Characterization of microbial souring in Berea‐sand porous medium with a North Sea oil field inoculum

Microbial souring (H₂S production) in porous medium was investigated in an anaerobic upflow porous medium reactor at 60°C using produced waters obtained from the North Sea Ninian oilfield as the inoculum. Multiple carbon sources commonly found in oil field waters (formate, acetate, propionate, iso‐ and n‐butyrates) with inorganic sulfate as the electron acceptor were used as the substrates. Stoichiometry and the rate of souring in the reactor column were calculated. A large proportion of H₂S was trapped in the column as FeS and possibly as a gas phase. Concentration gradients for the substrates (organic acids and sulfate) and H₂S were generated along the column. At steady state, the highest volumetric substrate consumption and H₂S production were found at the front part (inlet) of the reactor column. The average volumetric sulfate reduction rate after H₂S production had stabilized was calculated to be 203 ± 51 mg sulfate‐S.l^‐1.d^‐1. Comparison of the results with the authors’ previous work on the Alaska Kuparuk oilfield waters indicates that the two different microbial inocula (produced waters) exhibited the same experimental trends (rates and location) for souring in the experimental reactor system. This indicates that abiotic factors, as well as microbial parameters, may play an important role for microbial souring in the system.     

Flow‐injection determination of manganese (II) using surfactant enhanced diperiodatonickelate (IV)‐rhodamine 6G chemiluminescence

Chemiluminescence (CL) of the rhodamine 6‐G‐diperiodatonickelate (IV) (Rh6‐G‐Ni(IV) complex) in the presence of Brij‐35 was examined in an alkaline medium and implemented using flow‐injection analysis to analyze Mn(II) in natural waters. Brij‐35 was identified as the surfactant of choice that enhanced CL intensity by about 62% of the reaction. The calibration curves were linear in the range 1.7 × 10^?3 – 0.2 (0.9990, n = 7) and 8.0 × 10^?4 – 0.1 μg ml^?1 (0.9990, n = 7) with limits of detection (LODs) (S:N = 3) of 5.0 × 10^?4 and 2.4 × 10^?4 μg ml^?1 without and with using an in‐line 8‐hydroxyquinoline (8‐HQ) resin mini‐column, respectively. The sample throughput and relative standard deviation were 200 h^?1 and 1.7–2.2% in the range studied respectively. Mn(II) concentrations in certified reference materials and natural water samples was successfully determined. A brief discussion about the possible CL reaction mechanism is also given. In addition, analysis of V(III), Cr(III) and Fe(II) was also performed without and with using an in‐line 8–HQ column and selective elution of each metal ion was achieved by adjusting the pH of the sample carrier stream with aqueous HCl solution.     

Bacterial transport in volcanic tuff cores under saturated flow conditions

An antibiotic‐resistant bacterium was tested for transport through volcanic tuff and sandstone cores. Tuff cores were representative of the geology of Rainier Mesa located on the Nevada Test Site (NTS). Rapid bacterial transport occurred in some of the tuff cores and all sandstone cores under the hydraulic heads used (5–500 cm). Hydraulic conductivity of the tuff cores ranged widely, 9.6 × 10^‐5 to 7.2 x 10^‐3 cm h^‐1. A much narrower range was observed for sandstone cores, 1.6 × 10^‐2 to 5.9 X 10^‐2 cm h^‐1, which served as experimental controls. The percentage of the initial bacterial inoculum recovered within 3 pore volumes from tuff and sandstone cores ranged from 9.4 to 54.7% and 0.20 to 2.9%, respectively. Bacterial recovery appeared to be controlled by the structure of the flow paths in rock cores and not by overall hydraulic conductivity. Saturated clay‐infiltrated and unfractured zeolitized tuff cores were impermeable to water flow, and therefore bacterial transport was not detected. Three routes of bacterial transport were discerned in permeable rock cores by comparison of the breakthrough patterns of bacteria and tracer solution (chloride ions) in cores of differing lithologies. In sandstone cores, where water flowed evenly through the matrix, bacteria were transported in a dispersed manner throughout the sandstone, whereas bacteria were transported primarily along preferred flow paths (fractures or macropores) in permeable tuff cores.     

A Versatile Pyramidal Hauerite Anode in Congeniality Diglyme‐Based Electrolytes for Boosting Performance of Li‐ and Na‐Ion Batteries

For the first time, environmentally friendly sulfur‐rich pyramidal MnS₂ synthesized via a single‐step hydrothermal process is used as a high‐performance anode material in Li‐ion and Na‐ion batteries. The superior electrochemical performance of the MnS₂ electrode along with its high compatibility with ether‐based electrolytes are analyzed in both half‐ and full‐cell configurations. The reversible capacities of ≈84 mAh g^?1 and ≈74 mAh g^?1 at a current density of 50 mA g^?1 are retained in the Li‐ion and Na‐ion full‐cells, respectively, over 200 cycles with excellent capacity retentions. Moreover, important findings regarding activation processes in the presence of a new phase transition and protective electrolyte interphase layer are revealed using ab initio density function theory calculation and in situ potentio‐electrochemical impedance spectroscopy. The detailed complex redox mechanism of MnS₂ in Li/Na half‐cells is also elucidated by ex situ X‐ray photoelectron spectroscopy.     

Contribution of Crenarchaeota and Bacteria to autotrophy in the North Atlantic interior

Marine Crenarchaeota are among the most abundant groups of prokaryotes in the ocean and recent reports suggest that they oxidize ammonia as an energy source and inorganic carbon as carbon source, while other studies indicate that Crenarchaeota use organic carbon and hence, live heterotrophically. We used catalysed reporter deposition fluorescence in situ hybridization (CARD‐FISH) to determine the crenarchaeal and bacterial contribution to total prokaryotic abundance in the (sub)tropical Atlantic. Bacteria contributed ～50% to total prokaryotes throughout the water column. Marine Crenarchaeota Group I (MCGI) accounted for ～5% of the prokaryotes in subsurface waters (100 m depth) and between 10 and 20% in the oxygen minimum layer (250–500 m depth) and deep waters (North East Atlantic Deep Water). The fraction of both MCGI and Bacteria fixing inorganic carbon, determined by combining microautoradiography with CARD‐FISH (MICRO‐CARD‐FISH), decreased with depth, ranging from ～30% in the oxygen minimum zone to < 10% in the intermediate waters (Mediterranean Sea Outflow Water, Antarctic Intermediate Water). In the deeper water masses, however, MCGI were not taking up inorganic carbon. Using quantitative MICRO‐CARD‐FISH to determine autotrophy activity on a single cell level revealed that MCGI are incorporating inorganic carbon (0.002–0.1 fmol C cell^?1 day^?1) at a significantly lower rate than Bacteria (0.01–0.6 fmol C cell^?1 day^?1). Hence, it appears that MCGI contribute substantially less to autotrophy than Bacteria. Taking the stoichiometry of nitrification together with our findings suggests that MCGI might not dominate the ammonia oxidation step in the mesopelagic waters of the ocean to that extent as the reported dominance of archaeal over bacterial amoA would suggest.     

Isolation and characterization of a novel biosurfactant produced by hydrocarbon‐degrading bacterium Alcanivorax dieselolei B‐5

Aims: Our goal was to identify a novel biosurfactant produced by a marine oil‐degrading bacterium. Methods and Results: Biosurfactants were produced by Alcanivorax dieselolei strain B‐5^T growing with diesel oil as the sole carbon and energy source. Culture supernatant was first extracted with chloroform/methanol (1 : 1, v/v), then further purified step by step with a normal phase silica gel column, a Sephadex LH20 gel column and a preparative thin layer plate. The main component was determined to be a lipopeptide; it was chemically characterized with nuclear magnetic resonance, liquid chromatography‐quadrupole ion‐trap mass spectrometry, amino acid analysis and GC–MS and was found to be a mixture of proline lipids. The monomers of the proline lipids were composed of a proline residue and a fatty acid (C_14:0, C_16:0 or C_18:0). The critical micelle concentration of the mixed proline lipids was determined to be 40 mg l^?1. Moreover, activity variations in ranges of pH, temperature and salinity were also detected and showed reasonable stability. Conclusions: Alcanivorax dieselolei B‐5 produced a novel linear lipoamino biosurfactant, characterized as a proline lipid. Significance and Impact of the Study: A proline lipid was characterized for the first time as a bacterial biosurfactant. This product has potential in both environmental and industrial applications.     

Influence of elevated CO2 and nitrogen nutrition on photosynthesis and nitrate photo-assimilation in maize (Zea mays L.)

Measurements of CO₂ and O₂ gas exchange and chlorophyll a fluorescence were used to test the hypothesis that elevated atmospheric CO₂ inhibits nitrate (NO₃ ^– ) photo‐assimilation in the C₄ plant, maize (Zea mays L.). The assimilatory quotient (AQ), the ratio of net CO₂ assimilation to net O₂ evolution, decreases as NO₃ ^– photo‐assimilation increases so that the difference in AQ between the ammonium‐ and nitrate‐fed plants (ΔAQ) provided an in planta estimate of NO₃ ^– photo‐assimilation. In fully expanded maize leaves, NO₃ ^– photo‐assimilation was detectable only under high light and was not affected by CO₂ treatments. Furthermore, CO₂ assimilation and O₂ evolution were higher under NO₃ ^– than ammonia (NH₄⁺) regardless of CO₂ levels. In conclusion, NO₃ ^– photo‐assimilation in maize primarily occurred at high light when reducing equivalents were presumably not limiting. Nitrate photo‐assimilation enhanced C₄ photosynthesis, and in contrast to C₃ plants, elevated CO₂ did not inhibit foliar NO₃^– photo‐assimilation.     

Field studies of ammonia excretion in Aphanius iberus (Pisces; Cyprinodontidae): body size and habitat effects

The effects of body size and habitat variability on ammonia excretion rates (R_AMs) of Aphanius iberus were analyzed in situ for the first time. At hourly intervals during a 5‐h field experiment, ammonia excretion was measured in 75 mature specimens from three sampling sites (small creek, marine salt‐mine, and salt‐marsh) established in a gradient of water salinity (0–5; 35–40; 65–70‰). Our results showed a specific size dependence pattern of R_AMs in the reproduction period, which might reflect an effect of the reproductive effort. In addition, the results point to a significant decrease in mean R_AM values of each population from freshwater aquatic systems (3.81 ± 0.58 μmol g⁻¹ h⁻¹ in fish of 2.8 ± 0.3 mm total length, TL) to salt aquatic systems with significantly higher alkalinity (2.52 ± 0.35 μmol g⁻¹ h⁻¹ in fish of 3.1 ± 0.5 mm TL in marine salt‐mine; 1.98 ± 0.55 μmol g⁻¹ h⁻¹ in fish of 3.1 ± 0.4 mm TL in salt‐marsh). Due to the size‐dependent pattern, R_AM in different habitats cannot be compared directly; ancova , followed by residual compared analysis (regression‐related techniques), is seen as a valid method for this purpose. This work presents the first field data on ammonia excretion in the Aphanius genus and the flexible physiologic response characteristic of Cyprinodontids has been demonstrated.     

Estimation of the air/sea exchange of ammonia for the North Atlantic Basin

As gas phase atmospheric ammonia reacts with acidic aerosol particles it affects the chemical, physical, and optical properties of the particles. A knowledge of the source strengths of NH₃ is useful in determining the effect of NH₃ on aerosol properties on a regional basis. Here, an attempt is made to determine the direction and magnitude of the air/sea flux of ammonia for the North Atlantic Basin from both measured and modeled seawater and atmospheric ammonia concentrations. Previously reported measured seawater concentrations range from less than 30 to 4600 nM with the highest concentrations reported for the Caribbean Sea, the North Sea, and the Belgium coast. Measured atmospheric ammonia concentrations range from 2 to 500 nmol m^–3 with the largest values occurring over the Sargasso Sea, the Caribbean Sea, and the North Sea. For comparison to the measurements, seawater ammonia concentrations were calculated by the Hamburg Model of the Ocean Carbon Cycle (HAMOCC3). HAMOCC3 open ocean values agree well with the limited number of reported measured concentrations. Calculated coastal values are lower than those measured, however, due to the coarse resolution of the model. Atmospheric ammonia concentrations were calculated by the Acid Deposition Model of the Meteorological Synthesizing Center (MSC-W) and by the global 3-dimensional model Moguntia. The two models predict similar annually averaged values but are about an order of magnitude lower than the measured concentrations. Over the North Sea and the NE Atlantic, the direction and magnitude of the air/sea ammonia flux calculated from MSC-W and Moguntia agree within the uncertainty of the calculations. Flux estimates derived from measured data are larger in both the positive and negative direction than the model derived values. The discrepancies between the measured and modeled concentrations and fluxes may be a result of sampling artifacts, inadequate chemistry and transport schemes in the models, or the difficulty in comparing point measurements to time-averaged model values. Sensitivity tests were performed which indicate that, over the range of values expected for the North Atlantic, the accuracy of the calculated flux depends strongly on seawater and atmospheric ammonia concentrations. Clearly, simultaneous and accurate measurements of seawater and atmospheric ammonia concentrations are needed to reduce the uncertainty of the flux calculations, validate the model results, and characterize the role of oceanic ammonia emissions in aerosol processing and nitrogen cycling for the North Atlantic.     

Preparative isolation and purification of four flavonoids from the petals of nelumbo nucifera by high‐speed counter‐current chromatography

Introduction – Flavonoids, the primary constituents of the petals of Nelumbo nucifera, are known to have antioxidant properties and antibacterial bioactivities. However, efficient methods for the preparative isolation and purification of flavonoids from this plant are not currently available. Objective – To develop an efficient method for the preparative isolation and purification of flavonoids from the petals of N. nucifera by high‐speed counter‐current chromatography (HSCCC). Methodology – Following an initial clean‐up step on a polyamide column, HSCCC was utilised to separate and purify flavonoids. Purities and identities of the isolated compounds were established by HPLC‐PAD, ESI‐MS, ¹H‐NMR and ¹³C‐NMR. Results – The separation was performed using a two‐phase solvent system composed of ethyl acetate–methanol–water–acetic acid (4 : 1 : 5 : 0.1, by volume), in which the upper phase was used as the stationary phase and the lower phase was used as the mobile phase at a flow‐rate of 1.0 mL/min in the head‐to‐tail elution mode. Ultimately, 5.0 mg syringetin‐3‐O‐β‐d‐glucoside, 6.5 mg quercetin‐3‐O‐β‐d‐glucoside, 12.8 mg isorhamnetin‐3‐O‐β‐d‐glucoside and 32.5 mg kaempferol‐3‐O‐β‐d‐glucoside were obtained from 125 mg crude sample. Conclusion – The combination of HSCCC with a polyamide column is an efficient method for the preparative separation and purification of flavonoids from the petals of N. nucifera. Copyright © 2009 John Wiley & Sons, Ltd.     

High diversity of ammonia‐oxidizing archaea in permanent and seasonal oxygen‐deficient waters of the eastern South Pacific

The community structure of putative aerobic ammonia‐oxidizing archaea (AOA) was explored in two oxygen‐deficient ecosystems of the eastern South Pacific: the oxygen minimum zone off Peru and northern Chile (11°S–20°S), where permanent suboxic and low‐ammonium conditions are found at intermediate depths, and the continental shelf off central Chile (36°S), where seasonal oxygen‐deficient and relatively high‐ammonium conditions develop in the water column, particularly during the upwelling season. The AOA community composition based on the ammonia monooxygenase subunit A (amoA) genes changed according to the oxygen concentration in the water column and the ecosystem studied, showing a higher diversity in the seasonal low‐oxygen waters. The majority of the archaeal amoA genotypes was affiliated to the uncultured clusters A (64%) and B (35%), with Cluster A AOA being mainly associated with higher oxygen and ammonium concentrations and Cluster B AOA with permanent oxygen‐ and ammonium‐poor waters. Q‐PCR assays revealed that AOA are an abundant community (up to 10⁵amoA copies ml^?1), while bacterial amoA genes from β proteobacteria were undetected. Our results thus suggest that a diverse uncultured AOA community, for which, therefore, we do not have any physiological information, to date, is an important component of the nitrifying community in oxygen‐deficient marine ecosystems, and particularly in rich coastal upwelling ones.     

Determination and pharmacokinetic study of chiisanogenin in rat plasma by ultra performance liquid chromatography-tandem mass spectrometry

Introduction – Chiisanogenin existing in many Acanthopanax species has been reported to possess anti‐inflammatory, antibacterial and antiplatelet aggregatory activities. Objective – To develop and validate a rapid and sensitive ultra performance liquid chromatography‐tandem mass spectrometry method for the determination of chiisanogenin in rat plasma and to investigate its pharmacokinetics after oral administration of chiisanogenin or the extract of Acanthopanax sessiliflorus fruits. Methodology – The sample pretreatment involved a one‐step extraction of 0.2 mL plasma with diethyl ether. Acetaminophen was used as the internal standard. The separation was carried out on an ACQUITY UPLC? BEH C₁₈ column with a mobile phase of acetonitrile‐5 mM ammonium acetate (90:10, v/v) at a flow rate of 0.2 mL/min. The detection was performed on a triple quadrupole tandem mass spectrometer by multiple reaction monitoring (MRM) mode via electrospray ionization (ESI) source. Results – A high sample throughput was achieved with an analysis time of 1.1 min per sample. The calibration curve was linear (r² ≥ 0.99) over the concentration range of 5–500 ng/mL with a lower limit of quantification (LLOQ) of 5 ng/mL. The intra‐day and inter‐day precision (relative standard deviation, R.S.D.) values were below 11% and the accuracy (relative error, R.E.) was within 8% at all three quality control (QC) levels. Conclusion – The method was successfully applied to the pharmacokinetic study of chiisanogenin in rat after oral administration of chiisanogenin and the extract of Acanthopanax sessiliflorus fruits. Other constituents in the extract affected the pharmacokinetic behavior of chiisanogenin. Copyright © 2010 John Wiley & Sons, Ltd.     

Speciation of copper(II) in natural waters in the presence of ligands of high and intermediate strength

Abstract

A new procedure is presented for the determination of the ligands of copper(II) in natural waters, based on titration with the metal ion, monitored by measuring the concentration of copper(II) sorbed on the carboxylic resin Amberlite CG 50. The data are treated by the Ruzic linearization method to obtain the concentration of the ligands and the conditional stability constant of the complexes. Ligands with reaction coefficient α_M higher than 0.1 K*w/V are detected, where K* is the ratio of the concentration of sorbed metal to the concentration of free metal in solution, which can be evaluated from the sorption equilibria of copper(II) on Amberlite CG 50, w is the amount of water in the resin phase, and V the volume of the solution phase. Some natural waters at high and low salinity were examined. The ligand concentration determined in these samples ranged from around 50 to 2000 nM, while the original copper concentrations from 11 to 130 nM. The ligand concentration was always much higher than that of copper(II). The conditional stability constants were very high, particularly in low salinity waters, where values as high as K’= 10^15.7 were obtained. In high salinity waters values around 10⁹ were found for the complex formation constant of the ligands titrated with copper(II). The investigation was also extended to a model solution, containing EDTA, obtaining K’ = 10^15.5, in acceptable agreement with that evaluated from the literature values.     

The distribution and interconversion of ammonium and nitrate in the Skallingen salt marsh (Denmark) and their exchange with the adjacent coastal water

The potential nitrogen sources for the primary production in the intertidal area are nitrogen compounds obtained from mineralization in the sediment and the water column, nitrogen fixation, outflow from rivers and groundwater seeping from the mainland. The available inorganic nitrogen in the adjacent coastal waters decreases from 50–80 μmol NO₃ ^-/l and 6–15 μmol NH₄ ⁺/l in early spring to ca one tenth during the growing season. In the sediment of the tidal flats available ammonia and nitrate vary between 50 and 100 μmol/1 pw. In the salt marsh available ammonia increases from 200–300 nmol NH₄ ⁺/g fwt to approximately double the amount, and the available nitrate varies from 100–300 nmol NO₃ ^-/g fwt (250–750 μmol NO₃ ^-/l pw) to ca one third during the growing season. The exchange of NH₄ ⁺, NO₂ ^- and NO₃ ^- across the sediment water interface has been estimated during tidal cycles under light and dark conditions on the tidal flats. The flux of nitrogen was dependent on the flora and fauna as well as the time of the year. The tidal activity, frequency and length of inundation are considered the driving force in a two-way process between salt marshes and adjacent coastal waters. The role of marsh sediment, tidal water and sediments of the tidal flats as sites of accumulation, consumption and remineralization of organic matter is emphasized. The possible exchange of ammonia and nitrate between the salt marsh and the different compartments of the tidal water is discussed.     

南岭小坑藜蒴栲群落地上部分生物量分配规律

采用皆伐法对南岭小坑750m2天然藜蒴栲群落的生物量进行了实测,该群落有43个树种,其中藜蒴栲为优势种,获得了胸径2.0 cm以上的267株树的树干、枝、叶烘干重数据以及实测的胸径（D）、树高（H）数据。揭示了该森林群落地上部分总生物量(AGB)在森林各层次、各树种及乔木层各器官中的分配规律,并建立了该群落的生物量模型。结果表明,南岭小坑流域藜蒴栲群落地上部分总生物量是131.149 t.hm-2,其中乔木层是129.895 t.hm-2,下木层是1.563 t.hm-2,层间植物是0.267 t.hm-2,凋落物层是2.424 t.hm-2。树干、树枝、树叶生物量分别是乔木层地上部分总生物量的85.0%、10.6%和4.4%。优势树种藜蒴栲和小红栲生物量是乔木层地上部分总生物量的46.3%和9.8%,这说明在早期演替的森林群落中生物量主要集中分布在少数的几个优势种。乔木各径阶（DBH<5,5~10,10~15,15~20,20~25,≥25cm）的生物量占乔木层地上部分总生物量的百分比分别是1.0%, 13.1%,52.2%,26.4%,4.6%和2.7%。天然次生藜蒴栲群落以D为自变量的模型是Wtagb=0.116D2.384,R2=0.934,模型估算值比皆伐实测值低5.0%;以D2H为自变量的总生物量模型是Wtagb=184.274(D2H)0.881,R2=0.952,模型估算值比皆伐实测值低6.9%;这说明针对天然藜蒴栲群落,采用以D为自变量的总生物量模型更为实用。     

A combination of ultrasonic-assisted extraction with RRLC-QQQ method for the determination of artemisinin in the Chinese herb Artemisia annua L

Introduction – Artemisinin, the primary active ingredient of the Chinese herb Artemisia annua L., is known to have considerable anti‐malaria properties. However, rapid, sensitive and selective method for the determination of artemisinin in it is not currently available. Objective – To develop and validate an efficient method for extraction and analysis of artemisinin from the plant samples of Artemisia annua L. by rapid resolution liquid chromatography triple quadrupole mass spectrometry (RRLC‐QQQ). Methodology – Following ultrasound‐assisted extraction (USE), RRLC‐QQQ was utilised to separate and determine artemisinin from the plant sample of Artemisia annua L. The LC separation, QQQ‐MS detection and multiple reaction monitoring (MRM) mode were optimised, and the method validation concluding selectivity, calibration, accuracy and precision, and recovery were also evaluated. Results – LC separation was performed with an isocratic elution of 20% of methanol–water (10 mmol/L ammonium acetate, pH 4.0) on a C₁₈ column. The triple quadrupole MS detection was carried out under MRM mode of precursor ion [M + H]⁺ → fragment ions m/z 265.1 and m/z 247.2. The limits of detection and quantitation of artemisinin were 0.20 and 0.75 ng/mL, respectively. The intra‐ and inter‐day precisions did not exceed 3.71%, and the deviation of the intra‐ and inter‐day mean values did not exceed ±7.50. The average recoveries for artemisinin ranged from 92.45 to 103.8% with an RSD from 2.47 to 2.79%. Conclusion – The developed RRLC‐QQQ assay is an efficient method for separation and determination of artemisinin from the plant samples of Artemisia annua L. Copyright © 2011 John Wiley & Sons, Ltd.     

Seasonal variability of the parameters of the Ball–Berry model of stomatal conductance in maize (Zea mays L.) and sunflower (Helianthus annuus L.) under well‐watered and water‐stressed conditions

The Ball–Berry (BB) model of stomatal conductance (g_s) is frequently coupled with a model of assimilation to estimate water and carbon exchanges in plant canopies. The empirical slope (m) and ‘residual’ g_s (g₀) parameters of the BB model influence transpiration estimates, but the time‐intensive nature of measurement limits species‐specific data on seasonal and stress responses. We measured m and g₀ seasonally and under different water availability for maize and sunflower. The statistical method used to estimate parameters impacted values nominally when inter‐plant variability was low, but had substantial impact with larger inter‐plant variability. Values for maize (m = 4.53 ± 0.65; g₀ = 0.017 ± 0.016 mol m^?2 s^?1) were 40% higher than other published values. In maize, we found no seasonal changes in m or g₀, supporting the use of constant seasonal values, but water stress reduced both parameters. In sunflower, inter‐plant variability of m and g₀ was large (m = 8.84 ± 3.77; g₀ = 0.354 ± 0.226 mol m^?2 s^?1), presenting a challenge to clear interpretation of seasonal and water stress responses – m values were stable seasonally, even as g₀ values trended downward, and m values trended downward with water stress while g₀ values declined substantially.     

Experimental measurement of sediment nitrification and denitrification in Hamilton Harbour,Canada

This research examines the role of sediment nitrification and denitrification in the nitrogen cycle of Hamilton Harbour. The Harbour is subject to large ammonia and carbon loadings from a waste-water treatment plant and from steel industries. Spring ammonia concentrations rapidly decrease from 4.5 to 0.5 mg 1⁻¹, while spring nitrate concentrations increase from 1 to 2 mg l⁻¹, by mid-summer. A three-layer sediment model was developed. The first layer is aerobic; in it, oxidation of organics and nitrification occurs. The second layer is for denitrification, and the third layer is for anaerobic processes. Ammonia sources for nitrification include diffusion from the water column, sources associated with the oxidation of organics, sources from denitrification and from anaerobic processes. Diffusion of oxygen, ammonia and nitrate across the sediment-water interface occurs. Temperature effects are modelled using the Arrhenius concept. A combination of zero-order kinetics for nitrate or ammonia consumption with diffusion results in a half-order reaction, with respect to the water column loss rate to sediments. From experimental measurement, the rate of nitrification is 200 mg N 1⁻¹ sediment per day, while that of denitrification is 85 mg N 1–1 sediment per day at 20 °C. The Arrhenius activation energy is estimated as 15 000 cal/ mole-K and 17 000 cal/ mole-K for nitrification and denitrification, respectively, between 10 °C and 20 °C. Calculations of the flux of ammonia with the sediments, using the biofilm model, compare favourably with experimental observations. The ammonia flux from the water column is estimated to account for 20% of the observed decrease in water column stocks of ammonia, while the nitrate flux from the water column is estimated to account for 25% of the total nitrogen produced by the sediments.     

Development of an LC‐MS method for simultaneous quantitation of amentoflavone and biapigenin,the minor and major biflavones from Hypericum perforatum L., in human plasma and its application to real blood

Introduction – Biflavones of Hypericum perforatum L. are bioactive compounds used in the treatment of inflammation and depression. Determination of amentoflavone and biapigenin from blood is challenging owing to their similar structures and low concentrations. Objective – To develop a rapid, sensitive and accurate method based on liquid‐phase extraction followed by high‐performance liquid chromatography and electrospray ionisation mass spectrometry (HPLC‐ESI‐MS) for quantification of biflavones in human plasma. Methodology – After extraction from blood, the analytes were subjected to HPLC with an XTerra® MS C₁₈ column and a binary mobile phase consisting of 2% formic acid in water and acetonitrile under isocratic elution conditions, with ESI‐MS detection in the negative ion mode and multiple reaction monitoring (MRM). Results – Both calibration curves showed good linearity within the concentration range 1–500 ng/mL. Limits of detection (S/N = 3) were 0.1 ng for pure substances and the limits of quantitation (S/N = 5) were 1.0 ng/mL from analyte‐spiked serum. The grand mean recovery was 90% from several subsamples of each biflavone. The imprecision (RSD) of peak areas was between 5% (intraday) and 10% (interday) for high concentrations (250 ng/mL) and between 10% (intraday) and 15% (interday) for low concentrations (1 ng/mL). Inaccuracy of the mean was less than 20% at the lower limit of quantitation. Conclusion – The developed and validated method for determination of biflavones from human plasma was effectively applied to pharmacokinetic studies of 13 probands and preliminary results indicate biphasic concentration–time curves. Copyright © 2010 John Wiley & Sons, Ltd.