Relative molar mass distributions of chromophoric colloidal organic matter in coastal seawater determined by Flow Field-Flow Fractionation with UV absorbance and fluorescence detection

A new method for the characterization of chromophoric colloidal organic matter in seawater has been applied to samples from the Baltic Sea, Kattegatt and Skagerrak seas. Size fractionation of the sample by Flow Field-Flow Fractionation and measurement of the fluorescent and UV absorbing properties of the individual size fractions result in a relative molar mass distribution (RMM) of the optical properties. The RMM distributions have been used to estimate number and weight average relative molar masses, and polydispersity indices. At least two sources of coloured organic matter were identified from the ratio of fluorescence to UV: the Baltic surface water and the Skagerrak deep water. The dominating processes were mixing and dilution, but processes such as photo bleaching of fluorescence are also believed to be important. The RMM distribution derived from UV detection (1150–1300 Dalton) increased with increasing salinity while that derived for fluorescence (1500–1250 Dalton) decreased with increasing salinity. The specific UV absorbance taken as a proxy of the aromaticity of the chromophoric organic material showed decreasing trend with both increasing salinity and increasing UV derived weight average relative molar mass. Increasing polydispersity of the colloidal material was also observed as a function of salinity.     

胶州湾海水中悬浮颗粒对溶解态微量元素的影响

运用离子色谱离线螯合结合ICP-MS的方法,对胶州湾海水中的微量元素(V,Co,Ni,Cu,Mo,Cd,Pb,U,REEs)进行了精确的定量分析。在测试前对在同一站位不同层位采集的平行海水样品进行了两种不同的酸化处理:一份采取先过滤后酸化的方式,以获得海水中溶解态微量元素的含量;另一份采取直接酸化后分析的方式,以评估悬浮颗粒中的可交换态微量元素对溶解态微量元素测定结果可能造成的影响。通过对比研究发现,不同处理方法得到的V、Ni、Cu、Co、Pb以及稀土元素(REEs)的质量浓度存在很大差异,说明悬浮颗粒物质可能对海水中相应元素的测定产生较大的影响。各种微量元素之间的差异和相应离子或离子团的电荷性质、在海水中的配位作用以及悬浮颗粒物质的表面电荷性质有关。初步研究结果表明,在类似于胶州湾这样的近海海域,悬浮颗粒物质是控制微量元素分布特征的一个重要因素。     

Water, organic matter, nitrogen and phosphorus contents in sediment of a large-scale mariculture area in the Zhelin Bay of eastern Guangdong Province, China

The Zhelin Bay is one of the most important bays for large-scale mariculture in Guangdong Province, China. Owing to the increasing human population and the expanding mariculture in the last two decades, the ecological environment has greatly changed with frequent harmful algal blooms. A monthly survey of water content, organic matter （TOM）, and various forms of nitrogen and phosphorous in sediment from July 2002 to July 2003 in the bay was conducted. The results showed that the water content was correlated significantly with TOM and various forms of nitrogen and phosphorus and can be used as proxy for quick and rough estimate of these factors in the future surveys. TOM was also correlated significantly with various forms of nitrogen and phosphorus, indicating that it was one of the key factors affecting the concentrations and distributions of nitrogen and phosphorus in the investigated waters. Average total Kjeldhal nitrogen （TkN） content was（ 1 113.1 ± 382.5）μg/g and average total phosphorus （TP） content was（567.2± 223.3）μg/g, and both were much higher than those of similar estuaries in China and elsewhere. Average nitrogen and phosphorus tended to be higher inside than outside the bay, higher at aquaculture than non-aquaculture areas, and higher at fish-cage culture than oyster culture areas, suggesting that large-scale mariculture inside the bay played an important role in the eutrophication of the Zhelin Bay. Various forms of nitrogen and phosphorus concentrations were higher during the warm season （July--September）, which was due to the increased decomposition and concentration of organic matter resulted from the fast growth and high mortality of the cultured species. Compared with July 2002, TkN and TP contents were much higher in July 2003, in consonance with the eutrophication of the Zhelin Bay. Because exchangeable phosphorus （Ex-P）, iron-bounded phos- phorus （Fe-P） and organic phosphorus （OP） combined accounted for 34.3% of the TP and authigenic phosphorus （Au-P     

The fate of terrestrial organic matter in two Scottish sea lochs

Sea lochs are zones of rapid organic matter (OM) turnover. Most of this OM is of allochthonous origin, being introduced into the lochs via freshwater input. In this study the behaviour of terrestrially derived OM was elucidated using a combination of parameters which indicate OM diagenesis in the near surface sediments from two Scottish sea lochs, Loch Creran and Loch Etive. Alkaline CuO oxidation was used to determine lignin phenols which serve as biomarkers for terrestrial OM in sediments. Stable carbon isotope, total carbon and nitrogen and total OM (including the labile and refractory fractions) compositions were also determined.     

Semidiurnal Dynamics of Salinity, Nutrients and Suspended Particulate Matter in an Estuary in the Seto Inland Sea, Japan, during a Spring Tide Cycle

The physical and chemical variability of the water column at subtidal station of an estuary in the Seto Inland Sea, Japan, was studied over a 24-hour period during a spring tide (tidal range ca. 2 m) in May 1995. Surface water and several depths through the water column were monitored every one and two hours, respectively. At each occasion, water temperature, salinity and dissolved oxygen concentration were measured and water samples were collected for the determination of nutrients and suspended particulate matter (SPM). Disruptive changes in the physical and chemical characteristics of the water was produced by the tidal cycle and the mixing of water masses of different origin. These changes were highly significant both spatially and temporally, yet with varying effects on physical parameters, nutrients and the different components of SPM. Significant differences in nutrient concentrations were also observed when the data-set was divided into ebb and flood components, irrespective of the depth. Nitrate and nitrite rose to 1.8 times higher during the flood. Spatial differences of SPM were less marked than those of nutrients, only particulate organic carbon (POC) being significantly higher at the surface than in the intermediate and the lower layer. Both POC and pheopigment concentrations increased markedly through the water column, being highest shortly before the lower low tide. In contrast, suspended solid (SS) content increased sharply after the lower low tide (>40 mg l⁻¹) and this coincided with a marked decrease of the C/SS content (<20 mg g⁻¹). The lagtime between POC and SS tidal transport was caused by particle resuspension from the exposed intertidal sediments as the tidal level rose, and particle transport selection in relation to the tidal state. This revised version was published online in August 2006 with corrections to the Cover Date.     

Geochemical cycling in the Hooghly estuary, India

U–Th decay series isotopes, δ¹⁸O and Si measurements in the river estuarine waters and sediments of the polluted Hooghly estuary as well as the surface waters of the Bay of Bengal, its high salinity end member, are reported. Dissolved Si indicates that there are probably two mixing regimes, dissolved U behaviour is nonconservative and δ¹⁸O behaves conservatively in the overall estuarine region. Isotopes of reactive elements, viz. ²³⁴Th and ²¹⁰Po, are removed from the estuarine waters in <2 days and <1 month, respectively, which is due to high suspended matter (30–301 mg l⁻¹). ²²⁸Ra and ²²⁶Ra are profusely released into the estuarine waters in the low to mid-salinity regions.As expected, the opposite trend is observed in the case of estuarine sediments and suspended matter. Reactive isotopes of Th, ²¹⁰Pb and ²¹⁰Po are enriched, whereas Ra isotopes are depleted with respect to their parent nuclides in the estuarine sediments and suspended matter. ²³²Th/Al ratio appears well suited to study the distribution and mixing of the bed load sediments of the Ganga–Brahmaputra (G–B) and the Hooghly rivers with those from other rivers on the Bay of Bengal floor.     

Food web structure within kelp holdfasts (Laminaria): a stable isotope study

Kelp holdfasts are highly reticulated structures which host a large diversity of small fauna. These microhabitats have been reported to play a crucial role in the biodiversity associated to kelp forest ecosystems. This study aimed at identifying trophic links and the main food sources sustaining food webs within communities associated with kelp holdfasts, through a stable isotope (δ¹³C and δ¹⁵N) approach. Sampling of the main invertebrates inhabiting Laminaria digitata holdfasts, and of their potential food sources, took place in February and May 2007. Stable isotope results reveal that most of the primary consumers, including filter-feeders and deposit-feeders, rely on the particulate organic matter sedimented within kelp holdfasts. Only three grazers departed from this general pattern. The correspondence between the stable isotope ratios of predators and sediment consumers indicated that this source is at the base of the main pathway through which energy and matter transit in the food web. δ¹⁵N ranges found for consumers revealed that the food web associated with kelp holdfasts is composed of 3.5 levels. In spite of the low diversity of food sources at the base of the food web, these microhabitats can therefore be considered micro-scale ecosystems, from a functional perspective.     

水下荧光光谱探测装置控制系统的设计与实现

海水中有色可溶性有机物(CDOM,Chromophoric Dissolved Organic Matter,常称之为黄色物质)是影响海洋水色的三大成分之一,海水中CDOM的研究具有重要的意义。本文针对CDOM水下原位探测激光诱导荧光光谱探测装置开发了一套控制系统,该控制系统分为水上甲板控制和水下数据采集两部分,水上甲板控制部分通过8芯电缆与水下数据采集部分实现供电及通信,水下数据采集部分以PC104嵌入式工控机为核心,控制整体采集部分的工作,甲板控制部分通过远程控制软件来操控PC104以实现水下数据的采集和存储。实验室环境测试及近海现场实验表明,该系统能够可靠完成水下荧光光谱装置的控制和数据的采集及通信需求,实现海水中有色可溶性有机物的水下原位探测。     

赤道太平洋上层水体颗粒态生物硅分布及与营养盐的关系

依托中国“大洋一号”第20和第21调查航次,分析测定了东、西赤道太平洋4个站位的颗粒态生物硅浓度及其粒级结构。结果显示赤道太平洋采样站各层位颗粒态生物硅(PBSi)总浓度分布范围为5~65 nmol/dm³,东赤道太平洋的调查站位颗粒态生物硅的总浓度平均值达46 nmol/dm³,是西赤道太平洋的近3倍。PBSi的粒径结果显示在东赤道太平洋调查站位0.8~20 μm粒径颗粒是PBSi的主要来源,其平均贡献率高达64%;而在西赤道太平洋2种粒径的生物硅贡献率相当。营养盐分布对PBSi的浓度及粒径分布有显著的影响,并在一定程度上控制了“硅质泵”的组成结构,是控制大洋生物泵运转的重要因素。     

Kinetic and equilibrium studies of copper-dissolved organic matter complexation in water column of the stratified Krka River estuary (Croatia)

An interaction of dissolved natural organic matter (DNOM) with copper ions in the water column of the stratified Krka River estuary (Croatia) was studied. The experimental methodology was based on the differential pulse anodic stripping voltammetric (DPASV) determination of labile copper species by titrating the sample using increments of copper additions uniformly distributed on the logarithmic scale. A classical at-equilibrium approach (determination of copper complexing capacity, CuCC) and a kinetic approach (tracing of equilibrium reconstitution) of copper complexation were considered and compared. A model of discrete distribution of organic ligands forming inert copper complexes was applied. For both approaches, a home-written fitting program was used for the determination of apparent stability constants (K_i^equ), total ligands concentration (L_iT) and association/dissociation rate constants (k_i¹,k_i^- 1).A non-conservative behaviour of dissolved organic matter (DOC) and total copper concentration in a water column was registered. An enhanced biological activity at the freshwater–seawater interface (FSI) triggered an increase of total copper concentration and total ligand concentration in this water layer. The copper complexation in fresh water of Krka River was characterised by one type of binding ligands, while in most of the estuarine and marine samples two classes of ligands were identified. The distribution of apparent stability constants (log K₁^equ: 11.2–13.0, log K₂^equ:8.8–10.0) showed increasing trend towards higher salinities, indicating stronger copper complexation by autochthonous seawater organic matter.Copper complexation parameters (ligand concentrations and apparent stability constants) obtained by at-equilibrium model are in very good accordance with those of kinetic model. Calculated association rate constants (k₁¹:6.1–20 × 10³ (M s)^− 1, k₂¹: 1.3–6.3 × 10³ (M s)^− 1) indicate that copper complexation by DNOM takes place relatively slowly. The time needed to achieve a new pseudo-equilibrium induced by an increase of copper concentration (which is common for Krka River estuary during summer period due to the nautical traffic), is estimated to be from 2 to 4 h.It is found that in such oligotrophic environment (dissolved organic carbon content under 83 µM_C, i.e. 1 mg_CL^− 1) an increase of the total copper concentration above 12 nM could enhance a free copper concentration exceeding the level considered as potentially toxic for microorganisms (10 pM).