海水中腐殖质对溶解态铁的络合及其影响因素

腐殖质(humic substances,简称HS)是地表普遍存在的天然有机物,对海洋中重要的微量营养元素-铁(Fe)的分布及生物地球化学循环具有重要的影响作用。本文对腐殖质的来源、分布及对海水中溶解态铁的迁移转化的影响做了总结,特别论述了其在河口及沿岸水域的行为。大量研究表明河口、沿岸及开放海水中溶解态铁分布的变化可以用腐殖质的浓度及其铁结合能力的变化来解释。腐殖质的络合作用不仅能够阻止溶解态铁(DFe)在河口、沿岸等水域被去除,而且能够通过洋流将DFe迁移至外海及大洋区域,此外还能增加铁的溶解度及对海水中浮游植物的生物可利用性,并且促进铁的氧化还原循环。研究还发现两者之间的络合强度受到盐度、pH等理化因素的影响。盐度是影响HS与DFe配合能力的重要影响因素,盐度增加,导致HS中可以与Fe配合的位点数量降低,配合总量呈现指数降低,而pH的增加可以增加HS与DFe的配合量。另外HS还能影响海水中DFe的氧化还原,并以此影响浮游植物对DFe的吸收利用。因此腐殖质对溶解态铁的有机络合作用是影响其海洋生物地球化学循环的一个重要参数,对进一步研究海水中腐殖质的浓度和分布具有重要的意义。     

海水中不同价态铬的测定

本文研究了用Aliguat-336萃取,无焰原子吸收分光光度法测定海水中不同价态铬的方法。该方法有较好的精密度,变动系数为6.0%。回收率在80%左右,其特征量为6.3×10~(14)g,较好地应用于海水中不同价态铬的测定。     

光谱法测定海水中溶解态无机氮的研究进展

溶解态无机氮(dissolved inorganic nitrogen,DIN)主要由亚硝酸盐-氮(NO^-₂-N)、硝酸盐-氮(NO^-₃-N)和铵氮(NH⁺₄-N)组成,它们在海洋的生物地球化学循环过程中起重要作用。但人类活动向海洋输入了大量无机氮,导致一系列环境问题。为了更好地开展海洋氮循环研究和环境污染管理,需对海水中的DIN进行测定。在众多分析方法中,光谱法因其通用性好、适用范围广、所需设备简单,成为测定海水DIN的首选。本文总结了近10年来基于光谱法测定海水DIN的研究进展,包括紫外分光光度法测定NO^-₃-N、萘乙二胺分光光度法测定NO^-₂-N和NO^-₃-N、次溴酸盐氧化-分光光度法测定NH⁺₄-N、靛酚蓝分光光度法测定NH⁺₄-N...     

利用分光光度法间接测定海水中的羟胺

海洋生态系统中,羟胺作为多种微生物作用的中间产物,在氮的海洋生物地球化学循环中起着重要作用。目前,缺乏针对海洋中微量羟胺简便易行的测定方法。本研究借鉴海水中铁离子测定原理,首次应用硫酸铁铵-邻菲罗啉法间接测定海水中微量羟胺浓度,确定出该方法可在30—120min内稳定、快速地测定微量羟胺。通过对方法不确定度的系统评价得出,此方法灵敏度高、响应快、稳定性和重复性好,操作简便,适于羟胺检测浓度范围为0.020—0.800mg/L(R2=0.9996,P0.0001,n=32);天然海水中平均加标回收率达到106.9%(RSD=1.71%)。检测室内处于培养指数增长期的东海原甲藻(Prorocentrum donghaiense)藻液发现,羟胺主要被合成于藻细胞内部,其胞外含量低至检测下限附近。     

海水中钼的催化光度——流动注射分析法

近年来许多作者研究了直接测定海水及天然水中钼的方法,其中催化动力学法灵敏度高,适合于海水中痕量钼的测定Fuge(1970)和方肇伦(1983)等发展了钼的催化光度法并用于天然水中钼的分析。本文选用M_o-H_2O_2-KI-演粉催化体系,以因子设计和单纯形化法研究了测定海水中痕量钼的各种条件,本法检出限可满足     

夏季长江口海域溶解态铁的分布及混合行为研究

本文基于2015年7月长江口的现场调查资料,分析讨论了长江河口区溶解态铁(DFe)的含量分布与混合行为及其影响因素。结果表明:长江径流携带大量的DFe入海,且口内区(Ⅰ)浓度高于混合区(Ⅱ)和外海区(Ⅲ),平均浓度分别为166.45±6.26nmol/L,14.04±8.80nmol/L和6.18±1.51nmol/L。受去除作用和海水稀释的影响,在河口区DFe的浓度下降率达到96.92%。DFe浓度与盐度的关系符合指数模型,由模型与理论稀释线估算的长江口海域DFe的理论最大去除率为97.75%,与实际测得的最大浓度下降率相近。长江冲淡水、苏北沿岸流和台湾暖流影响DFe的水平分布。受长江冲淡水影响,长江口外海域DFe浓度高达176.50nmol/L。苏北沿岸流主要影响研究区域北部的表层水,其携带的DFe浓度低于长江冲淡水。台湾暖流是导致研究区域东南部DFe浓度较低的主要原因,使得中层和底层水中浓度分别低至4.04nmol/L和4.79nmol/L。另外,在表层海水中DFe的分布受到叶绿素a、溶解有机碳和溶解氧的共同影响,DFe与叶绿素a、溶解氧呈显著负相关,与溶解有机碳呈显著正相关。     

海洋沉积物中总硅的分光光度法测定

本文采用聚四氟乙烯高压罐消化海洋沉积物。这种密闭的消化体系避免了硅的挥发损失和玷污,能达到对高含量硅沉积物的完全消化,并且消除了氢氟酸的干扰;采用分光光度法测定总硅,简化了操作步骤,加快了测定速度。本法的精密度为0.8％,回收率为99—lOl％,测定水系沉积物标准样品的结果与推荐值的相对偏差小于O.5％。本法已应用于台湾海峡沉积物总硅的测定,获得满意的结果。     

大洋溶解铁的物质来源及其同位素示踪

铁（Fe）作为海洋初级生产所必需的微量和限制性营养元素影响着海洋生物群落结构、生态功能以及碳循环,理解溶解Fe的物质来源及其对气候变化的响应具有重要的科学意义。早期研究多强调风尘输入是维持大洋Fe循环的主要机制。近年来,随着海水Fe分析数据的积累,尤其是痕量元素及其同位素海洋生物地球化学循环研究计划（GEOTRACES）的开展,陆架沉积物和热液活动所释放Fe的贡献开始越来越受到重视。尽管如此,不同物源对开阔大洋溶解Fe的影响依然存在相当的不确定性。以海水溶解Fe的化学组分为出发点,强调有机配体对大洋Fe循环的决定性作用,综述了不同来源Fe的通量估计和第四纪大洋Fe来源的研究争议。铁同位素为理解大洋Fe的物源演变提供了新的工具。讨论了不同物源的Fe同位素特征,并提出结合沉积物的活动性Fe同位素和组分研究可能为理解过去陆架-热液活动-风尘输出与输运Fe的机制提供全新视角。     

海水COD流动注射测量技术研究

利用流动注射分析技术(FIA)快速、连续测定海水化学耗氧量(COD)。高锰酸钾作为氧化剂,NaOH溶液和硫酸溶液作为载流分别进入流路,“葡萄糖 谷氨酸”作为标准物质。采用人工海水与标准物质配制系列COD浓度的测量水样以及海水加标测量,得到的分析结果具有很好的重现性和分辨率。     

胶束增溶增敏分光光度法直接测定海水中的硼

首次以含量为１５ ％ 的非离子型乳化剂ＯＰ１００ 胶束体系为介质进行硼的分光光度法测定研究,确定最佳实验条件（ 最大吸收波长为５５５ｎｍ ,姜黄素用量为４ｍＬ,酸试剂用量为５ｍＬ,胶束用量为５ｍＬ,显色温度为５０ ℃,显色时间为１５ｍｉｎ） ,改进了现有的姜黄法,此方法适用于海水中硼的水相直接分光光度测定。实验结果表明测定灵敏度显著增加（Ｅ＝ １ ．５ ×１０５） ,线性范围变宽（０ ～１．２μｇ／２５ｍＬ） ,络合物稳定性好,稳定时间长达５０ｈ。     

Impact of environmental factors on in situ determination of iron in seawater by flow injection analysis

A sensitive method for iron determination in seawater has been adapted on a submersible chemical analyser for in situ measurements. The technique is based on flow injection analysis (FIA) coupled with spectrophotometric detection. When direct injection of seawater was used, the detection limit was 1.6 nM, and the precision 7%, for a triplicate injection of a 4 nM standard. At low iron concentrations, on line preconcentration using a column filled with 8-hydroxyquinoline (8HQ) resin was used. The detection limit was 0.15 nM (time of preconcentration = 240 s), and the precision 6%, for a triplicate determination of a 1 nM standard, allowing the determination of Fe in most of the oceanic regimes, except the most depleted surface waters. The effect of temperature, pressure, salinity, copper, manganese, and iron speciation on the response of the analyser was investigated. The slope of the calibration curves followed a linear relation as a function of pressure (C_p = 2.8 × 10^{− 5}P + 3.4 × 10^{− 2} s nmol^{− 1}, R² = 0.997, for Θ = 13 °C) and an exponential relation as a function of temperature (C_Θ = 0.009e^0.103Θ, R² = 0.832, for P = 3 bar). No statistical difference at 95% confidence level was observed for samples of different salinities (S = 0, 20, 35). Only very high concentration of copper (1000 × [Fe]) produced a detectable interference. The chemical analyser was deployed in the coastal environment of the Bay of Brest to investigate the effect of iron speciation on the response of the analyser. Direct injection was used and seawater samples were acidified on line for 80 s. Dissolved iron (DFe, filtered seawater (0.4 μm), acidified and stored at pH 1.8) corresponded to 29 ± 4% of Fe_a (unfiltered seawater, acidified in line at pH 1.8 for 80 s). Most of Fe_a (71 ± 4%) was probably a fraction of total dissolvable iron (TDFe, unfiltered seawater, acidified and stored at pH 1.8).     

Transformation dynamics and reactivity of dissolved and colloidal iron in coastal waters

We have investigated the chemical forms, reactivities and transformation kinetics of Fe(III) species present in coastal water with ion exchange and filtration methods. To simulate coastal water system, a mixture of ferric iron and fulvic acid was added to filtered seawater and incubated for a minute to a week. At each incubation time, the seawater sample was acidified with hydrochloric acid and then applied to anion exchange resin (AER) to separate negatively charged species (such as fulvic acid, its complexes with iron and iron oxyhydroxide coated with fulvic acid) from positively charged inorganic ferric iron (Fe(III)′). By monitoring the acid-induced Fe(III)′ over an hour, it was found that iron complexed by fulvic acid dissociated rapidly to a large extent (86–92% at pH 2), whereas amorphous ferric oxyhydroxide particles associated with fulvic acid (AFO-L) dissociated very slowly with the first-order dissociation rate constants ranging from 6.1 × 10^− 5 for pH 3 to 2.7 × 10^− 4 s^− 1 for pH 2. Therefore, a brief acidification followed by the AER treatment (acidification/AER method) was likely to be able to determine fulvic acid complexes and thus differentiate the complexes from the AFO-L particles (the dissolution of AFO-L was insignificant during the brief acidification). The acidification/AER method coupled with a simple filtration technique suggested that the iron–fulvic acid complexes exist in both the < 0.02 μm and 0.02–0.45 μm size fractions in our coastal water system. The truly dissolved iron (< 0.02 μm) was relatively long-lived with a life-time of 14 days, probably due to the complexation by strong ligands. Such an acid-labile iron may be an important source of bioavailable iron in coastal environments, as a significant relationship between the chemical lability and bioavailability of iron has been well recognised.     

Application of an automated method for dissolved sulphate analysis to marine and brackish waters

A fully automated method for the analysis of dissolved sulphate was tested for saline and brackish waters. A small sample volume of ? 2 ml is required, making the method very suitable for analysis of interstitial waters. The method was calibrated for samples from natural waters in the Dutch delta region, containing up to 2500 mg l^?1 of sulphate, and with a salinity of 30‰.     

Enhanced concentrations of dissolved gaseous mercury in the surface waters of the Arctic Ocean

During an almost three months long expedition in the Arctic Ocean, the Beringia 2005, dissolved gaseous mercury (DGM) was measured continuously in the surface water. The DGM concentration was measured using an equilibrium system, i.e. the DGM in the water phase equilibrated with a stream of gas and the gas was thereafter analysed with respect to its mercury content. The DGM concentrations were calculated using the following equation, DGM = Hg_eq / k_H' where Hg_eq is the equilibrated concentration of elemental mercury in the gas phase and k_H' is the dimensionless Henry's law constant at desired temperature and salinity. During the expedition several features were observed. For example, enhanced DGM concentration was measured underneath the ice which may indicate that the sea ice acted as a barrier for evasion of mercury from the Arctic Ocean to the atmosphere. Furthermore, elevated DGM concentrations were observed in water that might have originated from river discharge. The gas-exchange of mercury between the ocean and the atmosphere was calculated in the open water and both deposition and evasion were observed. The measurements showed significantly enhanced DGM concentrations, compared to more southern latitudes.     

The inventory and chemical characterization of dissolved proteins in oceanic waters

One-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and high resolution two-dimensional electrophoresis (2-DE) were applied to separate protein molecules in dissolved organic matter (DOM) from oceanic waters. Results were: (1) The 2-DE distinguished a total of 412 protein spots in 10 samples from five water columns over the Pacific, although fewer than 30 proteins were resolved as bands from the identical samples by SDS-PAGE. (2) Major and ubiquitous protein bands (34 and 39 kDa proteins) on the SDS-PAGE gel were resolved into horizontally spread arrays (trains) of spots on the 2-DE gels, indicating that these bands were a mixture of protein species that have the same molecular weight (MW) but different isoelectric points (pIs). (3) Proteins that exhibited such electrophoretic patterns on the 2-DE gels were glycosylated with variable linkages between the sugar and polypeptide chains. (4) N-terminal amino-acid sequencing demonstrated that individual spots within each train of spots had identical N-terminal amino-acid sequences.The N-terminal amino-acid sequences of the 39 and 34 kDa glycoprotein spots in samples collected at different sites were also identical. Protein isoforms with the same amino-acid sequence but different glycosylation profiles, termed glycoforms, were often observed on the 2-DE gel. Thirty-one and 24 spots on the 2-DE gels were glycoforms of two glycoproteins with MWs of 39 and 34 kDa, respectively; they were one protein species. The glycoforms of the 39 kDa protein were identified as a low molecular weight alkaline phosphatase (L-AP) of Pseudomonas aeruginosa PAO1 by a homology search through five amino-acid sequence databases. The present and earlier work indicates that all identified source organisms of dissolved proteins belong to the Pseudomonas group. We propose the hypothesis that proteins associated with membrane vesicles liberated from a minor member of the bacterioplankton assemblage, the marine Pseudomonas group, are one of the important sources of dissolved proteins in oceanic waters. This hypothesis may apply to the source pathway and survival not only of proteins and also to the universally occurring bacterial peptidoglycan and lipopolysaccharide components in DOM.     

Complexation of mercury by dissolved organic matter in surface waters of Galveston Bay, Texas

The chemical speciation of dissolved mercury in surface waters of Galveston Bay was determined using the concentrations of mercury-complexing ligands and conditional stability constants of mercury-ligand complexes. Two classes of natural ligands associated with dissolved organic matter were determined by a competitive ligand exchange-solvent solvent extraction (CLE-SSE) method: a strong class (L_s), ranging from 19 to 93 pM with an average conditional stability constant (K_HgLs) of 10²⁸, and a weak class (L_w) ranging from 1.4 to 9.8 nM with an average K_HgLs of 10²³. The range of conditional stability constants between mercury and natural ligands suggested that sulfides and thiolates are important binding sites for dissolved mercury in estuarine waters. A positive correlation between the estuarine distribution of dissolved glutathione and that of mercury-complexing ligands supported this suggestion. Thermodynamic equilibrium modeling using stability constants for HgL, HgCl_x, Hg(OH)_x, and HgCl(OH) and concentrations of each ligand demonstrated that almost all of the dissolved mercury (> 99%) in Galveston Bay was complexed by natural ligands associated with dissolved organic matter. The importance of low concentrations of high-affinity ligands that may originate in the biological system (i.e., glutathione and phytochelatin) suggests that the greater portion of bulk dissolved organic matter may not be important for mercury complexation in estuarine surface waters.     

Effects of fixation and storage on flow cytometric analysis of marine bacteria

Flow cytometry (FCM) is now becoming a routine tool for the enumeration and optical characterization of bacteria in marine environments. We investigated the effects of sample fixation and storage upon flow cytometric determination of marine bacteria. Fixed and unfixed seawater samples were analyzed by FCM immediately aboard ship and/or later in the laboratory, and the appearances of the fluorescence signals and bacterial counts of these samples were compared. Fixation and storage led to the formation of multiple peaks in fluorescence histograms; this was also seen in 22 out of 36 samples frozen in liquid nitrogen. Fixation did not, but storage did induce a decrease of bacterial counts: a rapid decrease during the first 3 days followed by a slower decline. The decline of cell numbers in stored samples was expressed by a regression model. Our studies indicate that precaution is necessary when interpreting the data from fixed and/or stored marine bacterial samples analyzed by FCM. The possibility that the procedure of fixation and storage leads to the appearance of high DNA and low DNA bacterial groups should be considered.     

A comparison of iron limitation of phytoplankton in natural oceanic waters and laboratory media conditioned with EDTA

The solubility of iron in oxic waters is so low that iron can be a limiting nutrient for phytoplankton growth in the open ocean. In order to mimic low iron concentrations in algal cultures, Ethylenediaminetetraacetate (EDTA) is commonly used. The presence of EDTA enables culture experiments to be performed at a low free metal concentration, while the total metal concentrations are high. Using EDTA provides for a more reproducible medium. In this study Fe speciation, as defined by EDTA in culture media, is compared with complexation by natural organic complexes in ocean water where Fe is thought to be limited. To grow oceanic species into iron limitation, a concentration of at least 10⁻⁴ M EDTA is necessary. Only then does the calculated [Fe³⁺] concentrations resemble those found in natural sea water, where the speciation is governed by natural dissolved organic ligands at nanomolar concentrations. Moreover, EDTA influences the redox speciation of iron, and thus frustrates research on the preferred source of Fe-uptake, Fe(III) or Fe(II), by algae. Nowadays, one can measure the extent of natural organic complexation in sea water, as well as the dissolved Fe(II) state, and can use ultra clean techniques in order to prevent contamination. Therefore, it is advisable to work with more natural conditions and not use EDTA to create iron limitation. This is especially important when the biological availability of the different chemical fractions of iron are the subject of research. Typically, many oceanic algae in the smallest size classes can still grow at very low ambient Fe and are not easily cultivated into limitation under ambient sea water conditions. However, the important class of large oceanic algae responsible for the major blooms and the large scale cycling of carbon, silicon and other elements, commonly has a high Fe requirement and can be grown into Fe limitation in ambient seawater.