海洋沉积物中有机质早期成岩矿化路径及其相对贡献

陆架边缘海沉积物是重要的生物地球化学反应器,海洋中90%以上的有机质沉积于此并在早期成岩作用过程中矿化.其矿化路径包括有氧呼吸、反硝化、锰氧化物还原、铁氧化物还原、SO4(-2)还原和CO2还原,并按生成自由能减少的顺序依次发生,构成理想的氧化还原序列.定量研究有机碳矿化路径及其对有机质矿化的相对贡献对揭示能量分配和碳...     

城市纳污河流沉积物微生物群落结构特征

以南京市运粮河沉积物为研究对象,通过磷脂脂肪酸(PLFA)技术分析了不同水期城市纳污河流沉积物微生物群落结构特征。结果表明:在不同的水期运粮河沉积物微生物量出现了显著差异,温度是导致微生物量在丰、平、枯三期出现显著差异的主要因素(P<0.05);在相同水期,营养物质含量高的地方对应着高的微生物量;16:0 iso、17:0 anteiso、15:0 iso这几种PLFA所指示的革兰氏阳性菌(G+)是影响运粮河沉积物微生物群落构成的主要菌落,导致沉积物微生物群落结构出现显著差异的环境因素是水期;单不饱和/支链脂肪酸比值可以作为反映水环境系统整体营养水平的指标,在C/N比值升高时微生物会将单不饱和脂肪酸转变成环丙基或者饱和脂肪酸以适应新的环境;PLFA含量比[c(i15:0)+c(i17:0)]/[c(a15:0)+c(a17:0)]可以作为指示水环境碳素含量的标志。     

南海东北部HD196A岩心的自生条状黃铁矿

自生黄铁矿是海洋沉积物缺氧硫酸盐还原过程的主要产物。南海东北部的HD196A岩心中发现大量条状的自生黄铁矿,以中空或实心为主。含量分析表明,岩心500cm附近为黄铁矿富集带,与沉积物有机碳(Corg)、硫酸盐[SO4]2-、甲烷(CH4)以及碳酸钙(CaCO3)的地球化学特征分界一致,是岩心的沉积边界,反映了沉积物所处的缺氧环境。岩心沉积物地球化学剖面表明,有机质参与的硫酸盐还原过程和甲烷厌氧氧化作用是黄铁矿形成的主要因素。黄铁矿异常可以作为指示沉积物甲烷异常的标志之一。     

陆架边缘海沉积物有机碳矿化及其对海洋碳循环的影响

边缘海沉积物是海洋重要的碳储库,其内部的碳循环主要是由有机质矿化分解过程来驱动的。有机碳进入边缘海沉积物后,矿化分解为溶解无机碳(DIC)进入沉积物孔隙水并扩散到上层水柱,参与海洋系统碳循环;同时还有部分DIC与钙镁等离子结合形成自生碳酸盐,保存于沉积物碳库。从生物地球化学角度探讨有机质埋藏机制和效率,在此基础上重点综述沉积物硫酸盐还原、产甲烷和甲烷厌氧氧化过程的耦合机制,以及有机质矿化对自生碳酸盐形成的影响等方面的研究进展,以期加深对陆架边缘海沉积物在全球碳循环收支平衡中的作用及其气候环境效应的认识。     

贵州红枫湖沉积物有机质的酶及微生物降解

文章通过DNA、α-葡萄糖苷酶和硫酸盐还原菌等的变化,研究了贵州红枫湖沉积物中有机质的酶及微生物降解.有机质在微生物及其分泌的胞外酶的作用下被降解,在沉积物深度11cm以下被降解到相对较低的含量.DNA的分布表明表层9cm的沉积物深度内微生物的活动较为强烈,是微生物降解有机质的主要位置.α-葡萄糖苷酶在悬浮层含量最高,达0.75μmol/min*g干沉积物,提示有机质中的淀粉和糖原等物质在悬浮层降解较为激烈,被大量分解;随着沉积物深度的增加α-葡萄糖苷酶活性减弱,在有机质降解明显开始变缓的11cm沉积物中,α-葡萄糖苷酶活性已降低到0.17μmol/ming干沉积物.分子生物学的研究表明红枫湖沉积物表层7cm是硫酸盐还原菌的主要分布位置,结合有机质和SO_2-4含量的研究结果,提示红枫湖沉积物中SO_2-4不可能成为有机质氧化的主要电子受体,硫酸盐还原的限制因素也不是有机质供应.     

海洋沉积物甲烷厌氧氧化作用(AOM)及其对无机硫循环的影响

甲烷厌氧氧化作用(AOM)在调控全球甲烷收支平衡以及缓解因甲烷引起的温室效应等方面扮演着十分重要的角色,成为近些年来海洋生物地球化学领域的研究热点之一.一般而言,海洋沉积物孔隙水硫酸盐还原主要是通过2种反应途径来完成,即氧化有机质途径和AOM途径.长期以来,与有机质氧化途径相关的硫酸盐还原作用研究已有充分展示,而由AOM驱动的硫酸盐还原及其对自生硫化铁形成与埋藏的重要贡献却被严重低估.侧重从生物地球化学、同位素地球化学等角度,综述近些年来不同环境条件下海洋沉积物AOM作用发生的地球化学证据和AOM对沉积物孔隙水硫酸盐消耗比例的贡献大小及其调控因素.AOM过程产生的H2S会与沉积物中活性铁结合形成自生铁硫化物.与沉积物浅表层条件相比,AOM过程固定的自生铁硫化物不容易发生再氧化,更利于在沉积物中埋藏保存起来.AOM与海洋沉积物硫酸盐还原作用相偶联,由AOM驱动的硫酸盐还原过程对海底自生铁硫化物形成与埋藏的重要贡献不容忽视.该综述有助加深对海洋沉积物AOM作用的认识及其对硫循环的全面理解.     

火山活动与海侵影响下的典型湖相页岩有机质保存差异分析

黑色富有机质页岩是页岩油气生成和赋存的主要母体,是强还原环境水体的沉积产物,在其形成过程中,细菌硫酸盐还原作用(BSR)对水体环境影响明显,但BSR强度如何影响有机质的保存尚未得到关注。我国陆相湖盆富有机质泥页岩广泛发育,形成过程中常常伴随有火山活动或者海侵等事件,大量硫酸盐进入湖盆,改变水体的沉积环境,不同环境下BSR对黑色页岩有机质保存的影响明显不同。本次研究选取鄂尔多斯盆地延长组长7段页岩、松辽盆地青山口组和嫩江组页岩作为对象,同时与现代沉积物进行对比。研究表明,TOC与TS之间关系复杂,但细菌硫酸盐还原强度指数(SRI)与TOC呈现幂指数变化,且表现出两阶段变化的特征。当SRI大于1.375时,TOC整体偏低,指示了强硫酸盐还原作用消耗大量有机质;当SRI小于1.375时,TOC明显较高,指示了弱硫酸盐还原作用对有机质消耗相对较少,更有利于有机质保存。火山活动和海侵作用均向水体提供了大量硫酸盐,但对陆相湖盆页岩中有机质的保存影响不同。火山活动影响的长7段页岩SRI普遍小于1.375,BSR对有机质消耗相对弱,页岩TOC高。而受海侵影响的青山口组一段底部和嫩江组一段底部页岩SRI大于1.375,BSR过度消耗了大量有机质,使得页岩TOC偏低。嫩江组一段下部SRI指数更高,海侵强度更大,BSR反应更强,更不利于有机质保存。     

海洋沉积物中自生硫化铁及其意义

自生硫化铁,指酸溶硫化铁和酸不溶硫化铁,广泛存在于海洋沉积物中。随着沉积环境的不同,其分布特征和酸溶硫化铁与残余硫化铁的比例关系也不同。这一问题受到地球化学家们的重视。 1.在海洋沉积物中,大量模拟实验表明,在早期成岩过程中,沉积物中硫酸盐在硫酸盐还原细菌的媒介下,参与了有机物质的降解反应,接受了某些有机物质因氧化而失去的电子,本身被还原。而S~(2-)与沉积物中Fe~(2+)有较强的亲合力,随即形成粗糙结晶形式的单硫化     

铁组分对早期海洋化学演化的指示

地球表生环境在地质历史时期经历了剧烈的波动,为当前建设宜居地球提供了重要参照。铁组分是重建古海洋氧化还原状态演化的重要指标,但现有的研究集中于FeHR/FeT和Fepy/FeHR两个比值的应用,而对其中不同组分所携带的信息缺少深入的挖掘。本研究统计了已发表的、泥盆纪之前的、采用程序萃取方法获得的铁组分数据,对其中不同的组分所可能指示的海洋化学信息进行了研究。我们发现氧化环境中氧化铁的含量有可能用于追踪长周期上大气-海洋系统的氧含量波动、总铁含量与海洋中铁的含量密切相关、铁化环境中黄铁矿铁的含量对海洋硫酸盐库大小的演化有很好的响应。我们的工作表明,铁组分指标是指示海洋局部氧化还原状态的强大指标,其不同的组分与海洋中氧气、碳和硫酸盐等存在极强的交互过程,可以被用来重建海洋的化学演化。     

莱州湾海岸带表层沉积物的黑碳及其与POPs的相关性研究

在莱州湾海岸带采集了62个表层沉积物样品,对黑碳(BC)的含量及其空间分布特征进行了研究,同时探讨了BC与持久性有机污染物(POPs)的关系。结果表明:(1)莱州湾海岸带表层沉积物中BC的含量范围为0.02~9.35 mg/g,平均为0.98 mg/g,低于欧美和我国其他海岸带区域;(2)河流沉积物中的BC含量呈现出明显的空间差异,主要是受点源排放、河流本身的特征和沉积物粒度等因素的影响;海洋沉积物中的BC分布不仅受到沉积物粒度的影响,河流输入和沉积速率也是其重要的影响因素;(3)由于POPs的来源和理化性质差异,POPs与BC和总有机碳(TOC)的相关性也存在一定程度的差异,其中六氯苯(HCB)与BC、TOC的相关性最好。就河流和海洋分区而言,海洋沉积物中POPs与BC、TOC的相关性明显好于河流沉积物,但都没有表现出POPs与BC的相关性优于POPs与TOC的相关性的现象。     

Hydrogen sulfide and organic carbon at the sediment–water interface in coastal brackish Lake Nakaumi, SW Japan

The relationship among H₂S, total organic carbon (TOC), total sulfur (TS) and total nitrogen contents of surface sediments (0–1 cm) was examined to quantify the relationship between H₂S concentrations and TOC content at the sediment water interface in a coastal brackish lake, Nakaumi, southwest Japan. In this lake, bottom water becomes anoxic during summer due to a strong halocline. Lake water has ample dissolved SO₄ ^2? and the surface sediments are rich in planktic organic matter (C/N 7–9), which is highly reactive in terms of sulfate reduction. In this setting the amount of TOC should be a critical factor regulating the activity of sulfate reduction and H₂S production. In portions of the lake where sediment TOC content is less than 3.5 %, H₂S was very low or absent in both bottom and pore waters. However, in areas with TOC >3.5 %, H₂S was correlated with TOC content (pore water H₂S (ppm) = 13.9 × TOC (%) ? 52.1, correlation coefficient: 0.72). H₂S was also present in areas with sediment TS above 1.2 % (present as iron sulfide), which suggests that iron sulfide formation is tied to the amount of TOC. Based on this relationship, H₂S production has progressively increased after the initiation of land reclamation projects in Lake Nakaumi, as the area of sapropel sediments has significantly increased. This TOC–H₂S relationship at sediment–water interface might be used to infer H₂S production in brackish–lagoonal systems similar to Lake Nakaumi, with readily available SO₄ ^2? and reactive organic matter.     

底泥原地稳定化过程中药剂对上覆水体的影响

采用底泥原地稳定化处理技术中的药剂投加方法,对苏州河底泥中投加零价铁(Fe0)、硝酸钙的上覆水体进行为期80 d研究比较.结果表明:投加Fe0后上覆水体的溶解氧(DO)被迅速消耗,体系易形成厌氧环境,而硝酸钙则减缓了上覆水体DO的消耗;投加零价铁或硝酸钙后都会使上覆水体的pH升高,Eh下降;投加Fe0后对上覆水体COD_Cr或TOC的影响较硝酸钙小;此外,两者上覆水体DO、pH和Eh与COD_Cr和TOC之间均具有一定的相关性.     

Quantification of co-occurring reaction rates in deep subseafloor sediments

Net rates of biogeochemical reactions in subseafloor sediments can be quantified from concentration profiles of dissolved reactants or products and physical properties of the sediment. To study net rates of microbial activities in deep sediments, we developed a robust approach that is well suited to use over a broad range of sediment depths. Our approach is based on a finite-difference solution to a continuity equation that considers molecular diffusion, sediment burial, fluid advection, and reaction under the assumption of steady state. Numerical procedures are adopted to identify the maximum number of depth intervals with statistically different reaction rates. The approach explicitly considers downcore variation in physical properties and sample spacing. Uncertainties in the rate estimates are quantified using a Monte Carlo technique. We tested our approach using synthetic concentration profiles generated from analytical solutions to the continuity equation. We then applied the approach to concentration profiles of dissolved sulfate, sulfide, methane, and manganese in the 420-m thick sediment column of eastern equatorial Pacific Ocean Drilling Program Site 1226. Our results indicate that (i) sulfate reduction and iron reduction occur at most sediment depths, (ii) net methane production occurs in discrete depth intervals and (iii) manganese reduction occurs near the seafloor and deep in the sediments. These results provide quantitative evidence that multiple respiration pathways co-exist in the same depth intervals of these deep subseafloor sediments.     

Microbial respiratory quinones as indicator of ecophysiological redox conditions

The bacterial respiratory quinones and membrane phospholipid fatty acids (PLFA) were measured to test the biochemical responses to the redox conditions after the respiration of diverse electron acceptors by microorganisms. Shewanella putrefaciens strain CN32 was examined for its growth with O₂, nitrate, ferrihydrite, ferric citrate, and sulfite as electron acceptors. The same parameters were also measured for Desulfovibrio desulfuricans strain G-20, Geobacter metallireducens strain GS-15, Thioploca spp., two strains of magnetotactic bacteria (Magneteospirilum magnetotactium marine vibrioid strain MV-1 and M. sp. strain AMB-1), and environmental sediments. Microorganisms with aerobic respiratory of oxygen (MV-1 and AMB-1) have high ratios of monounsaturated to saturated straight chain PLFA and ubiquinone to menaquinone ratios; while those that conduct strict anaerobic respirations (G-20 with sulfate and GS-15 with ferric iron) have low ratios of monounsaturated to saturated straight chain PLFA and uniquinone to menaquinone ratios. The facultative respiratory of nitrate (Thioploca) has these parameters in the middle. The ratios of menaquinones to ubiquinones in CN32 cells systematically increase according to the increase of redox potential and bioavalibility of electron acceptors. The correlation between σUQ-n/σMK-n ratios and redox conditions indicates the structure of respiratory quinone responses sensitively to the microbial ecophysiological conditions.     

融冰期北极楚科奇海陆架中心区硅限制与来源补充

相对氮亏损(N:P约为7,小于16)的太平洋入流水携带的营养盐是支撑北冰洋上层生态系统的重要物质基础。海冰消退,光限制消失,楚科奇海陆架存在强烈的营养盐消耗与利用,广泛认为其表现为氮限制,因此该区域重点关注氮元素循环,对于硅元素的相关研究较少。本文基于2016年中国第七次北极科学考察和中国-俄罗斯首次联合北极科学考察两个同步进行的航次调查结果,全面展示了融冰期整个楚科奇海陆架区的营养盐分布格局。结果显示,硝酸盐和亚硝酸盐表层基本耗尽;硅酸盐表现为中心低,周围高,陆架中心区是强烈的硅限制区域,受到硅和氮的共同限制。沿着太平洋入流方向,S01、R01、LV77-01站位30 m以深硅酸盐浓度高于太平洋入流水端员,说明沉积物孔隙水向底层水释放硅酸盐,因此在浅水陆架区孔隙水可作为上层海洋硅酸盐的潜在来源。本研究结合文献数据计算得到楚科奇海陆架沉积物-水界面硅酸盐年通量为630.78 mmol·m^-2·a^-1,总量为3.75×10¹¹ mol·a^-1,是太平洋入流水所携带硅酸盐年通量的一半(6.59×10¹¹ mol·a^-1),表明沉积物孔隙水也是楚科奇海陆架硅酸盐的重要来源。     

Biogeochemical processes involving acetate in sub-seafloor sediments from the Bering Sea shelf break

Biogeochemical processes involving acetate in sub-seafloor sediments from piston core PC23B from the Bering Sea shelf break were inferred by examining the stable carbon isotopic relationships between acetate and other relevant carbon compounds: total organic carbon (TOC) in the sediment solid phase, and dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in pore water. Throughout the core, the isotopic composition of acetate (δ¹³C_acetate), from −31‰ to −29‰, was ¹³C-depleted by ca. 7‰ vs. DOC (δ¹³C_DOC) and its depth profile approximately paralleled that of δ¹³C_DOC, suggesting that the principal process producing acetate was fermentation of dissolved organic compounds. However, the ¹³C depletion in δ¹³C_acetate indicates some contribution of acetogenesis to total acetate production, because acetogenesis results in ¹³C depletion of the acetate produced. The relative contribution of acetogenesis via the H₂/CO₂ reaction, calculated by using a two source isotope mixing model, increased with depth in the sulfate reduction zone from 10% to 15% and was constant at 19% in the methanogenic zone. The acetogenic contribution to acetate production in the methanogenic zone underlying the sulfate reduction zone is consistent with reported observations, whereas the occurrence of acetogenesis in the sulfate reduction zone may be related to the contribution of terrestrial organic matter (OM) to the sedimentary OM in that depth interval, because the terrestrial component likely includes precursors that favor organoautotrophic acetogenesis. The high acetate concentration (up to 81 μM) and TOC content (up to 1.4%) at the same depth (<200 cmbsf) suggest that some relationship exists between acetate production rate and TOC content, or that a temperature increase during core storage at room temperature might stimulate acetate-producing microbial activity in the high TOC sediment.     

Organic matter mineralization in sediment of a coastal freshwater lake and response to salinization

Solid phase and pore water chemical data collected in a sediment of the Haringvliet Lake are interpreted using a multi-component reactive transport model. This freshwater lake, which was formed as the result of a river impoundment along the southwestern coast of the Netherlands, is currently targeted for restoration of estuarine conditions. The model is used to assess the present-day biogeochemical dynamics in the sediment, and to forecast possible changes in organic carbon mineralization pathways and associated redox reactions upon salinization of the bottom waters. Model results indicate that oxic degradation (55%), denitrification (21%), and sulfate reduction (17%) are currently the main organic carbon degradation pathways in the upper 30 cm of sediment. Unlike in many other freshwater sediments, methanogenesis is a relatively minor carbon mineralization pathway (5%), because of significant supply of soluble electron acceptors from the well-mixed bottom waters. Although ascorbate-reducible Fe(III) mineral phases are present throughout the upper 30 cm of sediment, the contribution of dissimilatory iron reduction to overall sediment metabolism is negligible. Sensitivity analyses show that bioirrigation and bioturbation are important processes controlling the distribution of organic carbon degradation over the different pathways. Model simulations indicate that sulfate reduction would rapidly suppress methanogenesis upon seawater intrusion in the Haringvliet, and could lead to significant changes in the sediment’s solid-state iron speciation. The changes in Fe speciation would take place on time-scales of 20-100 years.     

Sediment community metabolism associated with continental shelf hypoxia, Northern Gulf of Mexico

Net fluxes of respiratory metabolites (O₂, dissolved inorganic carbon (DIC), NH₄ ⁺, NO₃ ^?, and NO₂ ^?) across the sediment-water interface were measured using in-situ benthic incubation chambers in the area of intermittent seasonal hypoxia associated with the Mississippi River plume. Sulfate reduction was measured in sediments incubated with trace levels of³⁵S-labeled sulfate. Heterotrophic remineralization, measured as nutrient regeneration, sediment community oxygen consumption (SOC), sulfate reduction, or DIC production, varied positively as a function of temperature. SOC was inversely related to oxygen concentration of the bottom water. The DIC fluxes were more than 2 times higher than SOC alone, under hypoxic conditions, suggesting that oxygen uptake alone cannot be used to estimate total community remineralization under conditions of low oxygen concentration in the water column. A carbon budget is constructed that compares sources, stocks, transformations, and sinks of carbon in the top meter of sediment. A comparison of remineralization processes within the sediments implicates sulfate reduction as most important, followed by aerobic respiration and denitrification. Bacteria accounted for more than 90% of the total community biomass, compared to the metazoan invertebrates, due presumably to hypoxic stress.     

Nitrogen and phosphorus in the sediments of a tidal,freshwater marsh in Massachusetts

Total organic nitrogen (TON) and phosphorus (TOP) were measured as a function of depth in 14 cores taken from a New England, tidal, freshwater marsh. TON and TOP ranged from 1.56 to 1.97% and 0.11 to 0.30% of dry weight sediments, respectively. The variation in both pool sizes over time was small and TON varied inconsistently with depth; however, TOP decreased regularly down to 20 cm. Consequently, the TON: TOP ratio increased linearly from 14∶1 at the surface to 32∶1 at 20 cm, then was nearly constant to 70 cm. This pattern may be a general feature of marsh sediments and may indicate 1) that phosphorus is recycled less efficiently than nitrogen, 2) that over time proportionately more introgen than phosphorus is incorporated into recalcitrant compounds, or 3) that phosphorus is more mobile than nitrogen in these marsh sediments. The total inorganic nitrogen pool was measured in this marsh also and was dominated by ammonium (97% of total). The annual average free ammonium concentration was 3.70±0.64 mg N per 1 at the surface and decreased to 0.92±0.18 mg N per 1 at 20 to 22 cm in the sediments. Sorptiondesorption studies showed that, on a fresh sediment volume basis, sediment sorbed ammonium was roughly equivalent to free porewater ammonium (K=0.8). The relationship between free and sorbed ammonium was linear between 0.4 and 24.0 mg NH₄·N per 1 of pore water. The depth distribution of ammonium in these sediments is probably maintained by a dynamic balance between net microbial mineralization of litter, plant uptake, transpiration, diffusion, and porewater advection.     

Short-term endproducts of sulfate reduction in a salt marsh: Formation of acid volatile sulfides,elemental sulfur,and pyrite

Rates of sulfate reduction, oxygen uptake and carbon dioxide production in sediments from a short Spartina alterniflora zone of Great Sippewissett Marsh were measured simultaneously during late summer. Surface sediments (0–2 cm) were dominated by aerobic metabolism which accounted for about 45% of the total carbon dioxide production over 0–15 cm. Rates of sulfate reduction agreed well with rates of total carbon dioxide production below 2 cm depth indicating that sulfate reduction was the primary pathway for sub-surface carbon metabolism. Sulfate reduction rates were determined using a radiotracer technique coupled with a chromous chloride digestion and carbon disulfide extraction of the sediment to determine the extent of formation of radiolabelled elemental sulfur and pyrite during shortterm (48 hr) incubations. In the surface 10 cm of the marsh sediments investigated, about 50% of the reduced radiosulfur was recovered as dissolved or acid volatile sulfides, 37% as carbon disulfide extractable sulfur, and only about 13% was recovered in a fraction operationally defined as pyrite. Correlations between the extent of sulfate depletion in the marsh sediments and the concentrations of dissolved and acid volatile sulfides supported the results of the radiotracer work. Our data suggest that sulfides and elemental sulfur may be major short-term end-products of sulfate reduction in salt marshes.