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Introduction: Hypoxia is defined as a critically low-oxygen condition of water, which, if prolonged, can be harmful to fish and many other aquatic species. In the context of ocean salmon fish farming, early detection of hypoxia events is critical for farm managers to mitigate these events to reduce fish stress, however in complex natural systems accurate forecasting tools are limited. The goal of this research is to use a machine learning approach to forecast oxygen concentration and predict hypoxia events in marine net-pen salmon farms. Methods: The developed model is based on gradient boosting and works in two stages. First, we apply auto-regression to build a forecasting model that predicts oxygen concentration levels within a cage. We take a global forecasting approach by building a model using the historical data provided by sensors at several marine fish farms located in eastern Canada. Then, the forecasts are transformed into binary probabilities that indicate the likelihood of a low-oxygen event. We leverage the cumulative distribution function to compute these probabilities. Results and discussion: We tested our model in a case study that included several cages across 14 fish farms. The experiments suggest that the model can detect future hypoxic events with a commercially acceptable false alarm rate. The resulting probabilistic predictions and oxygen concentration forecasts can help salmon farmers to prioritize resources, and reduce harm to crops. [ABSTRACT FROM AUTHOR]

Global warming is destabilizing the cryosphere, with consequences for glaciers, permafrost, sea ice and lake ice. Polar lakes have short ice‐free seasons, and small changes in ice cover duration have the potential to provoke alterations to ecosystem structure. However, these lakes are understudied, and the consequences for mixing regimes, thermal structures and biogeochemical processes remain unclear. We measured three annual cycles of dissolved oxygen, temperature and specific conductivity in a lake at ∼83°N to investigate limnological processes and their interannual variability. There were sharp interannual contrasts in lake dynamics, with state shifts in mixing, stratification and oxygen regimes due to air temperature variability and meteorological events. We also observed unusual thermal profiles that were associated with solute gradients. These striking differences underscore the sensitivity of high Arctic lakes to interannual variations in meteorological forcing, and their susceptibility to regime shifts in response to ongoing global change. Plain Language Summary: Lakes are biodiversity refuges, climate regulators and providers of ecosystem services. High Arctic lakes experience brief summer ice‐free periods and their annual dynamics remain largely unexplored despite their location in one of the most rapidly warming regions on Earth. In particular, patterns of thermal structure and oxygen dynamics have rarely been measured. We studied three complete annual cycles in a coastal lake less than 100 km south of the northernmost land on Earth. The observed limnological dynamics highlight the potential for rapid regime shifts in polar lakes and underline their sensitivity to interannual differences in environmental conditions. Key Points: Pronounced shifts in lake oxygen and temperature dynamics occur due to interannual air temperature variation and meteorological episodesDivergent annual trajectories in lake structure and functioning highlight the vulnerability of high Arctic lakes to climate change [ABSTRACT FROM AUTHOR]

IntroductionHypoxia is defined as a critically low-oxygen condition of water, which, if prolonged, can be harmful to fish and many other aquatic species. In the context of ocean salmon fish farming, early detection of hypoxia events is critical for farm managers to mitigate these events to reduce fish stress, however in complex natural systems accurate forecasting tools are limited. The goal of this research is to use a machine learning approach to forecast oxygen concentration and predict hypoxia events in marine net-pen salmon farms.MethodsThe developed model is based on gradient boosting and works in two stages. First, we apply auto-regression to build a forecasting model that predicts oxygen concentration levels within a cage. We take a global forecasting approach by building a model using the historical data provided by sensors at several marine fish farms located in eastern Canada. Then, the forecasts are transformed into binary probabilities that indicate the likelihood of a low-oxygen event. We leverage the cumulative distribution function to compute these probabilities.Results and discussionWe tested our model in a case study that included several cages across 14 fish farms. The experiments suggest that the model can detect future hypoxic events with a commercially acceptable false alarm rate. The resulting probabilistic predictions and oxygen concentration forecasts can help salmon farmers to prioritize resources, and reduce harm to crops.

Increasing evidence demonstrates that mammals have different reactions to hypoxia with varied oxygen dynamic patterns. It takes ∼24 h for tri-gas incubator to achieve steady cell hypoxia, which fails to recapitulate ultrafast oxygen dynamics of intestinal ischemia/reperfusion (IR) injury. Inspired from the structure of native intestinal villi, we engineered an intestinal organoid chip embedded with engineered artificial microvessels based on co-axial microfluidic technology by using pH-responsive ZIF-8/sodium alginate scaffold. The chip was featured on: (i) eight times the oxygen exchange efficiency compared with the conventional device, tri-gas incubator, (ii) implantation of intestinal organoid reproducing all types of intestinal epithelial cells, and (iii) bio-responsiveness to hypoxia and reoxygenation (HR) by presenting metabolism disorder, inflammatory reaction, and cell apoptosis. Strikingly, it was found for the first time that Olfactomedin 4 (Olfm4) was the most significantly down-regulated gene under a rapid HR condition by sequencing the RNA from the organoids. Mechanistically, OLFM4 played protective functions on HR-induced cell inflammation and tissue damage by inhibiting the NF-kappa B signaling activation, thus it could be used as a therapeutic target. Altogether, this study overcomes the issue of mismatched oxygen dynamics between in vitro and in vivo, and sets an example of next-generation multisystem-interactive organoid chip for finding precise therapeutic targets of IR injury.

Abstract Global warming is destabilizing the cryosphere, with consequences for glaciers, permafrost, sea ice and lake ice. Polar lakes have short ice‐free seasons, and small changes in ice cover duration have the potential to provoke alterations to ecosystem structure. However, these lakes are understudied, and the consequences for mixing regimes, thermal structures and biogeochemical processes remain unclear. We measured three annual cycles of dissolved oxygen, temperature and specific conductivity in a lake at ∼83°N to investigate limnological processes and their interannual variability. There were sharp interannual contrasts in lake dynamics, with state shifts in mixing, stratification and oxygen regimes due to air temperature variability and meteorological events. We also observed unusual thermal profiles that were associated with solute gradients. These striking differences underscore the sensitivity of high Arctic lakes to interannual variations in meteorological forcing, and their susceptibility to regime shifts in response to ongoing global change.

Direct observation of oxygen dynamics in an oxide‐based second‐order memristor can provide the valid evidence to clarify the memristive mechanism, however, which is still limited for now. In this study, the migration and diffusion of oxygen ions in the region of Pt/WO3‐x Schottky interface are observed in the WO3‐x second‐order memristor by using the technique of in situ transmission electron microscopy (TEM) and the electron energy loss spectroscopy. Interestingly, the coexistence of memristive and memcapacitive switching can be implemented in this memristor. Combined with the analysis of depth‐profile X‐ray photoelectron spectroscopy (XPS), an interface‐barrier‐modulation second‐order memristive model is proposed based on the above results. Notably, temporally correlative oxygen dynamics in the memristor offers the platform to integrate signals from multiple inputs, enabling the realization of the dendritic functions of synchronous and asynchronous integration for the application of logic operations with fault‐tolerance capability and associative learning. These findings provide the experimental evidence to in‐depth understanding of oxygen dynamics and switching mechanism in second‐order memristor, which can support the optimization of memristive performance and the achievement of biorealistic synaptic functions. [ABSTRACT FROM AUTHOR]

Adequate tissue O2 supply is crucial for plant function. We aimed to identify the environmental conditions and plant characteristics that affect plant tissue O2 status. We extracted data and performed meta-analysis on >1500 published tissue O2 measurements from 112 species. Tissue O2 status ranged from anoxic conditions in roots to >53 kPa in submerged, photosynthesising shoots. Using information-theoretic model selection, we identified 'submergence', 'light', 'tissue type' as well as 'light × submergence' interaction as significant drivers of tissue O2 status. Median O2 status were especially low (<50% of atmospheric equilibrium) in belowground rhizomes, potato (Solanum tuberosum) tubers and root nodules. Mean shoot and root O2 were ~25% higher in light than in dark when shoots had atmospheric contact. However, light showed a significant interaction with submergence on plant O2, with a submergence-induced 44% increase in light, compared with a 42% decline in dark, relative to plants with atmospheric contact. During submergence, ambient water column O2 and shoot tissue O2 correlated stronger in darkness than in light conditions. Although use of miniaturised Clark-type O2 electrodes has enhanced understanding of plant O2 dynamics, application of non-invasive methods in plants is still lacking behind its widespread use in mammalian tissues. We collected all (>1500) published measurements of plant O2 levels ever recorded, some measured more than 100 years ago. We found that plant O2 levels depended on in which plant part (e.g. roots or leaves) O2 was measured, and that plant O2 levels become low when plants are flooded, or in darkness. Our findings show that in terms of O2 supply, plants are especially vulnerable to flooded conditions. [ABSTRACT FROM AUTHOR]

Dissolved oxygen (DO) concentration is a fundamental metric to describe climate-related alterations in deep lakes. Increasing water temperatures enhance thermal stratification, leading in temperate basins to a growing isolation of deep waters. This leads to the depletion of hypolimnetic DO, which adds up to limited nutrient circulation and restricted replenishment of the trophogenic layers. With vanishing convective mixing, it is commonly believed that the only source of hypolimnetic DO replenishment will be represented by deep intrusions of cold oxygenated waters from the tributaries. In this study, we first analyse the 1993–2020 long-term observed trends of DO concentrations in the subalpine deep oligomictic Lake Maggiore (Italy/Switzerland). Then, through an algorithm calculating daily intrusion depths and mass discharges of DO for the major tributaries, we show that deep insertions are suppressed for increasing winter water temperatures and residual thermal stratification. Turbulent entrainment is proved fundamental for DO replenishment, leading to mass discharges of DO released into the deep hypolimnion up to more than two orders of magnitude larger than the original ones from the tributaries. Last, we discuss the results of simulations made through a one-dimensional coupled ecological–hydrodynamic model about the possible effects of a full turnover on DO concentrations in the deep hypolimnion. Two cases are displayed, with the turnover taking place either now or with an anoxic hypolimnion deriving from decades of isolation due to severe climate warming. Through this study, climate warming is shown to be a fundamental driver of DO in Lake Maggiore, its depletion harming both water quality and the ecosystem. [ABSTRACT FROM AUTHOR]

Understanding how microbial communities of aquatic ecosystems respond to environmental change remains a critical challenge in microbial ecology. In this study, we used light‐dependent oxic–anoxic micro‐ecosystems to understand how the functioning and diversity of aerobic and anaerobic lake analog communities are affected by a pulse light deprivation. Continuous measurements of oxygen concentration were made and a time series of full‐length 16S rRNA sequencing was used to quantify changes in alpha‐ and beta diversity. In the upper oxic layer, oxygen concentration decreased significantly under light reduction, but showed resilience in daily mean, minimum, and maximum after light conditions were restored to control level. Only the amplitude of diurnal fluctuations in oxygen concentrations did not recover fully, and instead tended to remain lower in treated ecosystems. Alpha diversity of the upper oxic layer communities showed a delayed increase after light conditions were restored, and was not resilient in the longer term. In contrast, alpha diversity of the anoxic lower layer communities increased during the light reduction, but was resilient in the longer term. Community composition changed significantly during light reduction, and showed resilience in the oxic layer and lack of resilience in the anoxic layer. Alpha diversity and the amplitude of daily oxygen fluctuations within and among treatments were strongly correlated, suggesting that higher diversity could lead to less variable oxygen concentrations, or vice versa. Our experiment showed that light deprivation induces multifaceted responses of community function (oxygen respiration) and structure, hence focusing on a single stability component could potentially be misleading. [ABSTRACT FROM AUTHOR]

Abstract Understanding how microbial communities of aquatic ecosystems respond to environmental change remains a critical challenge in microbial ecology. In this study, we used light‐dependent oxic–anoxic micro‐ecosystems to understand how the functioning and diversity of aerobic and anaerobic lake analog communities are affected by a pulse light deprivation. Continuous measurements of oxygen concentration were made and a time series of full‐length 16S rRNA sequencing was used to quantify changes in alpha‐ and beta diversity. In the upper oxic layer, oxygen concentration decreased significantly under light reduction, but showed resilience in daily mean, minimum, and maximum after light conditions were restored to control level. Only the amplitude of diurnal fluctuations in oxygen concentrations did not recover fully, and instead tended to remain lower in treated ecosystems. Alpha diversity of the upper oxic layer communities showed a delayed increase after light conditions were restored, and was not resilient in the longer term. In contrast, alpha diversity of the anoxic lower layer communities increased during the light reduction, but was resilient in the longer term. Community composition changed significantly during light reduction, and showed resilience in the oxic layer and lack of resilience in the anoxic layer. Alpha diversity and the amplitude of daily oxygen fluctuations within and among treatments were strongly correlated, suggesting that higher diversity could lead to less variable oxygen concentrations, or vice versa. Our experiment showed that light deprivation induces multifaceted responses of community function (oxygen respiration) and structure, hence focusing on a single stability component could potentially be misleading.

The aim of the current experiment was to examine the economic efficiency, growth and feed costs of the Nile tilapia subjected to different levels of areal feed inputs during the production cycle. Four feeding strategies were employed; the control treatment included continuous feeding of 8 grams commercial diet/m2/day for 155 days. T1, T2 and T3 included feeding corn at 1.5, 3 and 5 % of biomass, respectively for 60 days, followed by feeding commercial diet at 4, 6 and 8 g/m2/day for additional 95 days, respectively. Data of daytime net primary production (dNNP) among treatments nearly balanced nighttime community respiration (nCR) values. The similar average of dNPP and nCR values recorded in T3 treatment tanks indicated that the feed input of T3 treatment was approximately the maximum safe areal feed input limit without affecting oxygen demand. Daily algal production in rearing units constituted approximately 40% of total combined natural and artificial food available for fish in the control and T3 treatments during the growing season. The feed conversion ratio (1.12:1) and the daily weight gain (0.77 g/fish/day) were significantly improved in the control treatment compared to all other treatments (P<0.05). Consequently, it is recommended to feed Nile tilapia at 8 g diet/m2/day when rearing during the production cycle in order to obtain acceptable growth with higher economic returns. [ABSTRACT FROM AUTHOR]

In pursuing advanced neuromorphic applications, this study introduces the successful engineering of a flexible electronic synapse based on WO 3- x , structured as W/WO 3- x /Pt/Muscovite-Mica. This artificial synapse is designed to emulate crucial learning behaviors fundamental to in-memory computing. We systematically explore synaptic plasticity dynamics by implementing pulse measurements capturing potentiation and depression traits akin to biological synapses under flat and different bending conditions, thereby highlighting its potential suitability for flexible electronic applications. The findings demonstrate that the memristor accurately replicates essential properties of biological synapses, including short-term plasticity (STP), long-term plasticity (LTP), and the intriguing transition from STP to LTP. Furthermore, other variables are investigated, such as paired-pulse facilitation, spike rate-dependent plasticity, spike time-dependent plasticity, pulse duration-dependent plasticity, and pulse amplitude-dependent plasticity. Utilizing data from flat and differently bent synapses, neural network simulations for pattern recognition tasks using the Modified National Institute of Standards and Technology dataset reveal a high recognition accuracy of ∼95% with a fast learning speed that requires only 15 epochs to reach saturation., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

Background and Purpose: Oxygen dynamics may be important for the tissue-sparing effect observed at ultra-high dose rates (FLASH sparing effect). This study investigated the correlation between local instantaneous dose rate and radiation-induced oxygen pressure reduction during proton pencil beam scanning (PBS) irradiations of a sample and quantified the oxygen consumption g-value., Materials and Methods: A 0.2 ml phosphorescent sample (1 μM PtG4 Oxyphor probe in saline) was irradiated with a 244 MeV proton PBS beam. Four irradiations were performed with variations of a PBS spot pattern with 5 × 7 spots. During irradiation, the partial oxygen pressure (pO 2 ) was measured with 4.5 Hz temporal resolution with a phosphorometer (Oxyled) that optically excited the probe and recorded the subsequently emitted light. A calibration was performed to calculate the pO 2 level from the measured phosphorescence lifetime. A fiber-coupled scintillator simultaneously measured the instantaneous dose rate in the sample with 50 kHz sampling rate. The oxygen consumption g-value was determined on a spot-by-spot level and using the total pO 2 change for full spot pattern irradiation., Results: A high correlation was found between the local instantaneous dose rate and pO 2 reduction rate, with a correlation coefficient of 0.96-0.99. The g-vales were 0.18 ± 0.01 mmHg/Gy on a spot-by-spot level and 0.17 ± 0.01 mmHg/Gy for full spot pattern irradiation., Conclusions: The pO 2 reduction rate was directly related to the local instantaneous dose rate per delivered spot in PBS deliveries. The methodology presented here can be applied to irradiation at ultra-high dose rates with modifications in the experimental setup., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Author(s).)

Tropical instability vortices (TIVs) have a major influence on the physics and biogeochemistry of the equatorial Pacific. Using an eddy‐resolving configuration of the Community Earth System Model (CESM‐HR) and Lagrangian particle tracking, we examine TIV impacts on the three‐dimensional structure and variability of dissolved oxygen (O2) in the upper equatorial Pacific water column. In CESM‐HR, the simulated generation and westward propagation of TIVs from boreal summer through winter lead to the seasonal oxygenation of the upper northern equatorial Pacific, exhibited as a deepening of hypoxic depth west of 120°W. TIV effects on the equatorial Pacific oxygen balance are dominated by eddy‐advection and mixing, while indirect TIV effects on O2 consumption play minor roles. These advective effects reflect the transient displacements of isopycnals by eddy pumping as well as vortex transport of oxygen by eddy trapping, stirring, and subduction. TIVs influence on the upper equatorial Pacific O2 distribution and variability has important implications for understanding and modeling marine ecosystem dynamics and habitats, and should be taken into consideration in designing observation networks in this region. Plain Language Summary: Tropical instability vortices (TIVs) are eddies that stir and transport water masses in the equatorial Pacific. From summer through winter, vortices are generated in the eastern equatorial Pacific and propagate toward the west, causing major physical and biogeochemical changes in the upper equatorial Pacific. We examine their effects on oxygen distributions and variability in the equatorial Pacific using a global model of ocean circulation and biogeochemistry. From boreal summer through winter, TIVs oxygenate the upper ocean through a series of processes, namely their influence on upper ocean density layers and lateral and vertical water mass exchanges that lead to a temporary deepening of the oxygen minimum zones and an expansion of vertical habitable space along their paths. Our analysis demonstrates that TIVs comprise an important mechanism regulating simulated oxygen distributions in the equatorial Pacific; these important phenomena should be explored in observational campaigns and their effects should be considered in the context of improving climate models. Key Points: Tropical instability vortices (TIVs) oxygenate the northern upper equatorial PacificTIVs seasonality modulates the oxygen minimum zone structure and seasonal variability of ecosystem habitable space in the equatorial PacificTIVs' oxygenation effects are dominated by eddy advective effects while biogeochemical feedbacks play a minor role [ABSTRACT FROM AUTHOR]

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Benthic organisms in coastal sediments affect elemental cycling and control benthic-pelagic coupling through particle reworking and ventilation of their burrows. Bioirrigation and associated porewater advection create intermittently oxic regions within sediments. The spatio-temporal patterns of such biogenic redox oscillations likely respond to seasonal factors, but quantitative information on the seasonality of bioirrigator behaviors and associated redox dynamics is scarce. We examined bioirrigation by the maldanid polychaete Clymenella torquata and its impacts on sediment oxygenation patterns in permeable sediments using high-resolution planar optode oxygen imaging. In sediment mesocosms with reconstructed summer-collected sediment, the durations of pumping and resting varied inversely with temperature. The average durations of pumping and resting increased from 4 min/4 min at 21 °C, to 6 min/6 min at 12 °C, to 15 min/14 min at 5 °C. In intact cores collected in summer, irrigation patterns (3.5 min/3.5 min) were similar to those observed at 21 °C during the temperature ramp. Pumping and resting durations in intact cores collected in winter at 6 °C averaged 9 min/26 min, significantly different from patterns at comparable temperatures in the temperature ramp. Pumping patterns strongly affected the temporal patterns of redox dynamics in surrounding sediments. In addition, temperature strongly affected burrow irrigation depth (exclusively within the top ∼10 cm at 21 °C, and down to ∼20 cm at 5–6 °C with an apparent transition at ∼15 °C), indicating that the zone with dynamic redox conditions migrates vertically on a seasonal basis. The differences in pumping patterns between in- and out-of-season experiments and the effect of temperature on irrigation depth underscore the importance of conducting experiments with bioturbators in-season and at field temperatures. The observed seasonal differences in bioirrigation patterns and associated spatio-temporal redox dynamics suggest that rates and pathways of redox-sensitive diagenetic processes and benthic chemical fluxes in permeable sediments likely show considerable seasonal variation. [Display omitted] • The spatio-temporal pattern of burrow irrigation by C. torquata varies seasonally. • Summer irrigation (∼ 21 °C): ∼3.5 min pumping and resting intervals, 0–10 cm deep. • Winter irrigation (∼5 °C): ∼9 min pumping intervals, ∼26 min resting, 0–20 cm deep. • Sedimentary oxygen dynamics are driven by pumping activity patterns. • Seasonality in oxygen dynamics alters biogeochemical cycling and benthic fluxes. [ABSTRACT FROM AUTHOR]

Research on the environmental impacts of bottom fishing gears has focused mainly on structural characteristics of benthic habitats such as faunal composition and the physical features of the seafloor. This study focuses more on functional characteristics by addressing the biogeochemical consequences associated with tickler chain beam trawl and electric PulseWing trawl gears. In June 2017, professional fishermen trawled experimental transects with both types of gears in the Frisian Front area of the North Sea. Box core sediment samples and in situ landers were used to evaluate biogeochemical fluxes and sediment characteristics in untrawled and trawled areas (samples taken 3.5–70 h after fishing). A reduction of sedimentary chlorophyll a was observed, which was larger following tickler chain (83%) compared to PulseWing trawling (43%). This displacement of surface material caused significant decreases in the sediment oxygen consumption in tickler chain (41%) and PulseWing trawled samples (33%) along with a deeper penetration of oxygen in the sediment (tickler chain: 3.78 mm, PulseWing: 3.17 mm) compared to untrawled areas (2.27 mm). Our research implies that bottom trawl disturbance can lead to immediate declines in benthic community metabolism, with tickler chain trawling exhibiting more prominent alterations than PulseWing trawling on benthic biogeochemical processes. [ABSTRACT FROM AUTHOR]

Due to cultural eutrophication and global climate change, an exponential increase in the number and extent of hypoxic zones in marine and freshwater ecosystems has been observed in the last few decades. Hypoxia, or low dissolved oxygen (DO) concentrations, can produce strong negative ecological impacts and, therefore, is a management concern. We measured biomass and densities of Dreissena in Lake Erie, as well as bottom DO in 2014 using 19 high frequency data loggers distributed throughout the central basin to validate a three-dimensional hydrodynamic-ecological lake model. We found that a deep, offshore hypoxic zone was formed by early August, restricting the Dreissena population to shallow areas of the central basin. Deeper than 20 m, where bottom hypoxia routinely develops, only young of the year mussels were found in small numbers, indicating restricted recruitment and survival of young Dreissena . We suggest that monitoring Dreissena distribution can be an effective tool for mapping the extent and frequency of hypoxia in freshwater. In addition, our results suggest that an anticipated decrease in the spatial extent of hypoxia resulting from nutrient management has the potential to increase the spatial extent of profundal habitat in the central basin available for Dreissena expansion. [ABSTRACT FROM AUTHOR]

Abstract: Transformation and retention of nitrogen and other biologically reactive solutes in the hyporheic zones of running water contribute to an essential ecosystem service. However, the synoptic impact of intense agricultural or urban land‐uses, elevated nutrient loading, flow alterations, riparian clear‐cutting, and channelization on the source‐sink behavior of solutes in hyporheic zones remains largely uncharacterized and unquantified. Therefore, we studied nutrient dynamics in a hydromorphologically and chemically modified stream reach using a new monitoring approach allowing the simultaneous measurement of nutrient and water flux through a screened area in the subsurface of rivers (hyporheic passive flux meter, HPFM). With HPFMs we directly assessed time‐integrated lateral hyporheic nitrate fluxes during early spring and midsummer covering different temperature and discharge regimes. Contrary to our expectations, higher stream discharge coincided with substantially lower hyporheic exchange rates. While in streams featuring a natural morphology, bed form induced exchange commonly increases with surface flow, the influence of groundwater level was dominant in this reach. Furthermore, in contrast to less impacted environments, where progressive substrate depletion with depths reduces metabolic rates in the subsurface, we identified not the upper, but the intermediate layer of the hyporheic zone as hot spot of nutrient turnover. Overall, the hyporheic zone at the study site functioned partly as nitrate source, partly as a sink. Neither of the commonly used determinants redox state and residence time could explain this source or sink function. Our results give clear evidence to carefully transfer the knowledge of hyporheic zone processes from “natural” systems to anthropologically modified streams. [ABSTRACT FROM AUTHOR]

Wastewater Stabilization Ponds (WSPs) are passive treatment systems influenced by both the ambient environment and the manner in which they are operated. Construction of wastewater treatment facilities is particularly challenging in the Canadian Arctic because of the remoteness of the communities and the extreme climate. Here, experimental bench scale WSPs were used to simulate single cell WSPs operating under summer treatment conditions in the Arctic. Experiments were performed to examine factors (temperature, irradiance, initial carbon concentrations, and organic loading rate) that may influence the oxygen state and carbon removal. All four factors were found to significantly (p < 0.05) affect oxygen state and carbon removal, but temperature (5 °C vs 15 °C) and initial carbon concentration (80 vs 240 mg/l) were found to be the most important factors. Final CBOD 5 concentrations in the experimental columns ranged from <10 to 150 mg/l, and only experimental columns operated at low temperature and high initial carbon concentrations had final CBOD 5 concentrations >30 mg/l. Phytoplankton growth and metabolism appears to have a prominent impact on CBOD 5 removal and the oxygen status of the experimental WSPs. The findings suggest that WSPs operating in cool arctic climates are more sensitive to perturbation by weather or operational changes than similar systems in warmer climates, and greater consideration for process resiliency needs to be incorporated into the design of arctic WSPs. This study provides further evidence that WSPs are an appropriate municipal wastewater technology for the Arctic and can achieve effluent CBOD 5 concentrations that meet secondary wastewater treatment standards, provided they are appropriately sized, designed, and operated for arctic conditions. [ABSTRACT FROM AUTHOR]

Increasing evidence demonstrates that mammals have different reactions to hypoxia with varied oxygen dynamic patterns. It takes ∼24 h for tri-gas incubator to achieve steady cell hypoxia, which fails to recapitulate ultrafast oxygen dynamics of intestinal ischemia/reperfusion (IR) injury. Inspired from the structure of native intestinal villi, we engineered an intestinal organoid chip embedded with engineered artificial microvessels based on co-axial microfluidic technology by using pH-responsive ZIF-8/sodium alginate scaffold. The chip was featured on: (i) eight times the oxygen exchange efficiency compared with the conventional device, tri-gas incubator, (ii) implantation of intestinal organoid reproducing all types of intestinal epithelial cells, and (iii) bio-responsiveness to hypoxia and reoxygenation (HR) by presenting metabolism disorder, inflammatory reaction, and cell apoptosis. Strikingly, it was found for the first time that Olfactomedin 4 ( Olfm4 ) was the most significantly down-regulated gene under a rapid HR condition by sequencing the RNA from the organoids. Mechanistically, OLFM4 played protective functions on HR-induced cell inflammation and tissue damage by inhibiting the NF-kappa B signaling activation, thus it could be used as a therapeutic target. Altogether, this study overcomes the issue of mismatched oxygen dynamics between in vitro and in vivo , and sets an example of next-generation multisystem-interactive organoid chip for finding precise therapeutic targets of IR injury., Competing Interests: The authors declare that they do not have any competing interests., (© 2023 The Authors.)

The cerebral microvasculature plays a vital role in adequately supplying blood to the brain. Determining the health of the cerebral microvasculature is important during pathological conditions, such as stroke and dementia. Recent studies have shown the complex relationship between cerebral metabolic rate and transit time distribution, the transit times of all the possible pathways available dependent on network topology. In this paper, we extend a recently developed technique to solve for residue function, the amount of tracer left in the vasculature at any time, and transit time distribution in an existing model of the cerebral microvasculature to calculate cerebral metabolism. We present the mathematical theory needed to solve for oxygen concentration followed by results of the simulations. It is found that oxygen extraction fraction, the fraction of oxygen removed from the blood in the capillary network by the tissue, and cerebral metabolic rate are dependent on both mean and heterogeneity of the transit time distribution. For changes in cerebral blood flow, a positive correlation can be observed between mean transit time and oxygen extraction fraction, and a negative correlation between mean transit time and metabolic rate of oxygen. A negative correlation can also be observed between transit time heterogeneity and the metabolic rate of oxygen for a constant cerebral blood flow. A sensitivity analysis on the mean and heterogeneity of the transit time distribution was able to quantify their respective contributions to oxygen extraction fraction and metabolic rate of oxygen. Mean transit time has a greater contribution than the heterogeneity for oxygen extraction fraction. This is found to be opposite for metabolic rate of oxygen. These results provide information on the role of the cerebral microvasculature and its effects on flow and metabolism. They thus open up the possibility of obtaining additional valuable clinical information for diagnosing and treating cerebrovascular diseases. [ABSTRACT FROM AUTHOR]

The expression of plant cysteine oxidase (PCO) enzyme in Saccharomyces cerevisiae enables the Arg/Cys N-degron pathway (Cys-NDP) for selective protein degradation that, in plants, functions as direct oxygen perception mechanism. A synthetic construct based on the plant Cys-NDP substrate related to apetala 2.12 (RAP2.12), the dual luciferase oxygen reporter (DLOR), exploits the N-terminal Cys of RAP2.12, and its oxygen-dependent degradation through the Cys-NDP. The luminescent output of DLOR can be used as a proxy for intracellular oxygen dynamics in budding yeast. Replacement of the luciferase reporter of the DLOR with fluorescent proteins would furthermore facilitate the imaging of reporter dynamics in living cells. In this chapter, we describe the methods for delivering the DLOR synthetic construct to yeast and calibrating its output by means of oxygen quantification in the culture with a physical oxygen sensor. We explain the setup needed to carry out hypoxic treatments with several colonies as replicates. We also describe the method to measure oxygen concentration in the culture, the closest indication of intracellular oxygen levels, as a way that would serve to calibrate the DLOR output. Finally, we propose a strategy to replace the luminescent reporters in the DLOR with fluorescent proteins to visualize oxygen dynamics in vivo., (© 2023. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Soil oxygen (O2) availability influences nitrification and denitrification, the major biological processes responsible for nitrous oxide (N2O) production and emissions from soil. In this study O2-specific planar optodes were used to visualise O2 distribution with high spatial and temporal resolution in soils in which the same amount of solid fraction of pig manure had been distributed in three different ways (mixed, layered, single patch) and which were maintained at a water potential of -5 kPa (corresponding to 91% of water-filled pore space). In parallel, the greenhouse gas emissions (N2O, CO2 and CH4) from soil at high temporal resolution were monitored. At the end of the incubations, vertical profiles of mineral nitrogen (ammonium and nitrate) in the soil matrix were quantified. The optode results revealed that anoxia rapidly developed in zones with manure addition and gradually expanded to the entire soil during the 66-h experimental period. The anoxia in the soil developed more quickly as the heterogeneity of manure distribution decreased (from single patch to layered to mixed). The single patch distribution of manure solids delayed peak emission rates of both N2O and CO2, but stimulated the cumulative N2O emissions and reduced the cumulative CO2 fluxes. The faster the anoxia developed, the less the nitrification process appeared to contribute to N2O emissions. No treatment effects on CH4 emissions were observed. Combined high resolution imaging of O2 dynamics and measurements of N2O emission rates are essential to get a detailed understanding of how O2 availability regulates the distribution and coupling of denitrification and nitrification activity in soil. Such unique information on soil O2 dynamics could be used for further modelling and quantification of processes producing greenhouse gases from soil ecosystems. [ABSTRACT FROM AUTHOR]

Background and Aims Many stem-succulent halophytes experience regular or episodic flooding events, which may compromise gas exchange and reduce survival rates. This study assesses submergence tolerance, gas exchange and tissue oxygen (O2) status of two stem-succulent halophytes with different stem diameters and from different elevations of an inland marsh.Methods Responses to complete submergence in terms of stem internal O2 dynamics, photosynthesis and respiration were studied for the two halophytic stem-succulents Tecticornia auriculata and T. medusa. Plants were submerged in a glasshouse experiment for 3, 6 and 12 d and O2 levels within stems were measured with microelectrodes. Photosynthesis by stems in air after de-submergence was also measured.Key Results Tecticornia medusa showed 100 % survival in all submergence durations whereas T. auriculata did not survive longer than 6 d of submergence. O2 profiles and time traces showed that when submerged in water at air-equilibrium, the thicker stems of T. medusa were severely hypoxic (close to anoxic) when in darkness, whereas the smaller diameter stems of T. auriculata were moderately hypoxic. During light periods, underwater photosynthesis increased the internal O2 concentrations in the succulent stems of both species. Stems of T. auriculata temporally retained a gas film when first submerged, whereas T. medusa did not. The lower O2 in T. medusa than in T. auriculata when submerged in darkness was largely attributed to a less permeable epidermis. The submergence sensitivity of T. auriculata was associated with swelling and rupturing of the succulent stem tissues, which did not occur in T. medusa.Conclusions The higher submergence tolerance of T. medusa was not associated with better internal aeration of stems. Rather, this species has poor internal aeration of the succulent stems due to its less permeable epidermis; the low epidermal permeability might be related to resistance to swelling of succulent stem tissues when submerged. [ABSTRACT FROM AUTHOR]

Oxygen vacancy exchange between Sc ions in 0.5% Sc-doped ceria Sc 0.005 Ce 0.995 O 0.9975 is investigated by means of 2D exchange spectroscopy (EXSY). 45 Sc NMR spectrum of Sc-doped ceria contains two peaks—one corresponding to Sc ions coupled with an oxygen vacancy (Sc-7), and the other corresponding to Sc ions in a regular lattice site surrounded by eight oxygen ions (Sc-8). The vacancy exchange between these two Sc sites generates the cross-peaks in the EXSY spectrum. Relative amplitudes of the cross-peaks provide direct values of the exchange frequency at a given temperature. Arrhenius analysis of the exchange frequency gives the activation energy E a = 1.18 eV for the vacancy hopping between Sc sites. Most of this energy barrier is due to association energy which binds the vacancy to Sc 3 + . Large dopant–vacancy association energy in Sc doped ceria is demonstrated by 45 Sc NMR spectrum of La/Sc doubly doped sample, Sc x La x Ce 1 − 2x O 2 − x , x = 0.005, where the only line of Sc-7 site shows that all vacancies are bound by Sc 3 + ions. [ABSTRACT FROM AUTHOR]

Background and Aims Dynamic processes occurring at the soil–root interface crucially influence soil physical, chemical and biological properties at a local scale around the roots, and are technically challenging to capture in situ. This study presents a novel multi-imaging approach combining fluorescence and neutron radiography that is able to simultaneously monitor root growth, water content distribution, root respiration and root exudation. Methods Germinated seeds of white lupins (Lupinus albus) were planted in boron-free glass rhizotrons. After 11 d, the rhizotrons were wetted from the bottom and time series of fluorescence and neutron images were taken during the subsequent day and night cycles for 13 d. The following day (i.e. 25 d after planting) the rhizotrons were again wetted from the bottom and the measurements were repeated. Fluorescence sensor foils were attached to the inner sides of the glass and measurements of oxygen and pH were made on the basis of fluorescence intensity. The experimental set-up allowed for simultaneous fluorescence imaging and neutron radiography. Key Results The interrelated patterns of root growth and distribution in the soil, root respiration, exudation and water uptake could all be studied non-destructively and at high temporal and spatial resolution. The older parts of the root system with greater root-length density were associated with fast decreases of water content and rapid changes in oxygen concentration. pH values around the roots located in areas with low soil water content were significantly lower than the rest of the root system. Conclusions The results suggest that the combined imaging set-up developed here, incorporating fluorescence intensity measurements, is able to map important biogeochemical parameters in the soil around living plants with a spatial resolution that is sufficiently high enough to relate the patterns observed to the root system. [ABSTRACT FROM PUBLISHER]