Hypolimnetic Oxygenation Research Articles

Hypolimnetic oxygenation in Twin Lakes, WA. Part I: Distribution and movement of trout

Summer temperature/dissolved oxygen squeeze conditions have negatively impacted coldwater fisheries, including rainbow (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis), in North and South Twin lakes of northeastern Washington. In 2009, line diffuser hypolimnetic oxygenation (HO) was initiated in North Twin to prevent anoxia and increase summer trout habitat. Suitable trout habitat volume increased from a low of 0% preoxygenation to 100% of the North Twin hypolimnion following HO. To assess if trout utilized the expanded habitat following oxygenation, summer trout movements and habitat utilization were assessed from 2006 through 2012 using various combinations of ultrasonic telemetry, archival tags, gillnetting, and hydroacoustics. Trout utilized North Twin hypolimnetic habitat more frequently compared to pre-HO years and to unoxygenated South Twin, and swim speeds significantly decreased with oxygenation. Chaoborus zooplankton distributions have also changed following HO; water column densities were significantly lower with oxygenation compared to preoxygenation and to unoxygenated South Twin.

Flow routing with bottom withdrawal to improve water quality in Walnut Canyon Reservoir, California

Walnut Canyon Reservoir is a small source-water reservoir for the City of Anaheim, California. The reservoir receives raw water from the Metropolitan Water District of Southern California and is used for source water storage and emergency storage for the Lenain Filtration Plant. The reservoir naturally stratifies through the summer, with anoxia and elevated concentrations of phosphorus (P), nitrogen (N), manganese (Mn), and sulfide present in the hypolimnion. Water quality modeling using the 1-D DYRESM-CAEDYM model was conducted to evaluate different management strategies for the reservoir. Simulations evaluated the water column conditions in 2010 with (1) existing conditions, with operation of a SolarBee; (2) diffused aeration; (3) hypolimnetic oxygenation; and (4) flow routing with bottom withdrawal. Meteorological data from the nearby California Irrigation Management Information System stations were used to drive the hydrodynamic component of the model; the model was validated using available profile measurements and discrete sampling from April to July 2010. Diffused aeration, hypolimnetic oxygenation, and flow routing with bottom withdrawal were all predicted to improve dissolved oxygen conditions and lower concentrations of P, Mn, and other elements, although flow routing with bottom withdrawal could be implemented without incurring significant capital and operating costs; therefore, the flow routing strategy was implemented in spring 2011. Water column sampling demonstrated improved water quality in line with model predictions and indicated that flow routing with bottom withdrawal can serve as a practical and effective alternative to other engineered solutions under favorable hydraulic and source water quality conditions.

Understanding the role of induced mixing for management of nuisance algal blooms in an urbanized reservoir

Mixed layer dynamics were studied during June to August in 2008 to 2012 in Ford Lake, Michigan, using real-time data acquisition from in situ water temperature, dissolved oxygen, and chlorophyll sensors plus a shore-side weather station. The purpose of the study was to examine the effectiveness of managed hypolimnetic discharge for inducing vertical mixing, preventing hypolimnetic anoxia, and reducing the incidences of cyanobacterial blooms. Maximum mixed layer thickness each day was deduced from vertical density profiles measured at 30-minute intervals plus estimated kinetic energy supplied by wind stress and convection. Surface heat flux and resulting convection was more important to mixing dynamics than was wind stress. Selective withdrawal of hypolimnetic water was practiced in 2008 to 2011 and resulted in enhanced vertical mixing, hypolimnetic oxygenation, and absence of nuisance cyanobacterial blooms. In 2012, drought conditions restricted upstream water availability to such an extent that selective hypolimnetic withdrawal could not be used that year. The result was more than a month-long period of stable thermal stratification during which hypolimnetic oxygen concentrations became depleted and phosphate was released from anoxic sediments. A subsequent cold weather event induced temporary destratification, and a bloom of Aphanizomenon quickly ensued, despite reduced external loading of P from the influent river. Results of this study point to mixing dynamics and internal nutrient loading as the master variables responsible for nuisance algal blooms in this system.

Newman Lake restoration: A case study Part III. Hypolimnetic oxygenation

Since the mid-20th century, oxygen status at the sediment–water interface (SWI) has been implicated in regulating lake internal phosphorus loading. In deeper lakes, summer hypolimnetic oxygen depletion may thus play a critical role in phosphorus cycling and lake trophic status. Hypolimnetic aeration (HA) has been utilized for more than 4 decades to prevent development of anoxia, decrease internal phosphorus load, and enhance fisheries. Most recently, interest has shifted to hypolimnetic oxygenation (HO) for potential performance and economic advantages. In Newman Lake, hypolimnetic oxygenation was initiated in 1992 when the first lake application of downflow contact bubble oxygenation (Speece Cone technology) was installed. Oxygenation at Newman has reduced growing season Nürnberg Anoxic Factors (AF) from a range of about 30–60 d to <10 d. We propose that differences in predicted versus observed AF based on phosphorus may be utilized to assess lake restoration performance. Newman Lake has demonstrated the importance of operating the system at full capacity, as lower oxygen delivery rates do not produce proportional hypolimnetic oxygen concentrations, as well as other insights into HO system sizing and design.

Effects of artificial hypolimnetic oxygenation in a shallow lake. Part 2: Numerical modelling

A three-dimensional numerical model is used to simulate the thermal destratification caused by hypolimnetic jets releasing oxygen-rich water for lake restoration. Focussing on the case study described in the companion paper (Toffolon et al., 2013), i.e. the small, relatively shallow Lake Serraia (Trentino, Italy), a specific simplified sub-grid model is developed in the numerical model to reproduce jet entrainment with reduced computational costs, with the aim to simulate the whole lake dynamics along several weeks. The noticeable agreement between numerical results and available measurements suggests that the model can be used to understand the main effects of the hypolimnetic oxygenation in different scenarios. Therefore, different options can be evaluated and guidelines can be proposed for lake management, with the aim to preserve the typical thermal stratification while providing sufficient oxygen mass to proceed with the restoration phase.

Effects of artificial hypolimnetic oxygenation in a shallow lake. Part 1: Phenomenological description and management

Artificial oxygenation is a common management technique for lake restoration, but the use of hypolimnetic aeration in shallow basins can have dramatic effects on the dynamics of thermal stratification. This study presents the results of extensive field measurements performed in Lake Serraia (Trentino, Italy) after the installation of a Side Stream Pumping System, whereby oxygen-rich water is injected through 24 jets, uniformly distributed along an octagonal-shaped pipe at approximately 1 m above the sediment floor (10 m in depth). The lake is characterised by an average depth of 7 m, a volume of 3.1 × 106 m3 and a residence time of about one year. Prior to the installation of the pumping system, the undisturbed hypolimnion thickness during summer stratification was relatively small. After the start of oxygen injection (up to 0.5 m3/s of oxygen-saturated water), an increase of in-lake temperature over the entire water column was noted with a maximum hypolimnetic temperature increase of up to 9 °C. The analysis of the flow field data and the results of numerical simulations (presented in the companion paper), indicate that the jets were solely responsible for the observed increase in temperature. Moreover, this study shows that modelling efforts are useful to provide guidelines for optimising contrasting needs (e.g., increase in oxygen supply versus jet discharge rate).

Design and testing of a novel hypolimnetic oxygenation system to improve water quality in Lake Bard, California

Hypolimnetic oxygenation, the engineered addition of oxygen gas to the bottom of lakes and reservoirs, can improve water quality by repressing the accumulation of nutrients, metals, and toxic compounds in bottom waters. This study designed and tested an oxygenation system in Lake Bard, California. Hypolimnetic oxygen demand, a key design parameter, was estimated through the combination of sediment–water chamber incubations and numerical analysis of water column dissolved oxygen (DO) profiles. Chamber incubations showed that increased water velocity near the sediment–water interface substantially increased the rate of sediment oxygen uptake, and this observation was incorporated into system sizing. The chamber study also confirmed that maintenance of oxygenated conditions repressed sediment release of phosphate, ammonia, manganese, and sulfide. Phosphorus and manganese release rates were 6–8 mg/m2/d and 2–5 mg/m2/d under anoxic conditions, respectively, but negligible or negative under oxic conditions. The novel hypolimnetic oxygenation system used a waste product, oxygen-rich off-gas from an ozone contactor at a nearby water treatment plant, to sustainably improve source water quality. The system was tested over a 2 week period in June 2004. Oxygen addition averaged 380 kg/d and increased bottom water DO from 1–2 to 5–6 mg/L with a concurrent drop in water column phosphate and iron, and a delay in sediment release of ammonia. Manganese, with its slow oxidation kinetics, remained in bottom waters during the oxygenation test, indicating that the oxygenation system needs to be turned on earlier in the season to better control manganese accumulation in bottom waters.

Response of sediment microbial community structure in a freshwater reservoir to manipulations in oxygen availability

Hypolimnetic oxygenation systems (HOx) are being increasingly used in freshwater reservoirs to elevate dissolved oxygen levels in the hypolimnion and suppress sediment-water fluxes of soluble metals (e.g. Fe and Mn) which are often microbially mediated. We assessed changes in sediment microbial community structure and corresponding biogeochemical cycling on a reservoir-wide scale as a function of HOx operations. Sediment microbial biomass as quantified by DNA concentration was increased in regions most influenced by the HOx. Following an initial decrease in biomass in the upper sediment while oxygen concentrations were low, biomass typically increased at all depths as the 4-month-long oxygenation season progressed. A distinct shift in microbial community structure was only observed at the end of the season in the upper sediment near the HOx. While this shift was correlated to HOx-enhanced oxygen availability, increased TOC levels and precipitation of Fe- and Mn-oxides, abiotic controls on Fe and Mn cycling, and/or the adaptability of many bacteria to variations in prevailing electron acceptors may explain the delayed response and the comparatively limited changes at other locations. While the sediment microbial community proved remarkably resistant to relatively short-term changes in HOx operations, HOx-induced variation in microbial structure, biomass, and activity was observed after a full season of oxygenation.

Solving the problem at the source: Controlling Mn release at the sediment-water interface via hypolimnetic oxygenation

One of the primary goals of hypolimnetic oxygenation systems (HOx) from a drinking water perspective is to suppress sediment-water fluxes of reduced chemical species (e.g., manganese and iron) by replenishing dissolved oxygen (O 2) in the hypolimnion. Manganese (Mn) in particular is becoming a serious problem for water treatment on a global scale. While it has been established that HOx can increase sediment O 2 uptake rates and subsequently enhance the sediment oxic zone via elevated near-sediment O 2 and mixing, the influence of HOx on sediment-water fluxes of chemical species with more complicated redox kinetics like Mn has not been comprehensively evaluated. This study was based on Mn and O 2 data collected primarily in-situ to characterize both the sediment and water column in a drinking-water-supply reservoir equipped with an HOx. While diffusive Mn flux out of the sediment was enhanced by HOx operation due to an increased concentration driving force across the sediment-water interface, oxygenation maintained elevated near-sediment and porewater O 2 levels that facilitated biogeochemical cycling and subsequent retention of released Mn within the benthic region. Results show that soluble Mn levels in the lower hypolimnion increased substantially when the HOx was turned off for as little as ∼48 h and the upper sediment became anoxic. Turning off the HOx for longer periods (i.e., several weeks) significantly impaired water quality due to sediment Mn release. Continual oxygenation maintained an oxic benthic region sufficient to prevent Mn release to the overlying source water.

Increased sediment oxygen uptake caused by oxygenation-induced hypolimnetic mixing

Hypolimnetic oxygenation systems (HOx) are increasingly used in lakes and reservoirs to elevate dissolved oxygen (O 2) while preserving stratification, thereby decreasing concentrations of reduced chemical species in the hypolimnion. By maintaining an oxic zone in the upper sediment, HOx suppress fluxes of reduced soluble species from the sediment into the overlying water. However, diminished HOx performance has been observed due to HOx-induced increases in sediment O 2 uptake. Based on a series of in situ O 2 microprofile and current velocity measurements, this study evaluates the vertical O 2 distribution at the sediment-water interface as a function of HOx operation. These data were used to determine how sediment O 2 uptake rate ( J O 2 ) and sediment oxic-zone depth ( z max) were affected by applied oxygen-gas flow rate, changes in near-sediment mixing and O 2 concentration, and proximity to the HOx. The vertical sediment-water O 2 distribution was found to be strongly influenced by oxygenation on a reservoir-wide basis. Elevated J O 2 and an oxic sediment zone were maintained during continuous HOx operation, with z max increasing linearly with HOx flow rate. In contrast, J O 2 decreased to zero and the sediment became anoxic as the vertical O 2 distribution at the sediment-water interface collapsed during periods when the HOx was turned off and near-sediment mixing and O 2 concentrations decreased. J O 2 and z max throughout the reservoir were found to be largely governed by HOx-induced mixing rather than O 2 levels in the water column. By quantifying how J O 2 and z max vary in response to HOx operations, this work (1) characterizes how hypolimnetic oxygenation affects sediment O 2 dynamics, (2) contributes to the optimization of water quality and management of HOx-equipped lakes and reservoirs, and (3) enhances understanding of the effect of mixing and O 2 concentrations in other systems.

Phosphorus cycling in a managed lake ecosystem: Seasonal and longer-term trends

► P cycling in an oxygenated lake. ► Internal P loading during summer thermal stratification. ► Release of P from oxyhydroxide phases during periods of low dissolved oxygen. Irondequoit Bay, adjacent to Rochester, New York, is one of the larger embayments along the southern coast of Lake Ontario. Since the 1980s, management activities have been focused on improving water quality and the trophic status of the bay, including a program of hypolimnetic oxygenation. During the summers of 2003, 2004 and 2009, a program of basic water quality parameter profiles and sediment sampling completed. Results of these surveys show an increase in hypolimnetic P throughout each summer season. The increase in P is concordant with decreasing dissolved O 2 concentrations. Although the dissolved O 2 levels are persistent in the suboxic range for most of the summer season, the oxygenation program prevents anoxic conditions, limiting the release of P to that associated with Mn oxyhydroxides. Longer-term trends show an upward linear trend in metalimnetic P which is associated with the trophic status of the bay. This upward trend may be linked to cycling and enrichment of the near surface sediment in P.

A coupled bubble plume–reservoir model for hypolimnetic oxygenation

A model for a linear bubble plume used for hypolimnetic oxygenation was coupled with a three‐dimensional hydrodynamic model to simulate the complex interaction between bubble plumes and the large‐scale processes of transport and mixing. The coupled model accurately simulated the evolution of dissolved oxygen (DO) and temperature fields that occurred during two full‐scale diffuser tests in a water supply reservoir. The prediction of asymmetric circulation cells laterally and longitudinally on both sides of the linear diffuser was due to the uneven reservoir bathymetry. Simulation of diffuser operation resulted in baroclinic pressure gradients, which caused vertical oscillations above the hypolimnion and contributed to distribution of plume detrainment upstream and downstream of the diffuser. On the basis of a first‐order variance analysis, the largest source of uncertainty for both predicted DO and temperature was the model bathymetry, which accounted for about 90% of the overall uncertainty. Because the oxygen addition rate was 4 times the sediment oxygen uptake (SOU) rate, DO predictions were not sensitive to SOU. In addition to bathymetry, the momentum assigned to plume entrainment and detrainment is a significant source of uncertainty in the coupled model structure and appreciably affects the predicted intensity of mixing and lake circulation. For baseline runs, the entrainment and detrainment velocities were assumed to be half of the velocities through the flux face of the grid cells. Additional research on appropriate values of the plume detrainment momentum for the coupled model is required.

Water-Circulating Aerator: Optimizing Structure and Predicting Water Flow Rate and Oxygen Transfer

Thermal stratification is a common phenomenon in deep lakes and reservoirs, which often results in water-quality deterioration, including such problems as hypolimnetic anoxia, the release of pollutants from sediments, and algal blooms. Hypolimnetic oxygenation and destratification are the two commonly used methods for resolving these water-quality problems. A new water-quality improvement device, the water-circulating aerator, was designed to destratify lakes and reservoirs, by circulation and oxygenation of upper and lower layers of water. The design of the structure of the water-circulating aerator is detailed. Three mathematical models were built to optimize this structure, estimate the rate of water flow in the aerator, and calculate the rate of oxygen transfer from air bubbles to water in the aerator. These models were verified by experiments. The water-circulating aerator system has been successfully applied in a stratified reservoir to increase dissolved oxygen to reduce the releasing of ammonia-nitrogen from sediments under anoxic conditions.

Newman Lake restoration: A case study. Part I. Chemical and biological responses to phosphorus control

In the late 1960s and early 1970s, summer and fall blooms of cyanobacteria began to occur in Newman Lake, Washington (zavg: 5.6 m, zmax: 9.0 m); through the next decade, these blooms intensified and became an annual occurrence. Community efforts in the mid-1980s sparked a Restoration Feasibility assessment of the lake and watershed that indicated total annual gross phosphorus loading of at least 3000 kg, with a major portion (∼83%) attributable to internal recycling associated with summer hypolimnetic oxygen depletion. Implementation activities began September 1989, with watershed controls and a whole-lake alum treatment, followed in 1992 by installation of a Speece cone for hypolimnetic oxygenation and in 1997 by addition of a dual-port, microfloc alum injection system. Average summer volume-weighted total phosphorus has declined from prerestoration levels exceeding 50 μg-P/L to an average of 21 μg-P/L over the past 7 years (15–28 μg-P/L). Most notably, peak annual biovolumes of cyanobacteria and their representation within the phytoplankton community have decreased substantially, with increased prevalence of diatoms, green and golden-brown algae. A clearwater phase following spring blooms of diatom and/or golden-brown algae has occurred during those last 7 years, although this phenomenon was observed in the prior three decades. Overall, the restoration has been a success, and lake response to nutrient reduction at Newman Lake is consistent with worldwide observations that emphasize the need for long-term perspectives and commitment in lake restoration and management. Continuation of internal load controls and increased emphasis on external nutrient abatement will be necessary to continue the positive water quality trends despite future development increases and land use changes.

Effects of hypolimnetic oxygenation on water quality: results from five Danish lakes

Stratified eutrophic lakes often suffer from hypolimnetic oxygen depletion during summer. This may lead to low redox conditions and accumulation of phosphate and ammonia in the hypolimnion. Hypolimnetic oxygenation has been used as a lake management strategy to improve the water quality in five eutrophic dimictic Danish lakes where oxygenation was conducted for 4–20 years. In one lake, the hypolimnetic oxygen concentration clearly improved by oxygenation, whereas the other four lakes still exhibited low mean summer levels (<2.2 mg O2 l−1). Oxygenation generally increased the hypolimnetic water temperature by 0.5–2°C, but in one lake it increased by 4–6°C. In all lakes, oxygenation significantly reduced the hypolimnetic concentrations of phosphorus and ammonia during stratification. The accumulation of phosphorus and ammonia typically decreased by 40–88%. In two lakes oxygenation was stopped for 1–2 years and here hypolimnion concentrations of both phosphorus and ammonia increased again. Surface water quality only improved in one lake, but was likely also influenced by simultaneously occurring changes in external nutrient loading. Overall, it is concluded that hypolimnetic oxygenation reduces the hypolimnetic accumulation of phosphorus and ammonia and may prevent anoxia in the deeper parts of the lake. However, long-term oxygenation is required and it is uncertain whether the overall lake water quality can be improved by oxygenation. Reduction of the external nutrient loading is still essential to improve lake water quality.

Effect of hypolimnetic oxygenation on oxygen depletion rates in two water-supply reservoirs

Oxygenation systems, such as bubble-plume diffusers, are used to improve water quality by replenishing dissolved oxygen (DO) in the hypolimnia of water-supply reservoirs. The diffusers induce circulation and mixing, which helps distribute DO throughout the hypolimnion. Mixing, however, has also been observed to increase hypolimnetic oxygen demand (HOD) during system operation, thus accelerating oxygen depletion. Two water-supply reservoirs (Spring Hollow Reservoir (SHR) and Carvins Cove Reservoir (CCR)) that employ linear bubble-plume diffusers were studied to quantify diffuser effects on HOD. A recently validated plume model was used to predict oxygen addition rates. The results were used together with observed oxygen accumulation rates to evaluate HOD over a wide range of applied gas flow rates. Plume-induced mixing correlated well with applied gas flow rate and was observed to increase HOD. Linear relationships between applied gas flow rate and HOD were found for both SHR and CCR. HOD was also observed to be independent of bulk hypolimnion oxygen concentration, indicating that HOD is controlled by induced mixing. Despite transient increases in HOD, oxygenation caused an overall decrease in background HOD, as well as a decrease in induced HOD during diffuser operation, over several years. This suggests that the residual or background oxygen demand decreases from one year to the next. Despite diffuser-induced increases in HOD, hypolimnetic oxygenation remains a viable method for replenishing DO in thermally-stratified water-supply reservoirs such as SHR and CCR.

Controlling soluble iron and manganese in a water-supply reservoir using hypolimnetic oxygenation

Soluble metals such as iron (Fe) and manganese (Mn) often reach problematic levels in water-supply reservoirs during summer stratification following the onset of hypolimnetic hypoxia. The behavior of soluble and particulate Fe and Mn was studied following the installation of a hypolimnetic oxygenation system in Carvins Cove Reservoir, a water-supply impoundment managed by the Western Virginia Water Authority. During oxygenation, manganese concentrations were very low in the bulk hypolimnion (<0.05 mg l −1), but high concentrations (>2.0 mg l −1) were still observed in the benthic region close to the sediment, despite near-sediment dissolved oxygen concentrations in excess of 5.0 mg l −1. Oxygenation appears to affect the location of the oxic/anoxic boundary sufficiently to restrict substantial transport of soluble Mn to the bulk water of the hypolimnion. However, the position of the oxic/anoxic boundary was not uniformly affected along the reservoir bottom, allowing horizontal transport of soluble Mn from higher elevations in contact with hypoxic sediments. During one summer, when the oxygen system was turned off for a month, the soluble Mn in the bulk hypolimnion increased substantially. Oxygen concentrations were quickly restored after the system was turned back on, but elevated levels of soluble Mn persisted until the sedimentation rate of detritus through the hypolimnion increased. When operated without interruption, the oxygenation system was able to reduce the bulk average hypolimnion soluble Mn concentration by up to 97%, indicating that source water control of soluble Mn and Fe can be accomplished with hypolimnetic oxygenation in water-supply reservoirs.

Oxygen Controls the Phosphorus Release from Lake Sediments – a Long‐Lasting Paradigm in Limnology

AbstractThe pioneer works of Einsele, Mortimer, and Ohle on the linking between phosphorus (P) and iron (Fe) cycles seven decades ago created the theoretical basis for a long‐standing paradigm among limnologists i.e., ‘oxygen controls the P release from sediments’. While many empirical studies as well as strong correlations between oxygen depletion and P release seem to support this paradigm, various field observations, laboratory experiments, and repeated failures of hypolimnetic oxygenation measures cast doubt on its universal validity. The temporal existence of a thin oxidized sediment surface‐layer could affect only fluctuations of the temporary P pool at the sediment surface but not the long‐term P retention. On longer time scales P release is the imbalance between P sedimentation and P binding capacity of anoxic sediment layers. The P retention of lake sediments strongly depends on sediment characteristics and land use of the catchment. The presence of redox‐insensitive P‐binding systems such as Al(OH)3 and unreducible Fe(III) minerals can enhance the P retention and completely prevent P release even in case of anoxic conditions. Alternative release mechanisms such as a dissolution of calcium‐bound P and decomposition of organic P under both, aerobic and anaerobic conditions, are often more important than the redox driven Fe‐coupled P cycle. Additionally, bacteria affect P cycling not only by altering the redox conditions but also by releasing P during mineralization of organic matter and by accumulation and release of bacterial P. Since microbial processes consume oxygen and liberate P it is difficult to distinguish whether oxygen depletion is the result or the cause of P release. Nowadays, the old paradigm is discarded and a paradigm shift takes place. Sedimentary P exchange ought to be considered as a complex process which is mainly determined by the amount and species of settled P as well as their subsequent diagenetic transformation in the sediment. The classical paradigm is only valid in special cases since reality is much more complex than suggested by that paradigm.Everything should be made simple as possible, but not simpler! Albert Einstein (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Evaluation of Hypolimnetic Oxygen Demand in a Large Eutrophic Raw Water Reservoir, San Vicente Reservoir, Calif.

Hypolimnetic oxygenation can improve water quality by decreasing hypolimnetic accumulation of reduced compounds that complicate potable water treatment. Historically, aeration systems have been undersized because designers have not accounted for increases in sediment oxygen demand (SOD) resulting from the operation of aeration systems. A comprehensive study was performed to estimate the hypolimnetic oxygen demand (HOD) in San Vicente Reservoir, a eutrophic raw water reservoir in San Diego. Chamber experiments confirmed that turbulence and oxygen concentration at the sediment-water interface dramatically affected SOD. Values ranged from under 0.2 g∕ m2 ∕day under quiescent low-oxygen conditions to over 1.0 g∕ m2 ∕day under turbulent high-oxygen conditions. Based on a statistical evaluation of historical oxygen concentrations in the reservoir and anticipated increases in SOD resulting from operation of an oxygenation system, a design HOD of 16,400 kg∕day was estimated. This is approximately four times the H...

Linear bubble plume model for hypolimnetic oxygenation: Full‐scale validation and sensitivity analysis

An existing linear bubble plume model was improved, and data collected from a full‐scale diffuser installed in Spring Hollow Reservoir, Virginia, were used to validate the model. The depth of maximum plume rise was simulated well for two of the three diffuser tests. Temperature predictions deviated from measured profiles near the maximum plume rise height, but predicted dissolved oxygen profiles compared very well with observations. A sensitivity analysis was performed. The gas flow rate had the greatest effect on predicted plume rise height and induced water flow rate, both of which were directly proportional to gas flow rate. Oxygen transfer within the hypolimnion was independent of all parameters except initial bubble radius and was inversely proportional for radii greater than approximately 1 mm. The results of this work suggest that plume dynamics and oxygen transfer can successfully be predicted for linear bubble plumes using the discrete‐bubble approach.