Importance of organic Fe complexing ligands in the Mississippi River plume

As part of a larger program focused on understanding the biogeochemistry of large river plumes, we participated in two expeditions during 2000 to sample the Mississippi River plume. Surface water samples were collected using a trace metal clean towed fish and analyzed for total dissolved Fe, organic Fe complexing ligands and their associated conditional stability constants. The ligands in the river plume have conditional stability constants (log K′_FeL between 10.5 and 12.3 with an average of 11.2 and standard deviation of 0.6) very similar to ligands found in the open ocean. Comparison of high flow and low flow regimes indicates that variability in flow may be the main cause of the variability in Fe concentrations in the plume. The organic Fe complexing ligands are in greatest excess during a time of higher flow. These ligands are responsible for maintaining very high (5 nM) Fe concentrations throughout the plume. Due to complexation with these organic ligands, the concentration of Fe remains above the Fe-hydroxide solubility level until a salinity above 35 is reached where there appears to be a sink for Fe in the less productive waters. Therefore, Fe is transported a great distance from the river source and is available for biological utilization in the coastal zone.     

Marine diatom Thalassirosira weissflogii nutrient drawdown and its physiological status variation challenged to zinc and cadmium exposure

The uptake of zinc and cadmium by a species of marine diatom Thalassirosira weissflogii and the nutrient variation (phosphorus and silicon) in the culture medium were estimated when exposed to zinc and cadmium stress under controlled laboratory conditions.It was found that low cadmium addition could stimulate the culture to grow with a relatively high rate and exert its toxicity at the elevated concentration.The cellular uptake of zinc and cadmium by the diatom varied in the ranges of 1.21~3.75 and 0.060~0.629 fmol per cell respectively in the whole cultivation period.The mean cellular phosphorus and silicon drawdowns were constant with 0.26~0.42 and 0.30~0.46 pmol per cell respectively in those healthy cultures.It is illustrated that the algal cells can adjust some physiological mechanisms to decrease metal accumulation and keep metal homeostasis in the organism.The correlation analysis results further indicate that the cellular cadmium uptake might be closely related with the cellular phosphorus, silicon drawdown and the growth rate of diatom (P<0.05, 0.001, 0.01); and the cultures grow better in good conditions, the lower amount of phosphorus, silicon materials are consumed by a single cell to keep a high efficiency of utilization.     

Ecological Differences in the Distribution of two Tethya (Porifera, Demospongiae) Species Coexisting in a Mediterranean Coastal Lagoon

Abstract. In the Sicilian lagoon Stagnone di Marsala, Tethya aurantium and T. citrina show different ecological distributions, although some overlapping occurs. The first species reaches its highest density where linear currents are maximal, and in this habitat it is particularly frequent on Posidonia oceanica rhizomes. The second species is more abundant in still water locations and is equally common on Posidonia rhizomes and on calcareous concretions. Such distributions can be related to water movement, Posidonia shoot density, and associated factors such as sedimentation and food availability. These observations are consistent with an adaptive interpretation of the morphofunctional features distinguishing the two species.     

海黍子吸附重金属镉离子的研究

采用廉价的多细胞褐藻海黍子对重金属镉离子进行吸附，研究海黍子不同的预处理方法、溶液的pH值、初始Cd^3 浓度、外加盐等因素对Cd^3 的吸附特性的影响。并对吸附机理进行了初步的探讨，发现镉离子与海黍子中的钙离子发生离子交换作用，交换率占总吸附量的38％～50％。适宜的pH范围为3～6，海黍子的最大吸附量高达181mg/g，得出了适宜的吸附等温线方程，并进行了简单的洗脱研究。     

内蒙古哈素海区域高砷地下水化学特征及其成因

哈素海区域高砷地下水对当地居民饮用水安全造成严重威胁, 揭示其形成演化机制对科学合理的开发利用水资源、保障居民身体健康具有重要意义。本文在水文地质调查的基础上, 应用Piper三线图、PHREEQC的砷形态计算及相关性分析等方法, 研究高砷地下水化学特征、构建砷形态模型(SM)和砷吸附模型(HSM), 以揭示高砷地下水的成因机制。结果表明, 研究区砷浓度为0.2~231.5 μg/L, 高砷区主要分布在大青山以南的冲湖积平原区; 地下水砷的类型以As(Ⅲ)为主, SM分析显示优势形态为H3AsO3, HSM分析显示存在Hfo_wH2AsO3和H3AsO3两种主要形态。地下水中的砷化物可能来源于山区富砷岩石的风化溶解以及第四系富砷河湖相沉积物; 研究区河湖相沉积环境是高砷水形成的前提, 有机质分解主导的还原环境是导致砷从含水介质释放到地下水中的主要因素, 弱碱性环境和HCO– 3的竞争吸附也会引起砷的释放。     

Quantification of Water Content and Speciation in Synthetic Rhyolitic Glasses: Optimising the Analytical Method of Confocal Raman Spectrometry

Quantification of water content in silicate glasses is of vital significance in understanding magma evolution and metamorphic anataxis. Here we provide a method for the determination of total dissolved water content and water speciation in silicate melts by confocal laser Raman spectrometry based on a set of hydrous rhyolitic glasses. A series of alumino-silicate glasses with water contents from 0.33 to 9.05% m/m were synthesised in a piston cylinder apparatus. Synchrotron-FTIR mapping shows that these glasses have relatively homogeneous distributions of dissolved water. Total water contents of the glasses were precisely measured by TC/EA-MS and FTIR. Both external and internal calibration were established for the quantitative analysis of water content and water speciation in the silicate glasses based on excellent linear correlation between total dissolved water content and integrated area of the water Raman band. Furthermore, by decomposing the total water Raman bands into four Gaussians components, the relative concentration of water speciation (OH groups and molecules H₂O_m) dissolved in the glasses was determined with a similar trend to water speciation data derived from FTIR. We suggest that the relative concentration of water speciation can be estimated in rhyolitic glasses with 4–8% m/m H₂O. Our work provides an accurate method to determine total water content and a potential tool to limit the relative concentration of water speciation dissolved in silicic glasses.     

Measurement of Mass-Independent Perturbations of Cadmium in Nuclear Debris Samples

The isotopic composition of cadmium in nuclear debris was measured by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). Mass-independent perturbations due to fission product decay on the isotopes of Cd were observed. Relative fission yields for masses 111, 112, 114 and 116 were determined in each sample of nuclear debris and compared with reported values found in irradiated plutonium and uranium fuels. Mass spectrometry measurements of the valley fission product endpoints are extremely challenging due to the low cumulative fission yields and small amounts of each isotope that are produced. To overcome these challenges, a new purification method for Cd was developed and validated by examination of a number of geological reference materials.     

Geochemical speciation and spatial distributions of phosphorus in surface sediments from the basin of the Marcus-Wake seamounts in the western Pacific Ocean

The concentrations of five forms of phosphorus(P) including exchangeable or loosely adsorbed P(Ex-P), Febound P(Fe-P), authigenic P(Auth-P), detrital P(Det-P), and organic P(Org-P) from the basin among the Marcus-Wake seamounts(19.4°–24°N, 156.5°–161.5°E) in the western Pacific Ocean were quantified using a sequential extraction method(SEDEX) to investigate the distribution and sources of different P species.Concentrations of total P(TP) varied from 14.0 μmol/g to 44.1 μmol/g, with an average of...     

Speciation analysis of metals （Tl, Cd and Pb） in Tl-containing pyrite and its cinder from Yunfu Mine, China, by ICP-MS with sequential extraction

The speciation of heavy metals such as thallium, cadmium and lead existing in pyrite and pyrite cinder was analyzed by ICP-MS with a sequential extraction procedure. The distribution patterns of these metals including exchangeable, reducible, oxidizable and residual fractions were obtained. Tl, Cd and Pb in pyrite and pyrite cinder samples from each extraction step were determined by inductively coupled plasma mass spectrometry (ICP-MS). Under the optimized instrumental conditions, detection limits of Tl, Cd and Pb in different matrices were within the range of 0.006–0.07 μg/L, and the relative standard deviations ranged from 0.8% to 1.2%. The accuracy of Tl, Cd and Pb determination was checked by analyzing two certified reference materials. The results demonstrate that trace Tl, Cd and Pb in the samples can be accurately determined. The sequential extraction results revealed that the percent contents of Tl, Cd and Pb in exchangeable, reducible and oxidizable fractions in pyrite cinder are different from those in pyrite and in pyrite cinder. Tl, Cd and Pb mostly are distributed in residual fraction. Therefore, the mobility of metals in pyrite is higher than that in pyrite cinder. Although distributions of Tl, Cd and Pb in the non-residual fraction are not dominant in pyrite cinder, the total concentrations of them could not be ignored. Consequently, attention must be paid to the risk of potential pollution by pyrite cinder.     

Speciation of aluminum in the stream waters from the Susquehanna River watershed, Chesapeake Bay

 The aim of this paper was to analyze the processing and transport of aluminum speciation through the terrestrial and aquatic ecosystems of the Chesapeake Bay landscape. Stream waters were sampled in 14 different streams from the Susquehanna River watershed to the upper reach of Chesapeake Bay. The basic water quality data were documented and Al speciation was evaluated by modified MINEQL computer model. It was found that the increase in acidity in some of the stream waters near New York were closely linked with a marked decline in basic cation concentrations. In these areas, the sum of the toxic forms of Al³⁺ plus AlOH²⁺ and Al(OH)₂ ⁺ concentrations exceeds the critical level of 5 μmol l^–1. A potential threat from aluminum may occur. Received: 3 January 2000 · Accepted: 21 March 2000