Widespread dissolved oxygen supersaturation in Chinese warming lakes.

Physiological (antioxidant) responses of estuarine fishes to variability in dissolved oxygen

In this research the thermal stratification of the water in the Torogh Dam Basin and the resulted changes in its quality with respect to temperature, salinity and dissolved oxygen was investigated using the Dynamic Reservoir Simulation Model. The results indicated that in wet years such as 1998, when the average annual precipitation and the resulted inflows to the basin is higher than its long-term average, the water level in the basin reaches above 50 m. Under such conditions, thermal stratification starts from mid-spring and lasts to the end of summer, and establishes through the total depth of the basin. Consequently, considerable changes in water quality occur through the depth. However in dry years such as year 2000, the water level in the basin diminishes considerably (16 to 20m in depth) and thermal stratification either does not establish or if establishes, it is incomplete, starts much earlier and persists for much shorter periods of time. On the basis of the model’s results, the differences observed in the average temperatures of the surface and deep layers of the basin during the spring and summer seasons of 1998 were 10◦C and 11◦C, respectively while in the spring of 2002, the observed difference was only 1.5◦C. The results of the study also showed concurrent occurrence of salinity stratification with thermal stratification which results in increase in salinity with increase in depth. The difference between salt concentration of the surface and deep water layers of the basin was observed to be 43 mg/lit in the spring of 1998 and 10 mg/lit for the summer of the same year. In regard to the dissolved oxygen concentration, the simulation results showed a difference in the range of 0 to 9 mg/lit between the surface and deep water layers. With the start of stratification, oxygen concentration decreases gradually with depth., such that in July the lowest 10m layer of the basin becomes completely anaerobic, providing conditions for production of undesired odors, tastes and color. During the period of 1998 to 2004 (period of data analysis and simulation run), the water quality of the basin was observed to be uniform in autumn and winter months indicating a complete mixing condition in the basin. Key Words: Water Quality Models, Thermal Stratification, Water Salinity, Dissolved Oxygen, Dam’s Basin.

OPTIMALIZATION OF OXYGEN LEVELS IN ROOT SYSTEMS AS EFFECTIVE CULTIVATION TOOL

Hypolimnetic anoxia is often observed in large reservoirs during thermal stratification. In the hypolimnion layer, dissolved oxygen (DO) is continuously consumed by biological and chemical reactions, resulting in a stable anoxic zone at the bottom of the reservoir. The areal hypolimnetic oxygen depletion (AHOD) has been a widely used indicator for hypolimnetic DO depletion, but this indicator could not reflect the DO depletion process at the bottom of deep reservoirs with deposits of pollutant sediments. With Daheiting Reservoir as the study case, the concept of stratified areal hypolimnetic oxygen depletion (S-AHOD) was proposed, and an S-AHOD calculation model was built, which could accurately describe the DO depletion process in the anoxic zone at the bottom of Daheiting Reservoir, identify the DO depletion rate at different water depths in the anoxic zone and quantify the contribution of sediment oxygen demand to the overall oxygen depletion. It was found that sediment oxygen demand contributed considerably (41.4%) to the overall hypolimnetic DO depletion in the reservoir, DO depletion rate varied considerably at different water depths, which increased from the surface to the bottom of the reservoir and reached the maximum at the bottom layer. Finally, based on results of existing works, an AHOD calculation equation applicable to lakes and reservoirs with considerable deposits of heavily pollutant sediments was put forward.

The role of sediment oxygen demand (SOD) in causing dissolved oxygen (DO) depletion is widely acknowledged, with previous studies mainly focusing on chemical and biological SOD separately. However, the relationship between the putative functions of sediment microbes and SOD, and their impact on DO depletion in overlying water, remains unclear. In this study, DO depletion was observed in the downstream of the Gan River during the summer. Sediments were sampled from three downstream sites (YZ, Down1, and Down2) and one upstream site (CK) as a control. Aquatic physicochemical parameters and SOD levels were measured, and microbial functions were inferred from taxonomic genes through analyses of the 16S rRNA gene. The results showed that DO depletion sites exhibited a higher SOD rate compared to CK. The microbial community structure was influenced by the spatial variation of Proteobacteria, Chloroflexi, and Bacteroidota, with total organic carbon (TOC) content acting as a significant environmental driver. A negative correlation was observed between microbial diversity and DO concentration (p < 0.05). Aerobic microbes were more abundant in DO depletion sites, particularly Proteobacteria. Microbes involved in various biogeochemical cycles, such as carbon (methane oxidation, methanotrophs, and methylotrophs), nitrogen (nitrification and denitrification), sulfur (sulfide and sulfur compound oxidation), and manganese cycles (manganese oxidation), exhibited higher abundance in DO depletion sites, except for the iron cycle (iron oxidation). These processes were negatively correlated with DO concentration and positively with SOD (p < 0.05). Overall, the results highlight that aerobic bacteria's metabolic processes consume oxygen, increasing the SOD rate and contributing to DO depletion in the overlying water. Additionally, the study underscores the importance of targeting the removal of in situ microbial molecular mechanisms associated with toxic H2S and CH4 to support reoxygenation efforts in rehabilitating DO depletion sites in the Gan River, aiding in identifying factors controlling DO consumption and offering practical value for the river's restoration and management.

Feeding behaviour and growth of the Peruvian scallop (Argopecten purpuratus) under daily cyclic hypoxia conditions

Potential risk of eutrophication in the deepest lake of Southwest China: Insights from phosphorus enrichment in bottom water

Chapter 2 - Nonpersistent Organic Pollution

Dissolved oxygen (DO) is essential for an aquatic ecosystem since it controls the biological productivity. Here, we propose a unidimensional dynamic model for DO by incorporating biological (photosynthesis, respiration, and mineralization), physical (atmospheric reaeration) and chemical (nitrification) processes so characteristic of shallow coastal water bodies. The analytical study of the proposed model is focussed on supersaturation and undersaturation of oxygen in the water body. The controllability of the ecosystem health has also been investigated. Model results indicate that, while undersaturation of oxygen is largely governed by nitrification and Net Ecosystem Metabolism (NEM), the supersaturation is controlled by photosynthetic activity. The model results are corroborated with observed data collected from Chilka lagoon, India. Subsequently, a biogeochemical model to study the DO variations in Chilka lagoon has been constructed. The model is properly calibrated and validated with observed data. Two independent sets of data (2004-2005 and 2005-2006) were used for model calibration and validation and Chi-square tests supported its robustness (R2=0.982 and 0.987; P&lt;0.05). The model was used to evaluate independently the influence of individual taxa (diatoms, microphytobenthos, and cyanophyceans) on DO variations. Simulations indicate the vital role of microphytobenthos in lagoon DO dynamics and the overall wellbeing.

This paper uses derived distribution analysis to explore the process controls of the onset of and recovery from hypoxic conditions in Tokyo Bay, Japan. A conceptual, lumped model of dissolved oxygen (DO) dynamics in Tokyo Bay is proposed and, through comparison with a three‐dimensional simulation model, is verified to have sufficient accuracy for the prediction of the onset of and recovery from hypoxia. This conceptual DO model was implemented in continuous simulation mode, with 14 years of wind data and data on streamflow entering the Tokyo Bay, and was used to identify and quantify the various process controls of the onset of and recovery from hypoxia. The underlying process controls were identified to be streamflow discharge, as well as duration and strength of both northeast “positive” winds and southwest “negative” winds. The analysis helped to isolate, in particular, the potential for rapid and strong recovery from hypoxia due to “strong negative winds”, (i.e., negative winds that exceed a wind speed threshold of 10 m s−1) and the critical roles of the duration of these strong winds and the antecedent DO concentration on the strength of DO recovery. Motivated by these results, derived distribution analysis is adopted to predict the strength of DO recovery during periods of strong winds, using a simplified model of DO recovery, focused on isolated strong winds, that explicitly captures the effects of both wind duration and antecedent DO concentration.

This study was performed to investigate the effect of training under simulated hypoxic conditions. Hypoxia training was integrated into the normal training schedule of 12 endurance trained cyclists. Athletes were randomly assigned to two groups and performed three additional training bouts per week for six weeks on a bicycle ergometer. One group (HG) trained at the anaerobic threshold under hypoxic conditions (corresponding to an altitude of 3200 m) while the control group (NG) trained at the same relative intensity at 560 m. Preceding and following the six training weeks, performance tests were performed under normoxic and hypoxic conditions. Normoxic and hypoxic .VO2max, maximal power output as well as hypoxic work-capacity were not improved after the training period. Testing under hypoxic conditions revealed a significant increase in oxygen saturation (SpO 2, from 67.1 +/- 2.3 % to 70.0 +/- 1.7 %) and in maximal blood lactate concentration (from 7.0 to 9.1 mM) in HG only. Ferritin levels were decreased from 67.4 +/- 16.3 to 42.2 +/- 9.5 microg/l (p < 0.05) in the HG and from 54.3 +/- 6.9 to 31.4+/- 8.0 microg/l (p = 0.17) in the NG. Reticulocytes were significantly increased in both groups by a factor of two. In conclusion, the integration of six weeks of high intensity endurance training did not lead to improved performance in endurance trained athletes whether this training was carried out in hypoxic or normoxic conditions.

Modelling dissolved oxygen and benthic algae dynamics in a coastal ecosystem by exploiting real-time monitoring data

Accumulation and breakdown of large algal blooms often causes serious hypoxia in lakes, representing a major potential threat to zooplankton grazers such as Daphnia. Generally, populations comprise different age groups, whose molecular responses to environmental stressors are different. The aim of our study was to investigate the age-dependent effects of oxygen depletion on D. magna survival and selected gene expressions of energy-relevance and stress-defense. Four age groups of D. magna (1, 4, 7 and 14 days) were exposed to 0.0625, 0.125, 0.25 mM dissolved oxygen (DO) for 48 h. Results showed that survival rates of 14-day-old individuals in 0.0625 mM DO and 0.125 mM DO were much lower than those in 0.25 mM DO, while no significant difference was found in remaining age groups. Low DO up-regulated hemoglobin expression compared with the controls in all age groups; the similar pattern in a-esterase was observed when 1-day-old individuals were exposed to 0.0625 mM, 4and 7-day-old individuals at 0.125 mM, respectively. HSP70 and CAT expression were significantly upregulated in 1and 7-day-old individuals exposed to 0.125 mM. The findings indicate that age structure should be taken into account when interpreting dynamics of Daphnia populations affected by oxygen depletion. Age may modify energy reallocation and alter susceptibility of the organisms.

Salmonid embryos develop in cool waters over relatively long periods of time. Interestingly, hypoxic conditions have been found to be relatively common in some nesting sites (redds). The goals of this study were to determine the ontogeny of cardiac regulation in rainbow trout early life stages and how this is influenced by chronic hypoxia. The heart rate response to cholinergic and adrenergic receptor stimulation or inhibition was measured in individuals reared in normoxic (100% O(2) saturation) or hypoxic (30% O(2) saturation) conditions from fertilization to embryonic stages 22, 26 and 29, and larval stages 30 and 32. In normoxia, heart rate increased in response to β-adrenergic receptor stimulation (isoproterenol) as early as embryonic stage 22, and decreased with the antagonist propranolol after this stage. Cholinergic stimulation (acetylcholine) was ineffective at all stages, but atropine (acetylcholine antagonist) increased heart rate at larval stage 32. This demonstrates that cardiac β-adrenergic receptors are functional at early life stages, while cholinergic receptors are not responsive until after hatching. Collectively, embryos had cardio-acceleration control mechanisms in place just after the heartbeat stage, while cardio-inhibitory control was not functional until after hatching. Chronic hypoxia exposure triggered bradycardia, increased the response to adrenergic stimulation in embryos and larvae, and delayed the onset of cholinergic control in larvae. In non-motile stages, therefore, survival in chronic low oxygen may depend on the ability to alter the cardiac ontogenic program to meet the physiological requirements of the developing fish.

Obstructive sleep apnea (OSA) syndrome is a major health problem affecting 2 to 4% of the middle-aged population, so screening tests had to be established for the diagnosis of sleep-related breathing disorders. However, there isa great demand for polysomnography (PSGs), performing PSGs is a costly, labor-intensive uncomfortable techniqueand also not available in all areas. As oxygen saturation is often used as a main diagnostic criterion of these screening tests, so it is important to study the correlation between overnight oximetry and degree of obstructive sleep apnea. To investigate the relative usefulness of pulse oximetry in the diagnosis of OSA, and to determine sensitivityand specificity of average O2 saturation and minimum O2 saturation in predicting the degree of obstructive sleepapnea. This study was conducted during the period from December 2014 to November 2015 in Misurata, Libya. Itincluded 120 patients (52 women, 68 men) suspected to suffer from sleep apnea-syndrome. Participants underwentpulse oximetry recordings which was performed simultaneously during polysomnography for suspicion of OSA.Then oxygen saturation (pulse oximetry) was compared with respiratory disturbance index (RDI, polysomnography). An RDI ≥ 5/h and a minimal oxygen saturation &lt; 90% and/or more than 5 oxygen desaturations/h ≥ 4% wereregarded as pathological. We found high statistically significant positive correlation between the severity of RDIwith average O2 saturation and O2 Saturation Minimum. Minimum O2 Saturation is better than average O2 Saturation in predicting the severity of RDI and better in predicting severe cases than mild cases (Sensitivity = 70.6 % ,Specificity = 80.8 % and Accuracy = 75.9 % at cutoff "Minimum O2 Saturation ≤ 79.5 %").We concluded thatpulse oximetry in combination with a positive case history is a sensitive method to recognize sleep apnea-patients.