Molecular iodine reduction by natural and model organic substances in seawater

The reactivity of 2 µM molecular iodine in seawater toward various organic compounds containing aromatic, -keto, amino, olefinic and sugar functional groups was investigated. More detailed studies have been made of the reduction kinetics with salicylic acid, -ketoglutaric acid and the polypeptide oxidized glutathione, particularly to establish whether variation over the pH range 4–9 would provide a similar reduction reactivity or fingerprint to that of molecular iodine added to natural seawater. The data indicates that compounds with only one functional group react with first order kinetics whereas compounds with multiple functional groups show more complex behaviour. Kinetic and thermodynamic modelling indicates that HOI is the main iodine species reacting with organic matter at seawater pH of 8.2. Based on the pH fingerprints, peptides and compounds containing carbonyl or -keto groups are the key reductants of molecular iodine added to seawater. These compounds form C-I and N-I bonds which can allow for a rich organic iodine chemistry in seawater. The model compound results are discussed in relation to oceanic processes.     

Manganese cycling in a eutrophic lake — Rates and pathways

The redox processes regulating transport of Mn in the water column of a eutrophic, dimictic lake (Lake Norrviken, Sweden) are interpreted based on a one-dimensional diffusion-reaction model for Mn(II). It is found that rates and rate constants for oxidation and reduction vary greatly with depth and also with time during the season of stratification. Calculated rates show that Mn(II) oxidation and reduction generally occur in narrow depth intervals (25–50 cm). This is in good agreement with measured profiles of particulate Mn (MnO _x ). Maximum oxidation rate constants (assuming first order kinetics) at each date are in the first half of the season <1 d^–1, but then increases to a rather constant value of about 25 d^–1. These high rate constants are indicative of microbiological involvement in the Mn(II) oxidation. This is further evidenced by SEM-EDS analysis showing Mn enriched particles morphologically similar toMetallogenium. Reductive dissolution of Mn oxides occurs mainly in the zone just below the zone of maximum oxidation rate. The release of Mn(II) is accompanied by production of alkalinity and CO₂. The relation between production rates of Mn(II) and alkalinity indicates that Mn oxides act as terminal electron acceptors in the bacterially mediated oxidation of organic matter. However, the Mn²⁺/CO₂ ratio is significantly lower than what is expected from this process. It is suggested that the Mn reduction is coupled to fermentation. Close coexistence of Mn reduction and oxidation at high rates, such as found in the water column of this lake, facilitates rapid and continuous regeneration of reducible Mn oxides. This gives rise to a quantitatively important mechanism of organic matter oxidation in the water column.     

Decomposition of Phytoplankton in Seawater. Part I: Kinetic Analysis of the Effect of Organic Matter Concentration

Decomposition experiments were conducted on cultured phytoplankton (Skeletonema costatum) in seawater containing decomposer and consumer of size less than 500 μm. We determined the decomposition rates of bulk particulate organic matter (POM), the ratio of labile to semi-refractory fractions in the POM, and the POM carbon/ nitrogen (C/N) ratio during decomposition. To identify the kinetic mechanisms involved in the reactions of different order (e.g., first- and second-order), we studied the sensitivity of reaction rates to the initial concentration of POM, ranging from 2.4 to 71 mg-C L⁻¹. The results showed that decomposition consists of two first-order reactions: decomposition of labile and of semi-refractory particulate organic carbon (POC). The decomposition rate constants found for labile (0.13 day⁻¹ at 20°C), and semi-refractory POC (0.008 day⁻¹ at 20°C), and the carbon weight ratio of semi-refractory POC (13% at 20°C), were insensitive to the initial organic matter concentration. The time-dependence of the C/N ratio was also independent of this initial concentration. The decomposition rate constants and the content of semi-refractory POC did not change, regardless of the absence or presence of 25–500 μm organisms in natural seawater. This revised version was published online in July 2006 with corrections to the Cover Date.     

Bacterial kinetics and environmental capacity in he Western Xiamen Harbour

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Estimation of kinetic Monod parameters for anaerobic degradation of benzene in groundwater

To date, evidence for the degradation of benzene under anaerobic conditions has been established only in few studies under field and laboratory conditions. Recently, we demonstrated the mineralization of benzene under sulfate-reducing conditions in a large-scale column experiment at a field site by balancing electrons (Vogt et al. in Biodegradation, 2007, in press). Here, from a modelling approach, kinetic Monod parameters are estimated for the degradation of benzene in the columns, Monod kinetics proved useful to simulate benzene concentrations at the column outflow. The uncertainty of the obtained parameters is determined in a sensitivity analysis. A total mass of degraded benzene of 23 g or 80% of the total influx over a period of three months was calculated. The estimated maximum utilization rate was calculated to be around 70 times lower than from aerobic benzene degradation experiments.     

Seasonal characteristics of chlorophyll fluorescence kinetics of heteromorphic leaves in Populus Euphratica

Populus euphratica Oliver grown in desert areas have polymorphic leaves, which include lanceolate to serrate oval leaves.This paper measures the chlorophyll fluorescence-induction kinetics curves of two types of heteromorphic leaves(lanceolate and serrate oval) of P. euphratica over the growth season in the Ejina Desert area, China. This is in order to study the electron transport, as well as absoprtion, distribtution, and dissipation of light energy and their adaptation characteristics.The results indicate that(1) serrate oval leaves' photosystem II(PSII) initial light-energy-conversion efficiency(Fv/Fm),potential activity(Fv/F_0), and the light-energy-utilization parameter(PI) are higher than those of lanceolate leaves; the accumulated amount of Q_A-(V_j) and the relative speed of Q_A deoxidation(M_0) are lower than those of lanceolate leaves;(2)the reaction center density(RC/CS_0) and electron-transfer energy(ET_0/CS_0) in the unit cross-sectional area of serrate oval leaves are higher than those of lanceolate leaves; the energy consumed in unit cross-sectional area(DI_0/CS_0), and energyflow parameters(ABS/RC, ET_0/RC, TR_0/RC, and DI_0/RC) in the unit reaction center of serrate oval leaves are lower than those of lanceolate leaves;(3) the proportion of energy used for photochemical reaction and energy electron transport in serrate oval leaves(Φ_(P0), Ψ_0, and Φ_(E0)) are larger than those in lanceolate leaves, and the maximum quantum yield(Φ_(D0)) of nonphotochemical reaction is less than that of lanceolate leaves. Thus, serrate oval leaves of P. euphratica have a more efficient energy-distribution strategy and better adaptability to extreme environmental conditions than lanceolate leaves.     

过热蒸汽对熟制小龙虾优势腐败菌的杀菌动力学及其机理

【目的】研究过热蒸汽杀菌对熟制小龙虾优势腐败菌的杀菌效果。【方法】从腐败熟制小龙虾中分离腐败菌,根据16S rDNA基因序列信息鉴定其种属,研究过热蒸汽温度、流量和杀菌时间等的处理参数对小龙虾优势腐败菌的杀菌效果,并利用Weibull模型拟合其杀菌动力学过程。通过研究过热蒸汽处理对优势腐败菌菌悬液的电导率和紫外吸收的影响,以及通过扫描电子显微镜对菌体的微观结构进行观察,初步探讨其杀菌机理。【结果】熟制小龙虾优势腐败菌为短小芽孢杆菌(Bacillus pumilus)、解淀粉芽孢杆菌(Bacillus amyloliquefaciens)、蜡样芽孢杆菌(Bacillus cereus)和赖氨酸芽孢杆菌(Lysinibacillus macroides)。在过热蒸汽杀菌初期阶段,优势腐败菌的残活率迅速下降,随着杀菌时间延长,残活率下降速率变得缓慢,最后趋于稳定,说明过热蒸汽能完全杀灭小龙虾优势腐败菌。Weibull模型能较好拟合过热蒸汽对4种优势腐败菌的杀菌动力学,其R2≥0.935。Weibull模型得到的预测值与实测值接近程度较高。通过对模型的分析,提高过热蒸汽温度和增大流量,更容易到达灭活腐败菌的效果。过热蒸汽杀菌后,菌悬液的电导率值和吸光度迅速上升,之后趋于平缓;通过对微观结构的观察,发现杀菌后腐败菌的细胞膜完整性遭到严重破坏。【结论】过热蒸汽杀菌技术应用于小龙虾产品加工具有一定的可行性。     

荷载对钻孔应变测值影响的实验及力学解析

介绍了弦频钻孔应变仪和体积式应变仪二次地表荷载试验的结果。根据弹性力学的理论和方法,对钻孔地壳应变测量及荷载试验的力学模型、边界条件等予以简化,使得经典的集中力作用于半无限弹性体表面的布辛奈斯克(Boussinesq)解,可有条件地运用于钻孔应变测量中地表荷载变化问题的定量分析研究。所给出的实验方法、研究思路及计算方法等,对定量研究钻孔应变测量中的荷载干扰、研究岩石力学性质、制定台站钻孔应变观测技术标准及观测规范等具有一定意义。