Redox environment effect on redox sensitive elements in surface sediments of the Changjiang Estuary hypoxia zone     

Shumei XU  Shikui ZHAI  Aibin ZHANG  Huaijing ZHANG  Haijian LU 《Frontiers of Earth Science》2008,2(1):10-16

The grain size and element (including redox sensitive elements and terrigenous elements) concentration of surface sediments from the Changjiang Estuary hypoxia zone and its adjacent sea area were measured in this research. Based on the obtained data, the hypoxic environment’s influence on the distribution of elements in surface sediments was further studied. We believe that the “redox environment effect” greatly influences the distribution of the RSE, which reveals the “patchy enrichment pattern” offshore in the hypoxia zone, while the distribution of the terrigenous elements which shows the “stripped enrichment pattern” near shore is mainly affected by “granularity effects”. Due to the existence of the hypoxia zone of the Changjiang Estuary, the distribution of the RSE such as Mo, Cd and V in the study area exhibits the characteristics of “redox environment effects”. __________ Translated from Marine Geology & Quaternary Geology, 2007, 27(3):1–8 [译自: 海洋地质与第四纪地质]  相似文献   

Sulfur redox reactions: Hydrocarbons,native sulfur,Mississippi Valley-type deposits,and sulfuric acid karst in the Delaware Basin,New Mexico and Texas     

C. Hill 《Environmental Geology》1995,25(1):16-23

Hydrocarbons, native sulfur, Mississippi Valley-type (MVT) deposits, and sulfuric acid karst in the Delaware Basin, southeastern New Mexico, and west Texas, USA, are all genetically related through a series of sulfur redox reactions. The relationship began with hydrocarbons in the basin that reacted with sulfate ions from evaporite rock to produce isotopically light ( ³⁴S = -22 to -12) H₂S and bioepigenetic limestone (castiles). This light H₂S was then oxidized at the redox interface to produce economic native sulfur deposits ( ³⁴S = -15 to +9) in the castiles, paleokarst, and along graben-boundary faults. This isotopically light H₂S also migrated from the basin into its margins to accumulate in structural (anticlinal) and stratigraphic (Yates siltstone) traps, where it formed MVT deposits within the zone of reduction ( ³⁴S = -15 to +7). Later in time, in th zone of oxidation, this H₂S reacted with oxygenated water to produce sulfuric acid, which dissolved the caves (e.g., Carlsbad Cavern and Lechuguilla Cave, Guadalupe Mountains). Massive gypsum blocks on the floors of the caves ( ³⁴S = -25 to +4) were formed as a result of this reaction. The H₂S also produced istopically light cave sulfur ( ³⁴S = -24 to -15), which is now slowly oxidizing to gypsum in the presence of vadose drip water.  相似文献   

Spatial and Temporal Distribution of Oxidation Events Occurring Below the Sediment-Water Interface     

Stefan  Forster 《Marine Ecology》1996,17(1-3):309-319

Abstract. Irrigation and bioturbation lead to transport of dissolved oxygen into anoxic sediments. The depthdistribution of local oxygen input and the total time of oxygen presence was measured at randomly sampled locations within anoxic sediments, originating from the North Sea.
In the laboratory, continuous redox potential records, displaying a transient increase and decrease when in contact with oxygen for a limited time, were used to record oxidation events'. Oxygen microelectrodes were used to confm the presence of oxygen. Measurements were performed for 180 d at 230 locations in the top 6 cm of sediment cores containing the natural macrofauna community.
4783 oxidation events m^-2· d^-1 were recorded within the upper 6 cm of the sediment. The number and duration of oxidation events declined with sediment depth below the oxic zone. Oxygen was present in the anoxic sediment, as determined from redox potential measurements, ≥ 6 h per day at 10% of the randomly chosen locations within the upper 3 cm. The overall distribution of oxidation events and their duration suggest that local, pulsed additions of oxygen by irrigation may be sufficient to maintain an oxidised sediment layer ( sensu J orgensen amp; R evsbech , 1989). Oxic environments along burrow walls rapidly fluctuate between oxic and anoxic conditions. Using oxygen microelectrodes the presence of oxygen (oxic conditions) in these halos was found to range from 2 to 12 h per day. Continuous redox measurements show that oxidised conditions fluctuate with the oxygen pulses and display the same durations, although these may range up to 21 h per day. Oxic and oxidised sediment volumes are estimated to represent < 1% and 3.7%. respectively, of the anoxic sediment to 6 cm depth. Recognition of temporal variability and spatial heterogeneity of sedimentary conditions may prove valuable for future conclusions drawn in other research fields.  相似文献   

Precipitation of authigenic uranium in suboxic continental margin sediments from the Okinawa Trough   总被引：1，自引：0，他引：1  

Masatoshi Yamada  Zhong-Liang Wang  Yoshihisa Kato 《Estuarine, Coastal and Shelf Science》2006,66(3-4):570-579

Concentrations of U and Th isotopes in Okinawa Trough and East China Sea sediment cores were determined by isotope dilution inductively coupled plasma-mass spectrometry (ID-ICP-MS) to investigate the behavior of redox sensitive uranium in suboxic hemipelagic sediments and determine their significance in oceanic uranium balance. ²³⁸U concentrations and ²³⁸U/²³²Th activity ratios in the East China Sea sediments showed no remarkable variation with depth. However, ²³⁸U and ²³⁸U/²³²Th ratios in the Okinawa Trough sediments were low in the surface oxidizing layer but increased where the suboxic condition was encountered. The distribution profiles of ²³⁰Th and ²³²Th concentrations were relatively constant with depth in both the Okinawa Trough and East China Sea sediment cores. These results suggested that there has been post-depositional precipitation of authigenic uranium within the suboxic Okinawa Trough sediment column. The post-depositional precipitation rates of authigenic uranium were estimated to be 47 ± 5 to >62 ± 8 ng cm⁻² yr⁻¹; these rates were comparable to those previously reported for several anoxic sediments. A mechanism controlling precipitation of uranium may be the downward diffusion of uranium U(VI), reduction to U(IV) and finally precipitation onto the solid phase. The accumulation rate of uranium for the Okinawa Trough sediments was approximately eight times higher than the world average rate reported for suboxic sediments. This removal of uranium in the oceanic budget increases the importance of the suboxic sediment sink.  相似文献   

In vitro simulation of oxic/suboxic diagenesis in an estuarine fluid mud subjected to redox oscillations     

Gwenaël Abril  Marc-Vincent Commarieu  Henri Etcheber  Jonathan Deborde  Bruno Deflandre  Milos K. Živađinović  Gwenaëlle Chaillou  Pierre Anschutz 《Estuarine, Coastal and Shelf Science》2010

Estuarine turbidity maxima (ETMs) are sites of intense mineralisation of land-derived particulate organic matter (OM), which occurs under oxic/suboxic oscillating conditions owing to repetitive sedimentation and resuspension cycles at tidal and neap-spring time scales. To investigate the biogeochemical processes involved in OM mineralisation in ETMs, an experimental set up was developed to simulate in vitro oxic/anoxic oscillations in turbid waters and to follow the short timescale changes in oxygen, carbon, nitrogen, and manganese concentration and speciation. We present here the results of a 27-day experiment (three oxic periods and two anoxic periods) with an estuarine fluid mud from the Gironde estuary. Time courses of chemical species throughout the experiment evidenced the occurrence of four distinct characteristic periods with very different properties. Steady oxic conditions were characterised by oxygen consumption rates between 10 and 40 μmol L⁻¹ h⁻¹, dissolved inorganic carbon (DIC) production of 9–12 μmol L⁻¹ h⁻¹, very low NH₄⁺ and Mn²⁺ concentrations, and constant NO₃⁻ production rates (0.4 - 0.7 μmol L⁻¹ h⁻¹) due to coupled ammonification and nitrification. The beginning of anoxic periods (24 h following oxic to anoxic switches) showed DIC production rates of 2.5–8.6 μmol L⁻¹ h⁻¹ and very fast NO₃⁻ consumption (5.6–6.3 μmol L⁻¹ h⁻¹) and NH₄⁺ production (1.4–1.5 μmol L⁻¹ h⁻¹). The latter rates were positively correlated to NO₃⁻ concentration and were apparently caused by the predominance of denitrification and dissimilatory nitrate reduction to ammonia. Steady anoxic periods were characterised by constant and low NO₃⁻ concentrations and DIC and NH₄⁺ productions of less than 1.3 and 0.1 μmol L⁻¹ h⁻¹, respectively. Mn²⁺ and CH₄ were produced at constant rates (respectively 0.3 and 0.015 μmol L⁻¹ h⁻¹) throughout the whole anoxic periods and in the presence of nitrate. Finally, reoxidation periods (24–36 h following anoxic to oxic switches) showed rapid NH₄⁺ and Mn²⁺ decreases to zero (1.6 and 0.8–2 μmol L⁻¹ h⁻¹, respectively) and very fast NO₃⁻ production (3 μmol L⁻¹ h⁻¹). This NO₃⁻ production, together with marked transient peaks of dissolved organic carbon a few hours after anoxic to oxic switches, suggested that particulate OM mineralisation was enhanced during these transient reoxidation periods. An analysis based on C and N mass balance suggested that redox oscillation on short time scales (day to week) enhanced OM mineralisation relative to both steady oxic and steady anoxic conditions, making ETMs efficient biogeochemical reactors for the mineralisation of refractory terrestrial OM at the land-sea interface.  相似文献   

电位落差法与氧化系数法对砂岩型铀矿氧化还原环境判定研究     

乔浩  李鹏飞  邓长生  王斌堂  梁文展 《铀矿地质》2022,(1):143-148

岩石的电位差(△Eh)的变化与成矿机理及探矿找矿有密切关系。文章以高锰酸钾作为氧化剂,采用电位落差法、氧化系数法来研究砂岩型铀矿的氧化还原电位,系统研究两种方法对砂岩型铀矿△Eh测定结果的影响,提升砂岩型铀矿氧化还原性的检测效率。结果表明,通过矿物成分中的Fe3+/Fe2+值判断矿化带的氧化还原特性,与电位落差法测定的结果相吻合,两种方法得到佐证。可将该电位落差法测砂岩型铀矿氧化还原电位引入铀矿勘测现场,对环境影响较小,现场初步检测工作效率提升。为野外寻矿探矿现场快速地对砂型铀矿氧化还原性判断提供了理论及技术支持。  相似文献   

氧化还原动态变化对沉积物砷和氟释放的影响:以河北白洋淀平原为例     

曹元元  郭华明  高志鹏 《现代地质》2022,36(2):533-542

季风性波动引起的降雨、径流和排泄过程会引发浅层地下水系统周期性氧化还原动态变化,从而对地下水系统中有害组分的迁移转化产生影响。为探讨氧化还原动态过程对沉积物中砷(As)和氟(F)释放的影响,本研究选择河北白洋淀地区沉积物样品,利用发酵罐作为反应器,建立氧化还原动态实验体系,并监测动态变化过程中实验体系各组分含量的变化。结果表明,碱性和还原环境均有利于地下水中As、F的富集。还原阶段较高的pH条件有利于溶液中F^-的解吸,且体系中有机物降解会产生大量HC0₃^-和C0₃^2-,与F^-发生竞争吸附而有利于F^-的富集。对于溶液中As的富集,一方面是由于还原条件下体系中的As以As(III)为主,受沉积物的吸附作用较弱,从而有利于As被释放到溶液中;另一方面是因为还原阶段较高的pH也会使反应体系中As和沉积物间的吸附作用被减弱,造成As的解吸附。由于实验所用沉积物砷含量较低,不同S0₄^2-浓度条件对氧化还原动态过程中As、F迁移的影响不明显。总之,氧化还原动态变化过程会强烈影响地下水系统中砷、氟的富集。  相似文献   

砂岩型铀矿床层间氧化带前锋区稀有元素富集机制   总被引：3，自引：0，他引：3  

陈祖伊  郭庆银 《铀矿地质》2010,26(1):1-8

在深入研究砂岩型铀矿床层间氧化带各地球化学分带中铀及其伴生元素的分布规律时,发现一些单价态(不变价)元素也常常富集在层间氧化带前锋区,其典型代表是钪(Sc)、钇(Y)和稀土元素(REE)等。作者在综合分析前苏联众多砂岩型铀矿床各地球化学分带中各种元素大量测试数据的基础上,论述了层间氧化带前锋区Eh值和pH值的变化规律以及它们所导致的变价元素(U、Se、Mo和V)和不变价元素(Sc、Y和REE)的分布规律和富集机制。实际上,层间氧化带前锋区既是氧化-还原电位(Eh值)又是酸碱度(pH值)的急剧变化区,两者大致同步消长。层间氧化带前锋区有两类地球化学障:单纯的还原障和还原-碱性综合障。两种地球化学障的发育与强度取决于原始未氧化岩石中硫化物、有机质和碳酸盐的含量。  相似文献   

Influence of water flux and redox conditions on chlorobenzene concentrations in a contaminated streambed     

Christian Schmidt  Marion Martienssen  Edda Kalbus 《水文研究》2011,25(2):234-245

Significant natural attenuation may occur on the passage of groundwater plumes through streambed sediments because of the transition from anaerobic to aerobic conditions and an increased microbial activity. Varying directions and magnitudes of water flow in the streambed may enhance or inhibit the supply of oxygen to the streambed and thus influence the redox zoning. In a field study at a small stream in the industrial area of Bitterfeld‐Wolfen, we observed the variability of hydraulic gradients, streambed temperatures, redox conditions and monochlorobenzene (MCB) concentrations in the streambed over the course of 5 months. During the observation period, the hydrologic conditions changed from losing to gaining. Accordingly, the temperature‐derived water fluxes changed from recharge to discharge. Redox conditions were highly variable between ? 170 and 368 mV in the shallow streambed at a depth of 0·1 m below the streambed surface. Deeper in the streambed, at depths of 0·3 m and 0·5 m, the redox conditions were more stable between ? 198 and ? 81 mV and comparable to those typically found in the aquifer. MCB concentrations in the streambed at 0·3 and 0·5 m depth increased with increasing upward water flux. The MCB concentrations in the shallow streambed at 0·1 m depth appeared to be independent of the hydrologic conditions suggesting that degradation of MCB may have occured. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

沉积型锰矿床的形成及其与古海洋环境的协同演化     

徐林刚 《矿床地质》2020,39(6):959-973

海相沉积型锰矿的成矿过程受古海洋沉积环境影响，而古海洋环境又与超大陆聚合与裂解、极端地质事件、生命演化等密切相关，因此，海相富锰地层是岩石圈、水圈、大气圈和生物圈等多圈层耦合关系与物质循环相关信息的重要载体。深层海水缺氧模型、最小氧化带模型和幕式充氧模型都显示海水中氧化还原梯度的变化是导致锰矿形成的最主要原因。全球范围内海相沉积型锰矿主要形成于古元古代、新元古代和显生宙3个地质历史时期。其中，元古宙时期，地球上发育了完善的氧化还原分层的古海洋结构；古元古代早期和新元古代，超大陆裂解引起的海平面升降变化导致古海洋氧化还原结构产生动荡，并促使大规模沉积型锰成矿作用发生；地球沉寂期（1800~800 Ma）涵盖了整个中元古代，这一时期仅在华北地台发育了少量沉积型锰矿床，反映该时期古海洋中锰的迁移受到了抑制；显生宙地球再次进入活跃期，经历了数次海洋缺氧事件，冰室-温室气候交替促使海水的化学性质剧烈变化，并在局部氧化还原分层的沉积盆地中富集形成沉积型锰矿床。总之，古海洋氧化还原环境的变化是沉积型锰矿形成的必要条件，同时，区域性沉积盆地的结构、海平面的升降、火山作用导致的物缘供给等多种因素都会影响沉积型锰矿的形成。与沉积型铁矿相比，沉积型锰矿对局部海水化学性质的变化更加敏感，综合研究铁锰矿床的共生与分异过程，将有助于更加有效的识别不同尺度的沉积过程与古海洋环境变化。  相似文献