The amino acid composition of estuarine colloidal material

Amino acids were determined in estuarine colloidal and particulate material from near surface waters ranging from fresh to brackish water (12 g kg^?1 salinity). The hydrolizable amino acids and associated ammonia account for an average of 80% of the nitrogen present in colloidal samples, and approximately 75% of the nitrogen from particulate fractions of the same samples. The relative proportions of these amino acids are similar to those of a cultured estuarine diatom. There are no significant amounts of D amino acids, or non-protein amino acids characteristic of bacteria in sediments and soil. A single deep-water sample (25 m) shows some evidence of bottom mud resuspension by the presence of a possible aspartic acid-hydroxyproline dimer.     

Trace metal composition of and accumulation rates of sediments in the Upper Gulf of Thailand

Sediment cores and grab samples were collected in the Upper Gulf of Thailand to determine sedimentation rates and to determine if metal concentrations reflect anthropogenic inputs.Accumulation rates of sediments in the Upper Gulf measured using the ²¹⁰Pb method, appear to vary from ca. 4 to 11 mm yr^?1. Sediment budgets suggest that little of the sediment delivered to the Upper Gulf by the major rivers is ultimately transported to the Lower Gulf. Metal concentrations in Upper Gulf sediments appear to be dominantly controlled by natural inputs.     

The relationship between chromophoric dissolved organic matter and dissolved organic carbon in the European Atlantic coastal area and in the West Mediterranean Sea (Gulf of Lions)

The absorption coefficient of chromophoric dissolved organic matter (aCDOM) has been found to be correlated with fluorescence emission (excitation at 355 nm). In the coastal European Atlantic area and in the Western Mediterranean Sea (Gulf of Lions), a significant statistical dependence has been found between aCDOM and fluorescence with dissolved organic carbon (DOC) concentration. The relationship shows that, in the river plume areas (Rhine in the North Sea and Rhône in the Gulf of Lions), a consistent fraction of DOC (from 40% to 60% of the average of the DOC measured) is non-absorbing in visible light range, where the dissolved organic matter (DOM) is typically absorbent. In comparison, in the open sea, apparently not affected by the continental inputs, the entire DOC belongs to the chromophoric DOM whose specific absorption is lower (5 to 10 times) than that found in the river plume areas.     

海洋有机质的光谱分析方法评述

海洋有机质的光谱分析已成为海洋碳循环的研究热点之一。本文从天然有机质吸收光谱和荧光光谱分析的基本原理入手,系统梳理了有机质光谱分析中容易被忽视的基本概念,讨论了过滤与保存方式、p H值、荧光内滤效应等对有机质光谱分析的影响。结合色氨酸、酪氨酸、腐殖酸及大量现场样品的实验结果,对吸收光谱和三维荧光光谱的不同解析方法进行了系统的分析与对比。基于在南海、西菲律宾海获取的现场调查数据,对于文献中常用的荧光指数(FI)、腐殖化指数(HIX)、自生源指数(BIX)等光谱参数的内在含义及其在海洋环境中的适用性进行了评述。此外,还归纳和总结了胶体有机质和颗粒有机质荧光分析的最新进展,并对今后在光谱分析与观测领域有待完善和突破的一些关键领域进行了展望。     

Abundance, size distribution, and stable carbon and nitrogen isotopic compositions of marine organic matter isolated by tangential-flow ultrafiltration

Tangential-flow ultrafiltration was used to isolate particulate and high-molecular-weight dissolved material from seawater collected at various depths and geographic regions of the Pacific and Atlantic Oceans. Ultrafiltration proved to be a relatively fast and efficient method for the isolation of hundreds of milligrams of material. Optical and electron microscopy of the isolated materials revealed that relatively fragile materials were recovered intact. Depth-weighted results of the size distribution of organic matter in seawater indicated that ˜ 75% of marine organic carbon was low-molecular-weight (LMW) dissolved organic carbon (< 1 nm), ˜ 24% was high-molecular-weight (HMW) dissolved organic carbon (1–100 nm), and ˜ 1% was particulate organic carbon (> 100 nm). The distribution of carbon in surface water was shifted to greater relative abundances of larger size fractions, suggesting a diagenetic sequence from macromolecular material to small refractory molecules. The average C:N ratios of particulate organic matter (POM) and HMW dissolved organic matter (DOM) were 7.7 and 16.7, respectively. Differences in C:N ratios between POM and HMW DOM were large and invariant with depth and geographic region, indicating that the aggregation of HMW DOM to form POM must be of minor significance to overall carbon dynamics. The stable carbon isotope composition (δ¹³C) of POM averaged −22.7%. in surface water and −25.2%. in subsurface water. Several possible explanations for the observed isotopic shift with depth were explored, but we were unable to discern the cause. The δ¹³C of HMW DOM samples was relatively constant and averaged −21.7%., indicating a predominantly marine origin for this material. The δ¹⁵N values of POM were highly variable (5.8–15.4%.), and the availability of nitrate in surface waters appeared to be the major factor influencing δ¹⁵N values in the equatorial Pacific. In the upwelling region nitrate concentrations were relatively high and δ¹⁵N values of POM were low, whereas to the north and south of the upwelling nitrate concentrations were low and δ¹⁵N values were high. The δ¹⁵N values of HMW DOM reflected the same trends observed in the POM fraction and provided the first such evidence for biological cycling of dissolved organic nitrogen (DON). Using the observed δ¹⁵N values and an estimate of meridional advection velocity, we estimated a turnover time of 0.3 to 0.5% day⁻¹ for HMW DON. These results suggest a major role for DON in the upper ocean nitrogen cycle.     

Water and organic carbon fluxes from an irregularly flooded brackish marsh on the upper Texas coast,U.S.A.

Water flows, concentrations of total (TOC), dissolved (DOC), and particulate (POC) organic carbon and seston were monitored for 52 diel periods in the single creek draining a 270-ha Spartina patens-Distichlis spicata marsh on the upper Texas coast. Rainfall, creek water flows, and water levels in the creek and on the marsh were measured by recording instruments.Rainfall accounted for most marsh flooding, and water outflow was significantly correlated with both rainfall and marsh water level. Creek flows were predominantly outward because microtopographic features and dense vegetation restricted overmarsh water flows and thereby reduced tidal flooding while extending the time of precipitation runoff. Concentrations of organic carbon in water leaving the marsh were highest in spring and summer and averaged 25·62, 21·41 and 3·35 mg l^?1 of TOC, DOC and POC, respectively. These were 9·34, 9·93 and 0·04 mg l^?1, respectively, higher than bay water. Most POC was 0·3–28 μm in diameter. Seston > 28μ leaving the marsh was 95% amorphous material; the rest was plankton, grass particles and fecal pellets. Loss of organic carbon was directly correlated with net water flux, and thus rainfall accounted for most carbon loss. Net carbon loss averaged 196 kg TOC, 150 kg DOC and 32 kg POC per day. Net annual loss was 2·4–5·5% of net aerial primary productivity (NAPP), or 21·55-30·09 g TOC m^?2 year^?1.Export from this marsh falls within the range found for other marshes and the data collectively indicate that coastal marshes are not losing as much organic carbon as has been suggested by indirect measurements. The discrepancy between potential and realized export is explained by the fact that export is not a simple removal of excess detritus by tidal action but is a more complicated process mediated by the interaction of additional factors such as rainfall, vegetation structure, microtopographic variation and decomposition, which can serve to reduce the amount and quality of NAPP exported.     

Behaviour of colloidal trace metals (Cu, Pb and Cd) in estuarine waters: An approach using frontal ultrafiltration (UF) and stripping chronopotentiometric methods (SCP)

The frontal cascade ultrafiltration (UF) technique in conjunction with stripping chronopotentiometry (SCP) has been evaluated for determining the colloidal distribution of Cu, Pb and Cd in estuarine waters. Metallic concentrations in seven size fractions (0.45 μm–0.22 μm; 0.22 μm–300 kDa; 300–50 kDa; 50–30 kDa; 30–10 kDa; 10–5 kDa; <5 kDa) were determined with the aim to investigate their changes along the salinity gradient of the Penzé system (NW France). These data, completed by analysis of the total dissolved metals at 10 stations over the whole freshwater–seawater mixing zone, provided some insights in the removal and addition processes that affect Cu, Pb and Cd in estuaries.     

Relationship between the optical properties of chromophoric dissolved organic matter and total concentration of dissolved organic carbon in the southern Baltic Sea region

Absorption and fluorescence of chromophoric dissolved organic matter (CDOM) and dissolved organic carbon (DOC) measurements were performed during three oceanographic surveys in 1994 in the southern Baltic Sea (Polish area of the Baltic Proper). DOC was measured both by high-temperature catalytic oxidation (HTCO) and low-temperature oxidation (LTO) conventional persulphate methods. CDOM fluorescence was shown to be highly correlated with absorption, with the same regression parameters, despite the seasonal change in different hydrographic conditions and the fluorescence quantum yield variations (1.23 ± 0.07 in April and 0.97 ± 0.12 in September). The results show a good correlation between the optical parameters and DOC although ˜ 70% of the DOC does not display significant absorption in the UV-visible range (350–750 nm). The non-absorbing DOC measured with HTCO method appears unaffected by seasonal changes. Consequently, total DOC can be predicted by optical methods using remote sensing techniques. The non-absorbing DOC measured by LTO method varies from 62% (April) to 76% (September), which implies that there is requirement for estimates on a seasonal basis.     

Tracing dissolved organic matter in aquatic environments using a new approach to fluorescence spectroscopy

Dissolved organic matter (DOM) is a complex and poorly understood mixture of organic polymers that plays an influential role in aquatic ecosystems. In this study we have successfully characterised the fluorescent fraction of DOM in the catchment of a Danish estuary using fluorescence excitation–emission spectroscopy and parallel factor analysis (PARAFAC). PARAFAC aids the characterisation of fluorescent DOM by decomposing the fluorescence matrices into different independent fluorescent components. The results reveal that at least five different fluorescent DOM fractions present (in significant amounts) in the catchment and that the relative composition is dependent on the source (e.g. agricultural runoff, forest soil, aquatic production). Four different allochthonous fluorescent groups and one autochthonous fluorescent group were identified. The ability to trace the different fractions of the DOM pool using this relatively cheap and fast technique represents a significant advance within the fields of aquatic ecology and chemistry, and will prove to be useful for catchment management.     

Molecular weight and chemical reactivity of dissolved trace metals (Cd,Cu, Ni) in surface waters from the Mississippi River to Gulf of Mexico

It is generally assumed that estuarine mixing is continuous for metals from terrestrial sources, gradually decreasing towards the open ocean endmember. Here we show that, chemical reactivity, determined by ion exchange method, and molecular weight distributions, obtained using cross-flow ultrafiltration, of dissolved Cd, Cu, and Ni in the surface waters of the Gulf of Mexico varied systematically across the estuarine mixing zone of the Mississippi River. Most size or chemical affinity fractions of dissolved metals (<0.4 μm) were linearly related to salinity (10.8–36.6), suggesting that the distribution of these elements was mainly controlled by continuous mixing processes. Dissolved concentrations across the salinity gradient ranged for Cd: 87–187 pM; Cu: 1.4–18.3 nM; and Ni: 2.6–18.8 nM, with highest values near the Mississippi river mouth, and lowest concentrations in a warm core ring in the Gulf of Mexico. Dissolved Cd was mostly present as a truly dissolved (<10 kDa, 97 ± 1%) and cationic fraction (Chelex-100 extractable, 94 ± 4%). A novel observation across the estuarine mixing zone was that colloidal metal concentrations were identical to either inert (for Cu, Ni) or AMPG-labile anionic (Cu, Cd) fractions. The difference in behavior between Cu and the other two metals might indicate differences in the biopolymeric nature of the metal–organic chelates. In particular, the anionic-organic Cd fractions accounted for just 3 ± 1%, on average. However, for Cu, it was 24 ± 4%, and for Ni, it was 9 ± 6%. The fractions of the total dissolved metal fractions that were “inert” averaged 31 ± 10% for Cu and 29 ± 12% for Ni. Small but noticeable amounts (6 ± 3%) of dissolved inert Cd fractions were also present. Apparent non-local transport processes, likely associated with cross-shelf sediment resuspension processes, could have been responsible for the relatively high concentrations of ‘inert’ and ‘anionic’ metal fractions in high salinity coastal waters, and accounting for the persistence of metals bound to humic substances in the Gulf of Mexico.     

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.     

Measurements of dissolved organic carbon (DOC) in sea water by high temperature combustion method

Dissolved organic carbon (DOC) is the largest organic carbon reservoir in sea water and plays an imporrant role in the marine carbon cycle and other biogeochemical processes in the ocean. Accurate and precise determinalion of the bOC concentration in sea water is thus a prerequisite for any interpretation of DOC biogeochemistry. A key factor in analytical quality control is an accurate determination of the blank. The assessment and distinction of DOC blanks are essential for the precise measurements of oceanic DOC. The total DOC blank includes instrument and water blanks in the high temperature catalytic oxidation (HTCO) method. DOC can be measured accurately using the HTCO method only when the instrument blank is correctly distinguished from the total DOC blank and corrected in the sample measurements. Low DOC blanks can be achieved by extensive conditioning of new catalysts and the whole instrument system, whereas instrument blanks can be quantified by subtracting the water blank from the total DOC blank. We have been able to produce low carbon nanopure water [≤2μmol/dm³(C)] and have a low instrumental blank [< 5-6 μmol/dm³(C)] when using the HTCO method. Results of concentrations and distributions of DOC in the Gulf of Mexico and the North Atlantic are oceanographically consistent. Results from DOC measurements on samples from the international DOC methods comparison program further confirmed our low values of both nenopure water and the instrument blank.     

错流超滤技术在海水胶体态铀、钍、镭同位素和有机碳研究中的应用

建立了由预过滤装置、蠕动泵、中空纤维超滤膜(AmiconH10P10-20,标称截留分子量10KDa)和连接管组成的错流超滤系统,利用荧光标记的40KDa葡聚糖和已知放射性活度的234Th示踪剂评估了超滤膜的截留和吸附性质,探讨了234Th在超滤过程中的渗透行为,考查了该系统用于实际海水样品时铀、钍、镭同位素和有机碳的质量平衡状况.结果表明,10Kda中空纤维超滤膜对40Kda葡聚糖具有良好的截留效率(85%),而吸附损失率为18%.铀、钍、镭同位素和有机碳在超滤过程中均达到极佳的质量平衡,回收率R=95%～98%,优于大多数文献报道的值.234Th在超滤过程中的渗透行为可以很好地用渗透模型加以描述.研究组分胶体态含量占“溶解”态含量的份额大小顺序如下:钍同位素、有机碳、镭同位素约等于铀同位素,这与钍为强颗粒活性元素、铀和镭为水溶性元素的地球化学性质相吻合.     

Physico-chemical Speciation of Lead in South San Francisco Bay

The speciation of lead at a site in the South San Francisco Bay was determined using a combination of physical size fractionation and electrochemical analyses. The ‘ total dissolvable ’ Pb was 8·1 nM from analysis of an acidified unfiltered sample. The ‘ dissolved ’ Pb was equal to 0·20 nM (41 ng l⁻¹), only 2·5% of the ‘ total dissolvable ’ Pb. The difference yielded the ‘ particulate ’ Pb equal to 7·9 nM (1·6 μg l⁻¹). Results from crossflow ultrafiltration indicated that almost all (0·19 nM) of the dissolved Pb was ‘ in solution ’ [<10K nominal molecular weight (MW)] and that colloidal Pb (10K MW to 0·2 μm)accounted for onlyc. 1% of the dissolved Pb at this station. This small concentration (0·01 nM) of colloidal Pb may be attributed to the low amount of organic carbon associated with colloid size fraction as determined by dissolved organic carbon analyses.The chemical speciation of lead was determined in the dissolved sample and ultrafiltered sub-sample. Differential pulse anodic stripping voltammetry (DPASV) on a thin mercury film (TMF) rotating glassy carbon disk electrode (RGCDE) was used to distinguish the kinetically labile inorganic species (Pb′) from the Pb-chelated by organic ligands (PbL_i). Lead titration results were similar for both samples revealing that Pb′, PbL_iand excess unbound ligands were present primarily in the ultrafiltrate, rather than in the colloidal phase. The titration data can be interpreted as dissolved Pb being influenced by two classes of Pb-binding ligands. In the dissolved sample, the concentration of the stronger class of ligands was [L₁]=0·89±0·35 nM, with a conditional stability constant ofK^cond_L1,Pb′=3±1×10¹⁰M⁻¹. The weaker class was [L₂]=12·8±1·9 nM, withK^cond_L1,Pb′=4±1×10⁸ M⁻¹. The presence of these ligands, in excess of the dissolved Pb, resulted in [Pb′]=7±2 pM and [Pb²⁺]=0·3 pM (62 pg l⁻¹). While less than 2·4% of the ambient Pb was ‘ in solution ’, it existed chiefly in the form of organic complexes with [PbL₁]=0·15 nM and [PbL₂]=0·03 nM. More significantly, there were large concentrations of unchelated Pb-binding ligands, (L_i′), available to buffer the free Pb²⁺concentration in the event of perturbations in dissolved Pb.     

Comparison of high spatial resolution trace metal distributions with model simulations for surface waters of the Gulf of Cadiz

A multidisciplinary study in the Gulf of Cadiz is revisited, using additional diagnostic modelling tools. The dissolved trace metal (Cu, Ni, Zn, Co) distributions in the Gulf of Cadiz are analysed using modelled tracer evolutions, field observations and the concept of tracer ages. This study shows that a significant part of the observed metal distributions can be explained by the metal inputs of three river systems (Guadiana, Rio Tinto and Odiel, Guadalquivir) discharging into the Gulf of Cadiz, while the remainder of the signal is most likely associated with the benthic metal remobilisation along the shelf of this coastal region.     

基于切向超滤技术的胶体有机碳和无机氮分离及物源初探

利用切向超滤技术对九龙江口天然水体中胶体相(1 kDa～0. 45μm)、真溶解相(1 kDa)和"溶解相"(0. 45μm)的溶解有机碳和无机氮进行了分离与提取,初步探讨了水环境因子对其理化特性的影响机制,进而探讨了它们的来源和转化.结果表明,切向超滤过程的膜空白和质量平衡符合技术要求;溶解有机碳、亚硝酸盐氮、氨氮、硝酸盐氮和无机氮存在形式以真溶液相(1 kDa)为主,其在胶体相中的质量浓度分别为0. 207～0. 810 mg/dm3、0. 001～1. 870μg/dm3、ND～2. 08μg/dm3、0. 62～79. 30μg/dm3和1. 07～81. 10μg/dm3;胶体态溶解有机碳(COC)含量主要受陆源输入控制.     

Assessment of copper,cadmium and zinc remobilization in Mediterranean marine coastal sediments

The remobilization of copper, cadmium and zinc in sediments of three selected coastal microenvironments of the Aegean Sea (Eastern Mediterranean) is assessed. Various analytical methods and techniques were employed providing concentrations, profiles and forms of metals and organic matter in sediments and pore waters.     

莱州湾荧光溶解有机物的时空分布

利用三维荧光光谱-平行因子分析法(EEMs-PARAFAC)技术结合多元统计方法研究了莱州湾海域春季(2020年5月)和秋季(2020年10月)荧光溶解有机物(FDOM)的来源及时空分布特征。结果显示莱州湾海域FDOM由2类共4个荧光组分组成:C1、C4为类蛋白质组分,分别为色氨酸和酪氨酸; C2、C3为类腐殖质组分。并对各组分的来源及分布特征分析:春季FDOM分布主要受到陆源输入的影响,其中表层C1、C2、C3也受微生物活动影响。秋季表层C1、C2、C3分布受到陆源输入和浮游植物生产共同影响,秋季表层C4主要受生物现场生产影响,秋季底层C1、C2、C3主要受陆源输入影响,C4受陆源输入和浮游植物生产共同影响。各荧光组分在表层的季节性差异主要是由于春季部分FDOM经陆源输入后受偏南风作用,在莱州湾西部及南部海域扩散。FDOM在底层的季节性差异主要由于受到沉积物再悬浮的影响。HIX高值分布表明莱州湾西部和南部FDOM受陆源输入影响显著,BIX高值分布表明莱州湾远海FDOM受生物活动影响程度较高。总体上,陆源输入影响莱州湾FDOM分布的主要因素。     

墨西哥湾陆坡区冷泉碳酸盐岩的烷烃分布特征

对墨西哥湾北部水深2200m的Alaminos Canyon645区块（AC645区）和水深540m的Green Canyon185区块（GC185区）冷泉碳酸盐岩的有机质进行了研究,结果显示深水和浅水区冷泉碳酸盐岩的有机质丰度和烷烃组成差别较大,下陆坡深水AC区样品有机质含量低,正构烷烃、萜烷、甾烷各组分的含量相对较高,正构烷烃以低碳数占绝对优势,并含有种类丰富的三环萜烷和五环三萜烷,且以17a（H）,21B（H）-藿烷为主峰碳,反映了深水区冷泉碳酸盐岩的有机质来源于细菌和低等藻类,有少量的深部油气藏有机质的渗漏输入,并受微弱的微生物作用改造。上陆坡浅水GC区样品有机质含量较高,其中正构烷烃含量较低,并且以难以分开的复杂混合物（UCM）为主,同样含有种类丰富的以17α（H）,21β（H）-降藿烷为主峰碳的三环萜烷和五环三萜烷,表明有机质主要来源于深部油气藏渗漏的有机质,并遭受了强烈的微生物降解。本文系统地研究了冷泉碳酸盐岩中正构烷烃、萜烷、甾烷的组成和分布特征,并探讨了有机质来源和冷泉渗漏的关系。     

Dissolved organic carbon variability in a shallow coastal marine system (Gulf of Trieste,northern Adriatic Sea)

The variability of dissolved organic carbon (DOC) over days to a multi-year time span has been investigated in the Gulf of Trieste (northern Adriatic Sea) over a period of 5 years (January 1999 to December 2003). Samples were collected in a grid of 9 to 12 stations on monthly frequency and in one station on weekly (2003) and daily (1-month) frequency. DOC samples were analyzed by the HTCO method. DOC concentration varied over the five years in the range of 50 to 194 μM with annual median values ranging from 88 to 98 μM. Over the years 1999–2002, DOC showed a clear annual periodicity with winter minima and late summer maxima, higher in 1999 and 2000. During 2003 no seasonality was detected. The absence of DOC seasonality and the lower DOC concentrations during 2003 are most likely related to the drought that characterized the whole year. Accumulation was calculated as the difference between averaged winter minima (59 ± 7 μM) and the monthly averaged integrated value. DOC that had accumulated from spring to summer totally disappeared from the water column in winter when DOC concentrations reached the background value. The Gulf of Trieste, as with the rest of the Northern Adriatic each year, seems to be able to bring back DOC concentrations at low levels despite the significant external (mainly Isonzo River inputs) and internal organic matter loads. DOC concentration exhibited quite wide fluctuations weekly and daily, suggesting there might be DOC of different turnover time through production, consumption, migration and accumulation.