Stable isotope analysis reveals lower-order river dissolved inorganic carbon pools are highly dynamic

River systems draining peaty catchments are considered a source of atmospheric CO2,thus understanding the behavior of the dissolved inorganic carbon pool (DIC) is valuable. The carbon isotopic composition, delta13C(DIC), and concentration, [DIC], of fluvial samples collected diurnally, over 14 months, reveal the DIC pools to be dynamic in range (-22 to -4.9% per hundred, 0.012 to 0.468 mmol L(-1) C), responding predictably to environmental influences such as changing hydrologic conditions or increased levels of primary production. delta(18)O of dissolved oxygen (DO) corroborates the delta(13)C(DIC) interpretation. A nested catchment sampling matrix reveals that similar processes affect the DIC pool and thus delta(13)C(DIC) across catchment sizes. Not so with [DIC]: at high flow, the DIC export converges across catchment size, but at low flow catchments diverge in their DIC load. Contextualizing delta(13)C with discharge reveals that organic soil-waters and groundwaters comprise end-member sources, which in varying proportions constitute the fluvial DIC pool. Discharge and pH describe well [DIC] and delta(13)C(DIC), allowing carbon to be apportioned to each end-member from continuous profiles, demonstrated here for the hydrological year 2003-2004. This approach is powerful for assessing whether the dynamic response exhibited here is ubiquitous in other fluvial systems at the terrestrial-aquatic interface or in larger catchments.     

干红葡萄酒生产和瓶储过程中溶解氧变化规律的研究

本文通过对干红葡萄酒生产过程中溶解氧的跟踪检测,找出了酿造过程中每种工艺处理溶解氧的变化规律,发现葡萄酒中的溶氧量与葡萄酒生产工艺、游离二氧化硫、温度等密切相关,其中冷冻工艺、灌装工艺以及成品酒仓储阶段是溶解氧波动较大的环节。因此,掌握生产过程中各工艺环节溶解氧变化规律是解决溶解氧技术问题的前提。     

MEMS needle-type sensor array for in situ measurements of dissolved oxygen and redox potential

Microelectrodes are among the most accurate and reliable monitoring devices for measuring the dynamics of biofilm processes. This paper describes a novel needle-type microelectrode array (MEA) for simultaneous in situ measurements of dissolved oxygen (DO) and oxidation reduction potential (ORP) fabricated using microelectromechanical systems (MEMS) technologies. The MEA exhibits fast response times for both DO and ORP measurements and shows a substantial increase in DO sensitivity. To demonstrate the versatility of the new sensor, it was applied to the measurement of DO and ORP microprofiles in a multispecies biofilm. This work demonstrates that the MEA is able to monitor local concentration changes with a high spatial resolution and provide the versatility of the microelectrode technique needed for biofilm studies as well as the capability for repetitive measurements. In addition, the use of MEMS technologies and batch fabrication approaches enables integration, high consistency, high yields, and mass production. With further development, it may be possible to add additional sensors to the MEA (e.g., pH, phosphate) and integrate them with a reference electrode.     

Effect of dissolved organic carbon on the photoproduction of dissolved gaseous mercury in lakes: potential impacts of forestry

The production of dissolved gaseous mercury (DGM) in freshwater lakes is induced by solar radiation and is also thought to be linked to processes mediated by dissolved organic carbon (DOC). Studies investigating these processes using comparisons between lakes are often confounded by differences in DOC content and structure. In this study, we investigated the link between DOC concentrations and DGM production by using tangential ultrafiltration to manipulate DOC concentrations in water samples taken from a given lake. In this way, a range of samples with different DOC concentrations was produced without substantial changes to DOC structure or dissolved ions. This was repeated for four lakes in central Quebec: two with highly logged drainage basins and two with minimally logged drainage basins. On two separate days for each lake, water samples (filtered to remove >99% of microorganisms) with varying DOC concentrations were incubated in clear and dark Teflon bottles on the lake surface. DGM concentrations were measured at 3.5-h intervals over the course of 10.5 h. Levels of DGM concentrations increased with increasing cumulative irradiation for all lakes until approximately 4000 kJ m(-2) (400-750 nm, photosynthetically active radiation (PAR)), when DGM concentrations reached a plateau (between 20 and 200 pg L(-1)). When we assumed that DGM production was limited by the amount of photoreducible mercury, reversible first-order reaction kinetics fitted the observed data well (r2 ranging between 0.59 and 0.98, p < 0.05 with the exception of N70 100% DOC, 0% DOC, and K2 0% DOC with p = 0.06, 0.10, and 0.11, respectively). The DGM plateaus were independent of DOC concentrations but differed between lakes. In contrast, photoproduction efficiency (DGMprod) (i.e., the amount of DGM produced per unit radiation (fg L(-1) (kJ/m2)(-1)) below 4000 kJ m(-2) PAR) was linearly proportional to DOC concentration for both logged lakes (r2 = 0.97, p < 0.01) and nonlogged lakes (r2 = 0.52, p = 0.018) studied. Furthermore, logged lakes had a lower DGMprod per unit DOC (p < 0.01) than the nonlogged lakes. In these four lakes, the rate of DGM production per unit PAR was dependent on the concentration of DOC. The DGM plateau was independent of DOC concentration; however, there was a significant difference in DGM plateaus between lakes presumably due to different DOC structures and dissolved ions. This research demonstrates an important mechanism by which logging may exacerbate mercury levels in biota.     

Dynamic dissolved oxygen concentration control for enhancing the formation rate of torpedo-stage embryos in carrot somatic embryo culture

In utilizing somatic embryogenesis for transplant production, torpedo-stage embryos are harvested. In order to enhance the formation rate of torpedo-stage embryos to total embryos of all developmental stages in the culture at the time of harvest, a dynamic dissolved oxygen concentration (DO) control algorithm is proposed. The algorithm is based on the difference in developmental response of somatic embryogenesis to DO level depending on developmental stages, and the culture period was divided into three phases of different DO levels. The timing of the phase change was determined based on the formation rate of the embryos in each developmental stage in the suspension assessed by noninvasive monitoring of the culture. The induction of carrot (Daucus carroa L.) somatic embryogenesis resulted in doubled formation rate of torpedo-stage embryos by dynamic DO control compared to the 20% oxygen gas aeration, and 1.4 times higher formation rate compared to 6% oxygen gas aeration, while the total number of embryos did not differ among DO treatments. Plant conversion rate of torpedo-stage embryos cultured by the dynamic DO control was 70%, and was approximately the same as that in the control cultures. The relations between variations of medium pH and somatic embryogenesis were also analyzed.     

溶氧对耶氏解脂酵母油脂积累和柠檬酸分泌的影响

产油耶氏解脂酵母能将培养基中过量的碳源转化为油脂储存于细胞内并分泌大量的柠檬酸。在耶氏解脂酵母发酵过程中通过关联搅拌转速和通气量调控培养基中的溶氧含量处于5%、10%、20%、30%和不控制5种水平,来研究溶氧对其油脂积累和柠檬酸分泌的影响。结果表明,随着发酵培养基中溶氧的增加,耶氏解脂酵母细胞内油脂含量和柠檬酸分泌量均有所增加,且不控制培养基中溶氧时,细胞内油脂含量和柠檬酸产量均最高,油脂含量达到细胞干重的11.62%(w/w),柠檬酸产量达到21.0 g/L。培养基中不同的溶氧含量还会影响油脂的脂肪酸组成,高溶氧能够促进油酸含量的增加,溶氧不控制时油酸的含量最高,达到48.62%。本研究为耶氏解脂酵母产脂发酵培养过程中溶氧的控制提供了重要的实验依据。     

Effect of dissolved oxygen changes on activated sludge fungal bulking during lab-scale treatment of acidic industrial wastewater

The cloning and sequencing of fungal 18S rRNA genes followed by the identification of filamentous fungal species by fluorescent in situ hybridization (FISH) and the enumeration of filamentous fungal cells by flow cytometry-FISH (FC-FISH) were used to investigate the effect of dissolved oxygen (DO) changes on activated sludge (AS) fungal bulking during a lab-scale treatment of acidic industrial wastewater. By increasing DO levels from < .5 to > 2 mg L?1, bulking started to occur due to the outbreak of fungal filaments, whereas the chemical oxygen demand (COD) removals sharply increased from < 40 to > 70%. Clone library analyses revealed that all clonal fungal sequences were of yeast origin, and that only one and four yeast species were individually detected in AS at two DO levels. Subsequent FISH identification of filamentous yeast species within bulking sludge using self-designed oligonucleotide probes suggested that all probe-reactive cells of Trichosporon asahii had a filamentous morphology and were the dominating filamentous microorganism in the AS. The FC-FISH analyses of bacteria and two main yeast species showed that the DO shift resulted in a sharp increase of T. asahii, by a factor of 48-60, which caused filamentous yeast bulking. Subsequently, the restoration of DO levels to <0.5 mg L?1 effectively restored the sludge settlement and yeast community, as well as unacceptable COD removals.     

工业发酵中溶氧因素的探讨

工业发酵影响因素很多,其中发酵液中的溶氧浓度(DissolvedOxygen,简称DO)是最基本因素,对微生物的生长和产物形成有着极其重要的影响。在发酵过程中,必须供给适量的无菌空气,菌体才能繁殖和积累所需代谢产物。不同菌种及不同发酵阶段的菌体的需氧量是不同的,发酵液的DO值直接影响微生物的酶活性、代谢途径及产物产量。发酵过程中氧的传质速率主要受发酵液中溶解氧的浓度和传递阻力影响。研究溶氧对发酵的影响及控制对提高生产效率、改善产品质量等都有重要意义。     

Response of sulfate concentration and isotope composition in Icelandic rivers to the decline in global atmospheric SO2 emissions into the North Atlantic Region

This study presents the changes in dissolved sulfate concentration and isotope composition of Icelandic river waters between the peak of SO2 emissions in the United States and Europe and the present. Chloride concentration in Icelandic rivers has not changed much since 1972. The overall average change from 1972-1973 to 1996-2004 was -3%, indicating insignificant sea-salt contribution changes. More than 99% of the river-dissolved sulfur was in the form of sulfate. There are three main sources for dissolved sulfate in the rivers: rocks, sea-salts, and anthropogenic. Total dissolved sulfate, tdSO4(2-), and non-sea-salt sulfate, nssSO4(2-), decreased in all of the rivers from the early 1970s to 1996-2004. The percentage decrease varies from 13% to 65%. The decrease is smallest in rivers were there is considerable rock-derived dissolved SO4(2-). The overall average decrease was 39% for tdSO4(2-) and 46% for nssSO4(2-). The anthropogenic sulfate fraction has declined making most of the river waters delta34S values of sulfate higherthrough time. The overall decline in river sulfate and increase in delta34S, while SO2 emissions from Iceland has been increasing, demonstrates the response of river chemistry in the remote North Atlantic to the decline in man-made emissions of SO2 in North America and Europe.     

Effects of dissolved oxygen level on cell growth and total lipid accumulation in the cultivation of Rhodotorula glutinis

The total amount of lipids produced in Rhodotorula glutinis is a subject which has attracted increasing attention due to the potential biodiesel conversion from these microbial oils. The effects of the dissolved oxygen (DO) level in lipid accumulation were examined in this study. Variations of different medium volumes (30, 40 and 50ml) and shaking speed (60, 150 and 210rpm) in the flask trials were adopted to explore the DO effects on lipid production. All of the results revealed that a low DO could retard cell growth, while enhancing lipid accumulation. The 5l-fermentor results also confirm that a low DO (25 ± 10%) batch could have higher lipid content than that of high DO batch (60 ± 10%). Nevertheless, the DO level would not obviously affect the lipid composition profile. Oleic acid (C18:1) was the primary fatty acid in both batches. Due to the slow biomass growth rate resulting from the low DO, a two-stage DO controlled strategy (consisting of a high DO stage and following a low DO stage) was performed to improve the cell growth and lipid accumulation simultaneously. However, the strategy was not successful on the enhancement of total lipid production as compared to other batches. Conclusively, even a low DO could retard cell growth; the total production of lipids in the batch with low DO was higher that of the high DO batch due to the enhancement of lipid accumulation. Therefore, the batch operation of R. glutinis at the low DO was suggested for the purpose of lipid production.     

Enhancement and inhibition of denitrification by fluid-flow and dissolved oxygen flux to stream sediments

Microscale measurements of nitrate (NO3-) and dissolved oxygen (DO) concentrations in sediments were made in a laboratory channel under turbulent fluid-flow conditions to examine the effects of DO flux on denitrification rates. DO concentrations and flux within sediments increased with increasing velocity in the surface water. Under low fluid-flow conditions (shear stress velocity, u* < 0.23 cm s(-1)), increasing velocity increased NO3- loss from the bulk flow. For high fluid-flow conditions (u* > 0.39 cm s(-1)), increasing velocity inhibited NO3-loss. Sediment cores were collected and sliced to measure the depth distribution of denitrifying biomass in sediments. Quantities of nirK and nirS genes were higher within the surface layer and decreased with depth in the sediments. Microscale concentration profiles of DO and NO3- revealed that denitrification occurs within a thin region just below the oxic-anoxic interface in sediments. The interplay of mass transfer and DO flux generated threshold conditions for NO3- loss by denitrification. These results suggest that for a given sediment and environmental conditions (chemical, physical, microbiological), there exists an optimal range in velocities for enhancing denitrification in aquatic systems.     

Relating carbon monoxide photoproduction to dissolved organic matter functionality

Aqueous solutions of humic substances (HSs) and pure monomeric aromatics were irradiated to investigate the chemical controls upon carbon monoxide (CO) photoproduction from dissolved organic matter (DOM). HSs were isolated from lakes, rivers, marsh, and ocean. Inclusion of humic, fulvic, hydrophobic organic, and hydrophilic organic acid fractions from these environments provided samples diverse in source and isolation protocol. In spite of these major differences, HS absorption coefficients (a) and photoreactivities (a bleaching and CO production) were strongly dependent upon HS aromaticity (r2 > 0.90; n = 11), implying aromatic moieties are the principal chromophores and photoreactants within HSs, and by extension, DOM. Carbonyl carbon and CO photoproduction were not correlated, implying that carbonyl moieties are not quantitatively important in CO photoproduction. CO photoproduction efficiency of aqueous solutions of monomeric aromatic compounds that are common constituents of organic matter varied with the nature of ring substituents. Specifically, electron donating groups increased, while electron withdrawing groups decreased CO photoproductivity, supporting our conclusion that carbonyl substituents are not quantitatively important in CO photoproduction. Significantly, aromatic CO photoproduction efficiency spanned 3 orders of magnitude, indicating that variations in the CO apparent quantum yields of natural DOM may be related to variations in aromatic DOM substituent group chemistry.     

Photoirradiation of dissolved humic acid induces arsenic(III) oxidation

The fate of arsenic in aquatic systems is influenced by dissolved natural organic matter (DOM). Using UV-A and visible light from a medium-pressure mercury lamp, the photosensitized oxidation of As(III) to As(V) in the presence of Suwannee River humic acid was investigated. Pseudo-first-order kinetics was observed. For 5 mg L(-1) of dissolved organic carbon (DOC) and 1.85 mEinstein m(-2) s(-1) UV-A fluence rate, the rate coefficient k degrees exp was 21.2 +/- 3.2 10(-5) s(-1), corresponding to a half-life <1 h. Rates increased linearly with DOC and they increased by a factor of 10 from pH 4 to 8. Based on experiments with radical scavengers, heavy water, and surrogates for DOM, excited triplet states and/or phenoxyl radicals seem to be important photooxidants in this system (rather than singlet oxygen, hydrogen peroxide, hydroxyl radicals, and superoxide). Photoirradiation of natural samples from freshwater lakes, rivers, and rice field water (Bangladesh) showed similar photoinduced oxidation rates based on DOC. Fe(III) (as polynuclear Fe(III)-(hydr)oxo complexes or Fe(III)-DOC complexes) accelerates the rate of photoinduced As(III) oxidation in the presence of DOC by a factor of 1.5-2.     

Scale-dependent temporal variations in stream water geochemistry

A year-long study of four western Montana streams (two impacted by mining and two "pristine") evaluated surface water geochemical dynamics on various time scales (monthly, daily, and bi-hourly). Monthly changes were dominated by snowmelt and precipitation dynamics. On the daily scale, post-rain surges in some solute and particulate concentrations were similar to those of early spring runoff flushing characteristics on the monthly scale. On the bi-hourly scale, we observed diel (diurnal-nocturnal) cycling for pH, dissolved oxygen, water temperature, dissolved inorganic carbon, total suspended sediment, and some total recoverable metals at some or all sites. A comparison of the cumulative geochemical variability within each of the temporal groups reveals that for many water quality parameters there were large overlaps of concentration ranges among groups. We found that short-term (daily and bi-hourly) variations of some geochemical parameters covered large proportions of the variations found on a much longer term (monthly) time scale. These results show the importance of nesting short-term studies within long-term geochemical study designs to separate signals of environmental change from natural variability.     

Hypolimnetic oxygen depletion in eutrophic lakes

The oxygen-consuming processes in the hypolimnia of freshwater lakes leading to deep-water anoxia are still not well understood, thereby constraining suitable management concepts. This study presents data obtained from 11 eutrophic lakes and suggests a model describing the consumption of dissolved oxygen (O(2)) in the hypolimnia of eutrophic lakes as a result of only two fundamental processes: O(2) is consumed (i) by settled organic material at the sediment surface and (ii) by reduced substances diffusing from the sediment. Apart from a lake's productivity, its benthic O(2) consumption depends on the O(2) concentration in the water overlying the sediment and the molecular O(2) diffusion to the sediment. On the basis of observational evidence of long-term monitoring data from 11 eutrophic lakes, we found that the areal hypolimnetic mineralization rate ranging from 0.47 to 1.31 g of O(2) m(-2) d(-1) (average 0.90 ± 0.30) is a function of (i) a benthic flux of reduced substances (0.37 ± 0.12 g of O(2) m(-2) d(-1)) and (ii) an O(2) consumption which linearly increases with the mean hypolimnion thickness (z(H)) up to ～25 m. This model has important implications for predicting and interpreting the response of lakes and reservoirs to restoration measures.     

溶解氧控制对枯草芽孢杆菌发酵生产腺苷的影响

在50 L的生物反应器中,通过控制溶解氧水平为5%、10%、20%、30%四个水平考察枯草芽孢杆菌发酵生产腺苷的影响,发现该菌株生长的溶解氧浓度在10%～20%。并通过发酵过程中菌株的生长情况、菌体摄氧率和发酵产苷进行相关分析。结果表明,在发酵过程中DO水平控制在10%～20%时腺苷积累量高,发酵液中DO水平为5%和30%均不利于发酵液中的腺苷积累。通过对发酵终点丙酮酸的检测,发现枯草芽孢杆菌在低溶氧状态下比高溶氧状态下积累更多的丙酮酸。在此基础上,提出两阶段DO控制策略,最终腺苷积累量达到20.1 g/L。     

Effects of pH and dissolved oxygen on the synthesis of γ‐glutamyltranspeptidase from Bacillus subtilis SK 11.004

BACKGROUND: γ‐Glutamyltranspeptidase (GGT; EC 2.3.2.2) is a widely distributed enzyme that is of interest in the food industry. In this study the effects of pH and dissolved oxygen (DO) on GGT synthesis from Bacillus subtilis SK 11.004 were investigated. RESULTS: GGT production increased to 0.5 U mL^?1 when the pH value was controlled at 6.5. The control of a single DO level revealed that the highest specific growth rate (3.42 h^?1) and GGT production rate (0.40 U g^?1 mL^?1) were obtained at DO levels of 40 and 10% respectively. To satisfy the different oxygen demands at different stages of cell growth and GGT synthesis, a stage DO level control strategy was designed as follows: 40% from 0 to 4 h, 30% from 4 to 6 h and 10% from 6 to 18 h. Furthermore, the maximum biomass (2.27 g L^?1) and GGT production (3.05 U mL^?1) could be obtained using a fermentation strategy combining a constant pH value with stage DO level control. CONCLUSION: The proposed fermentation strategy resulted in a 13.7‐fold increase in GGT production. This finding should be of great importance for the industrial production of GGT. Copyright © 2011 Society of Chemical Industry     

Significant increase in recombinant protein production of a virus-infected Sf-9 insect cell culture of low MOI under low dissolved oxygen conditions

Spodoptera frugiperda Sf-9 insect cells were infected with recombinant Autographa californica nuclear polyhedrosis virus at a low multiplicity of infection (MOI) (0.1), and the effect of dissolved oxygen (DO) on the production of a polyhedrin promoter-driven recombinant protein (beta-galactosidase), intrinsic proteases (carboxyl and cysteine proteases), and the virus was determined. The DO concentrations used in the present study were 45%, 25%, 5%, and 1.3% of air saturation. At 5% DO the cell growth following viral infection was greatest and beta-galactosidase was about 5-fold increased in volumetric yield compared to that at 45% and 25% DO, whereas the growth at 1.3% DO was extremely poor. The virus titer in the medium at 4-8 d post-infection (dpi) was also highest at 5% DO, but the titer was significantly decreased by further increasing the culture time. This was in part attributed to the fact that baculovirus is susceptible to oxidative inactivation under aerobic conditions. The DO dependency of the specific oxygen consumption rate of virus-infected and uninfected Sf-9 cells was expressed by a Monod-type equation. A critical DO, above which the rate of oxygen utilization is not limited by DO, was estimated to be 3.5% of air saturation for virus-infected Sf-9 cells. These results indicated that for a baculovirus-infected Sf-9 insect cell culture of low MOI, the optimal DO was likely to be approximately 5% of air saturation, which is above the critical DO for the infected Sf-9 cells but sufficiently low to reduce the possibility of the oxidative inactivation of virus. For the production of carboxyl and cysteine proteases, the accumulation behavior and concentrations did not significantly vary with DO, except that a peak of cysteine protease activity was observed intracellularly only at 5% DO, coinciding with beta-galactosidase production.     

Effect of dissolved oxygen on the oxidative and structural characteristics of protein in beer during forced ageing

Oxygen is contributing to the deterioration of the beer and shortening the shelf-life of the packaged product. The effect of dissolved oxygen (DO) on oxidative and structural characteristics of protein in beer during forced ageing was examined. Results showed that increased DO decreased obviously protein content in beer, and further reduced antioxidant activities of beer and lipid transfer protein 1 (LTP1). Meanwhile, the increase of DO decreased significantly the free thiol groups content and enhanced the disulfide bonds level in beer and LTP1. Results from circular dichroism, surface hydrophobicity and zeta-potential illustrated that the increase of DO dramatically changed the secondary and tertiary structure of LTP1 with the decrease in the surface hydrophobicity, α-helix and β-turn contents, and the increase in the random coil and negative zeta potential. These results indicated that increased DO could damage the structure of LTP1 and had a negative impact on oxidative stability of beer.     

Model assessment of biogeochemical controls on dissolved organic carbon partitioning in an acid organic soil

A chemical model (constructed in the ORCHESTRA modeling framework) of an organic soil horizon was used to describe soil solution data (10 cm depth) and assess if seasonal variations in soil solution dissolved organic carbon (DOC) could be explained by purely abiotic (geochemical controls) mechanisms or whether factors related to biological activity are needed. The NICA-Donnan equation is used to describe the competitive binding of protons and cations and the charge on soil organic matter. Controls on organic matter solubility are surface charge and a parameter, gamma, that accounts for the distribution of humic molecules between hydrophobic and hydrophilic fractions. Calculations show that the variations in solute chemistry alone are not sufficient to account for the observed variations of DOC, but factors that alter gamma, such as biological activity, are. Assuming that DOC in organic soils is derived from soluble humic material and that gamma is modified seasonally due to biological activity (with monthly soil temperature used as a surrogate for biological activity) we are able to model the observed seasonality of soil solution DOC over a 10-year period. Furthermore, with modeled DOC coupled to other geochemical processes we also model soil solution pH and Al concentrations.