黄河三角洲浅层地下水化学特征与演化

2009年4月~2010年3月连续2年对黄河三角洲19口地下水监测井进行观测并对地下水离子化学成分分析,探讨了该区域浅层地下水化学成分、水化学类型及演化规律,为揭示区域地下水环境特征和演化具有现实意义。结果表明,黄河三角洲地区地下水p H值变化较小,地下水埋深较浅且年内变化幅度为1.0~3.0 m,但矿化度和各离子差异明显,地下水以Na+、Cl–占绝对优势;矿化度较低的测井的离子浓度变幅较小,反之,矿化度高的测井离子浓度变幅较大;地下水化学类型分为氯化物型、重碳酸盐氯化物型、重碳酸盐氯化物硫酸盐型和硫酸盐重碳酸盐型四大类型,主要包括Na+-Cl–、Na+-Cl–.3HCO?、Na+-Cl–.3HCO?、Na+-Cl–.3HCO?.24SO?、Na+-3HCO?.Cl–.24SO?和Na+-24SO?.3HCO?六种子类型,氯化物型主要分布于广饶县咸水入侵区和滨海区域,重碳酸盐氯化物型主要分布于黄河三角洲保护区内,重碳酸盐氯化物硫酸盐型分布在广饶县咸水入侵区,硫酸盐重碳酸盐型主要分布在靠近黄河流路附近;根据黄河三角洲流路变迁和Gibbs模型,黄河三角洲地区水样化学组成均落在Gibbs提出的Boomerang Envelope模型右上翼,表明研究区水样化学组成主要受蒸发和沉淀作用,海水控制起次要作用,土地利用变化、灌溉、施肥等人为活动的影响亦不能忽视。     

Effect of aluminate content in cement on the long-term sulfate resistance of cement stabilized sand

Abstract

Durability of cement-based materials for marine/coastal structures is an increasingly challenging problem. Sulfate ions in seawater can react with aluminate in cement to form erosion products, causing cracks and spalling. When cement is used to stabilize loose erodible sand in coastal areas, the resistance to sulfate attack is questionable. In this study, four cements with different aluminate contents were used to stabilize sand. Cement stabilized sands were immersed in 5% Na₂SO₄ solution for 300-days to simulate long-term sulfate attack process. The deterioration of engineering performance was evaluated based on expansion ratio, mass change, uniaxial compressive strength, and ultrasonic velocity. The deterioration mechanisms were analyzed through mineralogical and microstructural observations including X-ray diffraction, EDS, scanning electronic microscopy, and nuclear magnetic resonance. The results showed that the development of macro-scale mechanical performances could be divided into two stages (initial stage and erosion stage) when subjected to 300-days immersion in 5% Na₂SO₄ solution. Sand stabilized by low-aluminate-content cement displayed better engineering performance especially at the erosion stage. Mechanistically, more ettringite was formed in high-aluminate-content cement stabilized sand, leading to swelling and cracking. The formation of ettringite and gypsum were accompanied with the consumption of portlandite, leading to further strength loss.     

Concrete sulfate corrosion coupled with hydraulic pressure

Abstract

A type of sealed steel box was designed to simulate sulfate attack and hydraulic pressure on concrete. Cup-shaped concrete specimens with water/cement (w/c) ratios of 0.4, 0.5, and 0.6 were fabricated. During the 270 days corrosion time, corrosion behavior on concrete surfaces was observed every 30 days. The extent of damage on concrete was calculated on the basis of the results of periodic ultrasonic testing. After the completion of experiments, X-ray fluorescence analysis was conducted on the element contents at different depth locations of partial specimens. Experimental results showed that hydraulic pressure accelerated the sulfate attack on concrete, and high pressure yielded serious damage. In comparison with zero pressure, the accelerating coefficients of 0.1, 0.2, and 0.3?MPa hydraulic pressures were 1.48, 1.75, and 2.35, respectively. Hydraulic sulfate corrosion can bring additional sulfate ions into concrete and cause chemical and physical sulfate corrosions on concrete simultaneously, thereby resulting in serious damage on concrete. The reduction of w/c ratio and incorporation of fly ash are beneficial for concrete to resist hydraulic sulfate attack.     

Effect of sulphates and curing period on stress–strain curves and failure modes of soil–lime–natural pozzolana mixtures

Abstract

An experimental investigation was undertaken in order to assess the effect of sodium (Na₂SO₄) and calcium (CaSO₄·2H₂O) sulphates and curing period on stress–strain curves and failure modes of grey (GS) and red (RS) clayey soils stabilised by lime (L), natural pozzolana (NP) and their combinations (L–NP). Several soil–L–NP mixtures were studied to be used as subgrade soils for road pavements. Stress–strain curves were obtained from unconfined compressive strength (UCS) test made on several soil–L–NP specimens after curing for 7 and 120 days. Tests results showed that the use of L or L–NP without sulphates produced a significant increase in peaks stress of both clayey soils and then modified their stress–strain curves from nonlinear to linear behaviour almost up to 70% of peak stress after a longer curing period. However, the presence of 2% Na₂SO₄ or any CaSO₄·2H₂O content provided beneficial effects on peaks stress and stress–strain curves of both stabilised clayey soils and then improved their linearity almost up to 95% of peak stress after curing for 120 days. In contrast, the presence of 6% Na₂SO₄ caused undesirable effects. In addition, both sulphates greatly affected the failure modes of soil–L–NP specimens, particularly at a later stage.     

离子色谱法测定海水中氯离子和硫酸根离子

氯离子和硫酸根离子是海水中重要的无机阴离子,在研究海洋生态变化、海洋循环作用过程与海洋全球气候变化等领域具有重要的指示意义。其测定方法较多,但缺少相应的测试方法。本文对测定海水中Cl^–,SO₄^2–的离子色谱方法进行了优化,选用IonPacAS14碳酸盐选择性离子色谱柱,以3.5mmol/L Na₂CO₃+1 mmol/L NaHCO₃为流动相,可消除海水样品中碳酸盐及其他阴离子的干扰。该方法对Cl^–检出限为0.29mg/L,线性相关系数r²=0.999 2,对SO₄^2–检出限为0.42mg/L,线性相关系数r²=0.997 9。样品的加标回收率在95%～102%,Cl^–和SO₄^2–的相对标准偏差分别为1.92%和4.18%。该方法简便、迅速、灵敏、准确度高,可满足批量海水样品中Cl<...     

Seawater: an explanation of differential isothermal compressibility measurements in terms of hydration and ion-water interactions

Hydration, ion-water interactions, and water structure effects in seawater were studied by determining differences (Δβ) between the compressibilities of test salt solutions and the compressibilities of reference solutions. The reference solutions were distilled water and seawater (35%0), and the test salt solutions were either 0.13 m or 0.26m with respect to one of the following test salts: LiCl, NaCl, KCl, CsCl, NaF, NaI, MgCl₂, CaCl₂, BaCl₂, Na₂SO₄, K₂SO₄, and MgSO₄. The compressibility measurements (to 900 bars) were carried out at 2°C and also at 15°C using a differential method in which a pressure increase or a temperature increase causes Δβ to become less negative. At 1 bar and 15°C, the Δβ (0.26 m, distilled water reference) values ranged from ?1.14 × 10^?6 bar^? for NaI to ?3.84 × 10^?6 bar^?1 for Na₂SO₄, and the Δβ (0.26 m, seawater reference) values ranged from ?1.30 × 10^?6 bar^?1 for NaCl to ?3.04 × 10^?6 bar^?1 for Na₂SO₄. The Δβ values were used to calculate hydration numbers. Entropy of transfer, excess hydrogen bond breaking (determined by NMR), and effective radii of ions are properties which can be used to describe the influence of ions on water structure. The extent to which these properties correlate with Δβ values depends upon whether the ion is an anion or a cation, and this correlation forms the thesis that anions alter water structure in a different way than do cations.     

Sulphate complexation in seawater: A relation between the stability constants of sodium sulphate and magnesium sulphate in seawater from a determination of the stability constant of hydrogen sulphate and a calculation of the single ion activity coefficient of sulphate

The conditional stability constant of HSO₄^? has been determined at 25°C, 1 atm and a formal ionic strength of 0.7 M in solutions containing sodium, magnesium, chloride and sulphate. This was done spectrophotometrically (UV), using diphenylamine as indicator. The value obtained was 17.0 ± 0.1 (molar scale). Single ion activity coefficients for Na₂SO₄, K₂SO₄ and MgSO₄ have been calculated according to the Bates et al. (1970) model, assuming that the sulphate ion is not hydrated. It was found that the single ion activity coefficient of sulphate changes very little between Na₂SO₄, K₂SO₄ and MgSO₄ when the formal ionic strength is kept constant.These results have been used to obtain relations between the stability constants of NaSO₄^? and MgSO₄ valid for seawater.     

Diffusion coefficients of major ions in seawater

Self-diffusion coefficients of five major ions have been determined by a radioactive tracer method (capillary tube method) in seawater of salinity 34.86 at 25°C. Data are presented for Na⁺, Ca²⁺, Cl⁻, SO₄², and HCO₃⁻, which constitute about 95% by weight of sea salt. The influence of temperature and salinity on these coefficients has been studied for Na⁺ and Cl⁻ which are the major components of sea salt: self-diffusion coefficients of these two ions have been measured in seawater, at different temperatures for a salinity of 34.86 and at different salinities for a temperature of 25°C. Diffusion coefficients of the same ions have been determined at 25°C by using another radioactive tracer method (quasi-steady cell method). In this experiment, seawater ions were allowed to diffuse from natural seawater into dilute seawater. Data have been obtained at 25°C for Na⁺, Ca ²⁺, Cl⁻, SO₄²⁻ and HCO₃⁻, corresponding to different salinity gradients.     

Ion association of chloride and sulphate with sodium,potassium, magnesium and calcium in seawater at 25°C

Stoichiometric association constants, which have been measured for the ion pairs of Cl^? and SO₄^?2 with Na⁺, K⁺, Mg²⁺, and Ca²⁺, were used to determine the speciation in an artificial sea water containing only these ions. The resulting distribution is quite different to that found in earlier models in which chloride ion association was ignored. The concentrations of chloride ion pairs with the cations are 4 to 5 times larger than the concentrations of the sulphate ion pairs with the same cations. The total activity coefficients of the neutral salts in sea water calculated from the model are in good agreement with the experimentally measured values. The concentration of MgSO₄⁰ calculated to be present agrees with the amount determined from ultrasonic absorption data. The calculated solubility of gypsum is also in good agreement with the measured values.     

Dissolved inorganic carbon (DIC) and its carbon isotopic composition in sediment pore waters from the Shenhu area,northern South China Sea

The Shenhu area is one of the most favorable places for the occurrence of gas hydrates in the northern continental slope of the South China Sea. Pore water samples were collected in two piston cores (SH-A and SH-B) from this area, and the concentrations of sulfate and dissolved inorganic carbon (DIC) and its carbon isotopic composition were measured. The data revealed large DIC variations and very negative δ ¹³C-DIC values. Two reaction zones, 0–3 mbsf and below 3 mbsf, are identified in the sediment system. At site SH-A, the upper zone (0–3 mbsf) shows relatively constant sulfate and DIC concentrations and δ ¹³C-DIC values, possibly due to bioturbation and fluid advection. The lower zone (below 3 mbsf) displays good linear gradients for sulfate and DIC concentrations, and δ ¹³C-DIC values. At site SH-B, both zones show linear gradients, but the decreasing gradients for δ ¹³C-DIC and SO₄ ²⁻ in the lower zone below 3 mbsf are greater than those from the upper zone, 0–3 mbsf. The calculated sulfate-methane interface (SMI) depths of the two cores are 10.0 m and 11.1 m, respectively. The depth profiles of both DIC and δ ¹³C-DIC showed similar characteristics as those in other gas hydrate locations in the world oceans, such as the Blake Ridge. Overall, our results indicate an anaerobic methane oxidation (AMO) process in the sediments with large methane flux from depth in the studied area, which might be linked to the formation of gas hydrates in this area.     

The effects of sodium sulfate on the emissions characteristics of an emulsified marine diesel oil-fired furnace

Degraded diesel oils are commonly used in marine power plants to conform to the demands of shipowners for fuel economy. The burning of these marine fuel oils, which frequently contain various extents of oxides of iron, silicon, calcium, vanadium and potassium, such as Na₂SO₄, Fe₂O₃, SiO₂, CaO, V₂O₅, etc., are susceptible to form much more complex compounds of either gaseous or solid phases. The release of these emissions to the environment may cause atmospheric pollution and a health hazard to human beings. Emulsification of a fuel oil with water to produce a micro-water-particles-dispersed-in-oil (W/O) emulsion has been considered as one of the promising techniques to improve combustion characteristics of low-grade marine oils and in turn effectively help to reduce the release of air pollutants. Marine fuel oil A, which approximates ASTM No. 2D oil was used as the test oil and the surfactant Span 80 was used to promote the affinity and integrating force between the components of the emulsion. An emulsifying/homogenizing machine was employed to stir the emulsion mixture of the marine oil, distilled water, surfactant Span 80 and sodium sulfate (Na₂SO₄) powder of 300 ppm. The mechanically blended emulsion mixture was injected, atomized and burned in an oil-fired furnace using an automatic burner. Burning gas composition, burning efficiency and gas temperature were measured and analyzed. Compared to neat marine diesel oil, W/O emulsions had higher combustion efficiencies, higher concentrations of O₂ and SO₂, while gas temperatures were lowered and CO and NO_x production was reduced. The addition of sodium sulfate decreased combustion efficiency and NO_x concentration and increased O₂, CO, and SO₂ concentrations.     

Sulfur Isotopes in the Upper Part of the Black Sea Anoxic Zone

New data are reported on the sulfur isotope composition and concentration of sulfide and sulfate in the upper part of the Black Sea anoxic zone as a function of the potential water density. The observations were performed at a station with the coordinates 44.489° N and 37.869° E three times a week every two days. A local negative deficiency in sulfate concentration up to 1.7% related to the sulfate reduction processes was recorded. This anomaly in sulfate concentration was short-lived and did not affect the sulfur isotope composition. In the upper part of the anaerobic zone, the δ³⁴S(SO₄) value varied from 21.2 to 21.5‰, which could have occurred from mixing of water masses from the oxic zone (21.1‰) and the Bottom Convective Layer (23.0 ± 0.2‰). The sulfur isotope composition of sulfide ranged from ?40.8% at a depth of 250 m to ?39.4‰ at the upper boundary of the anoxic zone with a H₂S content of only 2.7 μM. Two models (mass balance and fractionation of sulfur isotopes using the Rayleigh equation) are considered to explain the differences in δ³⁴S(H₂S) values observed.     

Mechanisms of sulfur incorporation and isotope fractionation during early diagenesis in sediments of the gulf of California

Sediment cores were taken from the Gulf of California, and pore waters recovered by mechanical squeezing. The chemistry and isotopic abundance of sulfur in these pore fluids were compared with coexisting solid phases to deduce the mechanisms involved in pyrite formation. The results suggest that burrowing activities of benthonic organisms supply sulfate sulfur to sediments to depths of approximately 0.5 m from the surface. This is inferred from essentially constant pore water concentration profiles of dissolved ions in horizons where sulfate reduction is demonstrated by the presence of iron sulfides.For a core from Pescadero Basin, it is estimated that beneath the mixed zone, diffusion adds 0.4% sulfur by dry weight of sediment, whereas burial of sulfate adds less than 0.1% sulfur. It is shown that diffusion can add isotopically light sulfur to sediments, due to more rapid relative addition of ³²SO₄^2? compared to ³⁴SO₄^2? down a concentration gradient maintained by bacterial processes. The overall net isotopic value of the sulfate so added is $\text{δ}{}^{34}\text{S = ?4.5‰}$. The depth distribution of S-isotope in sulfur is controlled by the balance between a bacterial kinetic isotope effect preferentially removing ³²S relative to ³⁴S, and the supply of sulfate by diffusion. The isotopic fractionation factor, α, calculated by a mathematical formulation which takes diffusion into account, is larger (1.060±0.010) than when sulfate reduction is assumed to occur in a closed system (1.035). The larger value is supported by the sulfur isotope distribution in metastable iron sulfide. Essentially, the same open-system α was calculated for a core from Carmen Basin.     

~(35)SO_4~(2-)示踪法测定九龙江河口沉积中硫酸盐还原速率

在2011年7月利用35SO2-4培养示踪法测定九龙江河口两个站位(A站位位于咸淡混合区,盐度3~5;B站位位于海相区,盐度20~25)沉积柱中硫酸盐还原速率的垂直分布。结果显示A站位沉积柱中硫酸盐还原速率变化范围为54~2 345nmol/(cm3·d),从表层到底部先增大后减小,最大值出现在20cm深度附近;B站位硫酸盐还原速率在24~987nmol/(cm3·d)之间,分别在10cm和78cm深度附近出现两个峰值,分别为876nmol/(cm3·d)和987nmol/(cm3·d)。综合分析两个站位孔隙水中SO2-4、甲烷浓度和沉积物中总有机碳、温度和氧化还原电位的垂直变化趋势与其硫酸盐还原速率的分布规律,表明A站位沉积物中硫酸盐还原以有机矿化为主;B站位受到有机质矿化和甲烷厌氧氧化的共同作用;两个站位硫酸盐还原速率及垂直分布趋势受孔隙水中SO2-4浓度、有机质活性和温度的共同影响;根据各个层位硫酸盐还原速率估算两个站位硫酸盐还原通量(以硫计)分别为527.9mmol/(m2·d)和357.1mmol/(m2·d),表明硫酸盐还原是九龙江河口有机质厌氧矿化的重要路径。     

Influence of submersion season on the development of test panel biofouling communities in a tropical coast

The effect of test panel submersion season on the colonization of biofouling communities in a tropical coast revealed that the effects of panel submersion time should be taken into consideration for modelling fouling community recruitment dynamics in coastal systems or during the field trials of antifouling coatings. Wooden test panels fitted onto a raft were submerged during pre-monsoon, monsoon and post-monsoon seasons for the development of the biofouling community. Results showed considerable variation in the colonization of fouling communities on test panels submerged during different seasons. Barnacles, tubeworms, ascidians and seaweeds were the major fouling communities that colonized the test panels. The total biomass of the fouling communities that settled on the post-monsoon season panels varied from the initial value of 2.72 g dm⁻² to a maximum of 44.5 g dm⁻². On the panels submerged during monsoon season, the total biomass of fouling communities varied between 0.78 g dm⁻² and 69.9 g dm⁻². The total fouling biomass on the pre-monsoon season panels varied between 2.95 and 33.5 g dm⁻². Barnacles were the initial colonizers on the panels submerged during pre-monsoon and post-monsoon seasons. Soft-bodied organisms such as ascidians dominated the monsoon season-initiated panel series during the initial period.     

Kinetics of microbially mediated reactions: dissimilatory sulfate reduction in saltmarsh sediments (Sapelo Island, Georgia, USA)

A sediment disk reactor was tested in once flow-through mode to retrieve kinetic parameters for the Monod rate law that describes sulfate reduction. The experimental method was compared with a previously described procedure by the authors where a sediment plug-flow reactor was operated in a recirculation mode. In recirculation mode, accumulation of metabolic byproducts in certain cases may result in negative feedback, thus preventing accurate determination of kinetic information. The method described in this article provides an alternative to the recirculation sediment plug-flow-through reactor technique for retrieving kinetic parameters of microbially mediated reactions in aquatic sediments.For sulfate reduction in a saltmarsh site, a maximum estimate of the half-saturation concentration, K_s, of 204±26 μM and a maximum reaction rate, R_m, of 2846±129 nmol cm_{(wetsediment)}³ d⁻¹ was determined. The K_s value obtained was consistent with the one estimated previously (K_s=240±20 μM) from a different site within the same saltmarsh mud flat using a recirculating reactor. From the R_m value and reduction rates determined using ³⁵SO₄²⁻ incubation experiments, we infer that sulfate reduction is limited in the field. Substrate availability is not the main contributor for the limitation, however. Competition from other microbes, such as iron reducers affects the activity of sulfate reducers in the suboxic to anoxic zones, whereas aerobes compete in the oxic zone. High sulfide concentration in the pore water may also have acted as a toxin to the sulfate reducers in the field.     

Sulfate reduction and anaerobic methane oxidation in Black Sea sediments

Beyond the shelf break at ca. 150 m water depth, sulfate reduction is the only important process of organic matter oxidation in Black Sea sediments from the surface down to the sulfate–methane transition at 2–4 m depth. Sulfate reduction rates were measured experimentally with ³⁵SO₄²⁻, and the rates were compared with results of two diffusion-reaction models. The results showed that, even in these non-bioirrigated sediments without sulfide reoxidation, modeling strongly underestimated the high reduction rates near the sediment surface. A hybrid modeling approach, in which experimentally measured rates in the upper sediment layers force a model that includes also the deeper layers, probably provides the most realistic estimate of sulfate reduction rates. Areal rates of sulfate reduction were 0.65–1.43 mmol SO₄²⁻ m⁻² d⁻¹, highest in sediments just below the chemocline. Anaerobic methane oxidation accounted for 7–11% of the total sulfate reduction in slope and deep-sea sediments. Although this methane-driven sulfate reduction shaped the entire sulfate gradient, it was only equivalent to the sulfate reduction in the uppermost 1.5 cm of surface sediment. Methane oxidation was complete, yet the process was very sluggish with turnover times of methane within the sulfate–methane transition zone of 20 yr or more.     

Mechanisms of pore water organic matter adsorption to montmorillonite

The extent and mechanisms of adsorption of marine pore water organic matter to montmorillonite were studied in a series of batch and sequential adsorption experiments. Pore water natural organic matter (pNOM) and easily extracted natural organic matter (eNOM) were collected from Liberty Bay (Puget Sound, WA, USA) sediments. The pNOM and eNOM were each divided into two size fractions using a 1000 D ultrafilter. Batch adsorption isotherms were approximately linear, and the >1000 D fractions of both pNOM and eNOM had larger partition coefficients (K_d) than the <1000 D fractions. A two-component fit of the sequential adsorption data indicated that pNOM and eNOM contained a similar amount of NOM (30%) that was not surface reactive toward montmorillonite. After correcting the batch adsorption K_ds for the non-reactive components, the K_ds estimated by batch and sequential adsorption were identical (2.7 l/kg for >1000 D pNOM and eNOM, and 1.6 l/kg for <1000 D pNOM and eNOM). Mechanisms of adsorption were investigated by systematically changing conditions (pH, temperature and ionic composition) of >1000 D fractions during batch isotherm experiments. Adsorption of NOM was found to decrease with increased temperature, suggesting that hydrophobic effects were not the dominant adsorption mechanisms in this system. Ion exchange was also not an important adsorption mechanism because adsorption increased with ionic strength. The observed enhancement in adsorption with ionic strength indicated that van der Waals interactions were important in the adsorption of NOM. Ligand exchange was found to be a significant mechanism since the presence of SO₄²⁻ in solution reduced the amount of NOM adsorbed. Ca²⁺ enhanced adsorption slightly more than Na⁺, suggesting that cation bridging was involved. The relative contributions of van der Waals interactions, ligand exchange and cation bridging were estimated to be approximately 60%, 35% and 5%, respectively, for adsorption of NOM in a CaCl₂ solution.     

阳极溶出伏安法测定海水中低浓度镉

镉能积累于人体及生物体内造成慢性中毒,引起严重的“骨头病”[1],并与严重的心血管病有连带关系[2].海洋中镉的污染问题已引起人们极大的重视.目前,我国与世界其他国家一样,已将镉的污染列为国家海洋环境重点监测项目之一.