Total Dissolved Gas Research Articles

Excess air during aquifer storage and recovery in an arid basin (Las Vegas Valley, USA)

The Las Vegas Valley Water District in Nevada, USA, has operated an artificial recharge (AR) program since 1989. In summer 2001, observations of gas exsolving from tap water prompted a study that revealed total dissolved gas (TDG) pressures approaching 2 atm with a gas composition that it is predominantly air. Measurements of TDG pressure at well heads and in the distribution system indicated two potential mechanisms for elevated TDG pressures: (1) air entrainment during AR operations, and (2) temperature changes between the winter recharge season and the summer withdrawal season. Air entrainment during pumping was investigated by intentionally allowing the forebay (upstream reservoir) of a large pumping station to drawdown to the point of vortex formation. This resulted in up to a 0.7 atm increase in TDG pressure. In general, the solubility of gases in water decreases as the temperature increases. In the Las Vegas Valley, water that acquired a modest amount of dissolved gas during winter artificial recharge operations experienced an increase in dissolved gas pressure (0.04 atm/°C) as the water warmed in the subsurface. A combination of air entrainment during AR operations and its amplification by temperature increase after recharge can account for most of the observed amounts of excess gas at this site.

Effects of gas supersaturation on lethality and avoidance responses in juvenile rock carp (Procypris rabaudi Tchang)

Laboratory experiments were conducted to determine the effects of total dissolved gas (TDG) supersaturation on acute lethality and avoidance responses in juvenile rock carp (Procypris rabaudi Tchang). The juvenile rock carp were exposed to water with different levels of supersaturation (105%, 115%, 120%, 125%, 130%, 135%, 140%, and 145%) and depth of 0.20 m at 25 °C for 60 h. Median lethal time (LT(50)) was used to assess the lethal responses corresponding to different levels of gas supersaturation. The results show that half of the juvenile rock carp died at the 120%, 125%, 130%, 135%, 140%, and 145% levels of supersaturation, and the LT(50) corresponding to different levels of supersaturation was 18.7, 15.4, 8.2, 6.6, 3.5, and 1.7 h. When the level of supersaturated water is below 115%, the mortality is negligible. Avoidance responses were observed 5 min after the fish were put into equilibrated water (99%, 0.08 m deep) and water with different supersaturated levels (105%, 115%, 125%, 135%, and 145%, 0.08 m deep) at 25 °C. The fish exhibited strong avoidance responses in supersaturated water when the gas supersaturation was above 135%. However, they exhibited an obvious preference to supersaturated water when the gas supersaturation was below 115%. Thus, the juvenile rock carp can likely survive in water with a supersaturated level of 115%.

Simulations of the Three-Dimensional Total Dissolved Gas Saturation Downstream of Spillways Under Unsteady Conditions

Dams are often operated in a way to discharge over the spillways, which would cause a high dissolved concentration of air and be harmful to fish. The bubble transfer and the water surface transfer play an important role in affecting the concentration of the Total Dissolved Gas (TDG). Based on recent numerical simulations of the total dissolved gas saturation, in this article, a two-phase TDG transport equation is adopted to develop an unsteady three-dimensional (3-D) two-phase flow Computational Fluid Dynamics (CFD) model, including a number of parameters such as water depth, pressure and air volume entrained. This model is used to predict the hydrodynamics and the TDG distribution under unsteady discharge conditions. Good agreement between measured and numerical results is obtained for a case study.

Influence of the Hyporheic Zone on Supersaturated Gas Exposure to Incubating Chum Salmon

AbstractHydroelectric dam operation causes total dissolved gas (TDG) to be seasonally elevated in the lower Columbia River, as surface water concentrations approach 120%. Federally protected chum salmon Oncorhynchus keta embryos incubating in nearby spawning areas could be affected if depth‐compensated TDG concentrations within the hyporheic zone exceed 103%. The objective of this study was to determine whether TDG of the hyporheic zone in two chum salmon spawning areas—one in a side channel near Ives Island, Washington, and another on the main‐stem Columbia River near Multnomah Falls, Oregon—was affected by the elevated TDG of the surface water. Depth‐compensated hyporheic TDG did not exceed 103% at the Multnomah Falls site. However, in the Ives Island area, chum salmon redds were exposed to TDG greater than 103% for more than 300 h. In response to river depth fluctuations, TDG varied significantly in the Ives Island area, suggesting increased interaction between the hyporheic zone and surface water at that site. We conclude from this study that the interaction between surface water and the hyporheic zone affects the concentration of TDG within the hyporheic zone directly via physical mixing and indirectly by altering water chemistry and thus dissolved gas solubility. Consideration of these interactions is important when estimating TDG exposure within egg pocket environments and will enable resource managers to optimize recovery strategies.

Prediction for supersaturated total dissolved gas in high-dam hydropower projects

The supersaturated total dissolved gas (TDG) generated during high dam spills may cause gas bubble disease for fish and ultimately endanger their existence. As more and more high-dam hydropower projects have been constructed in China, the environmental assessment of the supersaturated TDG is becoming more and more important. It is of great importance for quantitative impact assessment of the supersaturated TDG of high dams and for the construction of ecological friendly high-dam hydropower projects. Based on the conceptual summarization of the TDG production process, the TDG prediction model for high-dam projects, in which the ski-jump energy dissipation is adopted, is developed in the paper. The model is validated by field data and employed in the TDG prediction of a high-dam hydropower project to be built in southwest China.

A multiphase model for the hydrodynamics and total dissolved gas in tailraces

Elevated supersaturation of total dissolved gas (TDG) has deleterious effects in aquatic organisms. To minimize the supersaturation of TDG at hydropower dams, spillway flow deflectors redirect spilled water horizontally forming a surface jet that prevents bubbles from plunging to depth in the stilling basin. A major issue regarding the prediction of the hydrodynamics and TDG in tailraces is the effect of the spillway bubbly surface jets on the flow field. Surface jets cause significant changes on the flow pattern since they attract water toward the jet region, a phenomenon called water entrainment. Bubbles create interfacial forces on the liquid, reduce the effective density and viscosity, and affect the liquid turbulence increasing the water entrainment. Most numerical studies on dams use standard single-phase models, which have demonstrated to fail to predict the hydrodynamics and TDG distribution. In this paper, an anisotropic two-phase flow model based on mechanistic principles capable of predicting water entrainment, gas volume fraction, bubble size and TDG concentration is presented. Good agreement between model results and field data is found in the tailrace of Wanapum Dam. The simulations capture the measured water entrainment and TDG distribution. The effect of the bubbles on the hydrodynamics and TDG distribution is analyzed.

Effects of nitrogen gas supersaturation on growth and survival in larval cod (Gadus morhua L.)

Gas supersaturation is one suggested cause of the extensive mortality that is often found during intensive production of Atlantic cod larvae (Gadus morhua L.). In the present study, cod larvae (32 to 64 days post-hatch (dph)) were exposed to nitrogen supersaturated water with levels of total dissolved gas (TDG) of 103 and 106%. A control group was given vacuum-degassed water (TDG <100%). Larvae were sampled weekly and standard length and dry weight were measured. Larval mortality was estimated regularly and at the termination of the experiment, the numbers of survivors were counted. As regards larval mortality, no effect of exposure to supersaturated water was evident. Towards the end of the experiment some larvae were found floating on the surface most likely as an effect of gas supersaturation. Growth rate was not affected during the first three weeks of treatment. By the time the larvae reached metamorphosis, a chronic effect of gas bubble trauma (GBT) was expressed as a reduction in growth. Even though not significant, the effect seemed to appear even at the lowest saturation level used (103%). Thus, even a low level of gas supersaturation should be avoided in intensive culture of cod larvae.

Effects of nitrogen gas supersaturation on growth and survival in juvenile Atlantic cod ( Gadus morhua L.)

Gas supersaturation is suggested to be one possible explanation for the extensive mortality that is sometimes experienced during the early life stages in intensive production of cod ( Gadus morhua). In the present study, cod (35 g) were exposed to nitrogen-supersaturated water with first rising levels of total dissolved gas (TDG) for two weeks until the TDG levels reached 103 and 105%, at which the treatment levels were maintained for five weeks. A third group was given vacuum-degassed water (control group, TDG < 100%). Water temperature, TDG, oxygen saturation and other water quality parameters were monitored daily in each tank. Eighty-five out of initially 330 fish in each tank were individually marked with floy tags (biomass was regularly adjusted to 21 kg m 3). Before initiation of treatment and two, four and seven weeks thereafter, all individually marked fish in each tank were measured for total length (TL, cm) and weight ( W, g). The weight of unmarked fish in each tank was measured by bulk weighing. And further, to study stress-related changes in the blood parameters due to supersaturation, a few unmarked fish were randomly sampled from each tank on the same days for blood analysis. Within both treatment groups some fish (1.75%) experienced exophthalmia (“pop eyes”), likely as a chronic effect of gas bubble trauma (GBT). No other effect of exposure to supersaturated water was evident with regard to mortality, growth rate, condition or any of the blood parameters. Juvenile cod are therefore suggested to be relatively tolerant to low to moderate levels of nitrogen gas supersaturated water.

Modeling Total Dissolved Gas Concentration Downstream of Spillways

Dams are often operated to facilitate downstream juvenile anadromous fish migration over the spillways, but such operation can cause high dissolved concentrations of oxygen and nitrogen that can be harmful to fish. The concentration of total dissolved gas (TDG) in the flow changes with distance downstream of the spillway crest and depends on the geometric configuration of the spillway and on hydraulic and operating conditions. A model is presented that simulates the physical processes of gas transfer with the goal of having an accurate and more widely applicable TDG model for plunging spillway discharges. Bubble transfer is dominant in the stilling basin, while water surface transfer is dominant downstream. Sensitivity analyses suggest which physical processes are important for accurate total dissolved gas predictions. Instantaneous bubble coalescence and breakup based upon local turbulence conditions is an appropriate assumption. Vertical bubble profiles do not need to be simulated in this type of model. Water surface roughness provides a significant increase to surface transfer. Tailwater depth is important to downstream TDG concentrations. Finally, a 10% difference in air entrained at the plunge point causes relatively minor differences in TDG of 1.4 and 3.1% at low and high discharges, respectively.

A multidimensional two-phase flow model for the total dissolved gas downstream of spillways

Elevated levels of dissolved gas in the spillway stilling basin, which are responsible for gas bubble disease in fish, constitute an important negative environmental effect of dams. Bubbles, entrained when a plunging jet impacts the tailwater pool, plunge beneath the surface and transfer mass to the liquid, causing an increase in the total dissolved gas (TDG) concentration. Most of the numerical studies onTDG downstream of spillways found in the literature are based on experimental correlations for the gas volume fraction.Abetter approach involves the use of a two-phase flowmodel. In this paper, a two-fluid model is used to calculate the gas volume fraction and velocity of the bubbles. A polydisperse model is used in which a Boltzmann transport equation predicts the bubble size distribution, to account for the different bubble sizes found in the flow downstream of spillways. The bubble mass is discretized considering groups of bubbles of variable mass, with the mass of the bubbles changing due to bubble/liquid mass transfer and pressure. A two-phase transport equation for the TDG is presented, whose source is the bubble/liquid mass transfer, which is a function of the gas volume fraction and bubble size distribution. Two-dimensional numerical results of TDG, gas volume fraction, bubble number density, and velocities are presented and discussed. The predictions of TDG downstream of a spillway are compared against field data in the stilling basin ofWanapum Dam, on the Columbia River.

Modeling total dissolved gas production and transport downstream of spillways: Three‐dimensional development and applications

Challenges a resource manager encounters concerning water quality downstream of dam spillways are well documented. The plunging and air‐entraining nature of spillway flows can lead to supersaturated water downstream of the dam. A multi‐dimensional numerical model is developed for predicting total dissolved gas (TDG) production and transport downstream of a hydropower dam spillway. The model is based on the Reynolds averaged Navier‐Stokes equations for flow hydrodynamics and a total dissolved gas model that incorporates the gas production, exchange and transport physics. A three‐dimensional version of the model is calibrated using one set of available field data with a moderate flow discharge. The applicable range of the model is established by applying the calibrated model to different spillway discharges and comparing results with field data. The model is then validated with TDG field data available for Wanapum Dam and applied to two practical engineering problems. The simulations successfully reproduce the convection dominated TDG levels downstream of spillways as well as the variation of TDG concentration across the channel.

Progression and Severity of Gas Bubble Trauma in Juvenile Salmonids

Abstract We conducted laboratory experiments to assess the progression and to quantify the severity of signs of gas bubble trauma (GBT) in juvenile chinook salmon Oncorhynchus tshawytscha and steelhead Oncorhynchus mykiss exposed to different levels of total dissolved gas (TDG), and we attempted to relate these signs to the likelihood of mortality. When fish were exposed to 110% TDG for up to 22 d, no fish died, and there were few signs of GBT in the lateral line or gills. Bubbles in the fins, however, were relatively common, and they progressively worsened over the experimental period. When fish were exposed to 120% TDG for up to 140 h, chinook salmon had an LT20 (time necessary to kill 20% of the fish) ranging from 40 to 120 h, whereas steelhead had LT20s ranging from 20 to 35 h. In steelhead, bubbles in the lateral line, fins, and gills displayed poor trends of worsening over time, showed substantial interindividual variability, and were poorly related to mortality. In chinook salmon, only bubbles in t...

Influence of Infection withRenibacterium salmoninarumon Susceptibility of Juvenile Spring Chinook Salmon to Gas Bubble Trauma

Abstract During experiments in our laboratory to assess the progression and severity of gas bubble trauma (GBT) in juvenile spring chinook salmon Oncorhynchus tshawytscha, we had the opportunity to assess the influence of Renibacterium salmoninarum (Rs), the causative agent of bacterial kidney disease, on the susceptibility of salmon to GBT. We exposed fish with an established infection of Rs to 120% total dissolved gas (TDG) for 96 h and monitored severity of GBT signs in the fins and gills, Rs infection level in kidneys by using an enzyme-linked immunosorbent assay (ELISA), and mortality. Mortality occurred rapidly after exposure to 120% TDG, with a LT20 (time necessary to kill 20% of the population) of about 37 h, which is at a minimum about 16% earlier than other bioassays we have conducted using fish that had no apparent signs of disease. Fish that died early (from 31 to 36 h and from 49 to 52 h) had significantly higher infection levels (mean ± SE ELISA absorbance = 1.532 ± 0.108) than fish that sur...

The Effects of Dissolved Gas Supersaturation on White Sturgeon Larvae

Spill at dams has caused supersaturation of atmospheric gas in waters of the Columbia and Snake rivers and raised concerns about the effects of dissolved gas supersaturation (DGS) on white sturgeons Acipenser transmontanus. The timing and location of white sturgeon spawning and the dispersal of white sturgeon larvae from incubation areas makes the larval stage potentially vulnerable to the effects of DGS. To assess the effects of DGS on white sturgeon larvae, we exposed larvae to mean total dissolved gas (TDG) levels of 118% and 131% saturation in laboratory bioassay tests. Gas bubble trauma (GBT) was manifested as a gas bubble in the buccal cavity, nares, or both and it first occurred at developmental stages characterized by the formation of the mouth and gills. Exposure times of 15 min were sufficient to elicit these signs in larvae in various stages of development. No mortality was observed in larvae exposed to 118% TDG for 10 d, but 50% mortality occurred after a 13-d exposure to 131% TDG. The signs of GBT we observed resulted in positive buoyancy and alterations in behavior that may affect the dispersal and predation vulnerability of white sturgeon larvae. The exact depth distribution of dispersing white sturgeon larvae in the Columbia River currently is unknown. Thus, our results may represent a worst-case scenario if white sturgeon larvae are dispersed at depths with insufficient hydrostatic pressure to compensate for high TDG levels.

Predator avoidance ability of juvenile chinook salmon (Oncorhynchus tshawytscha) subjected to sublethal exposures of gas-supersaturated water

To assess the effects of gas bubble trauma (GBT) on the predator avoidance ability of juvenile chinook salmon (Oncorhynchus tshawytscha), we created groups of fish that differed in prevalence and severity of gas emboli in their lateral lines, fins, and gills by exposing them to 112% total dissolved gas (TDG) for 13 days, 120% TDG for 8 h, or 130% TDG for 3.5 h. We subjected exposed and unexposed control fish simultaneously to predation by northern squawfish (Ptychocheilus oregonensis) in water of normal gas saturation in 6, 18, and 10 tests using prey exposed to 112, 120, and 130% TDG, respectively. Only fish exposed to 130% TDG showed a significant increase in vulnerability to predation. The signs of GBT exhibited by fish sampled just prior to predator exposure were generally more severe in fish exposed to 130% TDG, which had the most extensive occlusion of the lateral line and gill filaments with gas emboli. Fish exposed to 112% TDG had the most severe signs of GBT in the fins. Our results suggest that fish showing GBT signs similar to those of our fish exposed to 130% TDG, regardless of their precise exposure history, may be more vulnerable to predation.

Predator avoidance ability of juvenile chinook salmon (&lt;I&gt;Oncorhynchus tshawytsoha&lt;/I&gt;) subjected to sublethal exposures of gas-supersaturated water

To assess the effects of gas bubble trauma (GBT) on the predator avoidance ability of juvenile chinook salmon (Oncorhynchus tshawytscha), we created groups of fish that differed in prevalence and severity of gas emboli in their lateral lines, fins, and gills by exposing them to 112% total dissolved gas (TDG) for 13 days, 120% TDG for 8 h, or 130% TDG for 3.5 h. We subjected exposed and unexposed control fish simultaneously to predation by northern squawfish (Ptychocheilus oregonensis) in water of normal gas saturation in 6, 18, and 10 tests using prey exposed to 112, 120, and 130% TDG, respectively. Only fish exposed to 130% TDG showed a significant increase in vulnerability to predation. The signs of GBT exhibited by fish sampled just prior to predator exposure were generally more severe in fish exposed to 130% TDG, which had the most extensive occlusion of the lateral line and gill filaments with gas emboli. Fish exposed to 112% TDG had the most severe signs of GBT in the fins. Our results suggest that ...

QUALITY OF 1995 SPRING TOTAL DISSOLVED GAS DATA: COLUMBIA AND SNAKE RWERS1

ABSTRACT: The quality of the U.S. Army Corps of Engineers' (Corps) total dissolved gas (TDG) data base for the 1995 spring spill season was reviewed to determine the value of this information in real‐time management decisions regarding river operations. We concluded that problems in transmitting, archiving, correcting and interpreting the records constitute significant sources of data anomalies that affect the accuracy and reliability of information necessary to manage spill and TDG in the Columbia and Snake rivers. The data base that was reviewed covers 25 selected Columbia and Snake river stations, and includes real‐time TDG data needed to regulate spill operations to maintain gas levels within state water quality standards and to monitor effects on fish and aquatic life during the salmon migration season. A wide range of anomalies (daily averages missing or in error or based on incomplete records) was detected in more than one‐third (37 percent) of the Corps' gas data base. Extreme anomalies (daily averages including errors and discontinuities for more than eight hours in a day) were found in 16 percent of the data base. The Fish Passage Center, also reviewed the Corps' data and reported an overall 33 percent incidence of anomalous days. Despite arriving at similar findings about the Corps' data base, we detected a 28 percent discrepancy in the type of data anomalies between our analyses. Real. time improvements in the quality of the dissolved gas data base are necessary to provide managers with a reliable product from this monitoring effort.