Oxygen Diffusion Research Articles

Progress on oxygen-releasing bioactive polymeric scaffolds in tissue engineering and biomedical treatment: A review.

Tissue engineering presents promising avenues for addressing issues related to tissue defects and regenerative medicine. However, the translational efficacy of tissue engineering in clinical settings remains limited, primarily due to the inadequate survival rates of implanted tissue scaffolds. This is attributed to the grafts' inability to adequately supply oxygen and their dependence on the diffusion of oxygen from surrounding tissues for tissue regeneration. The integration of oxygen-releasing materials in human tissue engineering is anticipated to enhance the hypoxic microenvironment for tissue regeneration. In recent years, a variety of oxygen-producing or oxygen-carrying biomacromolecules, including gelatin, chitosan, and alginate, have been developed, offering innovative strategies for controlled drug release efficacy, regenerative medicine, and biological systems engineering. This review examines applications of these oxygen-releasing biological macromolecules, primarily derived from natural polymeric materials, in diverse facets of human tissue engineering including skin, heart tissue, tumor therapy. We also highlight recent advancements in this field, with an emphasis on current challenges, potential solutions, and future perspectives.

Predicting and understanding vacancy-modified oxygen diffusion in dilute Ni-based alloys by first-principles calculations

Predicting and understanding vacancy-modified oxygen diffusion in dilute Ni-based alloys by first-principles calculations

Thermo-oxidative degradation behavior of vulcanized butadiene rubber under thermal recycling conditions

Thermo-oxidative reclamation of tire rubber has been proven to be an energy-efficient method for upcycling end-of-life tire. As one of the key components, the complicated oxidative degradation behavior of butadiene rubber (BR) has significantly hindered the reclamation efficiency of tire rubber. This study investigated the thermo-oxidative degradation behavior of vulcanized BR in the temperature range (180-240°C) typically used for reclamation. The influence of oxygen diffusion on the degradation evolution of vulcanized BR was investigated using stacked sheet samples, by characterization of their chemical structure, network structure and mechanical properties during the degradation processes. The chemical structure changes indicated that increased surface oxidation led to more pronounced heterogeneous oxidative distribution within the stack. The different layers exhibited distinct degradation changes due to the competition among chain scission and recombination of rubber network structures in degraded BR. The depth profiles monitored by atomic force microscopy (AFM) observed a high-degree oxidized layer with newly crosslinked structures formed at the stacked sample surface, which was the main cause leading to the heterogeneous oxidative degradation. Additionally, the degradation degree of vulcanized BR was analyzed across different temperatures, with the highest degree of degradation was achieved at 210°C in 20 min.

Combined composite membrane and gas diffusion oxygen electrode toward alkaline electrolyzer for efficient electrocatalytic water splitting

Combined composite membrane and gas diffusion oxygen electrode toward alkaline electrolyzer for efficient electrocatalytic water splitting

Probing Impact of Support Pore Diameter on Three-phase Interfaces of Pt/C Catalysts by Molecular Dynamic Simulation.

Investigating how the size of carbon support pores influences the three-phase interface of platinum (Pt) particles in fuel cells is essential for enhancing catalyst utilization. This study employed molecular dynamics simulations and density functional theory calculation to examine the effects of mesoporous carbon support size, specifically its pore diameter, on Nafion ionomer distribution, as well as on proton and gas/liquid transport channels, and the utilization of Pt active sites. The findings show that when Pt particles are located within the pores of carbon support (Pt/PC), there is a significant enhancement in the spatial distribution of Nafion ionomer, along with a reduction in encapsulation around the Pt particles, compared to when Pt particles are positioned on the surface or in excessively large pores of the carbon support. While increasing pore diameter improves the construction of proton transport channels formed by sulfonate groups of Nafion ionomer and water molecules, it also raises the risk of obstructing oxygen diffusion. To achieve maximum Pt utilization and exchange current density, it is essential to balance the proton and gas/liquid transport channels. Among the models investigated, the Pt/PC-8 nm system demonstrates the highest Pt utilization. This work offers valuable insights for designing carbon support materials to optimize three-phase interfaces in the catalytic layer of fuel cells.

Pt‐Based 3D Electrocatalyst with Process‐Friendly Features for PEMFCs Possessing Fast Activation and Improved Mass‐Transfer Properties

AbstractPolymer‐electrolyte‐membrane fuel cells (PEMFCs) face the challenges like slow oxygen reduction reaction (ORR) kinetics and limited mass transport at high current densities, which affects their performance. The efficient water removal from the cathode is essential to improve oxygen diffusion. Addressing this, a catalyst is presented with platinum (Pt) nanoparticles distributed within a 3D carbon network (Pt/3DPDC) derived from the polydopamine‐coated melamine foam. This unique architecture enhances Pt utilization and water management due to its high porosity and ample free spaces, providing a process‐friendly feature for the electrode under PEMFC conditions. The pores and accessible texture of the 3D polydopamine derived carbon (3DPDC) framework facilitate ionomer uptake during the electrode fabrication, extending the active triple‐phase boundary and improving the membrane electrode assembly (MEA) performance. The high porosity of Pt/3DPDC is mitigated by adding a small amount of commercial fuel cell catalayst (Pt/C), which maintains the effective catalyst number density per unit area by utilizing the excess porosity of the 3DPDC framework. This controlled interplay of the unique catalyst structure and spatially confined distribution of Pt/C within the Pt/3DPDC framework offers fast activation, reduced electrode flooding, and improved current densities across the operating potential window. This carefully engineered catalyst, designed through bottom‐up strategies, is a promising electrocatalyst for practical PEMFC applications.

Single-Step Production of Doubly Re-entrant Microstructures Through Reaction-Diffusion Photolithography for Omniphobic Surfaces.

Omniphobic surfaces, which repel virtually any liquid regardless of its wettability, have been developed using doubly re-entrant microstructures. Although various microfabrication techniques have been explored, these often require multiple complex steps. In this study, reaction-diffusion photolithography (RDP) is used to fabricate micropost arrays with doubly re-entrant geometries through a single-step ultraviolet (UV) exposure process. To create a doubly re-entrant structure consisting of a central, elongated micropost topped with a short ridge, a photomask featuring a circular window surrounded by a narrow ring-shaped window is employed. This configuration is utilized in the RDP process, which relies on radical polymerization. Vertical growth of the structure from the photomask is achieved by introducing strong UV attenuation along the vertical axis, enabled by increasing the photoinitiator concentration. Concurrently, the growth of the ridge is slowed down by designing the ring window with minimal dimensions. This promotes rapid oxygen diffusion into the ring region, where the radicals generated by UV exposure are consumed through reactions with oxygen, thereby delaying the polymerization. This approach enables precise fabrication of full-length central microposts with short ridges in a single step. The resulting doubly re-entrant structures show high contact angles across various liquids and exhibit robust omniphobic performance.

Biogeochemical cycling of sedimentary organic carbon and benthic nutrient fluxes in the semi-enclosed Jinhae Bay, Korea: insights into benthic-pelagic coupling

The mineralization of organic matter at the sediment plays a crucial role in ecosystem functioning by facilitating the biogeochemical cycling of carbon and nutrients. This process not only supports nutrient availability for primary production but also regulates the long-term storage of carbon within sediments. To understand the biogeochemical processes associated with organic matter mineralization and nutrient regeneration, we estimated total and diffusive sediment oxygen uptake rates, benthic nutrient fluxes, and organic carbon (OC) budgets at four sites in the semi-enclosed Jinhae Bay (JB). The total oxygen uptake (TOU) rates ranged from 38.4 to 49.6 mmol O2 m–2 d–1, and diffusive oxygen uptake (DOU) rates ranged from 12.3 ± 1.8 to 15.1 ± 1.4 mmol O2 m–2 d–1. The average ratio of TOU : DOU ranged from 3.12 to 3.28 over JB, which suggests significant benthic faunal activities in JB sediments. The vertical flux of organic carbon ranged from 45.5 ± 7.0 to 93.0 ± 25.3 mmol C m-2 d–1, and mainly consisted of biodeposits associated with aquaculture activities. The burial flux into the sediment ranged from 3.96 ± 1.00 to 7.17 ± 1.64 mmol C m–2 d–1, and burial efficiencies were 4.25 to 15.8%, which indicated that deposited organic carbon was either mineralized in surface sediment before burial or laterally transferred by resuspension. The benthic nutrient fluxes at four sites ranged from 1.50 to 2.07 mmol m–2 d–1 for nitrogen, from 0.02 to 0.05 mmol m–2 d–1 for phosphate, and from 6.72 to 9.11 mmol m–2 d–1 for silicate. The benthic nitrogen and phosphate fluxes accounted for 82.1 to 149% and 23.1 to 57.6%, respectively, of the required levels for primary production in the water column. Our results suggest that OC oxidation in the JB sediment may significantly contribute to the biogeochemical OC cycles and tight benthic–pelagic coupling associated with nutrient regeneration.

Insights into the diverse roles of the terminal oxidases in Burkholderia cenocepacia H111

Burkholderia cenocepacia H111 is an obligate aerobic bacterium which has been isolated from a cystic fibrosis (CF) patient. In CF lungs the environment is considered micro-oxic or even oxygen-depleted due to bacterial activities and limited oxygen diffusion in the mucus layer. To adapt to low oxygen concentrations, bacteria possess multiple terminal oxidases. In this study, we identified six terminal oxidases of B. cenocepacia H111 and constructed reporter strains to monitor their expression in different environments. While the heme-copper oxidase aa3 (cta) was constitutively expressed, the bd-1 oxidase (cyd) was induced under oxygen-limited growth conditions. The cyanide-insensitive bd-type terminal oxidase (cio-1) was mainly expressed in cells grown on the surface of solid medium or in liquid cultures in presence of cyanide, which is known to be produced in the CF lung by the often co-residing CF pathogen Pseudomonas aeruginosa. Indeed, a cio-1 insertional mutant was not able to grow in the presence of cyanide confirming the important role of Cio-1 in cyanide resistance. The caa3 oxidase (caa), was only expressed under nutrient limitation when cells were grown on the surface of solid medium. We also investigated the involvement of two regulatory systems, Anr and RoxS/RoxR, in the expression of cio-1 and cyd. Our data suggest, that, given that Cio-1 is only present in prokaryotes and plays an important role in the defense against cyanide-producing P. aeruginosa, it may be a valuable drug target for treatment of polymicrobial infections in CF patients.

Thermo-Magnetic Bioconvection Flow in A Semi-Trapezoidal Enclosure Filled With A Porous Medium Containing Oxytactic Micro-Organisms: Modelling Hybrid Magnetic Bio-Fuel Cells

Abstract Hybrid fuel cells are becoming increasingly popular in 21st century energy systems engineering. These systems combine multiple features including various geometries, electromagnetic fluids, bacteria (micro-organisms), thermo-solutal convection and porous media. Motivated by these developments in the present work we simulate the two-dimensional magnetohydrodynamic (MHD) natural triple convection flow in a semi-trapezoidal enclosure saturated with electrically conducting water containing oxytactic microorganisms and oxygen species. Darcy?s model is deployed for porous media drag effects. The primitive governing partial differential conservation equations for mass, momentum, energy, oxygen species and motile micro-organism species density are transformed using a vorticity-stream function formulation and non-dimensional variables into a nonlinear boundary value problem. A numerical solution is obtained using a finite difference method with incremental time steps. The mathematical model features a number of controlling parameters i.e. Prandtl number, Rayleigh number, Bioconvective Rayleigh number, Darcy parameter, Hartmann (magnetic body force) number, Lewis number, Péclet number, Oxygen diffusion ratio, fraction of consumption oxygen to diffusion of oxygen parameter. Transport characteristics (streamlines, isotherms, oxygen iso-concentration and motile micro-organism concentration) are computed for several of these parameters. Microorganisms? impact on the rate of heat transfer at the boundaries is found to be beneficial or destructive, depending on combination of other parameters in the simulations. Additionally, Nusselt number and oxygen species Sherwood number are computed at the hot vertical wall. The simulations are relevant to hybrid electromagnetic microbial fuel cells.

Functionally Graded Oxide Scale on (Hf,Zr,Ti)B2 Coating with Exceptional Ablation Resistance Induced by Unique Ti Dissolving.

Multicomponent Ti-containing ultra-high temperature ceramics (UHTCs) have emerged as more promising ablation-resistant materials than typical UHTCs for applications above 2000 °C. However, the underlying mechanism of Ti improving the ablation performance is still obscure. Here, (Hf,Zr,Ti)B2 coatings are fabricated by supersonic atmospheric plasma spraying, and the effects of Ti content on the ablation performance under an oxyacetylene flame are investigated. The (Hf0.45Zr0.45Ti0.10)B2 coating shows superior ablation resistance and cycling reliability at ≈2200°C. A functionally graded oxide scale comprising an outer dense layer and an underlying fine granular layer formed. The former is a better oxygen barrier owing to fewer cracks and the latter has high strain tolerance due to finer grain size. The uniform dissolving of ≈4 mol% Ti in the inner layer results in grain refinement via sluggish diffusion and thus stress release. For the outer layer, Ti segregation at the nanoscale leads to a metastable cubic (Hf,Zr,Ti)O2 and local severe lattice distortion, inhibiting the propagation of cracks. Ti ions' unique dissolving in the oxide scale enables a strong oxygen diffusion barrier with high strain tolerance, which is responsible for superior performance. This study provides new insights into the ablation behavior of Ti-containing multicomponent UHTCs.

Correlation of srf performance to oxygen diffusion length of medium temperature heat treated cavities*

Abstract This comprehensive study, being part of the European XFEL R\&D effort, elucidates the influence of medium temperature (mid-T) heat treatments between 250°C and 350°C on the performance of 1.3~GHz superconducting radiofrequency (SRF) niobium cavities. 
Utilizing a refurbished niobium retort furnace equipped with an inter-vacuum chamber and cryopumps at DESY, we have embarked on an investigation to enhance the state-of-the-art SRF cavity technology. Our research reveals that mid-T heat treatments significantly boost the quality factor ($Q_0$) of the cavities, achieving values between $2\cdot10^{10}$ to $5\cdot10^{10}$ at field strengths around 16~MV/m, while the maximum field strengths are limited to 25-35~MV/m and enhanced sensitivity to trapped magnetic flux is observed. Moreover, we delve into the effects of surface impurity concentration changes, particularly the diffusion of oxygen content, and its impact on performance enhancements. By categorizing treatments based on calculated diffusion lengths using the whole temperature profile, we recognize patterns that suggest an optimal diffusion length conducive to optimizing cavity performance. SIMS results from samples confirm the calculated oxygen diffusion lengths in most instances. Deviations are primarily attributed to grain boundaries in fine-grain materials, necessitating repeated measurements on single-crystal materials to further investigate this phenomenon. Investigations into cooling rates and the resulting spatial temperature gradients across the cavities ranging from 0.04 to 0.2~K/mm reveal no significant correlation with performance following a mid-T heat treatment. However, the increased sensitivity to trapped magnetic flux leads to new challenges in the quest for next-generation accelerator technologies since the requirement for magnetic hygiene gets stricter.

Dehydrogenase versus oxidase function: the interplay between substrate binding and flavin microenvironment.

Redox enzymes, mostly equipped with metal or organic cofactors, can vary their reactivity with oxygen by orders of magnitudes. Understanding how oxygen reactivity is controlled by the protein milieu remains an open issue with broad implications for mechanistic enzymology and enzyme design. Here, we address this problem by focusing on a widespread group of flavoenzymes that oxidize phenolic compounds derived from microbial lignin degradation, using either oxygen or a cytochrome c as electron acceptors. A comprehensive phylogenetic analysis revealed conserved amino acid motifs in their flavin-binding site. Using a combination of kinetics, mutagenesis, structural, and computational methods, we examined the role of these residues. Our results demonstrate that subtle and localized changes in the flavin environment can drastically impact on oxygen reactivity. These effects are afforded through the creation or blockade of pathways for oxygen diffusion. Substrate binding plays a crucial role by potentially obstructing oxygen access to the flavin, thus influencing the enzyme's reactivity. The switch between oxidase and dehydrogenase functionalities is thereby achieved through targeted, site-specific amino acid replacements that finely tune the microenvironment around the flavin. Our findings explain how very similar enzymes can exhibit distinct functional properties, operating as oxidases or dehydrogenases. They further provide valuable insights for the rational design and engineering of enzymes with tailored functions.

First principles density functional theory study of tritium species adsorption on Ni(111) surface and diffusion in nickel-sublayer for tritium storage.

The nickel-plated zircaloy-4 is used as a tritium (3H) getter in the tritium-producing burnable absorber rods (TPBARs) to capture 3H produced in the 6Li-riched annular γ-LiAlO2 pellet under neutron irradiation. The experimental data and our previous theoretical results showed that the 3H species produced from the γ-LiAlO2 pellet were mainly 3H2 and 3H2O. These 3H species diffuse from the surface of the LiAlO2 pellet across vacuum to the nickel-plated zircaloy-4 getter and then further diffuse into the getter to chemically form metal hydrides. While a number of studies show that oxygen binds strongly as compared to 3H on the nickel (Ni) layer, the detailed mechanism of 3H species absorption and diffusion across the Ni plate and Ni/Zr interface are still unclear. By employing density functional theory calculations, here we explored the 3H2 and 3H2O species adsorption and dissociation on the Ni(111) surface and diffusion into the Ni sublayer. Our results indicated that the 3H2 and 3H2O dissociate on the Ni(111) surface. The NiOx and Ni(O3H)x could be formed in the Ni layer due to the higher oxygen (O) diffusion energy barrier and formation of Ni vacancy defects. The oxygen was found to be retained in the Ni layer from diffusing across the Ni-Zr interface. This was revealed by comparing the diffusion barriers for 3H with O. 3H was found to have nearly three times smaller diffusion barrier than for O, making 3H comparatively easier to diffuse through the Ni layer. The obtained results provide guidelines for experimental measurements on 3H retention behavior in TPBARs and may open further avenues to explore the impurity effects on 3H diffusion and storage at the Ni/zircaloy interfaces.

Enhanced accident tolerance properties of AlCrCuFeMoNbx high entropy coating for nuclear fuel cladding

High entropy alloy AlCrCuFeMoNbx (x=0.5, 0.8, 1.4, 2.0) coatings were deposited on Zr-1Nb alloy substrates by magnetron co-sputtering to improve the accident tolerance capability of the nuclear fuel cladding. The structural and accidental tolerant properties of high-entropy alloy coatings have been investigated comprehensively. The results show that coatings with varying Nb contents exhibit amorphous structures. The hardness and elastic modulus of the coatings increase with the Nb content, reaching their maximum values at x = 2.0, which are 11.38GPa and 186.05GPa, respectively. In both the simulated normal operating and accident environment of the nuclear fuel cladding, the oxidation resistance of the coating has been investigated. The best oxidation resistance was achieved at x=0.8 in pure water at 360℃under 18.6MPa for 3 days. The dense Cr2O3 and CrNbO4 oxide films generated on the surface hinder the diffusion of oxygen ions, and account for the lower weight gain 5.10mg/dm2, decreased by 56.4% compared to that of the uncoated zirconium alloy. The coating with x=0.5 showed a drastic reduction in oxidized weight gain by 84.02% compared to the uncoated zirconium alloy in water steam at 1200℃, demonstrating excellent accident tolerance, which is due to the dense α-Al2O3 and CrNbO4 protective layer generated on the surface of the coating. These findings suggest that high entropy alloy coatings have promising accidental tolerance capabilities for nuclear fuel cladding.

Analysis of remelted layers of DD6 single-crystal superalloys by water jet-guided laser processing

This study investigates the characteristics of the remelted layer in DD6 nickel-based single-crystal superalloy processed with a water-jet guided laser (WJGL). Analysis focused on changes in surface morphology, elemental distribution, and crystal structure. WJGL induced periodic thermal stresses, forming distinct ridges within the remelted layer, which differ in morphology from the unprocessed matrix. At the interface, interactions between oxygen and elements such as aluminum, nickel, and chromium led to the formation of oxides, which are strategically evaluated for their role in surface transformations. The oxygen diffusion coefficient, calculated at 1.5×10⁻¹⁵ m²/s using Fick's second law, illustrates the extent of these interactions. The study also reveals thin polycrystalline layers with minimal orientation deviations from the matrix, maintaining the alloy's overall structural integrity. Additionally, the processing direction was found to influence the crystal orientation in the remelted layer, moderated by the turbulence from the water jet. These findings contribute to understanding the microstructural effects of WJGL processing, with implications for optimizing high-temperature alloy applications in aerospace engineering.

Novel ionic liquid-infused PVA-based anion exchange membranes boosting bioelectricity yield from microbial fuel cells.

The goal of this research is to develop and characterize low-cost NH4I doped polyvinyl alcohol (PVA)-4-ethyl-4-methylmorpholiniumbromide (ionic liquid) anion exchange membranes (AEM) and its application for membrane cathode assembly. Physical characterization like FTIR, POM, and XRD notified the functional groups, basic structure, and amorphosity of the produced membrane, and it was employed in single-chambered microbial fuel cells (sMFCs) as a separator. The membranes in terms of oxygen diffusion, proton conductivity, and ion exchange capabilities were evaluated. PVA-ionic liquid composite membrane had a greater volumetric power density (PD) with a rise in the ionic liquid concentration, owing to lower internal resistance and reduced biofouling. Ionic conductivity also reduces as loading increases over a certain level of concentration. The incorporation of ionic liquid into the membrane had a considerable impact on impedance minimization (an enhancement in anionic conductivity) and biofouling. When MFC was used with a PVA-ionic liquid-based membrane cathode assembly (MCA), the highest PD of 7.98W/m3 was attained which is better than other composite membranes. The MCA surface area boosted the power output. The PVA-ionic liquid composite membrane proved to be a viable alternative to the more costly commercially available MFC membrane. This paper's novelty lies in synthesizing ammonium iodide (NH4I) doped PVA-ionic liquid membrane and further utilizing it as a separator in MFC. Also, this study demonstrates the membrane's potential for enhancing MFC performance, establishing it as a viable alternative to expensive commercial membranes.

Early vitrectomy in the management of diabetic macular oedema

Diabetic macular oedema (DMO) poses a significant challenge in the management of diabetic retinopathy (DR), contributing to substantial visual impairment in diabetic patients. Over the years, vitrectomy has emerged as a valuable surgical approach in the armamentarium against DMO, and has evolved to play a pivotal role in addressing cases refractory to conventional therapies, either as a standalone or as adjunctive therapy. The rationale behind this approach lies in the ability of vitrectomy to directly remove the vitreous scaffold, which is implicated in the pathogenesis of DMO via two basic mechanisms, the tractional and the biochemical.Vitrectomy can eliminate both the anterior‐posterior traction caused by the vitreous, and the tangential forces on the macula, caused by epiretinal membranes, both common contributors to DMO. Clearance of the vitreomacular interface alleviates the mechanical stress on the macula, leading to improvements in central retinal thickness and visual acuity. Furthermore, improved visualisation of the macula facilitates the monitoring and management of the DMO and the DR in the long term.In terms of the biochemical component, vitrectomy can play a significant role in modulating oxygen consumption of the vitreous and alleviating retinal hypoxia. The vitreous humour serves as a conduit for oxygen diffusion to the avascular inner retina. In diabetic eyes, vitreous liquefaction and retinal vascular deficiency disrupt oxygen transport, exacerbating retinal hypoxia and promoting VEGF production and neovascularisation. Studies have shown that vitrectomy can increase the oxygen delivery to the retina and improve the perifoveal capillary blood flow. Oxygen is known to suppress VEGF, and thus reduce vascular permeability leading to DMO improvement. Moreover, recent studies have shown that removal of the vitreous reduces the levels of histamine, VEGF, and free radicals in the preretinal space. Additionally, the foveal avascular zone has been shown to decrease after vitrectomy, which might indicate a protective effect on DMO, similar to anti‐VEGF injections.However, the exact mechanisms by which vitrectomy may improve DMO are not yet fully understood, neither is the prognosis for post‐operative visual improvement. The functional outcomes in different studies are very heterogenous and vary from significant vision gain to no improvement despite good anatomical results. The preoperative integrity of the external limiting membrane and the pre‐existing damage to the outer retina often limit the outcome. Additionally, a subretinal fluid component of DMO seems to affect the visual prognosis, while the advantage of inner limiting membrane peeling, in the cases of non‐tractional DMO, remains controversial, as there is no substantial data available to clarify its efficacy.Finally, another significant factor is the time of intervention, as it seems that early vitrectomy in treatment‐naive patients can offer better outcomes, and has been gaining ground among specialists.In conclusion, vitrectomy offers a multifaceted approach in the management of DMO addressing both mechanical and biochemical pathways. Early intervention has shown significant advantages. Continued research and longer‐term studies will further enhance our understanding and refine its therapeutic utility as a standalone and/or adjunctive treatment.

Foraminiferal denitrification and deep bioirrigation influence benthic biogeochemical cycling in a seasonally hypoxic fjord

Benthic macro- and micro-biota often play significant roles in controlling the biogeochemical dynamics in sediments. Their activity can be influenced by oxygen availability and impacted by the rise in global hypoxia in coastal regions over the last decades. To understand how these organisms interact with coastal hypoxia and influence sediment biogeochemistry, we undertook a study of early diagenesis in Bedford Basin, a seasonally hypoxic fjord on the West Atlantic coast in Nova Scotia, Canada, using a combination of observations and reaction-transport modeling. We observed that the seafloor was a source of ammonium and sink of nitrate with average fluxes of 2.2 ± 1.8 and −0.9 ± 0.7 mmol m−2 d−1 respectively. The diffusive oxygen uptake was 14 ± 4.6 mmol m−2 d−1 and the total organic carbon content in collected sediment cores was 5–7 % with a C/N ratio of ∼10. The pyrite content increased steadily from 0.5 wt% Fe at surface to ∼2 wt% Fe at 20 cm depth. Hydrogen sulfide was negligible down to 25 cm depth most of the time. The sediment was inhabited by tube-forming polychaete Spiochaetopterus sp. that formed tubes up to ∼30 cm in length. The living foraminiferal assemblage in the top 5 cm sediment was found to be dominated (>85 %) by nitrate-storing and denitrifying benthic foraminifera Stainforthia fusiformis. These observations were used to develop and constrain a biogeochemical reaction-transport model. The model results suggest that the observed decrease in porewater concentrations of ammonium and dissolved inorganic carbon below 5 cm depth, was due to deep bioirrigation by tubeworms, accounting for almost 50 % of the benthic efflux. The model further revealed that the deep bioirrigation along with bioturbation and iron cycling prevented accumulation of free sulfide in the top 25 cm sediment despite oxygen penetration depths of ∼1 mm. Modelled organic carbon and nitrogen deposition was 25.2 and 2.9 mmol m−2 d−1 with burial efficiencies of 23 % and 17 %, respectively. The model indicated a total denitrification rate of 1.3 mmol N m−2 d−1 that was largely (∼70 %) driven by benthic foraminifera. This study reports the first evidence of foraminiferal denitrification in western Atlantic coastal sediments, and suggests that eukaryote mediated denitrification is an important driver of sediment N-loss in seasonally hypoxic environments, a process that has been traditionally assumed to be carried out by prokaryotic microbes.

Pengaruh Deterjen Cair terhadap Mortalitas dan Perilaku Ikan Nila (Oreochromis niloticus)

The disposal of detergent waste into water bodies leads to environmental problems. The use of detergents is increasing, and the variety of detergents available is also becoming more diverse. This study examines the mortality and behavior of Nile tilapia (Oreochromis niloticus) in response to liquid detergent contaminants. The research was conducted from March to April 2023 at the Fish Behaviour Laboratory, Faculty of Fisheries and Marine Sciences, IPB University. We used 154 individuals of Nile tilapia measuring 5-7 cm. A total of 90 individuals were used for the preliminary test and most of them died at the highest concentration of 100 ml/L within five minutes. Sixty individuals were used for determining LD50–96 and we found that the LD50–96 was 1.29 ml/L. The behavior of four individuals of tilapia was observed using focal animal sampling in four sublethal concentrations. The results show that the detergent contaminant inhibits oxygen diffusion and damages the physiological functions of the tilapia. The detergent concentration level also affects the operculum opening and closing behavior, movement, feeding response, and mortality.