Movements and population structure of Atlantic menhaden indicated by tag returns

Over 968,000 adult Atlantic menhaden,Brevoortia tyrannus, were tagged from 1967 to 1969 and over 85,000 juvenile menhaden were tagged from 1969 to 1973. Recoveries of these tagged fish through 1975 provide direct evidence that Atlantic menhaden consist of a single population that over-winters in offshore waters off the southeastern coast of the United States, moves northward in spring and stratifies along the coast by age and size during summer, and moves southward in late autumn.     

Masses of carbon in the Earth’s hydrosphere

Recent data were summarized on the concentration and mass of inorganic and organic carbon in reservoirs of the Earth’s hydrosphere. We compared carbon masses and accumulation conditions in the surface hydrosphere and waters of the sedimentary shell and proportions between carbonate, dissolved, and suspended particulate organic carbon. It was shown that the total masses of carbon in the surface hydrosphere and in the waters of the sedimentary shell are approximately equal to 80 × 10¹⁸ g C at an organic to carbonate carbon ratio of 1 : 36 and 1 : 43, respectively. Three main forms of organic compounds in the ocean (living organisms, suspended particles, and dissolved species) occur in the proportion 1 : 13 : 250 and form the pyramid of masses 4 × 10¹⁵ g, 50 × 10¹⁵ g, and 1000 × 10¹⁵ g C_org. The descending sequence of the organic to carbonate carbon ratio in water, ocean (1 : 36) > glaciers (1 : 8) > lakes (1 : 2) > rivers (1 : 0.6) > wetlands (1 : 0.3), is in general consistent with an increase in the same direction in the mean concentrations of organic matter: 0.77 mg C_org/L in the ocean, 0.7 mg C_org/L in glaciers, 6–30 mg C_org/L in lakes, 15 mg C_org/L in rivers, and 75 mg C_org/L in wetlands. Both the mean concentrations and masses of dissolved organic matter in the pore waters of oceanic sediments and in the waters of the sedimentary shell are similar: 36–37 mg/L and 5 × 10¹⁸ and 5.6 × 10¹⁸ g, respectively. The mass of carbonate carbon in the pore waters of the ocean, (19–33) × 10¹⁸ g, is comparable with its mass in the water column, 38.1 × 10¹⁸ g.     

纳米铁去除饮用水中As(Ⅲ)和As(Ⅴ)

在好氧水体中,As(Ⅲ)比As(Ⅴ)更易迁移,而且在水处理过程中去除效率更低。在实验室合成制得BET比表面积为49.16 m2/g,直径范围为20~40 nm的纳米铁。通过批试验考察纳米铁对As(Ⅲ)和As(Ⅴ)去除能力及其反应动力学情况。结果表明,在pH为7,温度20℃时纳米铁能够快速地去除As(Ⅲ)和As(Ⅴ),在60 m in内,0.25 g纳米铁对起始浓度为968.6μg/L As(Ⅲ)和828.9μg/L As(Ⅴ)的去除率大于99.5%。反应遵循准一级反应动力学方程,标准化后的As(Ⅲ)和As(Ⅴ)比表面积速率常数kSA分别为1.30 mL/(m2.m in)和1.64 mL/(m2.m in)。由实验结果可知,具有高反应活性的纳米铁是用于含砷饮用水处理非常有效的吸附材料。     

The mobility of thorium in natural waters at low temperatures

Thermodynamic properties of 32 dissolved thorium species and 9 thorium-bearing solid phases have been collected from the literature, critically evaluated and estimated where necessary for 25°C and 1 atm pressure. Although the data are incomplete, especially for thorium minerals and organic complexes, some tentative conclusions can be drawn. Dissolved thorium is almost invariably complexed in natural waters. For example, based on ligand concentrations typical of ground water (ΣCl = 10 ppm, ΣF = 0.3 ppm, ΣSO₄ = 100 ppm, andΣPO₄ = 0.1 ppm), the predominant thorium species are Th(SO₄)⁰₂, ThF²⁺₂, and Th(HPO₄)₂⁰below pH ≈ 4.5; Th(HPO₄)^2?₃ from about pH 4.5 to 7.5; and Th(OH)⁰₄ above pH 7.5. Based on stability constants for thorium citrate, oxalate and EDTA complexes, it seems likely that organic complexes predominate over inorganic complexes of thorium in organic-rich stream waters, swamp waters, soil horizons, and waterlogged recent sediments. The thorium dissolved in seawater is probably present in organic complexes and as Th(OH)⁰₄. The tendency for thorium to form strong complexes enhances its potential for transport in natural waters by many orders of magnitude below pH 7 in the case of inorganic complexing, and below about pH 8 when organic complexing is important. The existence of complexes in addition to those formed with hydroxyl, is apparent from the fact that measured dissolved thorium in fresh surface waters (pH values generally 5–8) usually ranges from about 0.01 to 1 ppb and in surface seawater (pH = 8.1) is about 0.00064 ppb. This may be contrasted with the computed solubility of thorianite in pure water which is only 0.00001 ppb Th as Th(OH)⁰₄ above pH 5. Although complexing increases the solubility of thorium-bearing heavy minerals below pH 8, maximum thorium concentrations in natural waters are probably limited in general by the paucity and slow solution rate of these minerals and by sorption processes, rather than by mineral-solution equilibria.     

A survey of the inorganic chemistry of bottled mineral waters from the British Isles

The inorganic chemistry of 85 samples of bottled natural mineral waters and spring waters has been investigated from 67 sources across the British Isles (England, Wales, Scotland, Northern Ireland, Republic of Ireland). Sources include boreholes, springs and wells. Waters are from a diverse range of aquifer lithologies and are disproportionately derived from comparatively minor aquifers, the most represented being Lower Palaeozoic (10 sources), Devonian Sandstone (10 sources) and Carboniferous Limestone (9 sources). The waters show correspondingly variable major-ion compositions, ranging from Ca–HCO₃, through mixed-cation–mixed-anion to Na–HCO₃ types. Concentrations of total dissolved solids are mostly low to very low (range 58–800 mg/L). All samples analysed in the study had concentrations of inorganic constituents well within the limits for compliance with European and national standards for bottled waters. Concentrations of NO₃–N reached up to half the limit of 11.3 mg/L, although 62% of samples had concentrations <1 mg/L. Concentrations of Ba were high (up to 1010 μg/L) in two spring water samples. Such concentrations would have been non-compliant had they been classed as natural mineral waters, although no limit exists for Ba in European bottled spring water. In addition, though no European limit exists for U in bottled water, should a limit commensurate with the current WHO provisional guideline value for U in drinking water (15 μg/L) be introduced in the future, a small number of groundwater sources would have concentrations close to this value. Two sources had groundwater U concentrations > 10 μg/L, both being from the Welsh Devonian Sandstone. The highest observed U concentration was 13.6 μg/L.     

Microheterogeneity of element distribution and sulfur speciation in an organic surface horizon of a forested Histosol as revealed by synchrotron-based X-ray spectromicroscopy

In recent years, the relevance of physico-chemical heterogeneity patterns in soils at the micron and submicron scale for the regulation of biogeochemical processes has become increasingly evident. For an organic surface soil horizon from a forested Histosol in Germany, microspatial patterns of element distribution (sulfur, phosphorus, aluminium, silicon) and S speciation were investigated by synchrotron-based X-ray spectromicroscopy. Microspatial patterns of S, P, Al and Si contents in the organic topsoil were assessed for a sample region of 50 μm × 30 μm by spatially resolving μ-XRF. Sulfur speciation at four microsites was investigated by focused X-ray absorption near edge structure (μ-XANES) spectroscopy at the S K-edge. The results show a heterogeneous distribution of the investigated elements on the (sub)micron scale, allowing the identification of diatoms, aluminosilicate mineral particles and sulfide minerals in the organic soil matrix. Evaluation of the S K-edge μ-XANES spectra acquired at four different microsites by linear combination fitting revealed a substantial microspatial heterogeneity of S speciation, characterized by the presence of distinct enrichment zones of inorganic sulfide and zones with dominant organic disulfide S within a few micrometers distance, and coexistence of different S species (e.g. reduced inorganic and organic S compounds) at a spatial scale below the resolution of the instrument (60 nm × 60 nm; X-ray penetration depth: 30 μm).     

Elemental,infra-red spectrophotometric and electron spin resonance investigations of non-chemically isolated humic material

Naturally occurring organic material from a lake in the southeastern United States was isolated by ultrafiltration and analyzed by i.r. spectrophotometry and electron spin resonance spectrometry, and for its elemental composition without chemical pretreatment. The results of the study indicate the isolate is an apparent high molecular weight fulvic acid with associated, hydrated Mn²⁺ ion which does not appear strongly bound to the organic moiety.     

Origin of quartz cements in some sandstones from the Jurassic of the Inner Moray Firth (UK)

The extent of quartz cementation in shallow marine sandstones of the Brora Arenaceous Formation (Oxfordian) is closely related to the occurrence and abundance of Rhaxella perforata sponge spicules. Three cement morphologies are identified, chalcedonic quartz, microquartz and mesoquartz. Chalcedonic quartz forms matrix-supported cements which preserve moulds of Rhaxella spicules. Chalcedonic quartz crystals have inequant development of crystal faces, on average 0·1 μm in diameter, and are the first formed cement and reveal homogeneous dark grey tones on the SEM-CL/BEI. Microquartz forms 5–10 μm diameter crystals, which commonly grow on chalcedonic quartz substrates and show various grey tones under SEM-CL/BEI. Mesoquartz crystals grow in optical continuity with their host grains, have >20 μm a-axial diameter crystals, and exhibit distinctly zoned luminescence. Although no opaline silica is preserved, the quartz cement is interpreted to have formed from an opaline precursor. Detrital quartz has an average δ¹⁸O composition of + 12·2‰ and mesoquartz (syntaxial overgrowth) has an average δ¹⁸O composition of +20·0‰. Estimates of the δ¹⁸O compositions of microquartz and chalcedonic quartz are complicated by the problem of isolating the two textural types; mixtures of the two give consistently higher δ¹⁸O compositions than mesoquartz, the higher estimate being +39·2‰. From oxygen isotope data the formation of quartz, microquartz and chalcedonic quartz is interpreted to have taken place between 35 and 71°C in marine derived pore waters. Organic and inorganic maturation data constrain the upper temperature limit to less than 60°C.     

Role of metal species in flocculation rate during estuarine mixing

Flocculation can be considered as an effective mechanism in self-purification of metals during estuarine mixing. In the present investigation, flocculation of metals during mixing of Minab River water with the Strait of Hormuz (The Persian Gulf) water is studied for the first time. Flocculation behavior of metals (except for Pb) is governed by dissolved organic carbon. The source of dissolved organic carbon is terrigenous in the estuarine waters of study area. The general pattern of flocculation of studied metals is manganese (180 μg/L) > zinc (88 μg/L)> nickle (73 μg/L)> copper (30 μg/L)> lead (19 μg/L). The results of present study show that metal species are a very important factor in overall flocculation rate. It is found that solids and oxides have the highest and lowest flocculation levels, respectively. Eh-pH diagram indicated that lead is present as lead oxide in Minab River water and the least flocculation rate is attributed to this element. The results also showed that flocculation rate of metal species could be as solids > free ions ≈ hydroxides > oxides. The amount of metal flocculation is about 30.5, 6.6, 25.3, 10.4 and 62.5 ton/y for zinc, Pb, Ni, Cu and Mn, respectively.     

Anaerobic diagenesis within Recent, Pleistocene, and Eocene marine carbonate frameworks

Porewaters from a variety of Recent, Pleistocene, and Eocene lithified marine carbonate frameworks displayed similar chemical characteristics: highly depleted concentrations of dissolved oxygen (>20 μM), elevated levels of dissolved methane (25-5000 nM), and near-seawater sulphate levels. These porewaters also had low pH values (7·5-7·9), and contained elevated concentrations of sulphide (4–10 μM), dissolved inorganic carbon (2·05–2·46 mM), and inorganic nutrients. Hydrocarbon composition data indicate that the methane is biogenic, whereas the methane δ¹³C values (–47·4 ± 2·7%0) suggest that it has been subject to oxidation. The porewater dissolved inorganic carbon δ¹³C values varied from –0·6 to –39%0, suggesting input of carbon dioxide from organic matter oxidation. We conclude that anaerobic diagenesis involving bacterial degradation of organic matter is a common process in lithified marine carbonates and hypothesize that it may be an important factor controlling their carbonate geochemistry.     

Carbon dioxide concentration and atmospheric flux in the Hudson River

We made direct measurements of the partial pressure of CO₂ (P_{CO 2}) in the tidal-freshwater portion of the Hudson River Estuary over a 3.5-yr period. At all times the Hudson was supersaturated in CO₂ with respect to the atmosphere. P_{CO 2} in surface water averaged 1125±403 (SD) μatm while the atmosphere averaged 416±68 μatm. Weekly samples at a single, mid-river station showed a pronounced and reproducible seasonal cycle with highest values (～2000 μatm) in mid-to-late summer, and lowest values (～500 μatm) generally in late winter. Samples taken along the length of the 190-km section of river showed a general decline in CO₂ from north to south. This decline was most pronounced in summer and very slight in spring. Diel and vertical variation were small relative to the standing stock of CO₂. Over six diel cycles, all taken during the algal growing season, the mean range was 300±114 μatm. CO₂ tended to increase slightly with depth, but the gradient was small, about 0.5 μmol m^?1, or an increase of 190 μatm from top to within 1 m of the bottom. For a large subset of the samples (n=452) we also calculated CO₂ from measurements of pH and total DIC. Calculated and measured values of CO₂ were in reasonably good agreement and a regression of calculated versus measured values had a slope of 0.85±0.04 and an r₂ of 0.60. Combining our measurements with recent experimental studies of gas exchange in the Hudson, we estimate that the Hudson releases CO₂ at a rate of 70–162 g C m^?2 yr^?1 from the river to the atmosphere.     

The distribution of lithium in selected soils and surface waters of the southeastern U.S.A.

The distribution of Li in the environment is not well documented although its geochemistry is thought to influence human health and agriculture. This study examined the distribution of Li in the soils and surface waters of the southeastern U.S.A., contrasting the Piedmont and Coastal Plain regions. Previous studies have been limited to total, and to a lesser extent exchangeable, soil Li, usually at a single soil depth. This study evaluated more carefully the distribution of Li between the soil solution, exchange, and solid phases, and its distribution within soil profiles. Total soil Li was found to correlate strongly with clay content, and ranged from 3.74 to 59.93 mg/kg. Exchangeable Li ranged from 0.1 to 21.8 μmol/kg soil and constituted an insignificant portion of the total exchangeable cations (<0.09%) and total Li present (<1.1%) in the soils studied. Water-soluble Li ranged from 0.08 to 4.62 μg/l. Dissolved Li in 22 surface waters within the Piedmont and Coastal Plain regions of Georgia and South Carolina was also determined and ranged from 0.26 to 4.16 μg/l. The soils and surface waters of the Coastal Plain region were found to be depleted in Li relative to the Piedmont region of the southeastern U.S.A.     

Dissolved and particulate organic carbon in Chesapeake Bay

We measured dissolved and particulate organic carbon (DOC and POC) in samples collected along 13 transects of the salinity gradient of Chesapeake Bay. Riverine DOC and POC end-members averaged 232±19 μM and 151±53 μM, respectively, and coastal DOC and POC end-members averaged 172±19 μM and 43±6 μM, respectively. Within the chlorophyll maximum, POC accumulated to concentrations 50–150 μM above those expected from conservative mixing and it was significantly correlated with chlorophylla, indicating phytoplankton origin. POC accumulated primarily in bottom waters in spring, and primarily in surface waters in summer. Net DOC accumulation (60–120 μM) was observed within and downstream of the chlorophyll maximum, primarily during spring and summer in both surface and bottom waters, and it also appeared to be derived from phytoplankton. In the turbidity maximum, there were also net decreases in chlorophylla (?3 μg l^?1 to ?22 μg l^?1) and POC concentrations (?2 μM to ?89 μM) and transient DOC increases (9–88 μM), primarily in summer. These occurred as freshwater plankton blooms mixed with turbid, low salinity seawater, and we attribute the observed POC and DOC changes to lysis and sedimentation of freshwater plankton. DOC accumulation in both regions of Chesapeake Bay was estimated to be greater than atmospheric or terrestrial organic carbon inputs and was equivalent to ≈10% of estuarine primary production.     

Deformation of experimentally shock-loaded quartz powders: X-ray line broadening studies

Quartz powders (mean grain size: 22 μm) were pressed into sample discs of different green densities (ρ₀=1.65; 1.85 and 2.05 g/cm³) and subjected to shock pressure between 1.5 and 17.0 GPa. Peak shock pressures were determined by the impedance method using the Hugoniot curves of steel and quartz powders. Fourier techniques were used to analyse the line broadening of 5 X-ray reflections in each case. The Fourier coefficients were subjected to a Rothman-Cohen correction before further processing. The coherent domain size decreases abruptly from several thousand Ångström in the unshocked state to about 800 Å at 1.5 GPa, and reaches a constant mean value of about 200 to 300 Å at dynamic pressures of about 4 GPa. At very high dynamic pressures (?15 GPa) there is further fragmentation to very small domain size. There is no systematic correlation between sample density and coherent domain size produced by the shock event. A more or less linear dependency exists between microstrain and pressure for each starting density of the quartz powder. The observation that microstrain decreases with increasing starting density could be explained by the fact that increasingly larger portions of the input energy are consumed to create fresh surfaces by comminution. Consequently, less energy will be available for strain strengthening. The stored energies in the shocked quartz powders are of the same order as the surface energy. Shock-treated quartz should therefore be suitable for accelerating any activated process such as sintering.     

湘中与湘东南岩关阶组和龙潭组页岩气潜力

为了揭示湘中与湘东南坳陷海陆过渡相页岩含气潜力及勘探方向,对该区下石炭统岩关阶组和上二叠统龙潭组泥页岩进行总有机碳含量TOC、镜质体反射率R_ran、干酪根碳同位素、有机质显微组成、X衍射、扫描电镜、孔渗特征和等温吸附等测试。结果表明岩关阶组和龙潭组处于成熟-高成熟期、类型以Ⅲ型为主;龙潭组泥页岩TOC含量普遍较高、而岩关阶组泥页岩TOC含量较低。龙潭组和岩关阶关组泥页岩矿物主要为黏土矿物和石英,部分含有较高的方解石。这两套页岩的孔隙发育较差,主要孔隙类型为有机孔、溶蚀孔和层间裂缝。孔隙度为0.41%~2.76%、渗透率为（0.08~0.98）×10-3 μm2。孔隙度主要受TOC控制,不稳定矿物如长石和碳酸盐岩虽然能提供一定孔隙,但对页岩物性的影响有限。泥页岩的甲烷吸附量普遍在1.67~2.5 cm3/g,2015H-D3井龙潭组泥页岩现场解吸气量普遍大于0.5 cm3/g,最高为2.35 cm3/g,表明湘中和湘东南地区龙潭组具有一定的页岩气潜力,但岩关阶组勘探前景相对较差。      

Form and distribution of gold mobilized into surface waters and sediments from a gossan tailings pile,Murray Brook massive sulphide deposit,New Brunswick,Canada

Stream waters and sediments draining a gossan tailings pile at the Murray Brook massive sulphide deposit were collected to investigate Au mobility. Weathering of the massive sulphides at Murray Brook during the Late Tertiary period resulted in the concentration of Au in the gossan cap overlying the supergene Cu and unoxidized massive sulphide zones of the deposit. The gossan was mined between 1989 and 1992, and Au and Ag were extracted using a cyanide vat leach process. Although stream sediments prior to mining had Au<5 ppb (the detection limit), sediments collected in 1997 had Au contents ranging up to 256 ppm with values up to 6 ppm more than 3 km downstream from the deposit. Dissolved Au contents were similarly anomalous, up to 19 μg/L and in excess of 3 μg/L 3 km downstream. The elevated Au contents in the waters and sediments are interpreted to reflect complexation of Au (as Au(CN)₂⁻) by cyanide hosted within the gossan tailings pile. Precipitation recharges through the tailings pile with groundwater flow exiting to Gossan Creek. Degradation of cyanide along the flow path and within Gossan Creek allows colloidal Au to form via reduction of Au(I) by Fe²⁺, consistent with SEM observations of Au as <1 μm subrounded particles. In the surface waters, the majority of the Au must be in a form <0.45 μm in size to account for the similarity in Au contents between the <0.45 μm and unfiltered samples. The very elevated stream sediment Au values close to the headwaters of Gossan Creek near the tailings indicate that upon exiting to the surface environment, Au(CN)₂⁻ complexes are rapidly destroyed and Au removed from solution. However, the high Au_{<0.004 μm}/Au_total in the headwaters and the extended Au dispersion in Gossan Creek waters and sediments suggest that Au(CN)₂⁻ complexes persist for the full length of Gossan Creek. The decrease in aqueous Au which is less than 0.004 μm indicates that Au is converted from a complexed form to a colloidal form with increasing distance downstream, consistent with dissolved NO₃⁻ contents which decrease from 5210 μg/L near the headwaters to 1350 μg/L at the lower end of the stream.     

超高效液相色谱法直接快速测定环境水样中硝基苯和苯胺

建立了超高效液相色谱直接快速测定环境水样中硝基苯和苯胺的分析方法。取900μL水样与100μL乙腈混匀,用微孔滤膜(0.2μm,有机系)过滤。采用1.7μm小颗粒填料的BEH phenyl柱,以乙腈/醋酸铵溶液为流动相,硝基苯和苯胺分别用紫外和荧光检测器检测,分析时间仅1.1 min。硝基苯和苯胺的线性范围分别是0.485～4850μg/L和0.495～1978μg/L,方法检出限分别是0.194μg/L和0.099μg/L,相关系数均在0.995以上。硝基苯9.70μg/L、194μg/L、1940μg/L三个浓度水平回收率在98.3%～101%,相对标准偏差在1.11%～2.03%。苯胺9.89μg/L、198μg/L、1978μg/L三个浓度水平回收率在98.6%～104%,相对标准偏差在0.75%～5.85%。与传统液相分析方法相比,本方法线性范围更宽,灵敏度更高;直接进样简化了前处理环节,减少采样体积和有机试剂的使用;分析效率高,适用于地下水、地表水等多种水质样品中痕量到常量范围的硝基苯和苯胺快速测定。     

Development of hypoxia in well-mixed subtropical estuaries in the Southeastern USA

Esturies throughout much of the South Atlantic Bight (southeastern U.S.) have been considered to be relatively pristine, but are now experiencing elevated concentrations of both organic and inorganic nutrients. As is true in many parts of the world, this eutrophication is correlated with coastal population growth. These estuaries have been assumed to be immune from extended hypoxia, in large part because they are well mixed and do not generally exhibit the water column stratification that is traditionally associated with low concentrations of dissolved oxygen. data presented here show long-term (19 yr) decreases in dissolved oxygen in surface waters of the Skidaway estuary, a pattern that is occurring throughout coastal Georgia. More limited data from bottom waters exhibit the same trend. The decreases in dissolved oxygen occurred at the same time as observed increases in inorganic and organic nutrients and in bacteria concentrations, implying an increase in heterotrophic activity. These observations suggest that traditional paradigms long applied to stratified estuaries, wherein the cycle that leads to hypoxia is initiated by the uptake of inorganic nutrients by autotrophs that are then decomposed below the pycnocline, may need revision for well-mixed estuaries. Heterotrophic community metabolism, stimulated by anthropogenic loading of organic and inorganic nutrients, can overwhelm even vigorous vertical mixing and horizontal exchange to gradually cause declining oxygen concentrations and eventually hypoxia.     

Transport of particulate organic carbon by the Mississippi River and its fate in the Gulf of Mexico

This study was designed to determine the amount of particulate organic carbon (POC) introduced to the Gulf of Mexico by the Mississippi River and assess the influence of POC inputs on the development of hypoxia and burial of organic carbon on the Louisiana continental shelf. Samples of suspended sediment and supporting hydrographic data were collected from the river and >50 sites on the adjacent shelf. Suspended particles collected in the river averaged 1.8±0.3% organic carbon. Because of this uniformity, POC values (in μmol l^?1) correlated well with concentrations of total suspended matter. Net transport of total organic carbon by the Mississippi-Atchafalaya River system averaged 0.48×10¹² moles y^?1 with 66% of the total organic carbon carried as POC. Concentrations of POC decreased from as high as 600 μmol l^?1 in the river to <0.8 μmol l^?1 in offshore waters. In contrast, the organic carbon fraction of the suspended matter increased from <2% of the total mass in the river to >35% along the shelf at ≥10 km from the river mouth. River flow was a dominant factor in controlling particle and POC distributions; however, time-series data showed that tides and weather fronts can influence particle movement and POC concentrations. Values for apparent oxygen utilization (AOU) increased from ～60 μmol l^?1 to >200 μmol l^?1 along the shelf on approach to the region of chronic hypoxia. Short-term increases in AOU were related to transport of more particle-rich waters. Sediments buried on the shelf contained less organic carbon than incoming river particles. Orgamic carbon and δ¹³C values for shelf sediments indicated 3 that large amounts of both terrigenous and marine organic carbon are being decomposed in shelf waters and sediments to fuel observed hypoxia.     

Distribution of carbon in a tropical hypersaline estuary,the Casamance (Senegal,West Africa)

The Casamance estuary, on the coast of Senegal, is an inverse hypersaline estuary: salinity increases landward, and dry season salinity values are up to 172 psu due to the evaporation of seawater. Dissolved inorganic carbon (DIC) concentrations decreased landward as a negative linear function of salinity. Thermodynamic modelling and the absence of CaCO₃ in the sediments indicate that this loss of DIC was not due to calcite precipitation in the main water body. The innermost, almost landlocked, waters contained high phytoplankton biomass (50–300 μg chl I^?1) and high concentrations of allochthonous dissolved organic carbon. Photosynthetic uptake of DIC and subsequent particulate organic carbon sedimentation is proposed as hypothetical explanation of the relationship between DIC and salinity; localized overheating in shallow waters might also be involved.