Dissolved Oxygen Consumption Rate Research Articles

Summer bottom oxygen depletion dynamics and the associated physical structure in the Bohai Sea

Summertime oxygen depletion has been more and more frequently observed in the bottom water of the Bohai Sea in the last decade. Based on comprehensive hydrography and microstructure measurements in summer in the Bohai Sea, the physical structure and bottom dissolved oxygen (DO) dynamics were investigated. The study area is characterized by strong tidal currents and obvious horizontal temperature and DO gradients in the bottom boundary layer. The strong tidal forcing induces large near-bottom turbulent kinetic energy dissipation rates (ϵ ~ 5 × 10-5 W kg-1) which can be well parameterized by the law of the wall. Tidal horizontal advection effects dominate the short-term variations of bottom hydrography. Although the residual current is in a near-perpendicular direction with the horizontal DO gradient (~94°), the horizontal residual DO transport was calculated to be 67.4 mg m-2 d-1 which is ~ 33% of the magnitude of sediment oxygen demand. During the observation period, we observed an intense high-turbidity event leading to a severe drawdown of near-bottom DO concentration (0.16 mg L-1) in 1.5 hours. The DO consumption rate due to this event was then estimated to be ~ 33.3 g m-2 d-1 (1.39 g m-2 h-1) which is two orders of magnitude larger than the sediment oxygen demand. Rapid DO consumption can be induced by the great increase in bioavailable surface area in bottom water and seabed when benthic organic matter is resuspended. This process should be incorporated into the coupled physical-biogeochemical model to improve accuracy in simulating DO depletion.

Effect of oxygen on pitting corrosion of copper pipe in fire sprinkler system

In this study, pitting corrosion in copper pipe used for sprinkler according to dissolved oxygen (DO) concentration was investigated through failure analyses, flow visualization test, DO consumption rate analysis, electrochemical tests, surface analyses, and corrosion simulation test. As a result of the failure analysis, all 10 leaks were due to pitting corrosion, and 8 leaks occurred in the branch pipe at the end of sprinkler system. As a result of flow visualization test, there were air pockets occupying 20% of the maximum total volume at the end of the branch pipe due to pressure drops. DO consumption rate analysis showed that air pocket acted as the oxygen source to maintain high DO concentration. As a result of electrochemical tests, surface analyses, and corrosion simulation, the corrosion rate of the higher DO concentration is about 10 times higher than that of lower DO concentration due to the increased oxygen reduction reaction. Through these results, it was confirmed that an air pocket was formed at the end of the pipe in the sprinkler system, and this air pocket became an oxygen source and accelerated galvanic corrosion between inside and outside of the pit during pitting propagation. This can be used as a guideline to prevent water leakage for pitting corrosion on copper pipe.

Enhanced nitrogen removal of constructed wetlands by coupling with the bioelectrochemical system under low temperature: Performance and mechanism

Constructed wetland (CW) integrated with the bioelectrochemical system (BES-CW) is a novel and efficient low-strength wastewater treatment technology. In this study, the integrated CW (E-CW), open-circuit BES-CW (O-CW) and conventional CW (Control) were operated to investigate the performance and mechanism of nitrogen removal in E-CW under low temperature (10 °C). Results showed that low temperature nearly completely inhibited nitrate removal in Control and O-CW, but improved ammonia oxidation efficiencies (99.46% and 99.63%, respectively) due to high dissolved oxygen (DO) concentration in cold influent and enhanced ammonia oxidation archaea (AOA) growth. However, nitrite oxidation became the limited step of nitrification and partial nitrification and denitrification (PND) played the main role in TN removal under low temperature in Control and O-CW. On the contrary, nitrate was almost completely removed in E-CW (98.12%) on the 2nd day even at 10 °C due to its enhanced cold-resistant autotrophic denitrifying bacteria growth by applying low voltage and high DO consumption rate, and accordingly further improved its TN removal efficiency (82.26%), while the average nitrate and TN removal efficiencies in Control were only 11.10% and 37.26%, respectively. Thermomonas, Arenimonas, Gallionella and Thiobacillus were the main denitrifying bacteria attributed to nitrate removal in E-CW under low temperature involving autotrophic denitrification and cathode-driven bioelectrochemical denitrification. Moreover, extremely lower N2O emission from E-CW (0.81%) was obtained than the Control (12.76%), which indicated that the integration of CWs and the bioelectrochemical system is a viable technology for mitigation of greenhouse gas emission from CWs.

Applicability of the second-order rate law for modeling dissolved O2 consumption by Fe(II)-bearing geologic media

Fe(II)-bearing geologic media are promising agents for the consumption of dissolved oxygen (DO) remaining in geologic formations after the backfilling of radioactive waste repositories, which helps prevent redox-sensitive radionuclides from becoming soluble and mobile in groundwater. A second-order rate law has been proposed to describe DO consumption due to the oxidation of structural Fe(II) at the mineral surface; however, it has only been tested against a few Fe(II)-bearing geologic media via DO consumption experiments. Thus, this study investigates the applicability of the second-order rate law to Fe(II)-bearing geologic media and minerals by reanalyzing data from previous batch experiments of DO consumption. Additional DO consumption experiments were also performed on diatomaceous and siliceous mudstones to examine the influence of clay components and coexisting Fe(II)-bearing minerals on the DO consumption rate constant. The reanalysis results showed that the second-order rate law can effectively describe DO consumption by both natural geologic media and purified minerals. The derived consumption rate constants are relatively similar for natural geologic media and purified minerals, but not for media with a high clay content. In particular, the rate constants for sedimentary rocks with smectite components exhibit large variations and tend to be smaller than the theoretical lower limit for structural Fe(II) on silicate minerals. Conversely, the rate constants for mudstones containing non-swelling chlorite exhibit small variations. This implies that, in batch experiments on powdered samples containing smectite, DO is consumed not only by structural Fe(II) at the external surface but also by Fe(II) in the interlayers of the smectite, which is less accessible to DO in bulk solution. This may explain the prolonged reaction time and relatively small rate constants of sedimentary rocks with smectite components. This study suggests that the second-order rate law can be applied to model DO consumption in a variety of Fe(II)-bearing rocks. However, the rate constants may be underestimated with large variations when testing powdered rocks containing smectite.

Model-based analysis of dissolved oxygen supply to aquifers within riparian zones during river level fluctuations: Dynamics and influencing factors

Dissolved oxygen (DO) largely impacts the environmental function of riparian aquifers. However, the dynamics and influencing factors of DO supply to riparian aquifers are not well understood. In this study, we developed a model considering air–liquid two-phase flow, air entrapment and multi-phase transport of O2(g) in a riparian aquifer to investigate the hydrologic exchange flows and DO supply during river level fluctuations. A sensitivity analysis was conducted to quantify the influences of hydrological conditions of river, hydrogeological conditions of riparian aquifer, DO consumption rate constant and DO concentration in the river water on DO supply to the riparian aquifer. Results show that the river, the entrapped air and the unsaturated zone all provide a significant amount of DO to the riparian aquifer, and there are also noticeable differences in the spatial distribution of DO from the three different sources. Results also indicate there are a DO-rich strip and a DO-rich plume occurring in the top of the riparian aquifer and the channel-aquifer interface, respectively. Both DO-rich areas are the research focus in evaluating the environmental function of riparian zones. Further, the DO supply amount shows a significant increase as the river amplitude and period increase, and a losing river and increasing hydraulic conductivity also leads to the increasing DO supply flux because these incidents promote infiltration of the river water. In contrast, the high DO concentration in the river water increases the DO flux from river but reduces the DO supply from the entrapped air and the unsaturated zone because of the competition in different supply pathways. Moreover, the model simulations agree with the measurements of DO source in a field that has been reported. This work provides a useful tool for estimating DO supply to riparian aquifers and improves our understanding of the environmental function of riparian zones.

High Sensitivity of Lake Hypoxia to Air Temperatures, Winds, and Nutrient Loading: Insights From a 3‐D Lake Model

AbstractA three‐dimensional hydrodynamic‐ecological model is applied to Lake Erie to predict the response of dissolved oxygen (DO) to independent changes in air temperature, wind speeds and total phosphorus (TP) loading. Warmer temperatures and lower wind speeds increased the size and duration of hypoxic and anoxic regions by lengthening the stratified period. Decreased wind speed increased hypolimnion thickness while decreasing its temperature and DO consumption rate. Decreased TP loading improved DO conditions with a reduction of 75% effectively abolishing hypoxia. Anoxia was more sensitive to air temperature, wind, and nutrient changes than was hypoxia. New metrics that capture the spatial and temporal dimensions of low DO conditions were more sensitive than the commonly cited maximum areas of hypoxia or anoxia. Over most of the relevant range of forcing factors, the simple and first‐order effect of a 1°C temperature change was equivalent to a 10–14% change in TP loads, while a 1% change in wind speed was equivalent to a 2–3% change in TP loads. Reduced ice cover in warmer climates will likely increase air temperature effects even further.

The role of oxygen depletion and subsequent radioprotective effects during irradiation of mosquito pupae in water

BackgroundRadiation induced sterility is the basis of the Sterile Insect Technique, by which a target insect pest population is suppressed by releasing artificially reared sterile males of the pest species in overflooding numbers over a target site. In order for the sterile males to be of high biological quality, effective standard irradiation protocols are required. Following studies investigating the effects of mosquito pupae irradiation in water versus in air, there is a need to investigate the oxy-regulatory behavior of mosquito pupae in water to better understand the consequences of irradiation in hypoxic versus normoxic conditions.MethodsPupae of Aedes aegypti, Ae. albopictus, and Anopheles arabiensis were submerged in water inside air-tight 2 ml glass vials at a density of 100 pupae/ml and the dissolved oxygen (DO) levels in the water were measured and plotted over time. In addition, male pupae of Ae. aegypti (aged 40–44 h), Ae. albopictus (aged 40–44 h) and An. arabiensis (aged 20–24 h) were irradiated in a gammacell220 at increasing doses in either hypoxic (water with < 0.5% O2 content) or normoxic (in air) conditions. The males were then mated to virgin females and resulting eggs were checked for induced sterility.ResultsAll three species depleted the water of DO to levels under 0.5% within 30 minutes, with An. arabiensis consuming oxygen the fastest at under 10 minutes. Following irradiation, the protective effect of hypoxia was observed across species and doses (P < 0.0001), increasing at higher doses. This effect was most pronounced in An. arabiensis.ConclusionsThe consumption of dissolved oxygen by pupae submerged in water was significantly different between species, indicating that their oxy-regulatory capacity seems to have possibly evolved according to their preferred breeding site characteristics. This needs to be considered when sterilizing male mosquitoes at pupal stage in water. Depending on species, their DO consumption rates and their density, irradiation doses needed to achieve full sterility may vary significantly. Further assessments are required to ascertain optimal conditions in terms of ambient atmosphere during pupal irradiation to produce competitive sterile males, and temperature and density dependent effects are expected.

Dissolved oxygen level output feedback control based on discrete-time measurements during a Pseudomonas putida mt-2 fermentation

In this paper, the problem of controlling the dissolved oxygen level (DO) during an aerobic fermentation is considered. The proposed approach deals with three major difficulties in respect to the nonlinear dynamics of the DO, the poor accuracy of the empirical models for the oxygen consumption rate and the fact that only sampled measurements are available on-line. A nonlinear integral high-gain control law including a continuous-discrete time observer is designed to keep the DO in the neighborhood of a set point value without any knowledge on the dissolved oxygen consumption rate. The local stability of the control algorithm is proved using Lyapunov tools. The performance of the control scheme is first analyzed in simulation and then experimentally evaluated during a successfull fermentation of the bacteria over a period of three days. Pseudomonas putida mt-2.

Validation of the in vivo Iodo-Nitro-Tetrazolium (INT) Salt Reduction Method as a Proxy for Plankton Respiration

Knowledge of the magnitude and variability of plankton respiration is a crucial gap in our understanding of marine carbon cycling. In order to validate the INT reduction method as a proxy for plankton respiration, we have compiled and analysed a dataset (n = 376) of concurrent measurements of dissolved oxygen consumption (CRO2) and in vivo reduction of 2-para (iodophenyl)-3(nitrophenyl)-5(phenyl) tetrazolium chloride tetrazolium salt (INT) spanning a wide range of oceanic regions and physicochemical conditions. Data were randomly divided into two independent subgroups: two thirds of the data were used to derive a regression conversion between dissolved oxygen consumption and INT reduction (“training” dataset) and one third of the data was used to validate the regression (“test” dataset). There was a significant relationship between the log-transformed dissolved oxygen consumption rates and the log-transformed INT reduction rates (INTT) with the “training” dataset (logCRO2 = 0.72logINTT + 0.44, R2 = 0.69, n = 249, p 8 ˚C and chlorophyll-a concentrations >0.2 µg L-1 and reduced at lower temperatures and chlorophyll-a concentrations. The results of this study endorse the adequate performance and reliability of the INT method for natural plankton communities.

Organic matter decomposition sustains sedimentary nitrogen loss in the Pearl River Estuary, China

The Pearl River Estuary (PRE) has long received tremendous amounts of anthropogenic nitrogen, and is facing severe environmental problems. Denitrification and anaerobic ammonium oxidation (anammox) are known to be two major nitrogen removal pathways in estuarine sediments. Through the use of slurry and intact sediment core incubations, we examined the nitrogen removal pathways and quantified the in situ denitrification and anammox with associated gaseous nitrogen production rates. Sedimentary nitrogen removal was predominated by denitrification (93–100%) relative to a minimal contribution (<7%) from anammox. Among the detected environmental factors, salinity, bottom water NOx− (nitrate and nitrite) concentration, sedimentary organic matter and dissolved oxygen consumption rates showed good correlations with denitrification and anammox rates. Sedimentary nitrogen loss was mainly supported by endogenic coupled nitrification-denitrification (6.0 ± 1.5 × 106 mol N d−1), with water-column-delivered NOx− (2.1 ± 0.6 × 106 mol N d−1) as the secondary source. Such results suggested that sedimentary nitrogen removal involved mainly particulate organic form (allochthonous or autochthonous) deposited onto sediments, rather than inorganic forms in overlying water. Meanwhile, total N2O production from sediments was estimated to be 7.3 ± 2.1 × 104 mol N d−1, equivalent to ~35% of the daily N2O emissions in the PRE.

Hyporheic Source and Sink of Nitrous Oxide

AbstractNitrous oxide (N2O) is a potent greenhouse gas with an estimated 10% of anthropogenic N2O coming from the hyporheic zone of streams and rivers. However, difficulty in making accurate fine‐scale field measurements has prevented detailed understanding of the processes of N2O production and emission at the bedform and flowline scales. Using large‐scale, replicated flume experiments that employed high‐density chemical concentration measurements, we have been able to refine the current conceptualization of N2O production, consumption, and emission from the hyporheic zone. We present a predictive model based on a Damköhler‐type transformation (τ̃) in which the hyporheic residence times (τ) along the flowlines are multiplied by the dissolved oxygen consumption rate constants for those flowlines. This model can identify which bedforms have the potential to produce and emit N2O, as well as the portion and location from which those emissions may occur. Our results indicate that flowlines with τ̃up (τ̃ as the flowline returns to the surface flow) values between 0.54 and 4.4 are likely to produce and emit N2O. Flowlines with τ̃up values of less than 0.54 will have the same N2O as the surface water and those with values greater than 4.4 will likely sink N2O (reference conditions: 17C, surface dissolved oxygen 8.5 mg/L). N2O production peaks approximately at τ̃ = 1.8. A cumulative density function of τ̃up values for all flowlines in a bedform (or multiple bedforms) can be used to estimate the portion of flowlines, and in turn the portion of the streambed, with the potential to emit N2O.

Impacts of urban wastewater and hydrogeochemistry of the São Mateus River, Espírito Santo, Brazil

The waters of the River Sao Mateus and its tributaries, Abissinia and Preto do Sul, were analyzed to evaluate the impacts caused by the direct disposal of untreated domestic effluents generated on the city of Sao Mateus-ES, Brazil. Between the evaluated parameters, the most affected one was the dissolved oxygen (DO) in Abissinia River, which is completely consumed. Regarding Sao Mateus River, the situation is worrisome because its self-depurative capacity is exceeded and by the elevated levels of phosphorus nutrient, which may lead to eutrophication. A prototype was built to carry out the respirometric characterization of the effluents, aiming to determine the DO consumption rate (K1). This constant was used in the self-depuration model, which shows the need of effluent treatment with a minimum efficiency of 60% in removing the organic load. The chemical characterization revealed similar sodium chloride composition for these waters with contrasting patterns of lanthanides. Despite the low levels of toxic trace elements registered at Sao Mateus River, the concentrations of Pb and As were higher in the Preto do Sul River. This finding requires further investigation to track the source of these elements.

The importance of physical transport and oxygen consumption for the development of a metalimnetic oxygen minimum in a lake

AbstractAlthough the occurrence of metalimnetic oxygen minima (MOM) in lakes during summer stratification was described by early limnologists, not much is known about the processes leading to its formation. Generally, dissolved oxygen (DO) consumption and net transport contribute to the observed DO decrease, but the latter was rarely considered in former studies. To examine the importance of both processes to MOM development in Lake Arendsee, Germany, we measured DO concentration and temperature with high spatial and temporal resolution during a complete stratification period. Vertical turbulent diffusivities were estimated from temporal changes of the heat content of the lake. The MOM development was not caused by locally enhanced DO consumption rates, but rather by a combination of vertical gradients in DO concentration and consumption. A vertical DO mass balance revealed that net DO transport into the metalimnion was in the same order of magnitude as DO consumption in the MOM. We found that DO consumption was governed by microbial respiration and the vertical variations of DO depletion rates in the metalimnion could be explained by a minor contribution of temperature and a higher contribution of turbidity, implying that the downward flux of particulate organic carbon promoted the MOM development. The intensive metalimnetic respiration in lakes forming a MOM can be expected to accelerate nutrient cycling close to the photic zone and thus, may further stimulate primary production.

Kinetics of aerobic decomposition in the leaching phase of allochthonous plant detritus

AIMS: This study aimed to evaluate, through an experiment with short sampling intervals, (1) the effects of detritus quality on dissolved oxygen (DO) consumption, on dissolved inorganic carbon (DIC) formation and on the stoichiometric ratio between the DO consumed and mineralized carbon (O/C ratio) during leaching of plant detritus in the early decomposition; (2) the temporal variation of the variables mentioned above according to changes in the quality of each detritus over time. METHODS: The detritus of leaves, branches and litter (3 g) previously dried were incubated in decomposition chambers containing 1 L of inoculum. The chambers were maintained at 24 ± 2 °C in aerobic condition. The DO concentrations dissolved organic carbon (DOC) and DIC were evaluated. The consumption of DO was adjusted to a first-order kinetic model. The hourly rates of DO consumption, DIC production and O/C ratios were determined. RESULTS: The DO consumption (2.62 mg.g-1) and DIC production (1.20 mg.g-1) were higher in leaves decomposition, and smaller in litter (1.50 and 0.42 mg.g-1, respectively). Inversely, the O/C ratio was higher in the decomposition of litter (3.56). The rates of DO consumption (0.50 mg.g-1.h-1) and DIC production (0.41 mg.g-1.h-1) were greatest in the early decomposition of leaves. CONCLUSIONS: Short sampling intervals are key to understanding the dynamics of decomposition in the leaching phase. Higher consumption of DO in leaves decomposition indicated a higher content of labile compounds in this detritus. The highest O/C ratios in the litter decomposition can be attributed to its higher content of refractory substances. Variations in DO consumption rates and in O/C ratios over time suggest that the leachate is heterogeneous, comprising labile and refractory fractions, analogous to the detritus as a whole. In terms of water quality alterations, leaves constituted the most critical resource and the litter presented less pronounced effects.

Modeling the dynamics of oxygen consumption upon riverbank filtration by a stochastic–convective approach

Summary Dissolved oxygen (DO) is an important groundwater-quality parameter, especially within the context of drinking-water production by riverbank filtration. In riverbank sediments, a strong decrease of DO over the distance of a few meters has frequently been observed. The consumption rates may vary in time, which puts the representativeness of common, sporadic DO measurements in groundwater, based on monthly or even yearly sampling, into question. We present a new modeling approach that allows efficiently estimating DO concentrations in alluvial groundwater from measured DO concentrations in the river under various temperature and discharge conditions. The model is based on the stochastic–convective reactive approach and assumes a time-invariant lognormal travel-time distribution of the stream tube ensemble connecting the river and a groundwater observation well. DO consumption, resulting from aerobic respiration, is modeled by zero-order kinetics. According to high-resolution DO time series measured in the Thur River (NE-Switzerland) and an adjacent observation well, the DO consumption rate appears to depend on river temperature and discharge. While the temperature dependence of aerobic respiration is well known, the discharge dependence is probably related to an increased trapping of particulate organic matter (POM) within the riverbed during high-discharge events, thus enhancing the POM availability and DO consumption rate. We propose an empirical equation that quantifies the dependence between discharge and the DO consumption rate. The estimated parameterization at our field site suggests that an increasing discharge within the narrow window of 20–50 m 3 /s enhances the DO consumption rate by a factor of 4. By considering the measured DO in the river and including the dependence of the DO consumption rate on both discharge and temperature, the model was able to capture the diurnal, short-term (days to weeks), and seasonal dynamics of the observed DO within the alluvial aquifer. The temperature dependence of the DO consumption rate was found to be more important on a seasonal time scale, while the effect of discharge dominated the DO behavior during hydrological events extending over a few days to weeks. The presented modeling approach can be transferred to other riverbank-filtration systems to efficiently estimate DO concentrations in alluvial aquifers under various climatic and hydrologic conditions and, hence, assess the risk of approaching anoxic conditions in a changing climate.

Influence of the medium conditions on enzymatic oxidation of bisphenol A

AbstractA multistep response surface methodology (RSM) was successfully applied to optimise the medium conditions for the enzymatic polymerisation of bisphenol A (BPA). The laccase enzyme used as the catalyst was derived from Funalia trogii (ATCC 200800) yeast culture. The enzymatic polymerisation rate of BPA, based on the measurements of the initial dissolved oxygen (DO) consumption rate in a closed batch system, was studied through RSM. Initially the most effective medium factors, which are monomer concentration (mg/L), temperature (°C) and solvent content (% methanol), were determined through Plackett–Burman Design (PBD), then the steepest ascent combined with central composite design (CCD) steps were applied to evaluate the optimal reaction conditions for the enzymatic polymerisation. The optimal conditions were evaluated to be 748.46 mg/L, 32.24°C and 15.92% for monomer concentration, temperature and solvent content, respectively. A quadratic model was developed through RSM to represent DO consumption in the medium. The maximum DO consumption rate was calculated to be 0.093 mg DO/L min. Several repetitions were conducted at the optimal conditions to validate the system performance. The data evaluated from the quadratic model were in good agreement with those measured experimentally. The variations between the values did not exceed 10%. The correlation coefficient, R2, was calculated to be 0.95, which indicates that 95% of results can be explained by model.

Using stable isotopes of dissolved oxygen for the determination of gas exchange in the Grand River, Ontario, Canada

Gas exchange can be a key component of the dissolved oxygen (DO) mass balance in aquatic ecosystems. Quantification of gas transfer rates is essential for the estimation of DO production and consumption rates, and determination of assimilation capacities of systems receiving organic inputs. Currently, the accurate determination of gas transfer rate is a topic of debate in DO modeling, and there are a wide variety of approaches that have been proposed in the literature. The current study investigates the use of repeated measures of stable isotopes of O2 and DO and a dynamic dual mass-balance model to quantify gas transfer coefficients (k) in the Grand River, Ontario, Canada. Measurements were conducted over a longitudinal gradient that reflected watershed changes from agricultural to urban. Values of k in the Grand River ranged from 3.6 to 8.6 day−1, over discharges ranging from 5.6 to 22.4 m3 s−1, with one high-flow event of 73.1 m3 s−1. The k values were relatively constant over the range of discharge conditions studied. The range in discharge observed in this study is generally representative of non-storm and summer low-flow events; a greater range in k might be observed under a wider range of hydrologic conditions. Overall, k values obtained with the dual model for the Grand River were found to be lower than predicted by the traditional approaches evaluated, highlighting the importance of determining site-specific values of k. The dual mass balance approach provides a more constrained estimate of k than using DO only, and is applicable to large rivers where other approaches would be difficult to use. The addition of an isotopic mass balance provides for a corroboration of the input parameter estimates between the two balances. Constraining the range of potential input values allows for a direct estimate of k in large, productive systems where other k-estimation approaches may be uncertain or logistically infeasible.

Variable diffusion boundary layer and diffusion flux at sediment-water interface in response to dynamic forcing over an intertidal mudflat

The diffusion boundary layer (DBL) significantly limits the exchange between sediment and overlying water and therefore becomes a bottleneck of diffusive vertical flux at the sediment-water interface (SWI). Variable DBL thickness and diffusion flux in response to dynamic forcing may influence replenishment of nutrients and secondary pollution in coastal waters. In situ measurements of velocity in the bottom boundary layer (BBL) and oxygen concentration in the DBL were made over an intertidal mudflat, using an acoustic Doppler current and mini profiler. A linear distributed zone in the oxygen profile, the profile slope discontinuity and variance of concentration can be used to derive accurate DBL thickness. Diffusion fluxes calculated from the water column and sediment are identical, and their bias is less than 6%. A numerical model PROFILE is used to simulate the in situ dissolved oxygen profile, and layered dissolved oxygen consumption rates in the sediment are calculated. The DBL thickness (0.10–0.35 mm) and diffusion flux (15.4–53.6 mmol m−2 d−1) vary with a factor of 3.5 during a tidal period. Over an intertidal mudflat, DBL thickness is controlled by flow speed U in the BBL, according to δ DBL =1686.1DU −1+0.1 (D is the molecular diffusion coefficient). That is, the DBL thickness δDBL increases with decreasing flow speed U. Changes of diffusion flux at the SWI are caused by variations in the water above the sediment and the turbulent mixing intensity. The diffusion flux is positively related to the turbulent dissipation rate, friction velocity and turbulent energy. Under the influence of dynamics in the BBL, DBL thickness and flux vary significantly.

Empirical model for dissolved oxygen depletion during corrosion of drinking water copper pipes

Predictive models characterizing the evolution and interaction of key parameters of water chemistry are needed to better understand corrosion events in drinking water pipes. We performed experiments with new copper pipes under combinations of pH, dissolved oxygen (DO), temperature, chlorine, and dissolved inorganic carbon. We found that DO consumption during 24 h of stagnation was not limited by diffusion, thus the DO consumption rate in the bulk water could be used to probe the processes occurring at the pipe surface. We propose a quantitative dependency of the DO consumption rate on a rather limited set of physicochemical parameters.

Oxygen consumption of Litopenaeus vannamei juveniles in heterotrophic medium with zero water exchange

This work aimed at determining the dissolved oxygen consumption rate of Litopenaeus vannamei juveniles maintained in a microbial biofloc raceway system at high density with no aeration. Three 4 L bottles were filled for each treatment, sealed hermetically, and placed in an enclosed greenhouse raceway system. Four shrimp (13.2±1.42 g) were assigned to two sets of the bottles, which underwent the following treatments: light conditions with no shrimp; dark conditions with no shrimp; light conditions with shrimp; and dark conditions with shrimp. Dissolved oxygen content was measured every 10 min for 30 min. A quadratic behavior was observed in dissolved oxygen concentration over time. Significant differences for oxigen consumption were observed only at 10 and 20 min between shrimp maintained in the dark and those under light conditions. At 10 min, a higher value was observed in shrimp maintained under light, and at 20 min, in the dark. Significant differences between 10 and 20 min and between 10 and 30 min were observed when oxygen consumption was analyzed over time in the presence of light. Under dark conditions there were significant differences only between 20 and 30 min. Lethal oxygen concentration (0.65 mg L-1) would be reached in less than one hour either under light or dark conditions with no aeration.