Hypolimnetic Oxygen Demand Research Articles

Empirical modeling of hypolimnion and sediment oxygen demand in temperate Canadian lakes

ABSTRACT Sediment oxygen demand (SOD) and hypolimnetic oxygen demand (HOD) drive deep-water dissolved oxygen (DO) depletion in lakes, yet these parameters can be difficult to be measure routinely. To address this issue, we present an empirical DO depletion model from time-series measurements of hypolimnetic DO and water-column temperature profiles to estimate hypolimnion thickness (H). The model is based on a dataset that includes 3 temperate lakes (Lake Erie, Lake Simcoe, and Eagle Lake) in Ontario, Canada, of varying size and trophic state. We report SOD (mean [standard deviation]; 0.30 [0.07] g m−2 d−1) and HOD (0.08 [0.03] g m−3 d−1) values based on regression fits of (where t is time) and H from these lakes. The model shows that when vertical (through thermocline) and horizontal fluxes can be neglected in the DO budget during summer, SOD and HOD are the first-order parameters driving . The empirical model predicted hypolimnetic DO in the 3 lakes (root-mean-square error [RMSE] of DO < 3.58 g m−3) and was subsequently validated against observations from a fourth lake (Little Silver Lake, Ontario; RMSE of DO = 1.07 g m−3). The model provides insight into the importance of physical characteristics (i.e., 1/H) in the hypolimnetic DO budget and the relative impact of physical transport versus biogeochemical sources and sinks in the DO budget. When the spring turnover DO concentration is known, the model can be used to simulate depletion of DO in the hypolimnion, including the onset of hypoxia, using routinely collected temperature profile data. We suggest that the proposed values for SOD and HOD can serve as estimates for water quality model calibration when no information is available.

A hypolimnetic aeration system to meet the hypolimnetic oxygen demand by increasing the natural assimilation capacity of a reservoir

AbstractHypolimnetic aeration is a viable method to increase the assimilation capacity of lakes. In this study two lakes, one relatively small pond were chosen where aeration equipment was installed and one larger reservoir lake where the required aeration amount was found by calculation. A laboratory‐scale hypolimnetic aeration system (HAS) was designed. A hybrid system using wind and solar energy was implemented which was scaled up from the lab‐scale system. The pilot‐scale system was tested in the smaller volume Borabey Pond and the system’s efficiency was assessed. An aerial hypolimnetic oxygen demand (AHOD) decrease by 33% was observed in the pond due to the operation of the HAS. It was found that, although renewable wind and solar energy sources are applicable for small water bodies, conventional energy sources are needed for large water bodies.

Decreased oxygenation demand following hypolimnetic oxygenation

Gantzer PA, Preece EP, Nine B, Morris J. 2019. Decreased oxygenation demand following hypolimnetic oxygenation. Lake Reserv Manage. 35:292–307. We analyzed long-term oxygenation dynamics in 3 waterbodies: Spring Hollow Reservoir (SHR) and Carvins Cove Reservoir (CCR), which are water supply reservoirs, and North Twin Lake (NTL), a natural lake. Bubble plume line diffuser hypolimnetic oxygenation system (HOS) operation was for 13, 10, and 7 yr for SHR, CCR, and NTL, respectively. Water column profiles were measured in all 3 waterbodies. Additionally, remotely deployed sensors were used to monitor dissolved oxygen (DO) in NTL year-round, specifically to capture winter conditions during ice cover. Hypolimnetic oxygen demand (HOD) was observed to decrease after several years of HOS operation in all 3 waterbodies. Annual HOD decreased more for HOS operated year-round compared to recovery-based operation where HOS was started after DO decreased below 5.0 mg/L. Additionally, HOD throughout the summer stratified period was lower following maintenance of higher DO during spring prior to onset of stratification. An analogous result was observed during winter ice cover relative to DO conditions following fall turnover. Prior work showed increased HOD during HOS operation compared to pre-HOS. The increased HOD during HOS operation was termed diffuser-induced oxygen demand and implied the HOS was inducing oxygen demand. However, the current work shows HOS operation is not actually inducing oxygen demand; rather, it is addressing the existing oxygen demand already in the sediments. Our data suggest that a HOS is an effective tool to maintain hypolimnion DO in stratified lakes and reservoirs. When operated year-round or before DO decreases, HOS can decrease HOD and reduce overall long-term operational costs.

An integrated approach to assess the ecological and chemical status of lakes with HOD/AHOD: a case study of two lakes

The thermal stratification of the lakes impedes the transfer of atmospheric oxygen into the lower layers of the lake. In lakes which are affected by diverse anthropogenic influences, the increasing organic matter amounts lead to a sharp decrease in hypolimnetic oxygen amounts, aided by thermal stratification, and anaerobic conditions arise. The determination of hypolimnetic oxygen demand (HOD) and areal hypolimnetic oxygen demand (AHOD) and their monitoring represent an integrated approach to investigate the oxygenation of lakes, the nutrient conditions, and the physicochemical dynamics. In this study, two lakes differing by size and affected by different anthropogenic sources, are investigated in this respect. At first, bathymetric studies were conducted to determine the depth, surface area, and volume relationships. Then, based on monitoring studies conducted in 2013 and 2014, the thermal stratification dynamics and layer properties were established using the relative thermal resistance to mixing (RTRM) index based on temperature and density profiles. Following this, the oxygen depletion rates were determined by oxygen and temperature profiling in the hypolimnion. For the years of 2013 and 2014, the AHOD values for the Borabey Pond which is far from anthropogenic influences, were found to be 0.848 and 0.569 g O2/(m·d), respectively. The AHOD values for the Porsuk Reservoir which was overburdened for years by industrial and domestic pollution were found to be 4.263 and 5.099 g O2/(m·d), larger than its counterpart by almost sevenfold. The HOD and AHOD monitoring can be considered to a valuable tool for assessing the ecological and chemical status of lakes within Annex 5 of the Water Framework Directive and as an integrated approach to assess and monitor the status of lakes.

Characteristics of Sediment Oxygen Demand in a Drinking Water Reservoir

Depletion of dissolved oxygen (DO) in the hypolimnetic layer during stratification periods and its deleterious effects on water quality have been widely observed. However, it is still difficult to comprehend conceptually the processes of oxygen consumption at the sediment-water interface. The research presented here is, therefore, based on an areal hypolimnetic oxygen demand (AHOD) model to address three key themes related to the sediment oxygen demand (SOD):① the characteristics of sediment and its influences on SOD; ② evaluation of SOD with different turbulence levels overlying the sediment; and ③ the influence of microbial metabolic activity on SOD. Sediment samples were collected at the entrance to and over the basin area of Jinpen Reservoir, and a sediment-water experimental chamber was designed to achieve these goals. The results showed that, under quiescent conditions, the SOD5area(SOD at DO of 5 mg·L-1) were 0.13 g·(m2·d)-1 and 0.36 g·(m2·d)-1 in the arm and basin, respectively. Under dynamic conditions, the slight mixing of the water column near the sediment induced an increase in SOD and resulted in a gradual shift from first-order to zero-order DO uptake. The organic matter content in the reservoir arm and profundal sediment were 44.43 mg·g-1 and 45.12 mg·g-1, respectively. The microbial metabolic activity in the basin was stronger, and the total fluorescence intensity of the dissolved organic matter (DOM) in the profundal sediments was about 1.5 times that in the reservoir arm. These results suggest that SOD will be higher when microbial metabolic activity is stronger and organic matter content is higher in sediments. The oxygenation aeration techniques should be designed to meet the oxygen demand of the deep reservoir to provide a theoretical basis for improving the oxygenation efficiency.

The Chaoborus pump: Migrating phantom midge larvae sustain hypolimnetic oxygen deficiency and nutrient internal loading in lakes

Hypolimnetic oxygen demand in lakes is often assumed to be driven mainly by sediment microbial processes, while the role of Chaoborus larvae, which are prevalent in eutrophic lakes with hypoxic to anoxic bottoms, has been overlooked. We experimentally measured the respiration rates of C. flavicans at different temperatures yielding a Q10 of 1.44–1.71 and a respiratory quotient of 0.84–0.98. Applying the experimental data in a system analytical approach, we showed that migrating Chaoborus larvae can significantly add to the water column and sediment oxygen demand, and contribute to the observed linear relationship between water column respiration and depth. The estimated phosphorus excretion by Chaoborus in sediment is comparable in magnitude to the required phosphorus loading for eutrophication. Migrating Chaoborus larvae thereby essentially trap nutrients between the water column and the sediment, and this continuous internal loading of nutrients would delay lake remediation even when external inputs are stopped.

Powering up the “biogeochemical engine”: the impact of exceptional ventilation of a deep meromictic lake on the lacustrine redox, nutrient, and methane balances

The Lake Lugano North Basin has been meromictic for several decades, with anoxic waters below 100m depth. Two consecutive cold winters in 2005 and 2006 induced exceptional deep mixing, leading to a transient oxygenation of the whole water column. With the ventilation of deep waters and the oxidation of large quantities of reduced solutes, the lake's total redox-balance turned positive, and the overall hypolimnetic oxygen demand of the lake strongly decreased. The disappearance of 150 t dissolved phosphorous (P) during the first ventilation in March 2005 is attributed to the scavenging of water-column-borne P by newly formed metal oxyhydroxides and the temporary transfer to the sediments. The fixed nitrogen (N) inventory was reduced by ~30% (~1000 t). The water-column turnover induced the nitratation of the previously NO3--free deep hypolimnion by oxidation of large amounts of legacy NH4+ and by mixing with NO3--rich subsurface water masses. Sediments with a strong denitrifying potential, but NO3--starved for decades, were brought in contact with NO3--replete waters, invigorating benthic denitrification and rapid fixed N loss from the lake in spite of the overall more oxygenated conditions. Similarly, a large microbial aerobic CH4 oxidation (MOx) potential in the hypolimnion was capitalized with the ventilation of the deep basin. Almost all CH4, which had been built up over more than 40 years (~2800 t), was removed from the water column within 30 days. However, boosted MOx could only partly explain the disappearance of the CH4. The dominant fraction (75%) of the CH4 evaded to the atmosphere, through storage flux upon exposure of anoxic CH4-rich water to the atmosphere. As of today, the North Basin seems far from homeostasis regarding its fixed N and CH4 budgets, and the deep basin's CH4 pool is recharging at a net production rate of ~66 t y-1. The size of impending CH4 outbursts will depend on the frequency and intensity of exceptional mixing events in the future.

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.

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.

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...

Hypolimnetic Anoxia and Sediment Oxygen Demand in California Drinking Water Reservoirs

ABSTRACT Summertime hypolimnetic anoxia can occur in productive drinking water reservoirs as a result of the decay of phytoplankton. Anoxic conditions promote ecological processes that degrade water quality through the release of problem-causing compounds from anoxic sediments including phosphates, ammonia, sulfides, methyl-mercury, iron and manganese. Hypolimnetic aeration systems are commonly installed in reservoirs to prevent hypolimnetic anoxia, but these systems have been historically undersized due to an underestimation of the magnitude of oxygen demand in the hypolimnion. To gain insight into the sizing of hypolimnetic aeration systems, this study evaluated the effects of water current and DO concentration near the sediment-water interface on sediment oxygen demand (SOD) in nine California drinking water reservoirs of various size (5–220 million m3) and trophic status (mean annual chlorophyll a of 0.5–11 μg L−1). SOD measured under quiescent conditions in 1.8 L experimental chambers ranged from 0.1–0.8 g m2 d1 Currents near the sediment-water interface of 3–8 cm s1 induced a two to four-fold increase in SOD, and resulted in a shift from first-order to zero-order DO uptake by sediment with respect to DO concentration in overlaying water. Results support the diffusive boundary layer model for SOD, with increased DO concentration and currents resulting in a larger SOD since there is a greater diffusional driving force across a smaller diffusive boundary layer. The study also evaluated the effects of trophic status and morphometry on hypolimnetic anoxia at the nine study sites. A number of significant correlations were discovered between factor quantifying hypolimnetic anoxia (areal and mass based hypolimnetic oxygen demand, SOD) and those quantifying morphometry (mean depth of the hypolimnion, volume of the hypolimnion) and trophic status (mean annual chlorophyll a). These results suggest that both increased size of the hypolimnion and higher productivity lead to higher oxygen demand within the hypolimnion. In addition, shallower reservoirs had a larger fraction of their total oxygen demand exerted in the sediments versus the water column. As a result, increased mixing at the sediment-water interface after start-up of aeration systems, and the resulting stimulation of SOD, will be particularly important in productive reservoirs of moderate depth (mean depth of 10–15 m). Aeration systems should be designed to enhance SOD by maintaining high oxygen concentrations and by inducing currents at the sediment-water interface. This will increase the depth of penetration of DO into sediment and promote beneficial aerobic biogeochemical reactions in surface sediments. Aeration systems that utilize pure-oxygen with horizontal discharge of highly oxygenated water across the sediment surface, rather than the traditional air-lift aeration system, will be more successful in satisfying SOD and improving hypolimnetic water quality.

Oxygen consumption and ammonia accumulation in the hypolimnion of Walker Lake, Nevada

Walker Lake (area = 140 km2, Zmean = 19.3 m) is a large, terminal lake in western Nevada. As a result of anthropogenic desiccation, the lake has decreased in volume by 75% since the 1880s. The hypolimnion of the lake, now too small to meet the oxygen demand exerted by decaying matter, rapidly goes anoxic after thermal stratification. Field and laboratory studies were conducted to examine the feasibility of using oxygenation to avoid hypolimnetic anoxia and subsequent accumulation of ammonia in the hypolimnion, and to estimate the required DO capacity of an oxygenation system for the lake. The accumulation of inorganic nitrogen in water overlaying sediment was measured in laboratory chambers under various DO levels. Rates of ammonia accumulation ranged from 16.8 to 23.5 mg-N m−2 d−1 in chambers with 0, 2.5 and 4.8 mg L−1 DO, and ammonia release was not significantly different between treatments. Beggiatoa sp. on the sediment surface of the moderately aerated chambers (2.5 and 4.8 mg L−1 DO) indicated that oxygen penetration into sediment was minimal. In contrast, ammonia accumulation was reversed in chambers with 10 mg L−1 DO, where oxygen penetration into sediment stimulated nitrification and denitrification. Ammonia accumulation in anoxic chambers (18.1 and 20.6 mg-N m−2 d−1) was similar to ammonia accumulation in the hypolimnion from July through September of 1998 (16.5 mg-N m−2 d−1). Areal hypolimnetic oxygen demand averaged 1.2 g O2 m−2 d−1 for 1994–1996 and 1998. Sediment oxygen demand (SOD) determined in experimental chambers averaged approximately 0.14 g O2 m−2 d−1. Continuous water currents at the sediment-water interface of 5–6 cm s−1 resulted in a substantial increase in SOD (0.38 g O2 m−2 d−1). The recommended oxygen delivery capacity of an oxygenation system, taking into account increased SOD due to mixing in the hypolimnion after system start-up, is 215 Mg d−1. Experimental results suggest that the system should maintain high levels of DO at the sediment-water interface (∼10 mg L−1) to insure adequate oxygen penetration into the sediments, and a subsequent inhibition of ammonia accumulation in the hypolimnion of the lake.

A theoretical study on operational condition of hypolimnetic aerators

A theoretical basis for the operational condition of hypolimnetic aerators is described. The widely observed increase in hypolimnetic oxygen demand during aeration is ascribed to enhanced sediment oxygen demand due to induced circulation currents. The present model enables quantitative prediction of dissolved oxygen and phosphate concentrations during hypolimnetic aeration. Simple mass balance in the hypolimnoin shows a necessary condition to halt phosphate release. A time scale of changes in oxygen concentration is also discussed. These results will assist in designing an aerator and selecting an optimum operational condition.

A theoretical study on operational condition of hypolimnetic aerators

A theoretical basis for the operational condition of hypolimnetic aerators is described. The widely observed increase in hypolimnetic oxygen demand during aeration is ascribed to enhanced sediment oxygen demand due to induced circulation currents. The present model enables quantitative prediction of dissolved oxygen and phosphate concentrations during hypolimnetic aeration. Simple mass balance in the hypolimnoin shows a necessary condition to halt phosphate release. A time scale of changes in oxygen concentration is also discussed. These results will assist in designing an aerator and selecting an optimum operational condition.

On the occurrence, causes and potential consequences of low zooplankton to phytoplankton ratios in New Zealand lakes

SUMMARY. 1. New Zealand lakes are shown to have lower average zooplankton biomasses than north‐temperate lakes of similar average phytoplankton biomass, expressed as cell volume or chlorophyll a, or similar average total phosphorus concentration, typically by a factor of 5 or more.2. Evidence suggests that the relatively low zooplankton biomasses of New Zealand lakes may be related to a tendency for them to be dominated by large algae that are not directly available as food for zooplankton, with oligotrophy lakes in particular differing from north‐temperate lakes in this respect.3. This difference in turn may be related largely to their mixing regimes. All of the New Zealand lakes are polymietic or monomietic, whereas the northern lakes used for comparison are mostly dimietic. Also, hetero‐cystous cyanobacteria are favoured by the low inorganic nitrogen concentrations that are typical of New Zealand lakes.4. Poor nutritional quality of the phytoplankton, relating to nitrogen limitation in many New Zealand lakes, might supplement the effects of cell size.5. Low exploitation of phytoplankton by zooplankton can be expected to produce a shift in the metabolism of New Zealand lakes towards the sediments. Among the potential consequences of this effect are increased hypolimnetic oxygen demand with increased susceptibility to development of large internal loads of nutrients, and consequently, increased sensitivity to accelerated eutrophication from any increase in external nutrient loads.

Accelerated eutrophication in a New Zealand lake: Lake Rotoiti, central North Island

Abstract Lake Rotoiti, North Island, New Zealand, is a deep (maximum depth, 126 m) lake surrounded by a mostly forested and farmland catchment. However, it currently demonstrates several attributes characteristic of enriched waters. Algal production is high relative to other deep basin lakes of the central North Island. The hypolimnion deoxygenates completely each year, and a bloom‐forming species of blue‐green algae is numerically important in the summer phytoplankton. These features appear to be recent rather than longstanding properties of the Lake Rotoiti ecosystem. A detailed comparison of limnologieal measurements from 1955 onwards reveals a consistent decline in water clarity, a large and possibly exponential increase in hypolimnetic oxygen demand, and a conspicuous shift in the summer phytoplankton community towards blue‐green algal dominance. This recently accelerated change in the trophic status of Lake Rotoiti is probably a response to the Ohau Channel inflow from Lake Rotorua.

ENHANCEMENT OF RESERVOIR RELEASE QUALITY WITH LOCALIZED MIXING

ABSTRACT Density stratification limits or negates vertical mixing in lakes and reservoirs with the result that vertical strata of decreasing water quality are formed. Releases from the lowest of these strata, the hypolimnion, may be of generally poor quality due to oxygen deficiency resulting from the coupling of limited vertical mixing and hypolimnetic oxygen demand. A simple, cost-effective method to enhance these releases, localized mixing, utilizes the effects of jet mixing to transport high-quality epilimnetic water down to the hypolimnetic withdrawal zone and dilute the release. To effectively enhance downstream release quality, the localized mixing system must produce a jet of sufficient quantity and initial momentum so that it will both penetrate into the hypolimnion and adequately dilute the release. Laboratory investigations showed jet penetration into the hypolimnion to be a linear function of the densimetric Froude number at the thermocline. Dilution was observed to be a function of effective pumping ratios. An example design based on these laboratory results is given.

Potential Effect of Methane Oxidation and Nitrification-Denitrification on the Oxygen Budget of Hamilton Harbour

Abstract Samples of gas generated by Hamilton Harbour have been collected at a deep water station (20 m) for four months during the summer and early fall of 1975. Methane and nitrogen are the only significant gases collected at the sediments or at the top of the water column. Methane is lost from the rising gas bubble but nitrogen is not lost. Sources of methane and nitrogen gas production are reviewed. Complete oxidation of the methane lost from the gas bubble represents an oxygen sink of 0.3 gm O2/m2/day. Nitrogen production represents an oxygen sink of 0.1 gm O2/m2/day; this assumes that all nitrogen collected is due to nitrification-denitrification of ammonia produced in the sediments. These sinks are respectively estimated to account for 16–32% and 7–14% of the hypolimnetic oxygen demand. These data provide initial order estimates for two components of the hypolimnetic oxygen demand and a partial basis for construction and calibration of an oxygen model for Hamilton Harbour.