Evolution Of Dissolved Oxygen Research Articles

Oxygen evolution and its drivers in a stratified reservoir: A supply-side perspective for informing hypoxia alleviation strategies

Hypoxia in stratified waters greatly threatens aquatic ecology and societal development owing to enhanced nutrient discharge and increasing global temperature. Current research predominantly alleviates hypoxia by reducing dissolved oxygen (DO) consumption or conducting hypolimnetic oxygenation, yet their implementation has encountered bottlenecks. Therefore, this study explores the potential of increasing the inherent DO supplies in stratified reservoirs to mitigate hypoxia. High-frequency in situ observations and massive modeling experiments are integrated to discern the DO supply mode and the dominant driver of DO evolution. Results indicate that periodic thermodynamic conditions determine the DO supply relationships between oxygen sources (inflow carriage, reaeration, and photosynthesis) for different water layers. Thermal stratification causes the hypolimnion to rely mostly on the inflow for DO supply, leading to a fragile budget prone to hypoxia. However, episodic hydrodynamic events (turnover, wind stir, density current, and flood) can promote DO supply and inhibit hypoxia. Temperature and DO regimes are primarily driven by outflow conditions, followed by inflow and meteorology conditions. Furthermore, hypolimnetic hypoxia can be regulated by altering inflow volume, outflow volume, and outlet elevation. These findings highlight the importance of longitudinal solute exchange in DO evolution in stratified reservoirs, providing a basis for alleviating hypoxia through cascade reservoir operations.

Analysis of the influence of day and night temperature difference on oxygen concentration in ullage space of fuel tank

PurposeDetermining the variation law of the oxygen concentration in the ullage space of the fuel tank is the key to the design of the inert system. Among various factors affecting the oxygen concentration in the ullage space of the fuel tank, the temperature difference between day and night shows particular importance while relevant analysis and calculation are scarce.Design/methodology/approachThis study establishes a theoretical simulation model of the central wing fuel tank of an aircraft according to the relevant provisions of day-night temperature variation in FAR25 airworthiness regulations, verifies the model with the existing experimental data and discusses the corresponding relationship between the oxygen concentration in the ullage space of the fuel tank and the day-night temperature difference. The influence of day and night temperature difference, fuel type, fuel load rate, initial oxygen concentration, dissolved oxygen evolution and other factors on the oxygen concentration in the ullage space of the fuel tank were analyzed, and the limit of initial oxygen concentration of the fuel tank before the shutdown at night meeting the requirements of the airworthiness provisions was proposed.FindingsThe results show that the temperature difference between day and night, fuel load rate, initial oxygen concentration and other factors have different effects on the oxygen concentration in the ullage space of fuel tank. The initial oxygen concentration limit before shutdown shall be 2% below the 12% oxygen concentration stipulated by FAA.Research limitations/implicationsThe research results in this paper will be of good reference value to the design of the inert system and the calculation of the flammability exposure evaluation time. This paper aims to be good reference of the design of the inert system and the calculation of the flammability exposure evaluation time.Originality/valueThe research results of this paper can provide practical guidance for the current civil airworthiness certification work.

Oxygen concentration variation in ullage influenced by dissolved oxygen evolution

To determine the oxygen concentration variation in ullage that results from dissolved oxygen evolution in an inert aircraft fuel tank, the CFD method with a mass transfer source is applied in the present study. An experimental system is also designed to evaluate the accuracy of the CFD simulations. The dissolved oxygen evolution is simulated under different conditions of fuel load and initial oxygen concentration in ullage of an inert fuel tank with stimulations of heating and pressure decrease. The increase in the oxygen concentration in ullage ranges from 0.82% to 5.92% upon stimulation of heating and from 0.735% to 12.36% upon stimulation of a pressure decrease for an inert ullage in the simulations. The heating accelerates the release of the dissolved oxygen from the fuel by increasing the mass transfer rate in the mass transfer source and decreasing the pressure, thereby accelerating the dissolved oxygen evolution by increasing the concentration difference between the gas and the fuel. The time constant that represents the oxygen evolution rate is independent of the initial oxygen concentration in ullage of an inert tank but depends closely on the fuel load, temperature and pressure. The time constant can be fitted using a polynomial equation relating the fuel load to temperature in the heating stimulation with an accuracy of 4.77%. Upon stimulation of a pressure decrease, the time constant can be expressed in terms of the fuel load and the pressure, with an accuracy of 5.02%.

Temperature effects on photosynthesis in gametophytic and sporophytic stages of the freshwater red alga Sirodotia delicatula (Rhodophyta, Batrachospermales) under a global warming perspective

SUMMARYThe increase in Earth's global mean temperature due to human influence has become a major concern, with ecological consequences already being reported around the world. In tropical streams, benthic red algae belonging to the order Batrachospermales contribute to a large fraction of the community energy input and play an important role in sustaining autotrophic food webs. The Batrachospermales also have a unique life history, with heteromorphic life stages (gametophytes and sporophytes) occurring seasonally and with distinct ecological roles. Through “in vivo” chlorophyll fluorescence and dissolved oxygen evolution techniques, we evaluated the effects of projected temperature increases of two future scenarios (RCP 4.5 and RCP 8.5) on the photosynthetic response of Sirodotia delicatula gametophytes and sporophytes. In general, both chlorophyll fluorescence and dissolved oxygen showed that the RCP 8.5 scenario could severely jeopardize the photosynthetic performance of the sporophytes during the summer while also providing a stressful physiological situation to the gametophytes. Due to the crucial role of sporophytes in the development of this species, results indicate that this predicted scenario could affect this species. Given the position of these organisms at the base of the food web in tropical lotic environments, especially in shaded low‐order streams, such impact could generate unforeseen cascade effects on higher trophic levels.

Impact of carbon dioxide injection on oxygen dissolution rate during oxygen additions in a bubble column

Oxygen additions are common practice during oenological fermentations. Since oxygen dissolution under winemaking conditions is not completely understood, these additions are performed empirically. In particular, the influence of carbon dioxide produced by yeast cells on the oxygen dissolution rate remains unclear. In this paper, we present an oxygen mass balance model that describes the evolution of dissolved oxygen in a laboratory scale carbon dioxide bubbling column emulating wine fermentation hydrodynamic conditions during oxygen additions. The model consists of two partial differential equations for the liquid and gas phases and considers liquid recirculation and mixing. Considering only one fitting parameter, the model can reproduce well the observed dissolved oxygen evolution at different locations in the column. We found that carbon dioxide bubbling has two simultaneous antagonist effects: it enhances the volumetric mass transfer coefficient and decreases the oxygen equilibrium concentration mainly due to the dilution effect in the gas phase. Overall, the latter effect is shown to be more important and explains the reduction of almost 60% of the oxygen dissolution rate for high carbon dioxide bubbling conditions. The model developed here will help to design better oxygen addition systems for oenological fermentations.

Modelling photo-Fenton process for organic matter mineralization, hydrogen peroxide consumption and dissolved oxygen evolution

A kinetics model with lumped components and TOC fractionation is proposed to track paracetamol degradation, as a model pollutant, using the photo-Fenton process. The proposed structure shows acceptable predictive capabilities regarding hydrogen peroxide consumption, TOC mineralization and dissolved oxygen evolution. The number of model parameters is considered assumable in calibrating other pollutants and degradation mixtures when applying this technology. This study covers a pollutant load range between 4 and 25mM of TOC. The Fe2+ initial load varied between 0.089 and 0.44mM whilst the initial H2O2 concentration tested ranged from 9mM to 45mM. The influence of light intensity was considered explicitly within the model whilst temperature and pH conditions were held constant. The fixed structure model, containing 9 kinetic parameters and 3 stoichiometric coefficients, was later applied to a pollutant mixture with a successful prediction of hydrogen peroxide and TOC profiles.

Temporal and spatial distribution of dissolved oxygen in the Ria de Aveiro lagoon

Ria de Aveiro is a very important area of the Portuguese coast, which has been under an increasing anthropogenic pressure, for several decades, contributing to the degradation of the lagoon's water quality. A water quality model was applied to predict concentrations of inorganic nutrients, chlorophyll-a, and dissolved oxygen (DO) in the Ria de Aveiro lagoon, Portugal. Both data and modelling results point out that the DO distribution in the lagoon is controlled by tidal transport processes. The DO distribution in the Ria de Aveiro seems to be mainly controlled by tidal processes, as its concentration remains relatively high and close to sea values. The far end of the lagoon, where the intertidal salt marshes are important, the DO concentration is dominantly affected by re-aeration and the flooding/drying processes over the intertidal salt marshes, the phytoplankton activity, the nitrification processes and oxidation of the organic matter. These processes play an important role in the creation of the summer hypoxic/anoxic situations, when primary production and advective transport are low. Data and modelling results show strong relationship between nutrients and the CHL-a concentrations during spring–summer, but weak during winter–spring, evidencing the light and nutrients limiting effect during, respectively the last and the former period. High NO 3 and NH 4 concentrations or important spikes in the concentration precede or coincide, in general, with the CHL-a increase. The main results concerning the DO evolution and distribution demonstrate that a generalized eutrophication state is unlikely to occur within the lagoon, except near its very far end, during summer and in a situation of high BOD concentrations. The good connection between Ria de Aveiro lagoon and the sea and the circulation pattern inside the lagoon are, therefore, responsible for relatively high level of oxygen water content in the water column, throughout its main channels.

Short time dissolved oxygen dynamics in shallow water ecosystems

Dissolved oxygen evolution over time holds information about the recent and past history of the physics, the chemistry and the biology of aquatic systems. On the daily time scale various phenomena seem to repeat with a sort of regularity, leaving a trace in the further trend of oxygen dynamics. These are the wind calm of nocturnal and early morning hours, the advent of the afternoon breezes, the micro- and macro-algae diurnal production, the chemical and biochemical processes. On the larger seasonal scale, dissolved oxygen shows an almost periodical trend. In this case, a greater dependency on the climatic events leads to the colder and windy season, while the warm and hot period is closely related to the vegetable production, which frees remarkable amounts of oxygen in the water through photosynthesis. Result of experimental measurements of dissolved oxygen, acquired with an automatic equipement on a very short time scale (30 s), are shown and discussed. The experiments were run to detect oscillating phenomena characterized by a period which is shorter than the daily occurrence, as well as stochastic phenomena, led by almost periodical drifts, which contribute substantially to the oxygen dynamics on the longer time scale. To determine these pseudo-periodicities, or time variation for the oscillation period, the analysis of the temporal distances between local maxima of oxygen concentrations has been performed. This kind of analysis is based on the hypothesis that we are dealing with a dissipative dynamical system whose evolution is similar to the behavior of some non linear oscillating systems with a control, where the control can be represented by a simple function of the temporal interval between two consecutive peaks. The result of the analysis suggests the existence of dynamics on a 6–8 h time scale.

Methods for studying dissolved oxygen levels in coastal and estuarine waters receiving combined sewer overflows

One factor in determining the transport capacity of coastal interceptors in Combined Sewer Systems (CSS) is the reduction of Dissolved Oxygen (DO) in coastal waters originating from the overflows. The study of the evolution of DO in coastal zones is complex. The high computational cost of using mathematical models discriminates against the required probabilistic analysis being undertaken. Alternative methods, based on such mathematical modelling, employed in a limited number of cases, are therefore needed. In this paper two alternative methods are presented for the study of oxygen deficit resulting from overflows of CSS. In the first, statistical analyses focus on the causes of the deficit (the volume discharged). The second concentrates on the effects (the concentrations of oxygen in the sea). Both methods have been applied in a study of the coastal interceptor at Pasajes Estuary (Guipúzcoa, Spain) with similar results.

Methods for studying dissolved oxygen levels in coastal and estuarine waters receiving combined sewer overflows

One factor in determining the transport capacity of coastal interceptors in Combined Sewer Systems (CSS) is the reduction of Dissolved Oxygen (DO) in coastal waters originating from the overflows.The study of the evolution of DO in coastal zones is complex. The high computational cost of using mathematical models discriminates against the required probabilistic analysis being undertaken. Alternative methods, based on such mathematical modelling. employed in a limited number of cases, are therefore needed.In this paper two alternative methods are presented for the study of oxygen deficit resulting from overflows of CSS. In the first, statistical analyses focus on the causes of the deficit (the volume discharged). The second concentrates on the effects (the concentrations of oxygen in the sea). Both methods have been applied in a study of the coastal interceptor at Pasajes Estuary (Guipúzcoa, Spain) with similar results.