Corrosion failure of marine steel in sea-mud containing sulfate reducing bacteria

The corrosion failure behavior of marine steel is affected by stress, which exists in offshore structures at sea-mud region. The sulfate reducing bacteria (SRB) in the sea-mud made the steel more sensitive to stress corrosion cracking (SCC) and weaken the corrosion fatigue endurance. In this paper, a kind of natural sea-mud containing SRB was collected. Both SCC tests by slow strain rate technique and corrosion fatigue tests were performed on a kind of selected steel in sea-mud with and without SRB at corrosion and cathodic potentials. After this, the electrochemical response of static and cyclic stress of the specimen with and without cracks in sea-mud was analyzed in order to explain the failure mechanism. Hydrogen permeation tests were also performed in the sea-mud at corrosion and cathodic potentials. It is concluded that the effect of SRB on environment sensitive fracture maybe explained as the consequences of the acceleration of SRB on corrosion rate and hydrogen entry into the metal.

Effects of anaerobe in sea bottom sediment on the corrosion of carbon steel

The in-situ study of steel corrosion in sea bottom sediment (SBS) was carried out by Transplanting Burying Plate method (TBP method). It was found that the corrosion rate of steel in the sea bottom sediment with sulfate reducing bacteria (SRB) could be as high as ten times of that in sea bottom sediment without SRB. The experiments in simulated sea bottom sediments with different SRB contents by artificial culturing showed that the electrochemical behavior of steel in the sea bottom sediment with SRB was different from that without SRB. SRB altered the polarization behavior of steel significantly. The environment was acidified due to the activity of SRB and the corrosion of steel was accelerated. The corrosion of carbon steel in sea bottom sediment is anaerobic corrosion, and the main factor is anaerobe. There are SRB commonly in SBS, and the amount of SRB decreases along with the depth of sediment. Because of the asymmetry and variation of sea bottom sediment, the most dangerous corrosion breakage of steel in SBS is local corrosion caused by SRB. So the main countermeasure of corrosion protection of sea bottom steel facilities should be controlling of the corrosion caused by anaerobe.

Corrosion of carbon steel influenced by anaerobic biofilm in natural seawater

The bacteria in the anaerobic biofilm on rusted carbon steel immersed in natural seawater were characterized by culturing and molecular biology techniques. Two types of anaerobic bacterium, sulfate-reducing bacteria (SRB) Desulfovibrio caledoniensis and iron-reducing bacteria Clostridium sp. uncultured were found. The compositions of the rust layer were also analyzed and we found that iron oxide and sulfate green rust were the major components. To investigate the corrosion mechanisms, electrochemical impedance spectra was obtained based on the isolated sulfate-reducing bacteria and mixed bacteria cultured from rust layer in laboratory culture conditions. We found that single species produced iron sulfide and accelerated corrosion, but mixed species produced sulfate green rust and inhibited corrosion. The anaerobic corrosion mechanism of steel was proposed and its environmental significance was discussed. (c) 2008 Elsevier Ltd. All rights reserved.

Effects of sulfate-reducing bacteria on the corrosion behavior of carbon steel

The influences of the growing process of sulfate-reducing bacteria (SRB) in seawater system on the medium state and corrosion behavior of carbon steel were studied by detecting solution state parameters and using corrosion electrochemical methods. The growing process of SRB in the seawater shows the three stages of growing, death and residual phases. The solution state parameters of the concentration of sulfide, the pH value and the redox potential changed during the three stages of the SRB growing process. And the corrosion rate of D36 carbon steel was accelerated during the growing phase and stable during the death and residual phases. The results indicate that the medium state and the corrosion rate of the steel do not depend on the number of active SRB, but depend on the accumulation of the metabolism products of SRB. (c) 2007 Elsevier Ltd. All rights reserved.

Selective and specific detection of sulfate-reducing bacteria using potentiometric stripping analysis

A fast, sensitive and reliable potentiometric stripping analysis (PSA) is described for the selective detection of the marine pathogenic sulfate-reducing bacterium (SRB). Desulforibrio caledoiensis. The chemical and electrochemical parameters that exert influence on the deposition and stripping of lead ion, such as deposition potential, deposition time and pH value were carefully studied. The concentration of SRB was determined in acetate buffer solution (pH 5.2) under the optimized condition (deposition potential of -1.3 V. deposition time of 250 s, ionic strength of 0.2 mol L-1 and oxidant mercury (II) concentration of 40 mg L-1). A linear relationship between the stripping response and the logarithm of the bacterial concentration was observed in the range of 2.3 x 10 to 2.3 x 10(7) cfu mL(-1). In addition, the potentiometric stripping technique gave a distinct response to the SRB, but had no obvious response to Escherichia coli. The measurement system has a potential for further applications and provides a facile and sample method for detection of pathogenic bacteria. (C) 2010 Elsevier B.V. All rights reserved.

Effect of sulfate-reducing bacteria on corrosion behavior of mild steel in sea mud

Microbiologically influenced corrosion (MIC) is very severe corrosion for constructions buried under sea mud environment. Therefore it is of great importance to carry out the investigation of the corrosion behavior of marine steel in sea mud. In this paper, the effect of sulfate-reducing bacteria (SRB) on corrosion behavior of mild steel in sea mud was studied by weight loss, dual-compartment cell, electronic probe microanalysis (EPMA), transmission electron microscopy (TEM).combined with energy dispersive X-ray analysis (EDX) and electrochemical impedance spectroscopy (EIS). The results showed that corrosion rate and galvanic current were influenced by the metabolic activity of SRB. In the environment of sea mud containing SRB, the original corrosion products, ferric (oxyhydr) oxide, transformed to iron sulfide. With the excess of the dissolved H2S, the composition of the protective layer formed of FeS transformed to FeS2 or other non-stoichiometric polysulphide, which changed the state of the former layer and accelerated the corrosion process.

The hydrogen permeation investigation of API X56 steel in sea mud

It was found that the corrosion rate of steel in the sea mud with sulfate-reducing bacteria (SRB) could be as high as 10 times of that in the sea mud without SRB. And the hydrogen permeation reaction would occur when metals were corroded. So it is necessary to investigate the effect of living SRB on hydrogen permeation in the sea mud. Cathodic potential was often added to metals in order to protect them. But hydrogen permeation could be affected by the cathodic potential. So it is also necessary to study the effect of cathodic potential on hydrogen permeation. In this paper, the hydrogen permeation actions of APT X56 steel in the sea mud with and without SRB at corrosion and cathodic potential were studied with an improved Devanathan-Stachurski's electrolytic cell. Experimental results showed that during the growth of SRB, the current density curve of hydrogen permeation was accordant with the growth curve of SRB. But the hydrogen permeation current density of APT X56 steel hardly changed in the sterilized sea mud. Compared with the hydrogen permeation current density of APT X56 steel in the sterilized sea mud, the hydrogen permeation of APT X56 steel in the sea mud could be accelerated by living SRB. Experimental results also showed that the hydrogen permeation current density increased rapidly when the cathodic potential was added to the three-electrode system of the cathodic cell, and then the hydrogen permeation current density could obtain a stable value slowly. So the cathodic potential added to the cathodic cell could accelerate hydrogen permeation.

油气、微生物与砂岩型铀矿形成关系研究——以东胜铀矿床和钱家店铀矿床为例

Sandstone-type uranium deposits are frequently found close to oil fields or uraniferous sandstones contain bitumen or petroleum. However, few evidence has been presented to indicate the association of uranium mineralization with petroleum oxidation. Thus, Dongsheng uranium deposit in Ordos Basin and Qianjiadian deposit in Kailu Basin are taken for examples to solve the puzzle. Integration data from sedimentary petrology, mineralogy, race elements geochemistry, isotope geochemistry and organic geochemistry, the uranium and petroleum sources, and diagenetic paragenesis of the host sandstone are analyzed, and then the genetic relationship between microbes, petroleum and uranium deposits are discussed. The observation under microscope shows that the host sandstone samples from Middle Jurassic Zhiluo Formation in the Dongsheng deposit contained different kinds of metamorphic rock fragments, which should have been derived form outcrops north to this basin. The LREE/HREE ratios of gneiss and amphibolite sampled from outcrops were close to the highest and the lowest LREE/HREE ratios of the sandstones with well-compared chondrite-normalized REE patterns, respectively. So these results consistently indicated that parent rocks of sandstones were mainly contributed from these two kinds of metamorphic rocks. There was very high Th/U ratio for granite gneiss, which was a mainly potential U resource. Hydrocarbon inclusions and adsorbed hydrocarbons are observed under fluorescence microscope in the host sandstone of Dongsheng uranium deposit, suggesting that the sandstones may have been utilized as oil migration pathways. Based on biomarker parameters, it is indicated that the inclusion oils and adsorbed hydrocarbons were marginally mature to mature, and were derived from humic-sapropel type organic matter under poor reducing freshwater to semi-saline environment. The features are similar to those of organic matter extracted from Triassic sandstone and source rock, but are different from that of cretaceous sandstone. Thus, it can be concluded that the inclusion oils and adsorbed hydrocarbons were mainly derived from Triassic lacustrine facies source rock. Observation results under Scanning Electron Microscopy and Electron Microprobe with Energy Spectrum Analysis show that, in Dongsheng area, the main uranium ore mineral is coffinite. The coffinite is intimately intergrown or coexists with pyrite and calcite, thus, the solution during mineralization stage is inferred to be alkaline. The alkaline environment is not favored for uranium to be pre-concentrated by absorption, and then be reduced abiogenetically. δ34S of pyrite and δ13C of calcite indicate that pyrite was formed by bacterial sulfate reduction (BSR) and part of the carbon of calcite has been dirived from oxidation of petroleum, respectively. Additionally, petroleum is found biodegraded. All the lines of evidence consistently indicate that petroleum was involved in uranium mineralization. Coffinite with microbe-like structures is found in the high U sandstone samples and is composed of nanoparticles, indicating the coffinite is biogenic. The conclusion are also supportted by laboratory experiment studies, which have shown that SRB are capable of utilizing U(VI) as the preferred electron acceptor for respiration and reduce U(VI) to U(IV) directly, coupled the oxidaton of organic matter and sulfate reduction. Based on the research results mentioned above, in the Dongsheng area, coffinite is likely to have formed by mixing of brine containing petroleum derived from Triassic with uranium-bearing meteoric water from outcrops north to Ordos Basin. SRB utilize hydrocarbon as carbon source, and directly reduce U(VI) resulting in precipitation of coffinite. The product of metabolism, H2S and CO2, was precipitated as pyrite and calcite during mineralization stage. Petroleum in fluid inclusions and adsorbed type in host sandstone from Lower Cretaceous Yaojia Formation in Qianjiadian uranium deposit, Kailu Basin, are derived from Jurassic Jiufotang Formation in this basin and the uranium mineral consists mainly of pitchblende. The δ34S and δ13C values of pyrite and calcite during mineralization stage indicate SRB have likely degraded petroleum, which is similar to that of Dongsheng deposit. The alkaline environment as indicated by the diagenetic mineral assemblage calcite, Fe dolomite, pyrite and pitchblende deposit suggests that U ore in the Qiangjiajiadian has a similar origin, i.e., direct reduction by SRB. However, less part of pitchblende is intergrown with kaolinite, suggesting the solution during mineralization stage is acidic. The environment is favorable for U(VI) to be adsorded on quartz or other mineral, and then reduced by H2S produced by SRB. Thus, it can be concluded that U(VI) reduction with petroleum oxidation by SRB and other microbes is an important ore-forming mechanism in petroleum-related sandstone-type uranium deposits. The finding is significant in that it provides a theoretical basis for exploration of both uranium and petroleumr.

硫酸盐还原菌混合菌群胞外聚合物对Cu^2＋的吸附和机理

生物吸附法是处理含重金属废水的一种新兴的处理技术。微生物所分泌的胞外聚合物（EPS）在微生物吸附重金属中起重要作用。硫酸盐还原菌（SRB）混合菌群分泌的EPS能有效的吸附水溶液中的Cu^2＋，Langmuir等温方程和Freundlich等温方程都能拟合实验所得吸附数据，最大吸附容量达到478．47mg／gEPS。水溶液的初始pH值对EPS吸附Cu^2＋影响明显，在pH为7时，吸附效率最高，pH增减，吸附效率明显下降。SRB混合茵群分泌的EPS的FT—IR分析表明，EPS对Cu^2＋的吸附主要在于EPS中的蛋白质的酰胺（Ⅱ）、羧基、多聚糖的C-O-C、OH和脂类等基团对Cu^2＋的强络合能力.

硫酸盐还原菌混合菌群胞外聚合物对Zn^2＋的吸附和机理

硫酸盐还原菌（SRB）混合菌群分泌的胞外聚合物（EPS）能有效地吸附水溶液中的Zn^2＋在初始p（Zn^2＋）为500mg/L时，EPS对Zn^2＋的吸附量达到326．07mg/g，g。Freundlich方程能相对较好地拟合实验所得吸附数据。SRB混合菌群分泌的EPS的IR分析表明，EPS吸附Zn^2＋起主要作用的官能团是多聚糖C-O-C，羧基和脂类官能团，而蛋白质和多聚糖的-OH对Zn^2＋的结合能力有限.

贵阳市阿哈湖水体和沉积物间隙水中汞的含量和形态分布初步研究

为了弄清楚酸性矿井废水的排放是否对阿哈湖造成了汞污染,我们研究了阿哈湖中汞的各种赋存形态(包括溶解气态汞、活性汞、颗粒态汞、溶解态汞、溶解态甲基汞、颗粒态甲基汞,以及沉积物间隙水体的溶解态汞和溶解态甲基汞)及其在水体和沉积物间隙水中的剖面分布.实验数据表明,溶解态甲基汞浓度在沉积物下2～5 cm处最高,随深度增加而逐渐降低,与硫酸盐还原菌(SRB)的分布相吻合,说明水体-沉积物界面是甲基汞的产生地点;并且在沉积物中高浓度硫酸根浓度高达1100mg/L时,硫酸根浓度与甲基汞浓度依然一致.

红枫湖有机氯污染物的生物地球化学

本研究以红枫湖为主要研究对象，对环境各介质中PCBs和OCPs进行了研究，讨论了理化因素TOC、粒度、SPM、微生物等对于PCBs和OCPs的影响，对各介质中PCBs和OCPs的组成进行了分析，讨论了红枫湖地区PCBs和OCPs的来源，并对其污染水平进行了评价，得到以下几点认识： 1、对红枫湖水体和沉积物的理化性质进行了分析，和洱海进行了对比。湖泊沉积物有机质含量和C/N比值表明红枫湖沉积物有机质主要来源于河流输入和湖泊内部，洱海主要以湖泊内源为主，与后面PCBs和OCPs分析结果相符。湖泊沉积物有机质及DNA呈现同一规律，表层是有机质和DNA的含量较高的区域，表层至底层整体呈逐渐降低的趋势，表明表层是微生物量和活性最高的层段，有机质的降解主要发生在此区域。湖泊沉积物粒度与有机质和DNA变化趋势一致，暗示了有机质的降解过程主要发生在表层，SRI和SRB的分析表明微生物在有机质降解过程中起着至关重要的作用。 2、红枫湖沉积物中7种PCBs的含量范围在3.2～31.6ng/g之间，主要以PCB28和PCB52为主。其中PCB28的含量范围在0.5～4.6ng/g，平均为1.8ng/g， PCB52含量在0.4～28.1ng/g。PCB28和PCB52低氯取代的PCBs占PCBs总量的60%以上。各点沉积物中PCBs的组成基本一致，其含量的变化主要与其输入来源和环境条件相关。沉积物中PCBs随深度整体呈现降低的趋势，但表层含量比次表层低，表明近年PCBs的输入降低。PCBs与TOC和粒径呈现较显著的正相关关系，与其自身的理化性质相关，PCBs具有较高的憎水性，倾向于在颗粒态中分布，也暗示了其来源。 3、红枫湖沉积物中13种OCPs的组成主要以HCHs和DDTs为主。其中HCHs的含量范围1.6～8.9ng/g，平均值为3.2ng/g，沉积物柱均值表现为HW>DB>HE>JJD；DDTs的含量范围在0.9～25.7ng/g，平均值为7.8ng/g，沉积物柱均值表现为HW>HE>DB>JJD。HCHs按其组成来看，以β-HCH和γ-HCH为主，DDTs以p,p’-DDE和p,p’-DDT为主。α-HCH/γ-HCH的比值在范围在0.1~3.0之间，表明HCH在环境中发生了改变，而且林丹的用量高于混合HCHs。DDT/DDE+DDD的比值基本都小于1，暗示DDTs在环境中发生了较长期的变化，β-HCH和p,p’-DDE的高含量也暗示了大气来源可能也是红枫湖地区OCPs的主要来源之一。 4、红枫湖湖水、汇入汇出河流及其周边土壤中PCBs和OCPs的分析，显示PCBs和OCPS在过滤后水中含量较低，主要分配在悬浮颗粒物中，悬浮颗粒物中的PCBs和OCPs组成与周边土壤中的组成基本一致。HCHs和DDTs的组成和α-HCH/γ-HCH、DDT/DDE+DDD的比值暗示水中悬浮颗粒物及其PCBs和OCPs主要来源于周边土壤和大气沉降。 5、 红枫湖后五鱼体内PCBs主要以4～6氯取代的PCBs的同系物为主，OCPs以HCHs和DDTs为主。鱼体内PCBs和OCPs对于水体的富集系数达到102～105。PCBs富集系数随氯取代数目的增加而增加，表明其生物有效性随氯取代数目的增加而增加，高氯取代的PCBs更容易通过食物链在高营养级生物体内富集，对人体造成危害。 6、 大气总悬浮颗粒物TSP中及背景区土壤中PCBs和OCPs的分析，与其它环境介质中结果基本一致。红枫湖地区大气、水、沉积物、生物和土壤各环境介质中PCBs和OCPs的组成基本一致，表明其来源具有一致性。α-HCH/γ-HCH和 DDT/DDE+DDD的值，及β-HCH、p,p’-DDE的高的比例，暗示红枫湖地区OCPs在环境中经历了较长时间的变化，而且大气长距离传输对于该区OCPs和PCBs的来源具有一定的贡献。从各因子的分析可以得出，红枫湖为该地区PCBs和OCPs的汇。 7、我国PCBs和DDTs、HCHs的含量除了典型区外，在国内外都处于较低和中等污染水平，红枫湖地区整体处于较低污染水平。根据Long和Chapman等对沉积物中POPs的评价方法，红枫湖沉积物中PCBs只有一个样品处于ERL和ERM之间，其它都低于ERL值，表明PCBs对生物造成不利影响的可能性较低；DDTs的值大部分处于ERL和ERM值之间，对生物造成不利影响的可能性较大；γ-HCH的值都低于TEC值，对生物的潜在影响较小。

西南喀斯特坡地土壤硫的生物地球化学循环研究

我国西南喀斯特和酸沉降双重背景下的土壤硫循环实际上与碳酸盐岩溶解及土壤质量演化密切相关。目前，国内有关喀斯特地区土壤硫生物地球化学循环的研究还鲜见报道。 本论文以典型喀斯特地区石灰土和黄壤为研究对象，研究自然坡地土壤中硫的赋存状态及其同位素组成特征，硫循环关键微生物硫酸盐还原菌(SRB)的分布特征，结合土壤基本理化参数探讨喀斯特地区土壤中硫的生物地球化学循环的一般过程，得到如下认识：土壤中SO42-还原和有机硫矿化是同步进行的，而SO42-和有机硫的相互转化构成了土壤硫循环的主要内容。通过对比土壤各形态硫含量、SRB及各形态硫同位素组成的垂直分布特征，可以很好的阐释与土壤深度相关的硫循环过程，同时也可以很好的判别土壤内部的SO42-、有机硫和FeS2迁移过程。而影响各形态硫含量、SRB及硫氧化菌（SOB）在土壤中分布的因素不是单一的，与土壤类型、植被状况、土壤基本性质如有机碳、氮含量及pH值及土壤不同深度活性金属离子分布、厌氧状况等多因素的综合作用有关。

云贵高原湖泊近代沉积作用的Fe、Mn、S指示

铁、锰、硫具有强烈的氧化还原敏感性，在湖泊沉积地球化学过程中扮演着重要的角色。铁、锰、硫控制了沉积物中的氧化还原分带，对磷及其它一些微量金属元素的形态和分布具有重要影响。因此本文中我们选择铁、锰、硫来指示湖泊沉积作用中氧化还原过程的变化，为进一步高精度提取环境信息奠定基础。本文对比阿哈湖、洱海和阳宗海，通过铁、锰、硫在湖水、孔隙水和沉积物体系内的垂直剖面特征分析，阐述了三湖沉积物中氧化还原过程的区别、氧化还原边界层对铁锰循环的控制作用以及铁-锰-硫对重金属的控制作用，深入探讨了铁、锰、硫及微量元素记录的早期成岩改造特征及其对湖泊沉积作用的指示意义，进一步阐明了沉积物中的有机质降解规律及早期成岩机制，获得了如下结论：1．阿哈湖水中铁、锰出现季节性释放，锰的季节性释放强度比铁大；在冬季和夏季，阿哈湖沉积物界面铁、锰均出现富集。冬季的富集程度强于夏季，锰的富集程度远远强于铁。沉积物表层由冬季的黄褐色转变为夏季的黑色，表示铁、锰氧化物层转变为FeS层。2．洱海沉积物中，铁、锰均在沉积物一水界面出现富集，界面以下，铁、锰的含量逐渐递降。铁、锰在孔隙水中产生扩散迁移，而在沉积物表层形成富集，说明洱海沉积物表层处于较好的含氧状况，氧化还原边界层处于沉积物中；阳宗海沉积物孔隙水中铁锰峰值均位于界面2cm处，而沉积物中铁在表层出现亏损，表明夏季阳宗海表层处于缺氧状态，氧化还原边界层位于湖水中。3．铁、锰的界面扩散和沉降通量在不同湖间差异较大。但锰的扩散通量占沉降通量的比例高于铁，锰在界面的沉积后再迁移程度和沉积记录的改造程度比铁显著。湖泊中铁、锰在有机质降解过程的驱动下，围绕沉积物一水界面形成氧化还原循环。其中锰的循环相当激烈，铁则较为缓和。铁、锰界面循环受氧化还原边界层和沉积物—水界面的双重控制。4．三湖沉积物界面处均存在硫酸盐的还原作用。洱海硫酸盐由于其含量较低以及表层良好的含氧状况因此不可能成为有机质降解的主要氧化剂，而阳宗海和阿哈湖则情况相反。阿哈湖沉积物柱芯好氧菌和SRB的分布进一步证实了表层处硫酸盐在SRB的参与下强烈的还原作用，同时说明有机质的好氧和厌氧降解并不是完全对立的；水体向沉积物内部扩散是高硫酸盐浓度湖泊的主要清除作用，而对于低硫酸盐含量湖泊而言，水体浮游生物如藻类吸收和同化作用应是水体硫酸盐的主要清除机制。5．三湖沉积物硫主要都以黄铁矿存在。阳宗海的AVS含量较高，AVS和FeS_2在界面的富集进一步证实了在阳宗海沉积物界面存在着强烈的硫酸盐还原作用；阿哈湖沉积物中硫酸盐的还原与季节无太大联系。在夏季和冬季，沉积物表层均表现出明显的SO_4~(2-)还原作用。只不过随着氧化还原边界层的迁移，SO_4~(2-)还原作用的范围也随之发生迁移。铁氧化物作为电子受体参与有机质分解的过程中，水铁矿和纤铁矿等Feo首先被还原而溶解出来。同时，Feo和Fec是可以互相转化的，针铁矿和赤铁矿等晶体铁氧化物可以向水铁矿和纤铁矿转化。6．三湖中Corg都表示出明显的降解趋势，证明了沉积物表层存在的早期成岩作用。洱海表现出“沉降一降解一堆积”三阶段分布特征，而阳宗海和阿哈湖沉积物中Corg表现出“降解一堆积”二阶段分布特征；洱海沉积物中有机质的选择性分解不明显，C／N指示沉积物有机质主要来自无纤维束的陆源植物；阿哈湖沉积物中C／N很高，均>20，且随深度增加呈现上升的趋势，说明阿哈湖沉积物中有机质含易降解的低N和难降解的高C，有机质主要来源于陆源输入。7．洱海和阳宗海沉积物中均存在明显的重金属再迁移现象。洱海沉积物中铁、锰循环对Pb、Cu的迁移影响很大；颗粒物的吸附一解析作用是影响Cd迁移的主要因素；洱海沉积物中可迁移释放的Ni含量并不高。8．阳宗海沉积物孔隙水中Ni、Cu、Cd均与铁、锰表现出良好的相关性，铁、锰氧化物的还原是造成它们在孔隙水表层富集的主要控制因素。而Pb与铁、锰呈现微弱的正相关。Pb、Cd相对于Cu、Ni的释放趋势较强，再迁移作用较剧烈。Pb、Cd在表层孔隙水中与一些有机、无机化合物络合，由于沉积物的吸附作用而再次沉降到沉积物表层形成富集。沉积物中重金属的再迁移主要受有机质降解、铁锰氧化物还原和硫化物沉积控制，但是不同的湖泊控制因索各不相同。

季节性氧湖泊微量金属元素的界面地球化学行为

沉积物表层几厘米范围经常呈现某些微量金属元素富集的现象，过去常笼统地认为这是工业革命以来人为污染不断加剧的证据。但近来的研究却证明强烈的早期成岩作用可以在一定程度上造成微量金属元素在沉积物中的再迁移现象，使得其环境记录失真。因此沉积物中元素分布记录不能完全反映对流域输入的物质组成特征。另外，在一定条件下，沉积物中部分金属元素也可再次向上覆水体释放，造成“二次污染”问题，严重威胁到湖泊／水库的水质安全，成为埋藏在湖泊深处的一颗“定时炸弹”。各种地球化学过程在沉积物一水界面附近造成的重金属元素的源／汇效应因此日益受到人们的重视。近年来贵州红枫湖水质季节性恶化事件频繁出现，作为贵阳市饮用水源的阿哈湖水质也开始出现季节性恶化趋势。紧迫的环境问题及重要的科学意义促使我们系统开展了红枫湖、啊哈湖沉积物一水界面微量金属的地球化学行为研究。两湖都是黔中地区人工水库，具有岩溶湖泊的共性，也具有明显的区别。红枫湖湖水具有典型的岩溶水化学特征，湖水中度富营养化；而啊哈湖受矿山废水的影响，同时由于近年的人工石灰投放等原因，造成该湖湖水具有极硬水、硫酸盐型水特征，矿化度达到600tng／L。我们对上述两湖进行了详细研究，获得了如下的研究成果：1．硫酸盐还原细菌（SRB）及铁还原细菌（DIRB）的计数直观地指示了有机质早期成岩过程中各电子受体依次利用的分带性：即硫还原（锰还原）叶铁还原。孔隙水中硫酸根及溶解铁分布与SRB和D工RB的分布吻合。沉积物孔柱的模拟实验、各类还原性微生物计数及与孔隙水中铁锰、硫酸根分布的综合分析证实了微生物的作用是厌氧环境中各种还原反应的不可缺少的因素，界面附近氧含量的变化是引起水质恶化的基本外因。模拟实验的结果还解释了铁、锰、硫在季节性缺氧湖泊中的循环机理。2．微生物计数及生物大分子分析证实了上层沉积物（0-10厘米）是微生物活跃最为强烈的区域，易降解有机质在此区域被降解。红枫湖沉积物有机质降解持续的深度较深〔达到10cm），而啊哈湖沉积物有机质降解持续深度较浅，仅为4厘米，这主要是由于两湖都是季节性厌氧型湖泊，红枫湖在缺氧季节，有机质厌氧降解所需的电子受体迅速消耗，使得缺氧季节该湖有机质降解速率相对缓慢；啊哈湖受到大量煤矿废水注入，水体及沉积物中硫酸根、铁锰含量异常高，并在厌氧季节里为微生物厌氧呼吸提供充足的电子受体，因而易降解部分有机质在表层迅速被氧化，而且该湖沉积速率相对较慢，有机质有相对充裕的时间在上层被降解，避免了被掩埋的命运。3．啊哈湖沉积物孔隙水及界面水δ13CDIC及DIC浓度的分析，显示啊哈湖沉积物产甲烷过程很弱或不明显。这主要是受到硫酸盐还原作用的抑制。从δ34SSO42-SO42-相关关系及硫酸盐还原菌分布特征，可以在深度上划分为两种还原过程及硫同位素分馏过程：慢速还原阶段（6厘米以下），硫同位素分馏程度较大，最大分馏达13．71％。分馏因子约为1.024-1.026之间；快速还原阶段（0-6厘米），硫同位素具有明显分馏，最大达到38‰，这与快速还原过程硫同位素分馏较小的规律相反，主要原因是由于表层同时出现有还原态硫的氧化反应．产生较负的δ34S-so41，δ34S-SO42--SO42-的变化反映出混合过程。通过研究我们进一步还推断，采样点沉积物下部还有煤矿硫源的输入。4．两湖沉积物中铁、锰、硫的还原作用发生位置都具有季节性沿沉积深度上下迁移的特性，部分微量金属元素扩散通量因此发生季节性变化。受沉积物中铁锰含量的控制，红枫湖沉积物一水界面铁锰循环作用比啊哈湖弱。啊哈湖锰含量很高，导致界面附近锰的循环剧烈且远强于铁的循环，并在一定程度上引起部分微量金属在沉积物上层强烈富集。5．通过红枫湖后五沉积物剖面研究，我们发现各种微量元素由于其自身不同的地球化学性质差异，早期成岩过程对其在沉积物中的垂直分布特征的改造程度是不同的。①锰具有明显的向上富集趋势，铁在沉积物中的分布特征的后期改造作用就比较弱。②钻、镍分布的后期改造程度与铁相似，从总量来看再迁移程度比较弱。③铜、锌在早期成岩过程中逐渐向沉积物中上部富集，这主要是与铜锌强烈的亲硫性引起的。钥的表层富集现象最为明显，沉积后再迁移效应显著。由其含量在上层沉积物中的两重峰值，可以指示界面剧烈的锰循环及界面下硫酸盐还原作用对它的联合控制。6．与红枫湖相比，啊哈湖沉积物金属元素再迁移特征有很大的不同：①通过部分微量金属元素地球化学相态分析，各相态微量金属分布主要服从其总量分布特征。②沉积物稀土配分模式明确指示了啊哈湖成湖基底的位置，即沉积物－水界面下18-19厘米以下。③通过Ti、Zr、ΣREE＋Y等的分析也显示了成湖前原始基底的存在位置，同时它们在沉积物中的含量变化特征还反映了该湖扩容后陆源输入的减少。④在沉积深度上铁锰及部分微量金属元素出现明显的分离现象。⑤通过相关性分析，Fe与Cu，U、Mn与Pb，C0，Ni，Cd，Zn等都存在很好的相关性，表明它们之间具有相似的界面地球化学行为。Fe型元素与Mn型元素分布差异的原因可以简约的概括为：锰的界面循环极为强烈，导致再迁移程度很高；而铁的循环相对较弱，又容易受到上层硫酸盐还原作用的抑制，因此再迁移程度不高。此外，由岩溶地区湖泊较强的酸中和能力及近年来的人为石灰投放，沉淀PH不同导致微量金属元素间发生分离，引起下游大坝处金属元素的输入差异。因此，啊哈湖大坝附近沉积物中微量金属元素的分布特征应受到沉积后再迁移和受 pH控制的煤矿废水输送差异联合制约。