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Climate change has a significant impact on dissolved oxygen (DO) concentrations, particularly in coastal inlets where numerous human activities occur. Due to the various water quality (WQ), hydrological, and climatic parameters that influence this phenomenon, predicting and modeling DO variation is a challenging process. Accordingly, this study introduces an innovative Deep Learning Neural Network (DLNN) methodology to model and predict DO concentrations for the Egyptian Rashid coastal inlet, leveraging field-recorded WQ and hydroclimatic datasets. Initially, statistical and exploratory data analyses are performed to provide a thorough understanding of the relationship between DO fluctuations and associated WQ and hydroclimatic stressors. As an initial step towards developing an effective DO predictive model, conventional Machine Learning (ML) approaches such as Gaussian Process Regression (GPR), Support Vector Regression (SVR), and Decision Tree Regressor (DTR) are employed. Subsequently, a DLNN approach is utilized to validate the prediction capabilities of the investigated conventional ML approaches. Finally, a sensitivity analysis is conducted to evaluate the impact of WQ and hydroclimatic parameters on predicted DO. The outcomes demonstrate that DLNN significantly improves DO prediction accuracy by 4% compared to the best-performing ML approach, achieving a Correlation Coefficient of 0.95 with a root mean square error (RMSE) of 0.42 mg/l. Solar radiation (SR), pH, water levels (WL), and atmospheric pressure (P) emerge as the most significant hydroclimatic parameters influencing DO fluctuations. Ultimately, the developed models could serve as effective indicators for coastal authorities to monitor DO changes resulting from accelerated climate change along the Egyptian coast., Competing Interests: Declaration of competing interest 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., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Depletion of dissolved oxygen (DO) is a significant incentive for biological catastrophic events in freshwater lakes. Although predicting the DO concentrations in lakes with high-frequency real-time data to prevent hypoxic events is effective, few related experimental studies were made. In this study, a short-term predicting model was developed for DO concentrations in three problematic areas in China's Chaohu Lake. To predict the DO concentrations at these representative sites, which coincide with biological abnormal death areas, water quality indicators at the three sampling sites and hydrometeorological features were adopted as input variables. The monitoring data were collected every 4 h between 2020 and 2023 and applied separately to train and test the model at a ratio of 8:2. A new AC-BiLSTM coupling model of the convolution neural network (CNN) and the bidirectional long short-term memory (BiLSTM) with the attention mechanism (AM) was proposed to tackle characteristics of discontinuous dynamic change of DO concentrations in long time series. Compared with the BiLSTM and CNN-BiLSTM models, the AC-BiLSTM showed better performance in the evaluation criteria of MSE, MAE, and R 2 and a stronger ability to capture global dependency relationships. Although the prediction accuracy of hypoxic events was slightly worse, the general time series characteristics of abrupt DO depletion were captured. Water temperature regularly affects DO concentrations due to its periodic variations. The high correlation and the universal importance of total nitrogen (TN) and total phosphorus (TP) with DO reveals that point source pollution are critical cause of DO depletion in the freshwater lake. The importance of NTU at the Zhong Miao Station indicates the self-purification capacity of the lake is affected by the flow rate changes brought by the tributaries. Calculating linear correlations of variables in conjunction with a permutation variable importance analysis enhanced the interpretability of the proposed model results. This study demonstrates that the AC-BiLSTM model can complete the task of short-term prediction of DO concentration of lakes and reveal its response features of timing and magnitude of abrupt DO depletion., Competing Interests: Declaration of competing interest 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., (Copyright © 2024. Published by Elsevier Ltd.)

Oceanic dissolved oxygen (DO) is crucial for oceanic material cycles and marine biological activities. However, obtaining subsurface DO values directly from satellite observations is limited due to the restricted observed depth. Therefore, it is essential to develop a connection between surface oceanic parameters and subsurface DO values. Machine learning (ML) methods can effectively grasp the complex relationship between input attributes and target variables, making them a valuable approach for estimating subsurface DO values based on surface oceanic parameters. In this study, the potential of ML methods for subsurface DO retrieval is analyzed. Among the selected ML methods, namely support vector regression (SVR), random forest (RF) regression, and extreme gradient boosting (XGBoosting) regression, the RF method generally demonstrates superior performance. As the depth increases, the accuracy of DO estimates tends to initially decrease, then gradually improve, with the poorest performance occurring at the depth of 600 dbar. The range of determination coefficients (R 2 ) and root mean square error (RMSE) values based on the test dataset at different depths lies between 0.53 and 47.59 μmol/kg to 0.99 and 4.01 μmol/kg. In addition, compared to sea surface salinity (SSS) and sea surface chlorophyll-a (SCHL), sea surface temperature (SST) plays a more significant role in DO retrieval. Finally, compared to the pelagic interactions scheme for carbon and ecosystem studies (PISCES) model, the RF method achieves higher retrieval accuracies at depths above 700 dbar. In the deep ocean, the primary differences in DO values obtained from the RF method and the PISCES model-based method are noticeable in the vicinity of the equatorial region., Competing Interests: Declaration of competing interest 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., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Clarifying the role of sulfate and dissolved oxygen (DO) in methane production may allow for precise and accurate modeling of methane emissions in eutrophic lakes. We conducted field observations of sulfate, methane, and DO concentrations in Lake Abashiri, a typical brackish and eutrophic lake in a cold region, to develop a DO-based method for quantitively estimating methane production in a eutrophic lake and analyzed the results. We found that sulfate concentrations decreased rapidly from 900.0 mg/L in water overlying the sediments to nearly 0.0 mg/L in the bottom sediment. Methane production was almost uniform across sediment depths of 0.05 to 0.25 m, ranging from 1400 to 1800 µmol/m 2 /day. Also, methane production was found to be a function of DO concentrations in water overlying the bottom and could be modeled by a logistic function: constant production at 1,400 µmol/m 2 /day for DO concentrations of 0.0 to 3.0 mg/L, rapidly decreasing to 0 µmol/m 2 /day for DO concentrations of 3.0 to 6.0 mg/L. This methane model was verified using a simple one-dimensional numerical model that showed good agreement with field observations. Our results thus suggest that the proposed methane model reduces uncertainty in estimating methane production in a eutrophic lake., Competing Interests: Declaration of Competing Interest 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., (Copyright © 2022. Published by Elsevier B.V.)

Dissolved oxygen is a key parameter to measure water environment quality and ecosystem health. Currently, the problem of hypoxia (low oxygen) is prominent in coastal areas in China, but there is a lack of research on the spatiotemporal characteristics of dissolved oxygen and the control mechanism of hypoxia in the watershed-coastal system. Based on the data of 135 surface water (including estuaries) and 66 coastal water monitoring sites in Fujian Province from 2011 to 2020, this study analyzed the spatiotemporal variation pattern of dissolved oxygen at seasonal and interannual time scales. The data of hypoxia (10% quantile, corresponding to 67% saturation) were selected to study the characteristics and control mechanism of hypoxia in four types of water bodies (i.e., rivers, reservoirs, estuaries, and coastal waters) using mathematical statistics and a random forest model. The results showed that the dissolved oxygen saturation was the highest in the coast[(98.2±10.2)%] and the lowest in the estuary[(79.2±17.9)%]. Compared with that in the 12 th Five-Year Plan (2011-2015), the frequency of hypoxia detection in rivers and reservoirs in the 13 th Five-Year Plan (2016-2020) was significantly reduced, but the change in estuaries was not significant. Counting the points with hypoxia detection, the multi-year average hypoxia detection frequency of rivers and reservoirs was highest in autumn, and the frequency of estuaries was highest in summer. Hypoxia in reservoirs and estuaries was the most prominent but with different mechanisms. Specifically, hypoxia in reservoir reaches was related to summer runoff carrying large amounts of organic matter input, stratification leading to continuous oxygen depletion in the bottom water, and vertical mixing or discharge through dams in autumn, whereas hypoxia in estuaries was associated with strong pollution inputs and reductive materials. Systematic management and regionalized control mechanisms need to be established to further strengthen watershed-coastal pollution abatement to help mitigate eutrophication and hypoxia problems.

Several technologies have been employed to treat greywater (GW) for domestic use. Aerobic biological treatment has achieved high efficiency, the main cost being the necessary source of oxygen (O 2 ). This study explores the effects of lumen air pressure (LAP) on reactor performance and microbial community succession in an O 2 -based membrane biofilm reactor (O 2 -MBfR) treating GW. At high LAP (≥0.8 psi), the dissolved oxygen (DO) concentration inside the reactor was higher than 0.38 ± 0.02 mg/L, leading to removal efficiencies of 90%, 98%, and 80%, of total chemical oxygen demand, total linear alkylbenzene sulfonate (LAS), and total nitrogen, respectively. Lower LAP (<0.8 psi) led to a decrease in DO inside the system, and a less effective GW treatment. Low O 2 pressure decreased organic biodegradation and ammoniation, and caused LAS accumulation in the biofilm, leading to the solubilization of extracellular polymeric substances and cell lysis. Comprehensive consideration of reactor performance and energy input, DO inside the MBfR at 0.38 ± 0.02 mg/L could be selected as the optimized condition for GW treatment. Microbial community analyses results also revealed that improved LAP was favorable for the enrichment of LAS-biodegradation related genus (Pseudomonas, Parvibaculum, Magnetospirillum, Clostridium, Zoogloea, Dechloromonas and Mycobacterium), nitrifiers (Nitrosomonas and Sphingomonas) and facultative microorganisms (Dechloromonas, Flavobacterium, Pseudomonas, Aeromonas and Zoogloea) that can carry out denitrification under relatively high DO conditions (>0.38 mg/L), but led to the reduction of the relative abundance of heterotrophs (Acidovorax, Thermomonas, Brevundimonas and Enterobacter) that are more sensitive towards high DO conditions., Competing Interests: Declaration of competing interest 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., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

In this paper, the kinetics of bisphenol S (BPS) degradation in the presence of peroxydisulfate (PDS) or dissolved oxygen (DO) in ultrasound (US) system were investigated. For PDS (US/PDS), increased PDS concentration result in faster BPS degradation, but the enhancement was not remarkable with multiplying PDS dosages. Therefore, heterogeneous PDS activation model based on a Langmuir-type adsorption mechanism was proposed to explain the trait of BPS abatement. The equilibrium constant of PDS (K PDS ) was calculated to be 2.91 × 10 -4 /μM, which was much lower than that of BPS, suggesting that PDS was hard to adsorb on the gas-liquid interface of the cavitation bubble following by activation. Besides, the formation of •OH and SO 4 •- rather than •OH was the predominant radical, which was quite different from previous study. Dissolved oxygen largely improve the degradation of BPS in US system and •OH rather than O 4 was proved to be the main reactive oxygen species (ROS). The improvement of •OH generation possibly caused by the reaction of DO with •H so that it cannot recombine with •OH. The transformation of the BPS in US system mainly included BPS radical polymerization, hydroxylation and hydrolysis. Frustratingly, the acute toxicity assay of Vibrio fischeri suggests that the degradation products of BPS are more toxic. These results will improve the understanding on the activation mechanisms of PDS and the role of dissolved oxygen play in US. Further investigations may need to explore other treatment ways of BPS and evaluate the acute toxicity of degradation products.•- rather than •OH was the predominant radical, which was quite different from previous study. Dissolved oxygen largely improve the degradation of BPS in US system and •OH rather than O 2 •- was proved to be the main reactive oxygen species (ROS). The improvement of •OH generation possibly caused by the reaction of DO with •H so that it cannot recombine with •OH. The transformation of the BPS in US system mainly included BPS radical polymerization, hydroxylation and hydrolysis. Frustratingly, the acute toxicity assay of Vibrio fischeri suggests that the degradation products of BPS are more toxic. These results will improve the understanding on the activation mechanisms of PDS and the role of dissolved oxygen play in US. Further investigations may need to explore other treatment ways of BPS and evaluate the acute toxicity of degradation products., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

A temperature-control curtain (TCC) is a new technique of selective withdrawal for controlling the outflow temperature of a reservoir. A TCC can significantly affect the reservoir hydrodynamic and thermal structure, but its effects on water quality and ecology remain unknown. In this study, we developed and calibrated a hydro-thermal-water quality model to numerically analyze how a TCC located 1 km from a dam affected algal biomass and water quality in a reservoir. According to our results, when a TCC was used, the mean annual chlorophyll a (Chl-a) concentrations in the reservoir decreased. Chl-a concentrations remained constant during the heating period until normal water levels were reached, and increased during the cooling period and decreased until year-end drawdown levels were reached. The dissolved oxygen (DO) concentrations decreased and the anoxic proportions increased throughout the year. The yearly mean Chl-a and DO concentrations in the reservoir declined continuously as the water-retaining proportion (P r ) of the TCC increased from 0 to 87.5%, while the anoxic proportion (DO < 2 mg/L) first increased and then decreased, peaking at a P r of 62.5%. The change patterns of the anoxic proportion were consistent with those of thermal stability, demonstrating the applicability of thermal stability in predicting reservoir hypoxia. Moreover, the environmental impact of TCCs will increase under global warming, and TCCs can mitigate the increased algal biomass and further decrease DO in warmer climate conditions. Under a medium-high climate scenario, Representative Concentration Pathway 6.0, and a TCC having 75% P r , the yearly mean Chl-a, DO concentrations, and anoxic proportions of Sanbanxi Reservoir are predicted to reach 10.7 μg/L, 4.2 mg/L, and 39.6%, respectively, by 2046-2065. Thus, changes in the water environment and ecology (particularly the likely deterioration of water quality because of selective withdrawal under global warming) should be considered as a component of water management practices., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Mixed microbial cultures are a viable means for polyhydroxyalkanoate (PHA) production, which can produce polymers of commercial quality with high yields. Various PHA co-polymer blends can be produced by surplus full-scale municipal activated sludge fed with fermented waste feedstocks. In biological nutrient removal, ammonia is converted to nitrate by ammonia and nitrite oxidizing bacteria (AOBs and NOBs) through nitrification and removed as nitrogen gas through denitrification. Activated sludge can be enriched with significant PHA storage potential alongside nitrogen removal by denitrifying heterotrophic and nitrifying autotrophic bacteria. The latter adds complexity and aeration demand during the aerobic side-stream PHA accumulation stage since fermented organic residuals often contain significant amounts of ammonia. In the present work, the influence of dissolved oxygen (DO) levels on both PHA accumulation and nitrification rates for a municipal activated sludge were evaluated. The objective was to identify potential for a DO control strategy for PHA accumulation, which would mitigate the unnecessary nitrification activity during PHA production. A much higher apparent Michaelis-Menten DO affinity for volatile fatty acid (VFA) consumption (K DO &#95;VFA 0.1 ± 0.06 mg/L) was found as compared to nitrification (K DO &#95;NH4 2.87 ± 1.31 mg/L). Consequently, with lower DO levels, PHA production was not limited by oxygen supply, while nitrogen was removed by simultaneous nitrification and denitrification processes. This study suggests a method for PHA accumulation using nitrifying activated sludge, while feeding ammonia-containing organic feedstocks by means of DO level control where: (1) NOB activity and growth are both mitigated, (2) nitrogen removal is facilitated, (3) alkalinity is controlled through simultaneous denitrification, and (4) energy demand for aeration is reduced., (Copyright © 2019 Elsevier B.V. All rights reserved.)

A novel IBAF system (altered conventional biological aerated filter (BAF) for intermittent aeration) was used to treat BDD anodes electrochemical oxidation gasification wastewater effluent, after which 454 pyrosequencing was applied to investigate the bacterial community of IBAF and demonstrate the relationship between dissolved oxygen (DO) and the bacterial community. The results showed that the concentration of COD, NH 4 + -N and NO 3 - -N reached 55.08, 7.64 and 7.76 mg/L, respectively, in IBAF effluent because of changes in the DO concentration at 30 days after system start-up. The bacterial community results revealed that the 40 cm sample had the highest bacterial diversity. The bacterial species were approximate in total samples at phylum and family level, but the relative abundance was significantly different because of change in DO concentration. In addition, sample distance analysis indicated that the similarity of different samples was related to the DO concentration at different heights., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Water resources in many regions are stressed by impairments resulting from climate change, population growth and urbanization. In the United States (US), water quality criteria (WQC) and standards (WQS) were established to protect surface waters and associated designated uses, including aquatic life. In inland waters of the south central US, for example, depressed dissolved oxygen (DO) consistently results in impaired aquatic systems due to noncompliance with DO WQC and WQS. In the present study, we systematically examined currently available DO threshold data for freshwater fish and invertebrates and performed probabilistic aquatic hazard assessments with low DO toxicity data that were used to derive the US Environmental Protection Agency's (EPA) Ambient Water Quality Criteria (AWQC) for DO and newly published information. Aquatic hazard assessments predicted acute invertebrate DO thresholds for Ephemeroptera, Plecoptera, or Trichoptera (EPT) taxa and species inhabiting lotic systems to be more sensitive than fish. For example, these organisms were predicted to have acute low DO toxicity thresholds exceeding the US EPA guidelines 17, 26, 31 and 38% and 13, 24, 30 and 39% of the time at 8.0, 5.0, 4.0 and 3.0 mg DO/L, respectively. Based on our analysis, it appears possible that low DO effects to freshwater organisms have been underestimated. We also identified influences of temperature on low DO thresholds and pronounced differences in implementation and assessment of the US EPA AWQC among habitats, seasons, and geographic regions. These results suggest some implemented DO guidelines may adversely affect the survival, growth, and reproduction of freshwater aquatic organisms in a region susceptible to climate change and rapid population growth. Given the global decline of species, particularly invertebrates, low DO threshold information, including sublethal (e.g., reproduction, behavior) responses, for additional species (e.g., mollusks, other invertebrates, warm water fish) across seasons, habitats, and life history stages using consistent experimental designs is needed to support more sustainable environmental assessment efforts and management of biodiversity protection goals in inland waters.

The monochloroacetic, dichloroacetic and trichloroacetic acid (MCAA, DCAA and TCAA) removed by metallic iron under controlled dissolved oxygen conditions (0, 0.75, 1.52, 2.59, 3.47 or 7.09 mg/L DO) was investigated in well-mixed batch systems. The removal of CAAs increased first and then decreased with increasing DO concentration. Compared with anoxic condition, the reduction of MCAA and DCAA was substantially enhanced in the presence of O2, while TCAA reduction was significantly inhibited above 2.59 mg/L. The 1.52 mg/L DO was optimum for the formation of final product, acetic acid. Chlorine mass balances were 69-102%, and carbon mass balances were 92-105%. With sufficient mass transfer from bulk to the particle surface, the degradation of CAAs was limited by their reduction or migration rate within iron particles, which were dependent on the change of reducing agents and corrosion coatings. Under anoxic conditions, the reduction of CAAs was mainly inhibited by the available reducing agents in the conductive layer. Under low oxic conditions, the increasing reducing agents and thin lepidocrocite layer were favorable for CAA dechlorination. Under high oxic conditions, the redundant oxygen competing for reducing agents and significant lepidocrocite growth became the major restricting factors. Various CAA removal mechanisms could be potentially applied to explaining the effect of DO concentration on iron efficiency for contaminant reduction in water and wastewater treatment., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

In wastewater treatment plants (WWTPs), aeration is the major energetic cost, thus its minimisation will improve the cost-effectiveness of the process. This study shows that both the dissolved oxygen (DO) concentration and aerobic hydraulic retention time (HRT) affect the competition between polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs). At low DO levels, Accumulibacter PAOs were shown to have an advantage over Competibacter GAOs, as PAOs had a higher oxygen affinity and thus largely maintained their aerobic activity at low DO levels, while GAO activity decreased. Bioreactor operation at low DO levels was found to increase the PAO fraction of the sludge. Furthermore, an increase in aerobic HRT (at a DO level of 2 mg O2/L), promoted the proliferation of GAOs over PAOs, decreasing the EBPR efficiency. Overall, this study shows that low aeration can be beneficial for EBPR performance through selecting for PAOs over GAOs, which should be incorporated into WWTP models in order to minimise energetic costs and improve WWTP sustainability., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

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The distribution and concentration of dissolved oxygen (DO) play important roles in aerobic heterotroph activities and some slow chemical reactions, and can affect the water quality, biological communities, and ecosystem functions of rivers and lakes. In this work, the transport of high Schmidt number DO at the sediment-water interface of spanwise oscillating flow is investigated. The volume-averaged Navier-Stokes (VANS) equations and Monod equation are used to describe the flow in the sediment layer and the sediment oxygen demand of microorganisms. The phase-averaged velocities and concentrations of different amplitudes and periods are studied. The dependence of DO transfer on the amplitude and period is analyzed by means of phase-average statistical quantities. It is shown that the concentration in the sediment layer is positively correlated with the turbulence intensity, and the DO concentration and penetration depth in the sediment layer increases when the period and amplitude of the oscillating flow increase. Moreover, in the presence of oscillating flow, a specific scaling relationship exists between the Sherwood number/oxygen consumption of aerobic heterotrophs and the Reynolds number. [ABSTRACT FROM AUTHOR]

A double-chamber self pH-buffer microbial fuel cell (MFC) was used to investigate the effect of dissolved oxygen (DO) concentration on cathodic nitrification coupled with anodic denitrification MFC. It was found that nitrogen and COD removal, electricity generation were positively correlated with DO concentration in the cathode chamber. When total inorganic nitrogen of influent was 202.51 ± 7.82 mg/L at DO 6.8 mg/L, the maximum voltage output was 282 mV and the maximum power density was 149.76 mW/m2. After 82 h operation, the highest removal rate of total inorganic nitrogen was 91.71 ± 0.38%. Electrochemical impedance spectroscopy (EIS) test showed that the internal resistance of the reactor with different DO concentration was related to the diffusion internal resistance. The data of bacterial analysis in the cathode chamber revealed that there were not only ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), but also a large number of exoelectrogens. Compared with the traditional biological denitrification and related MFC denitrification research, this method does not need pH-buffer solution and external circulation device through the anion exchange membrane (AEM). It can generate electricity and remove nitrogen simultaneously, and the oxygen utilization rate in the cathode can also be enhanced. • Nitrification coupled with denitrification were realized in a self-buffer MFC. • The migration of NO 2 −/NO 3 − and the pH balance was achieved in a MFC through AEM. • N/COD removal and power generation were positively correlated with cathodic DO. [ABSTRACT FROM AUTHOR]

Highlights: [•] The volumetric oxygen mass transfer kLa was measured under different operational conditions. [•] Experiments in clean water and with activated sludge were done. [•] The experimental results were used to develop a high fit empirical model. [•] The airflow rate was the main factor affecting the kLa. [Copyright &y& Elsevier]

To evaluate the hypothesis that plant-mediated oxygen supplies decrease methane (CH4) production and total global warming potential (GWP) in a tropical peatland, the authors compared the fluxes and dissolved concentrations of greenhouse gases [GHGs; CH4, carbon dioxide (CO2) and nitrous oxide (N2O)] and dissolved oxygen (DO) at multiple peatland ecosystems in Central Kalimantan, Indonesia. Study ecosystems included tropical peat swamp forest and degraded peatland areas that were burned and/or drained during the rainy season. CH4fluxes were significantly influenced by land use and drainage, which were highest in the flooded burnt sites (5.75 ± 6.66 mg C m−2 h−1) followed by the flooded forest sites (1.37 ± 2.03 mg C m−2h−1), the drained burnt site (0.220 ± 0.143 mg C m−2 h−1), and the drained forest site (0.0084 ± 0.0321 mg C m−2 h−1). Dissolved CH4concentrations were also significantly affected by land use and drainage, which were highest in the flooded burnt sites (124 ± 84 μmol L−1) followed by the drained burnt site (45.2 ± 29.8 μmol L−1), the flooded forest sites (1.15 ± 1.38 μmol L−1) and the drained forest site (0.860 ± 0.819 μmol L−1). DO concentrations were influenced by land use only, which were significantly higher in the forest sites (6.9 ± 5.6 μmol L−1) compared to the burnt sites (4.0 ± 2.9 μmol L−1). These results suggest that CH4produced in the peat might be oxidized by plant-mediated oxygen supply in the forest sites. CO2fluxes were significantly higher in the drained forest site (340 ± 250 mg C m−2 h−1with a water table level of −20 to −60 cm) than in the drained burnt site (108 ± 115 mg C m−2 h−1with a water table level of −15 to +10 cm). Dissolved CO2concentrations were 0.6–3.5 mmol L−1, also highest in the drained forest site. These results suggested enhanced CO2emission by aerobic peat decomposition and plant respiration in the drained forest site. N2O fluxes ranged from −2.4 to −8.7 μg N m−2 h−1in the flooded sites and from 3.4 to 8.1 μg N m−2 h−1in the drained sites. The negative N2O fluxes might be caused by N2O consumption by denitrification under flooded conditions. Dissolved N2O concentrations were 0.005–0.22 μmol L−1but occurred at < 0.01 μmol L−1in most cases. GWP was mainly determined by CO2flux, with the highest levels in the drained forest site. Despite having almost the same CO2flux, GWP in the flooded burnt sites was 20% higher than that in the flooded forest sites due to the large CH4emission (not significant). N2O fluxes made little contribution to GWP. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Comparative economic performances of different aerators were investigated [•] Usefulness of various aerators at different initial pond DO concentrations and pond volumes is presented. [•] For a typical Indian major carp culture system in a pond of volume less than 1000m3, CSC or PCSC aerator is most economical. [•] For larger ponds of volume more than 5000m3, 1-hp paddle wheel or 2-hp paddle wheel aerator is more economical. [ABSTRACT FROM AUTHOR]

The design and development of the neural network based controller performance for the activated sludge process in sequencing batch reactor (SBR) is presented. In this paper, here we give a comparative study of various neural network based controllers such as the direct inverse control, internal model control and hybrid neural network control strategies to maintain the dissolved oxygen level of an activated sludge system by manipulating the air flow rate. The neural network inverse model based controller with the model-based scheme represents the controller, which relies solely upon the simple neural network inverse model. In the internal model control, both the forward and inverse model is used directly as elements within the feedback loop. The hybrid neural network control consists of a basic neural network (NN) controller in parallel with a proportional integral (PI) controller. Various simulation test involving multiple set point changes, disturbances rejection and noise effects were performed to review the performances of these various controllers. From the results it can be seen that hybrid controller gives best results in tracking set point changes value the disturbances and noise effects. [ABSTRACT FROM AUTHOR]

The aim of this study was examination possibility of Azolla caroliniana Willd. to aerate its medium enriched with Cd(II) and Hg(II) and comparison of DO and ODR methods in measurement aeration status of solutions. Azolla system has been chosen to verify the validity of the measuring ODR method in water solution. Water aeration measurements, one of important environmental tests, are performed most often by measurement of dissolved oxygen with oxygen sensors. Other similar method called oxygen diffusion rate is generally used in different porous materials such as soil. Our first objective was to check if these both methods are comparable and may be use exchangeable in water solution. The both types of measurements were performed in medium saturated at different oxygen concentrations. The linear relationship and high correlation ( R = 0.89) were found between values of ODR and DO. The object of the second part of our studies was A. caroliniana Willd. ( Azollaceae), a floating water fern living in symbiosis with cyanobacterium Anabaena azollae Strasb. ( Nostoceae) that fixes atmospheric nitrogen. Azolla plants are used for centuries as a nitrogen biofertilizer. The second aim of our work was to find out, if the fern reduces or increases oxygen concentration in water. The ODR method was used to determine the aeration status of the nutrient solution. During 12 days of the experiment at laboratory conditions, an active role of A. caroliniana in aeration of the nutrient solution containing Cd(II) and Hg(II) was stated. [ABSTRACT FROM AUTHOR]

Dissolved inorganic carbon (DIC) and dissolved oxygen (DO) are commonly measured to compute metabolism of aquatic ecosystems. However, concentrations of DIC and DO depend on many factors in addition to ecosystem metabolism, such as water temperature, gas exchange with the atmosphere, abiotic chemical reactions, and inputs in precipitation, groundwater, and surface water. We used 20-year time series from seven lakes to understand how DIC and DO concentrations are controlled as a function of time scale. Diel cycles of both solutes are controlled primarily by metabolism, exchange with the atmosphere, and temperature. At seasonal and annual scales, metabolism is important, but physical processes associated with Spring and autumn mixing, as well as solute loading from the watershed, have comparably large effects. At decadal scales, effects of metabolism are negligible. Controls of the two solutes diverge, with variance in DIC explained largely by solute inputs and variance in DO explained largely by water temperature. Like other indicators in many ecosystems, variability of DIC and DO is strongly scale dependent and associated with different drivers depending on the time scale of the analysis. [ABSTRACT FROM AUTHOR]

Abstract: The cosmopolitan dinoflagellate Prorocentrum minimum is a recurrent bloom forming species in the Chesapeake Bay and its tributaries, generally observed at its highest levels in late spring and summer. Laboratory studies were conducted to assess potential bloom impacts on diel oxygen concentrations in shallow littoral zones as well as settlement success and post-set growth of the eastern oyster Crassostrea virginica. Using light–dark and dark cultures and periodic diel sub-sampling, bloom levels of P. minimum produced supersaturated oxygen levels at the end of each day while darkened cultures were typified by rapid decreases in dissolved oxygen (DO) (1.1–1.3mgL-1h-1) to hypoxic and anoxic levels within 4 days. These data suggest shallow, poorly flushed systems and the biota in them will experience rapid and large diel variations in oxygen, implying recurrent P. minimum blooms need be considered as short-term oxygen stressors for Bay oyster spat and other living resources. Direct effects of P. minimum impacts on oysters were not as expected or previously reported. In one experiment, pre-bloom isolates of P. minimum were grown and then exposed to polyvinyl chloride (PVC) settlement plates to see whether dinoflagellate preconditioning of the hard substrate might affect oyster sets. No differences were noted between set on the PVC with P. minimum exposure to set recorded with filtered seawater, Instant Ocean®, or Isochrysis. In the second oyster experiment, spat on PVC plates were exposed to field collected P. minimum blooms and a commercial mixture of several other food types including Isochrysis. Oyster growth was significantly higher in P. minimum exposures than noted in the commercial mix. These results, compared to results with other isolates from the same region, indicate substantial positive impact from some of the P. minimum blooms of the area while others separated in space, time, or nutrient status could severely curtail oyster success through toxin production induced by nutrient limitation. [Copyright &y& Elsevier]

• Discontinuous streams can have reaches of dissolved oxygen (DO) below saturation. • The low DO reaches are related to reemerging groundwater and hyporheic flows. • Contemporary forest practices avoid impacts that contribute to low DO in streams. • Water quality standards for large streams may be unachievable in headwater streams. The concentration of oxygen dissolved in water affects aquatic organisms. Unrestrained logging and site preparation can depress dissolved oxygen (DO) concentrations in adjacent streams by elevating temperatures (with removal of riparian shade), impounding channels (reduced reaeration rates), and introducing fresh, oxygen-depleting slash. One of the first paired watershed studies investigating the use of streamside management zones, the Alsea Watershed Study (AWS) in coastal Oregon (1958–1973), highlighted the potential to depress DO concentrations in streams adjacent to harvest units. This and other studies spurred development of Best Management Practices (BMPs) and forest practice rules to maintain, among other things, favorable DO concentrations in streams. A new study of the Alsea watersheds (2006–2015) found little signal of management effects on DO concentrations. It did find that a discontinuously perennial stream (where reaches go subsurface during low flows) can experience naturally low DO concentrations. Forest managers can avoid exacerbating low DO conditions using simple BMPs, but discontinuously perennial forest streams are predisposed to low DO concentrations. [ABSTRACT FROM AUTHOR]

• Anammox bacteria contributed 50.3% of TN removal in aerobic period. • 6.12 × 109 gene copies/(g dry sludge) of AOB in whole biofilm was twice than in floc. • Alternating FA and oxygen starvation inhibited NOB with OUR of 4.02 mgO 2 /(gVSS h). • DO micro-distribution revealed protection mechanism of 1900 μm aerobic biofilm. • The whole biofilm was divided into five layers based on DO micro-distribution. A novel partial nitrification-Anammox biofilm reactor (PNABR) operated under high dissolved oxygen (DO) with pre-anoxic - aerobic - anoxic operational mode was developed for efficient denitrogenation from mature landfill leachate. With DO concentration gradually increasing to 4.03 ± 0.03 mg/L, the ammonia oxidation rate (AOR) was enhanced to 25.8 mgNH 4 +-N/(L h), while nitrite oxidation bacteria (NOB) was inhibited effectively by alternating free ammonia (FA) and oxygen starvation. DO micro-distribution revealed that estimated 1900 μm of aerobic biofilm could protect anammox biofilm underneath from being inhibited by high DO. qPCR analysis further suggested that ammonia oxidation bacteria (AOB) abundance in whole biofilm was 6.12 × 109 gene copies/(g dry sludge), which was twice than found in the floc. Anammox bacteria accounted for 2.39% of total bacteria in whole biofilm, contributing 90.0% to nitrogen removal. Nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) finally reached 396.6 gN/(m3 d) and 96.1%, respectively. [ABSTRACT FROM AUTHOR]