Dissolved Oxygen Concentration Research Articles

Species Selection for Profitable Commercial Fish Culture Through Biofloc Technology

Biofloc technology is a recent concept in Bangladesh, it has numerous advantages for enhancing aquaculture production in several countries, thereby contributing to achieve sustainable development goals. To identify the most suitable fish species for profitable commercial fish culture through Biofloc, a 100-day experiment was conducted at Pran Fisheries Project in Razapur Village, situated in Sreemangal Upazilla of Moulvibazar district, commencing in March 2021. The experiment comprised three treatments: Oreochromis niloticus, Anabus testudineus, and Labeo rohita with two replicates for each treatment. Water quality parameters were meticulously monitored to ensure optimal conditions. All treatments were conducted at a temperature of 26°C, with pH levels of 7.6-7.8, dissolved oxygen concentrations of 5-6 ppm. During the study, O. niloticus exhibited the highest body weight (66.23 ± 0.94) compared to A. testudineus (50.82 ± 0.94) and L. rohita (53.92 ± 0.17). Furthermore, L. rohita displayed a higher average daily weight gain (1.8 ± 0.003) and specific growth rate (3.29 ± 0.29). The best feed conversion ratio (FCR) was observed both for O. niloticus (0.98 ± 0.33) and A. testudineus (0.98 ± 0.03). In terms of survival rate, O. niloticus outperformed the other species, with a rate of 98%. However, O. niloticus demonstrated better aquaculture performance compared to the other species using biofloc technology. This research provides valuable insights in effective cultural techniques that can enhance fish production through biofloc technology, contributing to economic growth in aquaculture sector and national development. J. Bio-Sci. 31(1): 71-85, 2023

Analyzing the response distribution of DO concentration and its environmental factors under the influence of typhoon rain events with remote sensing

Typhoon rain events are important factors that trigger changes in dissolved oxygen concentrations in watersheds. The direction of the typhoon driving force is clear, but the mode of action and mechanism are complex. Moreover, quantifying the relationship between these actions and dissolved oxygen is challenging. This study collected measured data from water quality monitoring and remote sensing during the 2022 typhoon rain events. By analyzing the changes in typhoon driving factors and dissolved oxygen (DO) concentrations in water under various typhoon storms, extended MOORA plus the full multiplicative form (MULTIMOORA), Multiscale Geographic Weighted Regression (MGWR), and spatial autocorrelation analysis were used to evaluate the response of DO concentration. Furthermore, the effects of the atmospheric environment under the influence of human activities on the response distribution of the urban water environment were analyzed. The results of the study showed that under the effect of a typhoon with higher rainfall intensity, the response of DO concentration in the water body of the river in the center of the city was better. However, the response of DO concentration in the water body at the mouth of the sea had a tendency to become worse. Under the influence of typhoon rain events with smaller intensity, the scouring effect of rainwater dominated, and the DO concentration response in the water body had a tendency to become worse. The analysis of spatial heterogeneity under the influence of human activities showed that the ranking values of DO concentration response in rivers in the city area of Zhongshan, under the influence of typhoon rain events, were positively correlated with the distribution of ozone (O3) concentration and sulfur dioxide (SO2) concentration in the eastern, central, and western parts of Zhongshan. Conversely, it was negatively correlated with the distribution of O3 concentration and SO2 concentration in the northern and southern parts of Zhongshan. Based on the research results, we constructed a technique to evaluate the response of dissolved oxygen concentration during the typhoon transit period, which can provide an indicator reference for urban managers in water environment management.

Research on Optimization of Total Nitrogen Peak Suppression in Wastewater Treatment Based on the Data Driven Method

In order to solve the problems of water eutrophication, algae anoxic decay, and death by biological poisoning, which are caused by the excessive emission of total nitrogen in wastewater treatment process, this paper proposes a method of total nitrogen peak suppression which is based on neural network decision optimization. First, the SSORBF neural network is established according to the wastewater treatment process, and total nitrogen, inflow flow, current total nitrogen, dissolved oxygen concentration, and nitrate nitrogen concentration are selected to predict the total nitrogen concentration. Second, the density- and memory-based NSGA2 multiobjective optimization method is used to set the optimal solution to meet the requirement of energy consumption. If the prediction of total nitrogen exceeded the set value, the optimal control strategy is adopted to control the peak value of total nitrogen in advance, and it cannot exceed the national maximum allowable emission value. If the prediction of total nitrogen is lower than the set value, it continues to track the parameter set value. Finally, compared with other methods, the proposed method can effectively suppress the peak value of total nitrogen under 18 mg/L and reduce the energy consumption in wastewater treatment by 7.6%. It can provide decisions and advice for wastewater treatment plants.

Adaptive Anti-Disturbance Control of Dissolved Oxygen in Circulating Water Culture Systems

In the three-dimensional culture model, the breeding basket of the culture area is symmetrical and it is important to control the dissolved oxygen in the symmetrical region to improve the culture efficiency. Practical engineering issues, such as the influence of flow rate, pH, water temperature, and biological oxygen consumption on the dissolved oxygen content in the circulating water culture system, must be considered along with the presence of modeling errors in the control model. The authors propose an adaptive anti-disturbance control strategy for dissolved oxygen that combines nonlinear disturbance observation with an adaptive sliding model control. Initially, a dynamic model for controlling dissolved oxygen in a recirculating water aquaculture system was developed. The model considers external disturbances like artificial oxygenation, abrupt changes in system flow, and variations in culture oxygen consumption. Secondly, to enhance the robustness and accuracy of controlling dissolved oxygen concentration, the paper introduces a nonlinear adaptive disturbance observer for real-time estimation and observation of external disturbances and system uncertainties. This is accompanied by a sliding-mode control-based adaptive anti-disturbance strategy. Lastly, the simulation results demonstrate that the control strategy proposed in this paper shows resistance to system uncertainties and unknown external disturbances. Furthermore, it reduces the model accuracy requirements for the controller and proves to be suitable for accurately controlling dissolved oxygen in circulating water systems.

Spatial and temporal distribution of dissolved oxygen in the Ciliwung River, DKI Jakarta Province

The Ciliwung River is one of the main streams that pass Jakarta. This river flows through the city’s center and passes many villages, highly inhabited homes, and slums, necessitating special attention to the Ciliwung River’s water quality. Because dissolved oxygen is essential for aquatic life, it is the most critical measure of freshwater quality. This study aimed to analyze the spatial and temporal distribution of dissolved oxygen in the Ciliwung River in DKI Jakarta Province. Water quality was monitored during the rainy (February and June 2021) and the dry seasons (August and September 2021). The study area comprised 18 observation sites along the Ciliwung River in DKI Jakarta. Spatially, in Central and North Jakarta, the dissolved oxygen content of the Ciliwung River is relatively low. Temporarily, the dissolved oxygen concentration was somewhat more significant during the rainy season, but statistical testing revealed no statistically significant difference between the rainy and dry seasons.

The Effects of Water Column Dissolved Oxygen Concentrations on Lake Methane Emissions—Results From a Whole‐Lake Oxygenation Experiment

AbstractLakes contribute 9%–19% of global methane (CH4) emissions to the atmosphere. Dissolved molecular oxygen (DO) in lakes can inhibit the production of CH4 and promote CH4 oxidation. DO is therefore often considered an important regulator of CH4 emissions from lakes. Presence or absence of DO in the water above the sediments can affect CH4 production and emissions by (a) influencing if methane production can be fueled by the most reactive organic matter in the top sediment layer or rely on deeper and less degradable organic matter, and (b) enabling CH4 accumulation in deep waters and potentially large emissions upon water column turnover. However, the relative importance of these two DO effects on CH4 fluxes is still unclear. We assessed CH4 fluxes from two connected lake basins in northern boreal Sweden where one was experimentally oxygenated. Results showed no clear difference in summer CH4 emissions attributable to water column DO concentrations. Large amounts of CH4 accumulated in the anoxic hypolimnion of the reference basin but little of this may have been emitted because of incomplete mixing, and effective methane oxidation of stored CH4 reaching oxic water layers. Accordingly, ≤24% of the stored CH4 was likely emitted in the experimental lake. Overall, our results suggest that hypolimnetic DO and water column CH4 storage might have a smaller impact on CH4 emissions in boreal forest lakes than previous estimates, yet potential fluxes associated with water column turnover events remain a significant uncertainty in lake CH4 emission estimates.

THE NITROGEN COMPOUNDS CONCENTRATION IN WATER ECOSYSTEMS OF DIFFERENT TYPES

The study researches the changes in the nitrogen compounds concentration (NH4+, NO2¯ і NO3¯) in water ecosystems of different types (the river Stubelka, the Khrinnyky reservoir, Lake Zasvitske and Morozivka quarry) and discusses ecological consequences of their balance shift. The author defines ammonium and nitrites as the predominant form of the nitrogen compounds. It was recorded the exceeding of the maximum permissible concentrations of ammonium nitrogen in the water of river Stubelka (1.16–3.44 times), the Khrinnyky reservoir (1.26-2.06 times), Lake Zasvitske (1.49 times) and Morozivka quarry (1.62 times) that is primarily caused by precipitation, household and agricultural land sewage as a result of mineral and organic fertilizers use. The nitrites concentration exceeds the standard values in the water of the river Stubelka (2.26 times), the Khrinnyky reservoir (1.48-1.77 times) and Lake Zasvitske (3.90-24.64 times) that indicates a slowdown in their oxidation to nitrates and a high risk of secondary pollution of water reservoirs. The nitrates concentration is within the limits of permissible values. It is demonstrated that the nitrogen compounds concentration in water reservoirs changes as follows: NH4+ – river > reservoir > quarry > lake; NO2¯ – lake > river > reservoir > quarry; NO3¯ – reservoir > river > quarry > lake. The balance shift in the ammonium ↔ nitrite ↔ nitrate system towards nitrates is most often characteristic of all water reservoirs in summer and towards ammonium in autumn. NO3¯/NH4+ maximum ratio was found in the Khrinnyky reservoir (94.81), Morozivka quarry (9.55), Lake Zasvitske (5.84) and the river Stubelka (3.80). The pH changes in the water of the river Stubelka (6.7-7.3), the Khrinnyky reservoir (7.0-7.5), Lake Zasvitske (5.9-7.2) and Morozivka quarry (6.5-7.4). The study researches fluctuations in the dissolved oxygen concentration in the water of the river Stubelka (5.7-8.5 mg O2/dm3), the Khrinnyky reservoir (4.4-9.5 mg O2/dm3), Lake Zasvitske (8.6-10.0 mg O2/dm3) and Morozivskyi quarry (8.7-9.3 mg O2/dm3). The concentration of dissolved oxygen in water reservoirs is as follows: lake > quarry > reservoir > river. The presence of an indicator of «fresh» water pollution (ammonium nitrogen) in all reservoirs indicates a constant influx of pollutants, especially intensively to the river Stubelka and the Khrinnyky Reservoir.

Environmental influence on summer survival of Manila Clam Ruditapes philippinarum: A case study in an aquaculture bay

The aquaculture of Manila clam (Ruditapes philippinarum) is under threat due to its high mortality in summer. To investigate the environmental influence on mortality of the species, we have conducted field surveys in the aquaculture area in Laizhou Bay, during the summers of 2019 and 2020. Environmental and biological data were collected. The results of data analysis have shown that in 2020, large-scale mortality events were not recorded and spatial variations of environmental variables were no significant within the survey area. However, in August 2019, significant variations of environmental variables were detected in the middle tidal area. This area was charactered with relatively high-water temperature (with maximum temperature of 31.49 °C and mean value of 26.17 ± 1.62 °C), elevated hydrogen sulfide concentrations (with a maximum concentration of 24.72 μmol/L and a mean concentration of 7.89 ± 4.14 μmol/L), and low dissolved oxygen concentrations (with a minimum concentration of 3.35 mg/L and a mean concentration of 6.27 ± 0.42 mg/L). Correspondingly, high mortality of the clam was recorded in the area, the abundance of live Manila clams has decreased by 80%. No significant abnormalities of environmental variables and clam growth were observed in other regions in 2019. Glycogen content and condition index of the clam were analyzed to investigate the relationship between environmental stress and the health of the clam. Compared to the condition index, glycogen content is a more sensitive indicator of the health status of the clam because changes in glycogen content appeared earlier than changes in condition index and mortality. A principal component analysis further indicated that the high mortality of the clam corresponds with a few environmental variables, including elevated temperature, hypoxia and the concentration of hydrogen sulfide. The simultaneous presence of these multiple environmental stressors could have triggered alterations in the physiological responses of the clam.

The mean condition dynamics of Pachymelania byronensis (Wood, 1828) (Gastropoda: Thiaridae) in the Cross River, Nigeria

The monthly mean condition index (Kmean) of Pachymelania byronensis was computed from a unique combination of the body weight–shell height relationship parameters (i.e. a, b). Shell height (H) and weight (W) were measured for each specimen. There was a wide (827.7 –fold) variation, from a minimum of 0.012 in October to a maximum of 9.932 in December. Mean annual value was 8.064. The relatively low values of the condition index in February – May, August -- October were attributed to declines in body weight as the gametes are released during spawning. This gastropod species spawns three times a year, a feature that is responsible for the high density of the gastropod in the river and its capacity to sustain a year-round strong fishing pressure. The monthly condition indices significantly correlated with river hydrological parameters, including rainfall, surface temperature, discharge, transparency, pH, and dissolved oxygen concentration.

Properties of Antarctic Bottom Water in the Western Gap (Azores-Gibraltar Fracture Zone, Northeast Atlantic) in 2021

We present the results of measurements of thermohaline and dynamical structures, as well as hydrochemical parameters of near-bottom water in the Western Gap (Azores-Gibraltar Fracture Zone, Northeast Atlantic). The data were collected during cruise 59 of the research vessel Akademik Ioffe in October 2021. The results of the analysis showed that water with potential temperatures lower than 2.00 °C had crossed the Entrance Sill, but was not detected inside the interior basin of the Western Gap. The velocities of currents at the Entrance Sill were high (up to 30 cm/s) leading to mixing of the water overflowing the sill. While Antarctic Bottom Water (AABW) flows from the Entrance Sill to the Exit Sill it is subjected to modification. Bottom water becomes less dense after the sill due to mixing during overflow and in addition not all cold water overflows the sill. The dissolved oxygen concentration in the bottom layer increases from the Entrance Sill (239–242 μmol/kg) to the Exit Sill (241–248 μmol/kg) indicating the transformation of AABW as it circulates in the Western Gap and mixes with North Atlantic Deep Water propagating from the north. All velocity measurements indicate that north velocity component is a characteristic property of the bottom flow. Thus, water with specific chemical composition of AABW is transported to the Iberian Basin despite that its potential temperature becomes higher than 2 °C.

The use of effective microorganisms changed the soil microbiota of canals in Maricá city, Brazil

The objective of this study was to evaluate the effect of bioremediation, through the application of two different strategies of effective microorganisms as treatment of effluents in the parameters of water quality and in the bacteriological profile of the soil of ‘Canal da Cidade’ - Maricá, Rio de Janeiro, Brazil. The metagenomic analyzes indicated that the abundance and richness of microorganisms in the substrate increased significantly after the bioremediation strategy used in this study. Because of bioremediation, 31 bacterial species disappeared from the environment when comparing the initial and final bacterial profiles of the soil, where 94% of these 31 species were anaerobic. Furthermore, 61 new aerobic or facultative aerobic species appeared in the channel substrate after bioremediation. As a consequence of bioremediation, the dissolved oxygen concentration and pH values increased significantly throughout the bioremediation process, indicating that the changes found in the microbiological profile of the soil contributed to the improvement of water quality parameters, helping the environment to move from anaerobic to aerobic characteristics. Thus, it is possible to state that the use of effective microorganisms directly affected the physical-chemical parameters of water quality and the microbial profile of the soil community of ‘Canal da Cidade’.

Effects of Light and Oxygen Conditions on Nonenzymatic Metmyoglobin Reduction In Vitro

Previous research indicated that inherently present electron donors and carriers contribute to nonenzymatic metmyoglobin reduction. However, limited knowledge is currently available on how light and oxygen influence nonenzymatic metmyoglobin reduction. The objective of this study was to evaluate the effect of light and oxygen levels on nonenzymatic metmyoglobin reduction in vitro. Two experiments were conducted using equine metmyoglobin solution at pH 5.6 (represents typical postmortem muscle pH) with different electron donors and electron carriers in a 96-well plate. A gas blend of 80% oxygen and 20% carbon dioxide or a pure 99.9% nitrogen gas was bubbled in phosphate buffers and myoglobin solutions to create 2 oxygen levels (low oxygen [4%] and high oxygen [160%]). The desired dissolved oxygen content was measured using a NeoFox oxygen probe (atmospheric oxygen level was 20% oxygen). There were significant effects of electron donors, carriers, and light on nonenzymatic metmyoglobin reduction. Ascorbate and nicotinamide adenine dinucleotide reduced form (NADH) in the presence of methylene blue and ethylenediaminetetraacetic acid (EDTA) exhibited a greater nonenzymatic metmyoglobin reduction in light than dark. An increase in nonenzymatic metmyoglobin-reducing activity (P<0.0001) was observed for the combination of NADH+methylene blue+EDTA in the high-oxygen condition in comparison with the low-oxygen levels. The results indicate that light and oxygen levels increase nonenzymatic metmyoglobin reduction. Characterizing the cofactors required for nonenzymatic metmyoglobin reduction and understanding the conditions conducive to reduction enhance knowledge related to meat color changes.

Exploiting the prediction of mass transfer performance in aerated coaxial mixers containing biopolymer solutions using empirical correlations and neural networks

AbstractThe volumetric mass transfer coefficient is commonly used to assess the mixing effectiveness of gas–liquid bioreactor systems. Analyzing mass transfer performance in non‐Newtonian fluids inside coaxial mixers can be challenging due to the complex interaction between process variables, which requires developing robust characterization and estimation approaches. This study aims to investigate the gas dispersion in shear‐thinning biopolymers with yield stress using coaxial mixers in order to evaluate the effects of aeration and agitation on the volumetric mass transfer coefficient. A mixing configuration comprising a pitched blade turbine and an anchor was employed to disperse air into xanthan gum solutions, and the mass transfer performance was obtained at different impeller speeds and biopolymer concentrations by measuring the dissolved oxygen concentration. A dimensionless empirical correlation was proposed, and the results showed that the mass transfer was positively influenced by aeration intensity and agitation mechanism, quantified by the gas flow number and Reynolds number, respectively. Additionally, a strategy using stacking‐ensemble artificial neural networks was developed to accurately estimate the volumetric mass transfer coefficient, with a correlation coefficient of 0.998. The proposed mass transfer characterization approach overcame the complexities of analyzing aerated coaxial mixer systems and provided a reliable design model for bioreactor systems containing non‐Newtonian fluids.

Niobium Oxide Nanorods Obtained by Hydrothermal Synthesis—Structure, Morphology, and Electrochemical Detection of Oxygen Via Oxygen Reduction Reaction

Niobium oxides are promising materials for applications within various research fields, especially as electrocatalysts for various chemical reactions. The tuning of the synthetic parameters can achieve a successful compromise between morphology and structure, aiming to obtain certain properties. Hence, this study aimed to investigate the influence of hydrothermal synthesis parameters on the morphology and structure of niobium oxide growth on a niobium metallic plate. The effect of annealing on the material performance was also evaluated. Afterward, the most crystalline sample was tested for the electrochemical determination of dissolved oxygen, a fundamental reaction in corrosion, biomedicine, and environmental monitoring. This is the first work using this material configuration as an electrochemical sensor. The hydrothermal synthesis produced nanorods formed by poorly crystalline, acidic, hydrated Nb2O5. Increasing the mineralizer concentration could increase the crystallinity and the nanorod growth rate, but it could also promote a lack of structural and morphological uniformity throughout the surface. Heat treatment allowed the increase in crystallinity and favored orthorhombic Nb2O5. Raman spectroscopy revealed that, at the first moment, acidic, hydrated niobium oxide structures were formed as precursors of crystalline niobium oxide that would be developed with longer reaction times and a higher mineralizer concentration. The obtained niobium oxide showed electrocatalytic activity toward the oxygen reduction reaction, with comparable performance between the samples with and without heat treatment. At all analyzed pH values, the amperometric response was linearly correlated with the dissolved oxygen concentration. pH influenced the sensitivity of the material; a maximum sensitivity of 0.0417 mA/cm2·mg/L O2 was achieved at pH = 6. The participation of the acidic functionalities of the surface in the ORR reaction was confirmed by Raman spectroscopy.

Habitat and food habits of the endemic fish Oryzias eversi in Tana Toraja, South Sulawesi, Indonesia

Abstract. Lamba T, Ambeng, Andriani I. 2023. Habitat and food habits of the endemic fish Oryzias eversi in Tana Toraja, South Sulawesi, Indonesia. Biodiversitas 24: 5137-5145. The population of the medaka fish species, Oryzias eversi, was categorized as Near Threatened by the International Union for Conservation of Nature (IUCN) 2019 due to its restricted distribution and occurrence in a single threatened location. One way to protect this species from extinction is through captive breeding, which requires understanding its habitat conditions and food habits. Therefore, this research aimed to analyze the habitat conditions and food habits of Oryzias eversi (Hadiaty & Nolte, 2012) in Tilanga Pool, Tana Toraja. Purposive random sampling was used to obtain fish samples, while habitat conditions were determined by measuring environmental parameters, and the abundance and diversity of plankton. Food habits were analyzed by calculating the Index of Preponderance (IP) and Relative Gut Length (RGL). The results indicated that O. eversi inhabited a highly polluted habitat with dissolved oxygen content that ranged from 3.95 to 4.16 mg/L. The abundance of phytoplankton and zooplankton ranged from 185-435 cells/L and 10-25 ind/L, respectively. Phytoplankton diversity was in the moderate category, while zooplankton was low, with average values of Diversity Index (H’) ranging from 1.61-1.93 and 0.69-024, respectively. IP and RGL showed that O. eversi was an omnivore-carnivore fish. The average IP of zooplankton and phytoplankton ranged from 0.35-61.11% and 0.69-1.04%, respectively. Meanwhile, the RGL ranged from 0.48 to 0.62, respectively. Cyclops sp. larvae were identified as the primary food source for O. eversi with IP above 40% and Eurycercus sp. with IP range of 4-40% as additional food.

Environmental implications of phosphate-based fertilizer industrial waste and its management practices.

During the green revolution in the mid-twentieth century, the consumption of inorganic phosphorous and phosphate-based fertilizers (P-fertilizers) in the developing world skyrocketed, resulting in a proliferation of P-fertilizer industries. Phosphate-based fertilizer industries are ranked among the most environment-polluting industries. The worldwide phosphorus market, which was 68.5 million metric tons in 2020, is expected to increase at a compound annual growth rate (CAGR) of 2.5% to 81 million metric tons by 2027. The release of untreated hazardous pollutants from these fertilizer industries into the soil, water, and atmosphere has resulted in severe environmental health issues. Excessive surface runoff of phosphorus from agricultural fields and its deposition in water promote the growth of algae and macrophytes and lower dissolved oxygen concentration through eutrophication, which is detrimental to aquatic life. Fluorides (F-) and sulfur dioxide (SO2) and/or heavy metals (potentially toxic elements, PTEs) are also detected in the emissions from these fertilizer industries. The main solid waste generated from the phospho-gypsum plant produced up to 5 tons of di-hydrogen phosphate (H2PO4), including PTEs and radioactive substances. Phosphates and fluorenes from these industries are usually disposed of as sludge in storage ponds or trash piles. Humans inhaling poisonous gases released from the P-fertilizer industries can develop hepatic failure, autoimmune diseases, pulmonary disorders, and other health problems. The objectives of this review are to provide guidelines for eliminating the bottleneck pollutions that occur from the phosphate-based fertilizer industries and explore the management practices for its green development.

Effects of Lotus (Nelumbo nucifera Gaertn.) on the Methane Emission in Littoral Zones of a Subtropical Lake, China

Freshwater lakes represent a potential source of methane (CH4) emission into the atmosphere. However, the CH4 emission contribution to the total emission in the littoral zones of lakes, especially emergent macrophytes (e.g., lotus), is poorly known. Lotus has been cultivated in almost all provinces in China; it is not only an aquatic plant, but also a kind of vegetable. In this study, two sampling zones (lotus plant and open water) were established in the lake of the middle reaches of the Yangtze River. The CH4 emission was measured using a floating opaque chamber and gas chromatography between April and December in the years 2021 and 2022. The results indicated that the flux of CH4 emissions ranged from 0.10 to 59.75 mg m−2 h−1, with an average value of 5.61 mg m−2 h−1, in the open water, while ranging from 0.19 to 57.32 mg m−2 h−1, with an average value of 17.14 mg m−2 h−1, in the lotus plant zone. The maximal CH4 emissions occurred in July and August for the open water, which was highly related to the air and water temperature, whereas it happened in September for the lotus plant zone, possibly due to the high vegetation biomass, indirectly enhancing the high soil organic carbon content, plant-mediated CH4 emission, as well as the lower dissolved oxygen concentration, thus strengthening the production and emissions of CH4. Considering the carbon emissions (both CH4 and CO2) and plant productivity, although greater CH4 emission occurred in the lotus plant zone, it could still represent a potential carbon sink (213 g m−2 yr−1) compared to the open water.

Effect of hypoxia duration and pattern on channel Catfish (Ictalurus punctatus) neuropeptide gene expression and hematology.

Commercial aquaculture production of channel catfish (Ictalurus punctatus) occurs in shallow ponds with daily cycling of dissolved oxygen concentration ranging from supersaturation to severe hypoxia. Once daily minimum dissolved oxygen concentration falls below 3.0mg O2/L, channel catfish have a reduced appetite, leading to reduced growth rates. In other fishes, upregulation of the neuropeptides corticotropin-releasing factor (CRF) and urotensin I (UI) have been implicated as initiating the mechanism responsible for decreasing appetite once an environmental stressor is detected. Channel catfish maintained at 27°C in aquaria were subjected to varying durations and patterns of hypoxia (1.75 ± 0.07mg O2/L) to evaluate underlying physiological responses to hypoxia and determine if hypothalamic CRF and UI are responsible for hypoxia-induced anorexia in channel catfish. During a short exposure to hypoxia (12h), venous PO2 was significantly lower within 6h and was coupled with an increase of hematocrit and decrease of blood osmolality, yet all responses reversed within 12h after returning to normoxia. When this pattern of hypoxia and normoxia was repeated cyclically for 5days, these physiological responses repeated daily. Extended periods of hypoxia (5days) resulted in similar hematological responses, which did not recover to baseline values during the hypoxia exposure. This study did not find a significant change in hypothalamic transcription of CRF and UI during hypoxia challenges but did identify multiple physiological adaptive responses that work together to reduce the severity of experimentally induced hypoxia in channel catfish.

Oxygenation of the Baltoscandian shelf linked to Ordovician biodiversification

AbstractMarine biodiversity increased markedly during the Ordovician Period (~487–443 million years ago). Some intervals within the Ordovician were associated with unusually rapid and prominent rises in taxonomic richness, the reasons for which remain debated. Links between increased oxygenation and biodiversification have been proposed, although supporting marine oxygen proxy data are limited. Here we present an expansive multi-site iodine-to-calcium (I/Ca) record from Lower–Middle Ordovician marine carbonates in Baltoscandia that provides a detailed account of the spatio-temporal development of oxygen conditions across this palaeoshelf. The data document progressive oxygenation of regional seafloor environments, with well-oxygenated waters sourced from the palaeoequatorward Iapetus Ocean and peak I/Ca values (that is, dissolved oxygen concentrations) coinciding with the most pronounced biodiversity increases and ecosystem reorganizations during this time interval. This occurred while the climate cooled, global sea level dropped and carbonate deposits became regionally dominant. The results suggest that ventilation of shelves played a critical role in regulating early Palaeozoic marine biodiversity via development of ecospace and aerobic–metabolic conditions.

Physiological oxygen measurements in vitro-Schrödinger's cat in 3D cell biology.

After the development of 3D cell culture methods in the middle of the last century and the plethora of data generated with this culture configuration up to date, it could be shown that a three-dimensional arrangement of cells in most of the cases leads to a more physiological behavior of the generated tissue. However, a major determinant for an organotypic function, namely, the dissolved oxygen concentration in the used in vitro-system, has been neglected in most of the studies. This is due to the fact that the oxygen measurement in the beginning was simply not feasible and, if so, disturbed the measurement and/or the in vitro-system itself. This is especially true for the meanwhile more widespread use of 3D culture systems. Therefore, the tissues analyzed by these techniques can be considered as the Schrödinger's cat in 3D cell biology. In this perspective paper we will outline how the measurement and, moreover, the regulation of the dissolved oxygen concentration in vitro-3D culture systems could be established at all and how it may be possible to determine the oxygen concentration in organoid cultures and the respiratory capacity via mito stress tests, especially in spheroids in the size range of a few hundred micrometers, under physiological culture conditions, without disturbances or stress induction in the system and in a high-throughput fashion. By this, such systems will help to more efficiently translate tissue engineering approaches into new in vitro-platforms for fundamental and applied research as well as preclinical safety testing and clinical applications.