Oxygen Cycle Research Articles

Genome-resolved metagenomics revealed metal-resistance, geochemical cycles in a Himalayan hot spring.

The hot spring microbiome is a complex assemblage of micro- and macro-organisms; however, the understanding and projection of enzymatic repertoire that access earth's integral ecosystem processes remains ambivalent. Here, the Khirganga hot spring characterized with white microbial mat and ions rich in sulfate, chlorine, sodium, and magnesium ions is investigated and displayed the examination of 41 high and medium qualified metagenome-assembled genomes (MAGs) belonged to at least 12 bacterial and 2 archaeal phyla which aids to drive sulfur, oxygen, iron, and nitrogen cycles with metabolic mechanisms involved in heavy metal tolerance. These MAGs possess over 1749 genes putatively involved in crucial metabolism of elements viz. nitrogen, phosphorus, and sulfur and 598 genes encoding enzymes for czc efflux system, chromium, arsenic, and copper heavy metals resistance. The MAGs also constitute 229 biosynthetic gene clusters classified abundantly as bacteriocins and terpenes. The metabolic roles possibly involved in altering linkages in nitrogen biogeochemical cycles and explored a discerned rate of carbon fixation exclusively in archaeal member Methanospirillum hungatei inhabited in microbial mat. Higher Pfam entropy scores of biogeochemical cycling in Proteobacteria members assuring their major contribution in assimilation of ammonia and sequestration of nitrate and sulfate components as electron acceptors. This study will readily improve the understanding of the composite relationship between bacterial species owning metal resistance genes (MRGs) and underline the exploration of adaptive mechanism of these MAGs in multi-metal contaminated environment. KEY POINTS: • Identification of 41 novel bacterial and archaeal species in habitats of hot spring • Genome-resolved metagenomics revealed MRGs (n = 598) against Cr, Co, Zn, Cd, As, and Cu • Highest entropies of N (0.48) and Fe (0.44) cycles were detected within the MAGs.

Combination Therapy of Radiation and Hyperthermia, Focusing on the Synergistic Anti-Cancer Effects and Research Trends.

Despite significant therapeutic advances, the toxicity of conventional therapies remains a major obstacle to their application. Radiation therapy (RT) is an important component of cancer treatment. Therapeutic hyperthermia (HT) can be defined as the local heating of a tumor to 40-44 °C. Both RT and HT have the advantage of being able to induce and regulate oxidative stress. Here, we discuss the effects and mechanisms of RT and HT based on experimental research investigations and summarize the results by separating them into three phases. Phase (1): RT + HT is effective and does not provide clear mechanisms; phase (2): RT + HT induces apoptosis via oxygenation, DNA damage, and cell cycle arrest; phase (3): RT + HT improves immunological responses and activates immune cells. Overall, RT + HT is an effective cancer modality complementary to conventional therapy and stimulates the immune response, which has the potential to improve cancer treatments, including immunotherapy, in the future.

Biphasic oxygen tension promotes the formation of transferable blastocysts in patients without euploid embryos in previous monophasic oxygen cycles

This study evaluated whether the concentration of biphasic O2 (5–2%) promotes the formation of qualified blastocysts (QBs) and euploid blastocysts and the probability of cycles with transferable blastocysts. The paired experimental design included a total 90 patients (180 cycles) without euploid blastocysts in previous monophasic O2 (5%) cycles were enrolled for an additional cycle of biphasic O2 (5–2%). In the biphasic O2 (5–2%) group, the QB rate (35.8%, 225/628) was significantly higher than that in the monophasic O2 (5%) group (23.5%, 137/582; p < 0.001). In addition, the euploid blastocyst number (0.5 ± 0.8) and the percentage of cycles with transferable blastocysts were significantly higher in the biphasic O2 (5–2%) group (57.8%, 52/90) than those in the monophasic O2 (5%) group (0 and 35.6%, 32/90, respectively; p < 0.01). Multivariable regression analysis also indicated that the QB rate and the probability of cycles with transferable blastocysts correlated with O2 tension (OR 1.535, 95% CI 1.325–1.777, and OR 3.191, 95% CI 1.638–5.679, respectively; p < 0.001). Biphasic O2 culture can be used as an alternative strategy to increase the euploid QBs and the probability of cycles with transferable blastocysts in patients with a poor prognosis.

Introduction of oxygen vacancy to Bi2Mn4O10 supported by nickel foam for 1O2 dominated metronidazole degradation under dielectric barrier discharge plasma

Antibiotics in surface water adversely affect food safety and aquatic ecosystem, which hinder biological water treatment, and advanced oxidation technology (AOPs) is of great significance. This study achieved nitroimidazole antibiotic metronidazole (MNZ) removal in a dielectric barrier discharge plasma (DBDP) process. A ternary Bi2Mn4O10/NiF (BMON) was synthesized via microwave-assistant to enhance the DBDP process. Compared with Bi2Mn4O10, BMON has a more stable structure with lower ion dissolution but higher oxygen vacancy (Vö) content. The DBDP process generates active species, and O2⋅− acts as an intermediate in forming 1O2⋅− to degrade MNZ through multipath. The cycle of lattice oxygen (OL)/O2 and Mn+/M(n−1)+ maintain the charge balance on the BMON surface, during which the transformation of Vö and 1O2 improve the catalytic efficiency. Furthermore, MNZ possible degradation pathways were proposed by DFT calculations and ESI-QTOF-MS detection. The DBDP/BMON process exhibited great potential for heterogeneous catalytic in nitroimidazole antibiotic degradation.

Hydrogen Peroxide Production by Inorganic Photocatalysts Consisting of Gold Nanoparticle and Metal Oxide toward Oxygen Cycle Chemistry

Hydrogen peroxide (H2O2) is not only a versatile clean and strong oxidant but also a promising fuel for fuel cells. This Feature Article has shown that gold nanoparticle (NP)-loaded metal oxides (Au/MOs) can be promising photocatalysts for H2O2 production via two electron-oxygen reduction reaction (2e–-ORR). The fundamental parts deal with the general requirements for the H2O2 synthesis, electrocatalytic activity of Au NPs for 2e–-ORR, Fermi level control of the Au NP of Au/MOs in the dark and under light irradiation, and the factors for governing the catalytic activity for H2O2 production. Subsequently, an artificial photosynthesis of H2O2 from water and O2 under visible light irradiation at ambient temperature and pressure is described. Finally, the conclusions are summarized with a direction of the future research on the hot topics.

New constraints of terrestrial and oceanic global gross primary productions from the triple oxygen isotopic composition of atmospheric CO2 and O2

Representations of the changing global carbon cycle under climatic and environmental perturbations require highly detailed accounting of all atmosphere and biosphere exchange. These fluxes remain unsatisfactory, as a consequence of only having data with limited spatiotemporal coverage and precision, which restrict accurate assessments. Through the nature of intimate coupling of global carbon and oxygen cycles via O2 and CO2 and their unique triple oxygen isotope compositions in the biosphere and atmosphere, greater insight is available. We report analysis of their isotopic compositions with the widest geographical and temporal coverage (123 new measurements for CO2) and constrain, on an annual basis, the global CO2 recycling time (1.5 ± 0.2 year) and gross primary productivities of terrestrial (~ 170–200 PgC/year) and oceanic (~ 90–120 PgC/year) biospheres. Observed inter-annual variations in CO2 triple oxygen isotopic compositions were observed at a magnitude close to the largest contrast set by the terrestrial and oceanic biospheres. The seasonal cycles between the east and west Pacific Ocean were found to be drastically different. This intra-annual variability implies that the entire atmospheric CO2 turnover time is not much longer than the tropospheric mixing time (less than ~ 5 months), verifying the derived recycling time. The new measurements, analyses, and incorporation of other global data sets allow development of an independent approach, providing a strong constraint to biogeochemical models.

Catalytic ignition of CO over CuCeZr based catalysts: New insights into the support effects and reaction pathways

Self-sustained catalytic combustion is a promising strategy to remove CO from the off-gas produced during steelmaking, where the potential catalysts are bulk copper-cerium-zirconium mixed oxides or those supported on TiO2 or ZSM-5 substrates. In this study, the effects of the catalyst support on the CO catalytic ignition performance and reaction pathways were investigated by FTIR coupled with a novel in-situ cell, together with the state-of-the-art characterization techniques. The Infrared (IR) transmission cell equipped with a magnetically driven system, could effectively prevent overlaps between active intermediate peaks (Cu+-CO and Cu+(CO)2) and gaseous CO peaks. The Cu+ cations located at the phase interface are the main active sites. The Cu and Ce interactions lead to the formation of solid solutions of CuCe0.75Zr0.25Oδ (CuCeZr). The monocarbonyls [Cu+-CO] are the dominant species during CO oxidation, and the vacancies in the solid solutions are occupied by oxygen, accelerating the oxygen cycle. The TiO2 or ZSM-5 supports promote copper dispersion over CuCe0.75Zr0.25Oδ/TiO2 (CuCeZr/T) and CuCe0.75Zr0.25Oδ/ZSM-5 (CuCeZr/Z) catalysts, which can be attributed to their high surface areas (168.2 and 346.3 m2/g, respectively), while the Cu-Ce interactions are less relevant. Hence, CO oxidation mainly occurs at the phase interface between copper oxide and TiO2/ZSM-5. Dicarbonyls [Cu+(CO)2] are the main intermediates for the CuCeZr/T and CuCeZr/Z catalysts, and the Cu2+ species are reduced to form dicarbonyls that also take part in the oxidation process. Although a well copper dispersion enhances the activity of individual copper sites on the CuCeZr/T and CuCeZr/Z catalysts, considering the redshift of the carbonyl bands and the increase in CO adsorption, the close interactions and high contents of Cu and Ce favor the local accumulation of heat and mass transfer over bulk CuCeZr, leading to the ignition of CO at low temperatures.

The evolution of ecological security and its drivers in the Yellow River Basin.

Ecological security is the state achieved once an ecosystem maintains its stability under external stress. The Yellow River Basin (YRB) is the largest river basin in northwest and north China and an important area for grain and energy production. The assessment and attribution of ecological security in the YRB are important for protecting the natural environment and ensuring sustainable development. Here, the ecological security of the YRB was assessed by the ecological security index (ESI), a comprehensive index based on the oxygen cycle, and its drivers were attributed to climate change, human activities, vegetation, and soil factors. The spatial pattern of ecological security in the YRB showed high heterogeneity. Ecological insecurity occurred mainly in the middle reaches and regions where the major stream of the Yellow River passes through. The ESI decreased at a rate of - 0.82/year since 2000, which indicated the natural environment continued to be improved in the YRB. Climate change dominated the evolution of ecological security in the upper reaches. The level of ecological security has been improved in the middle reaches after a series of ecological restoration projects conducted. With higher intensity of industrial activity, human activities played a more critical role in ecological security in the lower reaches. Our results suggested that government and local people need to adopt different strategies and actions based on the dominant drivers in the upper, middle, and lower reaches to ensure protection of the natural environment and achieve sustainable development targets.

The Roles of Tidal Marshes in the Estuarine Biochemical Processes: A Numerical Modeling Study

AbstractObservations suggest that the existence of tidal marsh can alter the oxygen and nutrient dynamics in adjacent water bodies, but assessing the impacts of large tidal marshes on an estuary is challenging. In this study, we use a modeling approach to investigate the roles of tidal marshes on the estuarine biochemical processes. The marsh model, which simulates the ecological functions of marshes at seasonal and annual time‐scales, is embedded inside an unstructured‐grid three‐dimensional hydrodynamic and eutrophication model (SCHISM‐ICM). This modeling system simulates the growth and metabolism of the tidal marshes and links biological processes to nutrient dynamics in the water column and sediment. This model dynamically simulates nutrient recycling and physical transport of the materials between marshes and open water through wetting‐drying processes. This coupled model system is validated and successfully applied to the York River Estuary. Model results suggest that tidal marshes influence the local diurnal dissolved oxygen (DO) cycle by exporting dissolved organic carbon and high sediment oxygen demand in the marsh system through the tidal exchange. The high deposition rates of organics and diurnal DO cycle enhance the sediment release of phosphorus. On the other hand, marshes tend to decrease dissolved inorganic nitrogen in the water column by settling particulate nutrients and enhancing the denitrification process. The study demonstrates that tidal marshes exert substantial impacts on the estuarine biochemical processes. The developed tidal marsh model enhances eutrophication modeling and advances the understanding of the feedback effects between marsh biogeochemistry and estuarine eutrophication processes on a systemic scale.

The Effect of Eutrophication on Drinking Water

The effects of eutrophication on the environment may have deteriorate consequences of health of exposed animal and human populations through various path way’s. when fresh water, extracted from eutrophic areas, is used for the production of drinking water severe impacts can also occur during watering in eutrophic waters. eutrophication is complex processes which occurs both in fresh and marine waters, where certain types of algae disturbs the aquatic ecosystem and become a threat for animals and human health the primary cause of eutrophication is an excessive concentration of plant nutrient’s originating from agriculture of sewage treatment. The main cause of eutrophication is the large input of nutrient mixed to water body and the main effect is imbalance in the food web that results in the high levels of phytoplankton, zooplankton, algae biomass in stratified water bodies. This can lead algal blooms. The direct consequences is in an excess of oxygen consumption near bottom of the water body. eutrophication processes can be divided in to two categories depending on weather they are linked to the nutrients dispersion and phytoplankaton growth to oxygen cycle near the bottom of the water body. Various effects can be observed depending upon the severity of the eutrophication. Treatment of eutrophic water for producing drinking water. algae disturbs the aquatic ecosystems a threat for animal and human health..eutrophication concern the availability of oxygens. Some species of algae may also contain toxins but incidents where fresh water algae or the origin of cause human or animal illness. Some cynobacteria have capacity to produces toxins dangerous to human beings. A variety of symptoms depending on toxins implicated our observed such as fatigues, headache, diarrhoea, vomiting, and some throat fever skin irritations. Good practices to inform people about risks of bathing or sporting activity in normally colored or turbid waters. Allergic bathers of people walking along shore of water body affected by algae blooms. Any allergies releasing not only toxin but also allergic compounds. In some specific case; local authorities must rely on eutrophic water for producing drinking water.

Labile and refractory fractions of sedimentary organic carbon off the Changjiang Estuary and its implications for sedimentary oxygen consumption

Estuarine and coastal area is dynamic zone for both marine carbon and oxygen cycles. There is limited evaluation of the labile and refractory fraction of sedimentary organic carbon and further a lack of attention to the corresponding potential in dissolved oxygen utilization. In this study, we collected sediment samples from the Changjiang estuary and adjacent coastal areas in the East China Sea in June 2019 to reveal the distribution, main controlling factor, and implications of four operational fractions of sediment organic carbon that range from labile to refraction. In the laboratory, we processed and defined the four operational fractions of sedimentary organic carbon, includes 1) pure water extractable carbon (WEC), 2) salt (K2SO4 solution) extractable carbon (SEC), 3) Microbial biomass carbon (MBC; chloroform extractable carbon), and 4) refractory organic carbon (ROC; the acid-processed fraction). We revealed that off the Changjiang Estuary, the bulk sedimentary organic carbon (SOC), WEC, SEC, MBC, and ROC were 9.43 ± 3.07 g/kg, 0.12 ± 0.10 g/kg, 0.16 ± 0.07 g/kg, 1.58 ± 0.45 g/kg, and 4.38 ± 1.95 g/kg, respectively. Sediment grain size played a vital role in constraining the LOC fractions, and samples from aquaculture areas showed extra-higher levels of LOC when compared to samples from the non-aquaculture area. The LOC and MBC fraction showed clear negative relation with dissolved oxygen (DO) in the near bottom waters under high DO background (DO &amp;gt; 5.5 mg/L), whereas in a low DO background (DO &amp;lt; 3-4 mg/L) no clear relation can be found. Based on our observed LOC content and DO concentration in the near bottom waters, the depth of hypoxia in the near bottom waters, which would be caused by a total decomposition of 4 mm of LOC in the top sediment, ranged between 0.3 m to 4.7 m with an average depth of 2 m. This value (2 m) means that sedimentary oxygen consumption would contribute 10% in the occurrence of hypoxia, with the rest contributing from water column respiration. Overall, we used the LOC fraction of sedimentary organic carbon to address the dissolved oxygen consumption in the near bottom waters and further study is needed to evaluate this approach.

Constructing asymmetrical dual catalytic sites in manganese oxides enables fast and stable lithium–oxygen catalysis

A general asymmetrical dual-site (Mn–Ru or Mn–Ir) construction strategy on manganese oxides is demonstrated to significantly improve the oxygen catalytic activity and cycling stability toward lithium–oxygen batteries.

Study on Influencing Factors of Molecular Sieve Oxygen-Production System

Molecular sieve oxygen-production technology, as a kind of air separation–oxygen production, is receiving more and more attention from every oxygen industry. The two-bed molecular sieve oxygen-production system studied in this paper can generally produce enriched gas with an oxygen concentration of more than 90%, which has the characteristics of strong applicability, high reliability, low cost and high efficiency. However, the gas oxygen concentration of a production system is greatly affected by internal and external factors such as the molecular sieve materials, atmospheric pressure and temperature environment. Through the continuous research of the molecular sieve oxygen-production system, it has been found that the oxygen cycle of the molecular sieve bed and the diameter of the washing and sizing hole also have an effect on the gas oxygen concentration of the production system. Therefore, in this paper, the two-bed molecular sieve oxygen-production device is the research object, with different oxygen-production cycles (including pressure time) and different washing and sizing hole diameter simulation experiments used to explore the molecular sieve oxygen-production system’s optimal oxygen-production cycle (including pressure time) and the rinsing sizing hole’s optimal aperture, to find the structure of the oxygen-production system and the control parameters for the oxygen-production efficiency of the law. The results show that the optimal oxygen-production cycle of the molecular sieve system is 8.0 s (pressure equalization time is 1.3 s), and the optimal diameter of the washing and sizing hole is 0.8 mm.

Enhanced Biogeochemical Cycling Along the U.S. West Coast Shelf

AbstractContinental margins play an essential role in global ocean biogeochemistry and the carbon cycle; however, global assessments of this role remain highly uncertain. This uncertainty arises from the large variability over a broad range of temporal and spatial scales of the processes that characterize these environments. High‐resolution simulations with ocean biogeochemical models have emerged as essential tools to advance biogeochemical assessments at regional scales. Here, we examine the processes and balances for carbon, oxygen, and nitrogen cycles along the U.S. West Coast in an 11‐year hindcast simulation with a submesoscale‐permitting oceanic circulation coupled to a biogeochemical model. We describe and quantify the biogeochemical cycles on the continental shelf, and their connection to the broader regional context encompassing the California Current System. On the shelf, coastal and wind stress curl upwelling drive a vigorous overturning circulation that supports biogeochemical rates and fluxes that are approximately twice as large as offshore. Exchanges with the proximate sediments, submesoscale shelf currents, bottom boundary layer transport, and intensified cross‐shelf export of shelf‐produced materials further impact coastal and open‐ocean balances. While regional variability prevents extrapolation of our results to global margins, our approach provides a powerful tool to identify the dominant dynamics in different shelf setting and quantify their large‐scale consequences.

Rates of seafloor and continental weathering govern Phanerozoic marine phosphate levels

Phosphate is an essential macronutrient for all organisms with a key role in setting levels of marine primary productivity. Despite its importance for marine biogeochemical cycles and its role in shaping the evolution of marine organisms, the factors controlling phosphate bioavailability on geologic timescales remain poorly understood. Here we develop a statistical model of the coupled cycles of phosphate, carbon, oxygen and calcium to constrain the weathering-derived fluxes and seawater concentrations of phosphate through Phanerozoic time (541 million years ago to the present). Our model includes input parameters and time-dependent forcings derived from geologic and geochemical data. We find that the climate sensitivity of chemical weathering of the oceanic crust by low-temperature fluids exerts a first-order control on phosphate availability. Specifically, continental weathering is a source of the limiting nutrient phosphate, but seafloor weathering is considered to be a minor phosphate sink. Consequently, times in Earth history during which seafloor weathering constituted a large fraction of the total (seafloor + continental) weathering were also times during which phosphate influxes to and concentrations in the ocean were relatively low. Lower seawater phosphate levels during those times probably resulted in lower primary productivity and oceanic and atmospheric oxygen concentrations.

Estimating ocean net primary productivity from daily cycles of carbon biomass measured by profiling floats

AbstractThe dependence of net primary productivity (NPP), a central metric in ecology and biogeochemistry, on sunlight drives daily cycles in carbon biomass in the ocean's euphotic zone. In this study, we infer NPP from the daily cycle of biomass. These estimates were extracted from bio‐optical measurements collected by an array of robotic profilers distributed across temperate and polar regions of the southern hemisphere. We estimate NPP in the region south of 30°S as ~11.4 Pg C yr−1, and south of 50°S (the Southern Ocean) as ~4.6 Pg C yr−1. We obtain comparable estimates when complementary daily cycles of oxygen are used instead (11.7 and 3.5 Pg C yr−1). This approach will be valuable for providing the basin‐scale, ground‐truthed information necessary to assess changes in subsurface primary productivity related to climate.

On the Use of Dissolved Oxygen Isotopologues as Biogeochemical Tracers in the Northeast Pacific Ocean

AbstractThe isotopic composition of dissolved oxygen offers a family of potentially unique tracers of respiration and transport in the subsurface ocean. Uncertainties in transport parameters and isotopic fractionation factors, however, have limited the strength of the constraints offered by 18O/16O and 17O/16O ratios in dissolved oxygen. To improve our understanding of oxygen cycling in the ocean's interior, we investigated the systematics of oxygen isotopologues in the subsurface Pacific using new data and a 2‐D isotopologue‐enabled isopycnal reaction‐transport model. We measured 18O/16O and 17O/16O ratios, as well as the “clumped” 18O18O isotopologue in the northeast Pacific, and compared the results to previously published data. We find evidence that oxygen consumption in the northeast Pacific follows different mass‐dependent fractionation exponents from those typically used in oceanographic studies. These fractionation factors imply that an elevated proportion of 17O compared to 18O in dissolved oxygen—that is, its triple‐oxygen isotope composition—may not uniquely reflect only gross primary productivity and mixing. For all oxygen isotopologues, transport, respiration, and photosynthesis comprise important parts of their respective budgets. Mechanisms of oxygen removal in the subsurface ocean are discussed.

Enhancement of Oceanic Eddy Activity by Fine‐Scale Orographic Winds Drives High Productivity, Low Oxygen, and Low pH Conditions in the Santa Barbara Channel

AbstractThe Santa Barbara Channel is one of the most productive regions of the California Current System. Yet, the physical processes that sustain this high productivity remain unclear. We use a high‐resolution physical‐biogeochemical model to show that submesoscale eddies generated by islands are energized by orographic effects on the wind, with significant impacts on nutrient, carbon, and oxygen cycles. These eddies are modulated by two co‐occurring air‐sea‐land interactions: transfer of wind energy to ocean currents that intensifies ocean eddies, and a wind‐current feedback that tends to dampen them. Here we show that the dampening is overwhelmed by fine scale wind patterns induced by the presence of surrounding capes and islands. The fine‐scale winds cause an additional transfer of momentum from the atmosphere to the ocean that energizes submesoscale eddies. This drives upward doming of isopycnals in the center of the channel, allowing a more efficient injection of nutrients to the surface, and triggering intense phytoplankton blooms that nearly double productivity relative to the case without fine‐scale winds. The intensification of the doming effect by the wind‐curl and submesoscale eddies pumps deep low oxygen, acidic waters to the center of the cyclonic eddies. These eddies are then transported away from the Channel into the California Current, where they impact a wider area along the central coast, with potential ecological consequences. Our study highlights the important role of air‐sea‐land interactions in modulating coastal processes, and suggests that submesoscale resolving models are required to correctly represent coastal processes and their ecological impacts.

Capture-bonding Super Assembly of Nanoscale Dispersed Bimetal on Uniform CeO2 Nanorod for the Toluene Oxidation.

Elimination of VOCs by catalytic oxidation is an important technology. Here, a general synergistic capture-bonding superassembly strategy was proposed to obtain the nanoscale dispersed 5.8% PtFe3 -CeO2 catalyst, which showed a high toluene oxidation activity (T100 =226 °C), excellent catalytic stability (125 h, >99.5%) and a good water resistance ability (70 h, >99.5%). Through the detailed XPS analysis, oxygen cycle experiment, hydrogen reduction experiment, and in-situ DRIFT experiment, we could deduce that PtFe3 -CeO2 had two reaction pathways. The surface adsorbed oxygen resulting from PtFe3 nanoparticles played a dominant role, due to the fast cycling between the surface adsorbed oxygen and oxygen vacancy. In contrast, the lattice oxygen resulting from CeO2 nanorods played an important role due to the relationship between the toluene oxidation activity and the metal-oxygen bonding energy. Furthermore, DFT simulation verified Pt sites were the dominant reaction active sites during this reaction.

The dissolved oxygen budget of a small Canadian Shield lake during winter

AbstractDeep‐water hypoxia is an environmental concern in temperate lakes. Seasonal turnover events provide a mechanism for deep‐water oxygenation; however, the lake oxygen budget and mixing dynamics during turnovers are poorly understood. In the present study, the oxygen cycle in a small dimictic lake was investigated from long‐term field measurements supplemented with output from a three‐dimensional numerical model. Photosynthetic production and atmospheric exchange were modeled to predominate during spring and fall turnovers, respectively, contributing 92% (surprisingly) and 8% of the net dissolved oxygen (DO) input to the lake. Of the DO production, 41% occurred under‐ice, with a potential to supply 17% ± 11% of the hypolimnetic DO saturation deficit at spring turnover. The corresponding DO sinks were sediment oxygen demand (− 54%), mineralization (− 33%), and nitrification (− 13%). The watercolumn circulation and stratification during pre‐winter and spring turnover controlled the inter‐annual variability in hypoxia during the following summer. Warm winters (~ 4°C watercolumn leading to rapid summer stratification) and severely cold winters (strong winter stratification with shallow convective mixing in spring) were followed by incomplete spring turnover, whereas, following cold winters (moderate winter stratification and extended convection) turnover was complete. This underscores the connection between winter hydrodynamics and summer water quality in dimictic lakes.