transition times are found to be smaller in presence of glucose, which has been related to an effective membrane area reduction in presence of glucose. The membrane system corresponding to the mixture solution shows a behavior similar to the single high concentration NaCl membrane system, indicating that the observed behavior is mainly associated to the Na+ ions transport in higher proportion. In this case, the glucose presence does not affect significantly the investigated properties of the membrane, which is interesting for its utilization in a glucose fuel cell.

Convective mass transfer from a submerged drop in a thin falling film

We investigate the fluid mechanics of removing a passive tracer contained in small, thin, viscous drops attached to a flat inclined substrate using thin gravity-driven film flows. We focus on the case where the drop cannot be detached either partially or completely from the surface by the mechanical forces exerted by the cleaning fluid on the drop surface. Instead, a convective mass transfer establishes across the drop–film interface and the dilute passive tracer dispersed in the drop diffuses into the film flow, which then transports them away. The Péclet number for the passive tracer in the film phase is very high, whereas the Péclet number in the drop phase varies from $\mathit{Pe}_{d}\approx 10^{-2}$ to $1$. The characteristic transport time in the drop is much larger than in the film. We model the mass transfer of the passive tracer from the bulk of the drop phase into the film phase using an empirical model based on an analogy with Newton’s law of cooling. This simple empirical model is supported by a theoretical model solving the quasi-steady two-dimensional advection–diffusion equation in the film, coupled with a time-dependent one-dimensional diffusion equation in the drop. We find excellent agreement between our experimental data and the two models, which predict an exponential decrease in time of the tracer concentration in the drop. The results are valid for all drop and film Péclet numbers studied. The overall transport characteristic time is related to the drop diffusion time scale, as diffusion within the drop is the limiting process. This result remains valid even for $\mathit{Pe}_{d}\approx 1$. Finally, our theoretical model predicts the well-known relationship between the Sherwood number and the Reynolds number in the case of a well-mixed drop $\mathit{Sh}\propto \mathit{Re}_{L}^{1/3}=({\it\gamma}L^{2}/{\it\nu}_{f})^{1/3}$, based on the drop length $L$, film shear rate ${\it\gamma}$ and film kinematic viscosity ${\it\nu}_{f}$. We show that this relationship is mathematically equivalent to a more physically intuitive relationship $\mathit{Sh}\propto \mathit{Re}_{{\it\delta}}$, based on the diffusive boundary-layer thickness ${\it\delta}$. The model also predicts a correction in the case of a non-uniform drop concentration. The correction depends on $Re_{{\it\delta}}$, the film Schmidt number, the drop aspect ratio and the diffusivity ratio between the two phases. This prediction is in remarkable agreement with experimental data at low drop Péclet number. It continues to agree as $\mathit{Pe}_{d}$ approaches $1$, although the influence of the Reynolds number increases such that $\mathit{Sh}\propto \mathit{Re}_{{\it\delta}}$.

In situ evaluation of DGT techniques for measurement of trace metals in estuarine waters: a comparison of four binding layers with open and restricted diffusive layers.

Four different DGT binding layers were used to make selective measurements of trace metals in coastal waters within The Broadwater (Gold Coast, Queensland). Chelex and PAMPAA (polyacrylamide-polyacrylic acid) binding layers were used to measure cations (Cd, Co, Cu, Mn, Ni, Pb, Zn), and Metsorb was used to measure anions (Al, As, Mo, Sb, V, W). A mixed binding layer (MBL) containing both Chelex and Metsorb was used to measure each of the trace metals and determine diffusive boundary layer (DBL) thicknesses. DGT measurements that were not corrected for the DBL thickness (0.049-0.087) were underestimated by 70% on average. Good agreement was observed between DGT-MBL and DGT-Chelex for measurement of Cd, Co, Cu, Ni, Pb and Zn, and between DGT-MBL and DGT-Metsorb for As, Sb and V. DGT-MBL measured significantly higher concentrations for Mn (compared with DGT-Chelex) and Al (compared with DGT-Metsorb). DGT-Chelex measured only 6-8% of Al species measured by either DGT-MBL or DGT-Metsorb. DGT-PAMPAA measurements of Cu, Pb and Al were lower than those of either DGT-MBL or DGT-Chelex varying from 74-81% for Cu to 54-70% for Pb and 51-55% for anionic Al(OH)4(-), suggesting that this binding layer may make more selective measurements. All measured trace metal concentrations were well below ANZECC water quality guidelines, except for Cu which was 2 to 10 times higher than trigger values. Each of the DGT techniques was deployed using both open and restricted diffusive layers (ODL and RDL). Most trace metal measurements were not significantly different with ODL and RDL for all binding layers. However, concentrations of Cu (CRDL/CODL = 0.68-0.75) and Al (CRDL/CODL = 0.73-0.79) were significantly different with DGT-MBL, DGT-Chelex and DGT-Metsorb.

Impact of chemical reaction on Cu, Al2O3 and SWCNTs–nanofluid flow under slip conditions

Single walled carbon nanotube, alumina and copper nanoparticles on convective mass transfer in the presence of base fluid (water) over a horizontal plate are investigated numerically. The governing partial differential equations with auxiliary conditions are reduced into the system of coupled ordinary differential equations via similarity transformation and it has been solved numerically using fourth or fifth order Runge–Kutta–Fehlberg method with shooting technique. The results display that the diffusion boundary layer thickness of the water based Cu and SWCNTs is stronger than Al2O3–water with increase of chemical reaction.

Investigations on the interfacial capacitance and the diffusion boundary layer thickness of ion exchange membrane using electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) is a powerful tool to investigate the electrochemical processes. This work investigated the interfacial properties of ion exchange membranes using EIS. Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and zeta potential were also used to characterize the membranes. With the comparison of two equivalent circuits and the consideration of the physical and electrochemical understanding of the ion exchange membrane systems (IEMs), a better equivalent circuit was selected for quantitatively analyzing each component of the systems. The diffusion boundary layer thickness was estimated with the derived equation (δ=3RdCdD). The effects of solution concentration, flow rate and temperature on the IEMs were investigated in a systematic way. The results clearly showed that the effective capacitance and the electrical double layer resistance were consistent with the concentration dependence of the Debye equation; the diffusion boundary layer thickness decreased with the increase of solution concentration, flow rate and temperature. The effective capacitance and the thickness of the membranes interface obtained by EIS were important for understanding the relationship with membrane surface microstructure, ion transport and electrical properties. It is confirmed that the EIS can be used as an alternative method to characterize the ion exchange membrane systems.

Development and evaluation of a diffusive gradients in a thin film technique for measuring ammonium in freshwaters

A new diffusive gradients in a thin film (DGT) technique, using Microlite PrCH cation exchange resin, was developed and evaluated for measuring NH4–N in freshwaters. Microlite PrCH had high uptake (>92.5%) and elution efficiencies (87.2% using 2 mol L−1 NaCl). Mass vs. time validation experiments over 24 h demonstrated excellent linearity (R2 ≥ 0.996). PrCH-DGT binding layers had an extremely high intrinsic binding capacity for NH4–N (∼3000 μg). NH4–N uptake was quantitative over pH ranges 3.5–8.5 and ionic strength (up to 0.012 mol L−1 as NaCl) typical of freshwater systems. Several cations (Na+, K+, Ca2+ and Mg2+) were found to compete with NH4–N for uptake by PrCH-DGT, but NH4–N uptake was quantitative over concentration ranges typical of freshwater (up to 0.012 mol L−1 Na+, 0.006 mol L−1 K+, 0.003 mol L−1 Ca2+ and 0.004 mol L−1 Mg2+). Effective diffusion coefficients determined from mass vs. time experiments changed non-linearly with electrical conductivity. Field deployments of DGT samplers with varying diffusive layer thicknesses validated the use of the technique in situ, allowed deployment times to be manipulated with respect to NH4–N concentration, and enable the calculation of the diffusive boundary layer thickness. Daily grab sample NH4–N concentrations were observed to vary considerably independent of major rainfall events, but good agreements were obtained between PrCH-DGT values and mean grab sample measurements of NH4–N (CDGT:CSOLN 0.83–1.3). Reproducibility of DGT measurements in the field was good (relative standard deviation < 11%). Limit of detection was 0.63 μg L−1 (equivalent to 0.045 μmol L−1) based on 24 h deployments.

Effect of interphase mass transfer on the coalescence of two bubbles under constant approach velocity

The equations for the drainage of a full mobile liquid film between two bubbles under a constant approach velocity are extended to investigate the effect of interphase mass transfer on bubble coalescence. The diffusion boundary layer thickness in the bubble is considered to be on the same order of bubble radius because of the high diffusion rate of the gas phase, and as a result the solute concentration in the bubble is approximated to be constant. The numerical results indicate that the Marangoni effect induced by mass transfer prevents bubble coalescence for positive systems, while it promotes coalescence for negative systems, which is consistent with experimental results for bulk distillation processes. In addition, the effects of Marangoni number, surface Peclet number, and film Peclet number on film drainage rate are reported.

Wall effect on heat transfer crisis

Various evaporation regimes were studied experimentally in a wide range of droplet sizes and wall temperatures at a change in thermal–physical and geometrical characteristics of the wall. With the increasing diameter of the wetting spot of a water sample from 1 to 30mm, the width of the transition region of boiling crisis increases. Dynamics of large droplets boiling is determined not only by wall overheating, but also by the droplet shape. Evaporation of droplets on the surfaces, whose longitudinal dimensions are much larger than the droplet diameter, should take into account free convection of gas and thickness of diffusion boundary layer, which depends on the droplet diameter. Wall surface polishing causes a multiple increase in evaporation time within the transitional boiling region, in contrast to the rough wall. For We≈0 and polished surface of the wall, the time of evaporation and Leidenfrost temperature in the transitional boiling region increase many times, in contrast to the rough wall (for high We number the result is opposite). To assess the effect of wall thickness on the rate of evaporation, it is important to consider the ratio of the droplet diameter to the wall thickness, depth of solid wall cooling, ratio of wall thermal conductivity to conductivity of liquid, and values of dimensionless Bio (Bi) and Fourier (Fo) numbers.

Oscillating grid mesocosm for studying oxygen dynamics under controlled unsteady turbulence

AbstractIn shallow environments, common unsteady flows, such as tides, waves or wind‐driven currents modulate the diffusive boundary layer thickness that controls the exchange of electron acceptors for mineralization and oxidation processes in surficial sediment. This study demonstrated the ability of an oscillating grid mesocosm to (1) produce homogenous turbulence at the sediment‐water interface of multiple sediment cores (between‐core variability &lt; within core variability; 16% on average); (2) simulate diffusive boundary layer thickness dynamics on different timescales by easy control of turbulence intensity and (3) study transient oxygen dynamics of organic matter mineralization under varying turbulent conditions. The relationship between turbulence intensity and oxygen diffusive boundary layer thickness, and oxygen penetration depth in the sediment was investigated with different organic matter enrichments and sediment permeability. Oxygen diffusive boundary layer thickness decreased linearly as URMS increased. Oxygen penetration depth increased with turbulence intensity, and converging to an upper limit with a larger value for low (3.28 mm ± 5.8%) than for high (1.77 mm ± 11.8%) organic matter content in muddy sediment. In sandy sediment, advective flows and resuspension led to a continuous increase of oxygen penetration depth with turbulence intensity, up to 13.2 mm ± 19% for turbulent velocities of 9.6 cm s−1. This mesocosm device will enable the experimental study of microbial dynamics under transient oxygen dynamics, to improve early diagenesis modeling under unsteady flows.

Modeling of kinetically limited growth rate for solution-synthesized germanium nanocrystals

Solution synthesis is a common method for preparing semiconductor nanocrystals (NCs). For such solution synthesis, many investigations have considered diffusion-limited growth, in which the diffusion of reactants through the boundary layer (BL) limits the NC growth rate. These studies often model the growth rate with a diffusion BL thickness much larger than the NC size and with unphysically low diffusion constants on the order of 10−12 cm2 s−1. In this work, we have examined the growth of Ge NCs synthesized by injecting Ge amide precursors into a solution of 1-octadecene, oleylamine, and hexadecylamine. We have previously established this low-temperature, low-pressure synthesis route. The resulting Ge growth rate compares well with our model, in which we consider both BL diffusion and surface kinetics of Ge precursors and organic ligand adsorbates. Our modeling results suggest that the NC growth is limited not by diffusion, but by the surface adsorption and desorption kinetics. The BL thickness in the stirred reaction vessel is calculated to be on the same order of magnitude as the crystal radius; therefore, the surface kinetics cannot be ignored. Furthermore, the synthesis temperature is near 300 °C, where the Ge monomer diffusion coefficient within the growth solution is substantially increased and estimated to be on the order of 10−5 cm2 s−1. These considerations agree well with our experimentally measured growth rate and strongly suggest that the NC size evolution is controlled primarily by the surface kinetics.

Dealloying of Magnesium Alloys

The corrosion behavior of cast Mg-Al alloys such as AZ91D and AM60B is strongly dependent on the alloy composition and microstructure. Alloy grain size, area fraction of phases and spatial distribution of the phases are important factors governing both full immersion and atmospheric corrosion behavior. Mg-Al alloy systems can be broadly characterized as being composed of a primary a-Mg matrix (grains) containing Al in solid solution and b-phase intermetallic particles mainly distributed within and adjacent to grain boundaries. Heat treatment of the as-cast alloys significantly modifies the microstructure altering grain size, phase amounts and distribution as well as the a-Mg phase composition. The general scenario that we envision evolving during corrosion of cast Mg-Al alloys is the following. In near-neutral electrolytes containing chloride, second phase particles such as the Mg17Al12 b-phase serve as cathodes for water reduction resulting in increases in pH. The corresponding dissolution reaction involves the dealloying of Mg from a-matrix grains resulting in enrichment and redistribution of solid solution Al as well as impurities (such as Fe) that may be present within the grains. The redistributed Al will form Al clusters on the surface of the now dealloyed a-phase that can also serve as cathodes. If the pH rises to ~ 9-9.5, the a-phase will begin to passivate and the b-phase can in principle dealloy (selective dissolution of Al) since the corrosion potential (~1.5V vs. SCE) is high enough for this to occur. At this elevated pH, aluminum may dissolve as the soluble aluminate and will tend to precipitate on to the dissolving alloy surface. Thus, owing to these pH changes local cathodes can become anodes and vice versa. The degree to which these processes affect corrosion behaviors depends on the spatial density (mean separation) of existing and evolving surface cathodes and how this length scale compares to the thickness of a electrolyte diffusion boundary layer or condensed liquid layer (atmospheric corrosion) and grain size. Given this hypothesis for corrosion behavior, we have been examining dealloying of AZ91D and AM60B as well the constituent a- and b-phases. Instead of relying on a technique such as EDS to characterize the time-dependent change in Al concentration on a corroding surface we developed an electrochemical assay involving Li underpotential deposition (UPD) that measures the electrochemically active surface area (ECSA) of Al. We show results comparing the new assay protocol yielding the ECSA of Al to that obtained from EDS. Anodic dissolution behaviors of the alloys and constituent phases have been measured in an ionic liquid electrolyte (neat1:2 molar ratio of choline chloride:urea) which allows for accurate determination of the evolving surface composition as a function of well-defined anodic dealloying rates. We discuss these results together with some preliminary Kinetic Monte Carlo modeling of corrosion processes of the constituent a-phase.

Slow-flow habitats as refugia for coastal calcifiers from ocean acidification.

The pH of the oceans' surface water is dropping, termed ocean acidification (OA), and the 0.4 unit reduction in pH by 2100 is projected to negatively impact benthic coastal organisms that produce calcium carbonate "skeletons." Research has focussed on identifying species that are susceptible to OA, but there is an urgent need to discover refuge habitats that will afford protection to vulnerable species. The susceptibility of calcium carbonate skeletons to dissolution by OA depends on the pH at their surface, and this is controlled by the interaction between seawater velocity and organismal metabolism. This perspective considers how seawater velocity modifies the responses of calcifying organisms (seaweed, shellfish, and tropical corals) to OA through its action on controlling diffusion boundary layer thickness and thereby the pH and calcium carbonate saturation state (Ω) at the organisms' surface. Evidence is presented to support the idea that slow-flow habitats, such as wave-sheltered bays or the within canopies of seaweed/seagrass beds, might provide inexpensive refugia from OA for vulnerable coastal calcifiers.

Uncertainty and sensitivity evaluation of aerosol deposition in PHEBUS containment during FPT-2 experiment

During a hypothetical severe accident at a nuclear power plant (NPP), the aerosols and radionuclides could be released from the reactor through the engineering systems to the surrounding atmosphere. The last barrier preventing release is the containment, which surrounds the reactor and the main engineering systems. Most of radioactivity is released in the form of particles (aerosols). Therefore, aerosol transport and deposition processes are very important for NPP safety. Description of these processes requires a lot of physical parameters and conditions. Naturally, these parameters bring their own uncertainties, and so uncertainty and sensitivity analyses are necessary for final assessment of the accuracy of results. This paper presents the uncertainty and sensitivity analysis of PHEBUS FPT-2 simulation performed with the SUSA software. The containment simulation results were received using the lumped-parameter code COCOSYS. This paper includes a description of the PHEBUS containment, nodalisation, initial and boundary conditions, results and conclusions. The uncertainty analysis was performed assuming 95/95 probability, and tolerance limits showed that the measured values of the aerosol mass suspended in the gas phase were within the calculated uncertainty limits. However, the deposition on the vertical containment walls is not within the calculated limits. The sensitivity analysis showed that the parameters having the largest influence on the investigated parameters (mass suspended in gas phase, deposition on containment elliptic floor, deposition on condensers, deposition on vertical walls) are the following: the Mass Median Diameter (MMD), the dynamic shape factor, the particle agglomeration factor, the water film thickness, the initial pressure, the Geometric Standard Deviation of particle diameter, and the thickness of diffusive boundary layer.

Numerical evaluation of lateral diffusion inside diffusive gradients in thin films samplers.

Using numerical simulation of diffusion inside diffusive gradients in thin films (DGT) samplers, we show that the effect of lateral diffusion inside the sampler on the solute flux into the sampler is a nonlinear function of the diffusion layer thickness and the physical sampling window size. In contrast, earlier work concluded that this effect was constant irrespective of parameters of the sampler geometry. The flux increase caused by lateral diffusion inside the sampler was determined to be ∼8.8% for standard samplers, which is considerably lower than the previous estimate of ∼20%. Lateral diffusion is also propagated to the diffusive boundary layer (DBL), where it leads to a slightly stronger decrease in the mass uptake than suggested by the common 1D diffusion model that is applied for evaluating DGT results. We introduce a simple correction procedure for lateral diffusion and demonstrate how the effect of lateral diffusion on diffusion in the DBL can be accounted for. These corrections often result in better estimates of the DBL thickness (δ) and the DGT-measured concentration than earlier approaches and will contribute to more accurate concentration measurements in solute monitoring in waters.

Mass transfer in reverse electrodialysis: Flow entrance effects and diffusion boundary layer thickness

Power generation by reverse electrodialysis (RED) depends on ionic mass transfer through alternately arranged cation- and anion-exchange membranes. Chronopotentiometric measurements were carried out in an EDR-Z Mini stack (MEGA a.s.), equipped with Ralex heterogeneous membranes, separated by either sheet flow spacers or mesh-free gaskets. Various concentrations of model NaCl solutions were used to study the ohmic and non-ohmic resistances in the stack under different hydrodynamic conditions. In order to eliminate the uncertainties associated with a non-uniform distribution of the applied current over the membrane surface, the relaxation zone of the obtained chronopotentiograms was used to estimate the diffusion boundary layer thickness. It was found that this approach provide more accurate data under RED operating conditions, which are strongly influenced by entrance effects on mass transfer, especially for a spacer-free channel configuration. For shorter flow channels, since the salt concentration profile across the diffusion boundary layer is not yet fully developed, more power can be obtained than in the case of longer channels. The presence of spacers was found to reduce the boundary layer thickness, but also increased the ohmic resistance, due to their shadow effect over the membrane surface. The description of the impact of flow entrance effects on mass transfer, and therefore on diffusion boundary layer thickness, can be useful for characterization and further design and/or optimization of RED stacks performance.

O2, pH, and Redox Potential Microprofiles around Potamogeton malaianus Measured Using Microsensors

This study aimed to elucidate the effects of periphyton on the microprofiles of oxygen (O2), pH, and oxidation-reduction potential around the stems and leaves of a submerged macrophyte Potamogeton malaianus and on the plant growth in the eutrophic shallow Taihu Lake, China. The microprofiles were measured using a motorized microprofiling system equipped with microsensors. The leaf age of the macrophyte and periphyton exerted significant effects on the microprofiles of O2, pH, and oxidation-reduction potential. O2 concentration and pH increased whereas the oxidation-reduction potential decreased with decreasing distance to the stem/leaf surface. The fluctuation amplitudes of O2, pH, and oxidation-reduction potential were the largest in the microprofiles of mature leaves and the lowest in senescent leaves. The periphyton increased the thickness of the broad diffusive boundary layer and fluctuation amplitudes of O2, pH, and oxidation-reduction potential. When the periphyton was removed, the thickness of the broad diffusive boundary layer in the microprofiles of stems, senescent leaves, and mature leaves reduced by 29.0%, 49.72%, and 70.34%, and the O2, pH, and oxidation-reduction potential fluctuation amplitudes also declined accordingly. Our results suggest that a thick periphyton exerted negative effects on the growth of macrophytes by providing extensive shading and creating a barrier that hindered the transport of dissolved substances such as O2, and led to premature decline in macrophytes in the eutrophic Taihu Lake. The consequent implications can help to elucidate the control mechanism of the broad diffusive boundary layer around macrophytes on nutrient cycling in eutrophic waters and to better understand the role of this layer in the Taihu Lake and other similar eutrophic waters.

The mechanism of improved aeration due to gas films on leaves of submerged rice

Some terrestrial wetland plants, such as rice, have super-hydrophobic leaf surfaces which retain a gas film when submerged. O2 movement through the diffusive boundary layer (DBL) of floodwater, gas film and stomata into leaf mesophyll was explored by means of a reaction-diffusion model that was solved in a three-dimensional leaf anatomy model. The anatomy and dark respiration of leaves of rice (Oryza sativa L.) were measured and used to compute O2 fluxes and partial pressure of O2 (pO2 ) in the DBL, gas film and leaf when submerged. The effects of floodwater pO2 , DBL thickness, cuticle permeability, presence of gas film and stomatal opening were explored. Under O2 -limiting conditions of the bulk water (pO2 < 10 kPa), the gas film significantly increases the O2 flux into submerged leaves regardless of whether stomata are fully or partly open. With a gas film, tissue pO2 substantially increases, even for the slightest stomatal opening, but not when stomata are completely closed. The effect of gas films increases with decreasing cuticle permeability. O2 flux and tissue pO2 decrease with increasing DBL thickness. The present modelling analysis provides a mechanistic understanding of how leaf gas films facilitate O2 entry into submerged plants.

Evidence and Recommendations to Support the Use of a Novel Passive Water Sampler to Quantify Antibiotics in Wastewaters

A novel passive water sampler (diffusive gradients in thin-films for organics, o-DGT) was previously developed and successfully tested in the laboratory, but has not yet been validated in the field. Here, o-DGT samplers were deployed in the influent and effluent of a typical UK wastewater treatment plant (WWTP); the influent was also sampled with a conventional automatic sampler (Auto) and by grab (Grab) sampling. All the samples were analyzed by LC-MS/MS for 40 target antibiotics (including 16 sulfonamides (SAs), 12 fluoroquinolones, 6 macrolides, 2 ionophores, 2 diaminopyimidines, 1 aminocoumarin, and 1 lincosamide). The diffusion coefficients (D) of these antibiotics in o-DGT, measured in the laboratory, ranged from 0.58 × 10(-06) to 6.24 × 10(-06) cm(2) s(-1). The derived surface area normalized sampling rates (RS/A, 0.54-5.74 mL d(-1) cm(-2)) were comparable with those for another passive sampler called POCIS. Fourteen antibiotics were detected in the actively sampled water samples, with 10 of the 14 detected in o-DGT devices deployed for more than 7 days. Most of the antibiotics detected in o-DGT, except sulfapyridine, were continually accumulated by o-DGT for ~10 days. Deployment for 7 days is recommended to integrate ambient concentrations over time, without risks of reaching capacity and significant biofouling. Diffusive boundary layer (DBL) thickness had less effect on the o-DGT measurement than reported for other passive samplers. The comparison between o-DGT and Auto and Grab samplings showed that o-DGT was more efficient in terms of cost, time, and labor. This study demonstrates for the first time in a real environment that o-DGT is an effective tool for the routine monitoring of antibiotics in wastewaters and provides a powerful approach to studying their occurrence, fate, and behavior in the environment.

Diffusive boundary layer influenced by bottom boundary hydrodynamics in tidal flows

[1] Field measurements of the diffusive boundary layer (DBL) and bottom boundary layer (BBL) in two distinctly different coastal ocean environments are analyzed. The dynamic conditions of the BBL have a strong influence on the DBL thickness (δDBL) and oxygen diffusive fluxes at the sediment-water interface. Three different estimates of the Batchelor length (LB) in the BBL are obtained from the measured dissipation rate of turbulent kinetic energy (εm), turbulent friction velocity (u*), and tidal velocity (Um) and bottom roughness length (z0). The two estimates of LB from εm and u* have low correlations with δDBL. The estimate of LB from Um and z0 has a higher correlation with δDBL at both sites, suggesting a simple estimation of δDBL.

Water-flow mediated oxygen dynamics within massive Porites-algal turf interactions

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 490:1-10 (2013) - DOI: https://doi.org/10.3354/meps10467 FEATURE ARTICLE Water-flow mediated oxygen dynamics within massive Porites-algal turf interactions Anya L. Brown1,2,*, Robert C. Carpenter1 1California State University, 15111 Nordhoff Street, Northridge, California 91330, USA 2Present address: University of Florida, Gainesville, Florida 32611, USA *Email: anyabrown@ufl.edu ABSTRACT: Negative interactions between corals and algae have been implicated in preventing coral reef recovery. A recent hypothesis is that algae indirectly cause coral tissue mortality by fueling microbial growth, which drives hypoxic conditions at the interface between corals and algae. However, previous studies have largely ignored how water flow influences oxygen concentrations at the interface between corals and algae. This study quantified the effect of water flow on oxygen concentrations above the zone of interaction between massive Porites spp. and algal turf during the day and at night. Coral-algal interactions were exposed to 3 flow speeds (0, 7.7, 14.5 cm s-1), and diffusive boundary layer (DBL) thicknesses were measured in the light and dark. DBL thickness (<500 to 2500 µm) decreased with increasing water flow, but remained thicker above algal turf and the zone of interaction (~1000 µm) than over corals (370 µm) in the dark. Oxygen extremes above the zone of interaction were most similar to concentrations above algal turf in low flow (34 to 43% oxygen saturation). The influence of microbes on oxygen conditions was estimated by adding antibiotic (50 µg ampicillin ml-1) to algal turf-massive Porites interactions. The results showed no indication of microbially mediated hypoxic conditions. These results suggest that water flow likely limits the effectiveness of hypoxia or hyperoxia-mediated coral-algal competition under natural reef conditions. KEY WORDS: Water flow · Oxygen concentrations · Coral-algal interactions · Microbially mediated interactions Full text in pdf format Information about this Feature Article NextCite this article as: Brown AL, Carpenter RC (2013) Water-flow mediated oxygen dynamics within massive Porites-algal turf interactions. Mar Ecol Prog Ser 490:1-10. https://doi.org/10.3354/meps10467 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 490. Online publication date: September 17, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.