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1.
Degradation of marine organic carbon provides a major source of atmospheric carbon dioxide, whereas preservation in sediments results in accumulation of oxygen. These processes involve the slow decay of chemically recalcitrant compounds and physical protection. To assess the importance of physical protection, we constructed a reaction-diffusion model in which organic matter differs only in its accessibility to microbial degradation but not its intrinsic reactivity. The model predicts that organic matter decays logarithmically with time t and that decay rates decrease approximately as 0.2 x t(-1) until burial. Analyses of sediment-core data are consistent with these predictions. 相似文献
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Steroids are used to illustrate some of the significant advances that have been made in recent years in understanding the biological origin and geological fate of the organic compounds in sediments. The precursor sterols are transformed, initially by microbial activity and later by physicochemical constraints, into thermodynamically more stable saturated and aromatic hydrocarbons in mature sediments and petroleums. The steps in this transformation result in a complex web linking biogenesis, diagenesis, and catagenesis. Indeed, the complexity and variety of biological lipids such as the steroids are evidently matched in the corresponding geolipids. The extent of preservation of the biochemical imprint in the structures and stereochemistry of these geolipids, even over hundreds of millions of years, is startling, as is the systematic and sequential nature of the geochemical changes they evidently undergo. This new understanding of molecular organic geochemistry has applications in petroleum geochemistry, where biological marker compounds are valuable in the assessment of sediment maturity and in correlation work. 相似文献
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以西藏拟溞(Daphniopsis tibetana Sars)为优势浮游动物物种的低盐度盐湖是西藏湖泊的一个重要类型,以达则错为代表,分析了其沉积背景及沉积物组成。结果如下:(1)湖泊敞水区无机沉积以内生化学沉积为主,可代表深水盐湖无机沉积物的自然沉积过程。(2)达则错盐湖浮游植物以蓝藻、硅藻、裸藻、绿藻为主,总生物量11.35 mg/L;浮游动物生物量为4.92 mg/L,其中西藏拟溞占 82.30%;浮游植物残体受盐梯度影响在盐梯度层之上聚集,而浮游动物残体及粪粒(Fecal pellets)因外表有碳酸盐附着可穿过盐梯度层沉积湖底,生物残体与浮游动物代谢产物构成了沉积有机物的物质基础。(3)表层沉积物平均含水量为66.70%,粒径0.004-0.02 mm范围内的颗粒物含量最大,占20.42%,其次为<0.004 mm的粘土,占4.53%。(4)表层沉积物总有机碳(TOC)平均含量为27.99 mg/g(干重),其中颗粒有机碳(POC)约为18.11 mg/g,占TOC的64.70%;在POC中,西藏拟溞粪粒贡献最大,约占POC的60.48%,占TOC的39.06%,占沉积物总量的1.12%,其次为西藏拟溞残体,占POC的38.85%。分析结果表明盐湖因其独特的水化学和生物学特征具有较强的沉积能力,以化学沉积为主的无机沉积及以西藏拟溞粪粒和残肢碎屑为主的有机沉积构成了该类型盐湖颗粒物沉降及沉积的主要过程。 相似文献
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A technique has been developed to artificially fossilize microscopic algae in crystalline silica under conditions of moderately elevated temperature and pressure. The technique is designed to simulate geochemical processes thought to have resulted in the preservation of organic microfossils in Precambrian bedded cherts. In degree of preservation and mineralogic setting, the artificially permineralized microorganisms are comparable to naturally occurring fossil algae. 相似文献
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An enigmatic stepwise increase in oxygen in the late Precambrian is widely considered a prerequisite for the expansion of animal life. Accumulation of oxygen requires organic matter burial in sediments, which is largely controlled by the sheltering or preservational effects of detrital clay minerals in modern marine continental margin depocenters. Here, we show mineralogical and geochemical evidence for an increase in clay mineral deposition in the Neoproterozoic that immediately predated the first metazoans. Today most clay minerals originate in biologically active soils, so initial expansion of a primitive land biota would greatly enhance production of pedogenic clay minerals (the "clay mineral factory"), leading to increased marine burial of organic carbon via mineral surface preservation. 相似文献
6.
Johnson TC 《Science (New York, N.Y.)》1976,192(4242):887-890
A map of the preservation pattern of siliceous microfossils was constructed from an examination of 125 piston and gravity cores of Quaternary sediments from throughout the eastern tropical Pacific. Preservation is enhanced where high surface water productivity supplies a high input rate of siliceous tests to the sea floor, except in a large area north of 5 degrees N, east of the East Pacific Rise. Here a high input rate of terrigenous silicates may adversely affect preservation of biogenic opal in the sea-floor sediments. 相似文献
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深渊是迄今人类认识最少的海洋环境之一。深渊蕴含着丰富的微生物生物量，表现出活跃的有机碳周转特征，是深海有机碳降解的“热点”区域。然而，人类对深渊微生物的物种组成和代谢潜力还知之甚少。本文通过宏基因组技术与生物信息学分析，研究马里亚纳海沟“挑战者深渊”表层沉积物（水深10,853米）中的微生物群落组成和功能特征，揭示深渊表层沉积物中微生物驱动深海生物地球化学循环的潜在机制及其相应的生态效应。研究结果表明，变形菌门（Proteobacteria）、奇古菌门（Thaumarchaeota）、拟杆菌门（Bacteroidetes）、放线菌门（Actinobacteria）和浮霉菌门（Planctomycetes）是马里亚纳海沟表层沉积物中微生物的优势类群。表层沉积物中微生物的代谢分析表明其主要营异养代谢，可以降解多种有机物，包括一些难降解有机碳化合物（如邻苯二甲酸盐或其他芳香族化合物）。这些结果说明深渊沉积物中的微生物群落具有多样化的有机碳代谢能力，可以支持其开展活跃的有机碳降解过程。除了异养代谢过程，氨氧化等自养代谢过程在本研究的深渊微生物群落中也占据着重要地位，说明自养固碳可能是深渊表层沉积物中有机碳的重要来源。 相似文献
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长江口沉积物总有机碳（TOC, Total Organic Carbon）含量会随着外源磷的输入而发生变化。采用泥（沉积物）水质量比约为1：1，周期为56d的室内模拟试验系统。设置包括对照组在内的6个输入过磷酸钠的浓度梯度试验组，研究不同水平的外源磷输入所引起的沉积物中TOC含量的变化特征。同时，运用紫外—可见光吸收光谱方法，研究含磷物质的加入对沉积物中溶解有机质结构变化的影响。实验结果显示：各试验组沉积物TOC含量在第56天比对照组分别减少了3.60%、7.08%、8.09%、9.33%、11.80%，表明随着外源磷输入量增加，长江口沉积物中TOC加速分解。在试验周期内,沉积物溶解有机质的腐殖化程度、芳香化程度最大值与磷的输入量呈正相关。溶解有机质分子量和芳香环结构变化幅度与外源磷的输入量呈正相关，说明外源磷输入量的增大能够加快沉积物溶解有机质的变化。随着试验时间的增加，不同磷水平的溶解有机质的腐殖化程度和芳香化程度呈现先上升，随后开始下降的趋势；而溶解有机质的分子量随着时间的增加逐渐减小，其芳香环取代基上的取代基逐渐替换为更具有活性的官能团。表明沉积物有机碳含量减少过程中，先生成腐殖质，随着腐殖质继续分解，其腐殖化程度降低，且腐殖化程度和芳香化程度具有同一性。 相似文献
10.
In several places in Southern California bituminous sediments of the Monterey Formation-siliceous shales, phosphatic rocks, dolomites, and arkoses-were affected during the Pleistocene and as late as the l9th century by spontaneous subsurface combustion of organic matter, during which temperatures up to 1600 degrees C were reached. This oxidative heating (combustion metamorphism) affected rock complexes over areas of tens of square kilometers that tend to occur in clusters. As a result of these processes, the rocks recrystallized and partially melted to form pseudomagmas which intruded the country rocks. The chemical compositions of these melts differ from those of igneous magmas. Acid and intermediate siliceous melts as well as phosphatic melts have formed. These two types are generally immiscible. The following high-temperature minerals were determined: alpha- and beta-cristobalite, quartz, calcic plagioclase, diopsidic pyroxene, wollastonite, cordierite, graphite, fluorapatite, and fluorite; at lower temperature pyrite, gypsum, aragonite, calcite, jarosite, and hexahydrite crystallized. 相似文献
11.
Humic substances (HSs) are the natural organic polyelectrolytes formed from the biochemical weathering of plant and animal remains. Their macromolecular structure and chemistry determine their role in biogeochemical processes. In situ spectromicroscopic evidence showed that the HS macromolecular structures (size and shape) vary as a function of HS origin (soil versus fluvial), solution chemistry, and the associated mineralogy. The HSs do not simply form coils in acidic or strong electrolyte solutions and elongated structures in dilute alkaline solutions. The macromolecular structural changes of HSs are likely to modify contaminant solubility, biotransformation, and the carbon cycle in soils and sediments. 相似文献
12.
通过对河水、河床底泥、岸边土壤剖面、地下水样品的测定,对太行山前平原磁河地区地下水中苯系物在水土系统中的分布特征进行了研究。结果表明,各种介质中的苯系物(苯、甲苯、乙苯、二甲苯)具有一定的相关性,与河不同距离和不同深度土壤中的苯系污染物主要来自污水河。但是,由于有机污染物在土壤中的吸附等作用过程,有机污染物浓度在一定的距离内迅速降低。在河岸边不同距离的地下水中,仅少量地下水水样中检出了苯系物,但它们的浓度均低于生活饮用水的要求限值。 相似文献
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由于砷、铬等含金属和非金属的木竹材保护剂对土壤和水生环境存在潜在危害,以及经处理的木竹材的废弃处理等问题引起越来越多的关注,人们把注意力转移到有机杀菌剂。现已筛选出能够抵抗或消灭木竹材腐朽菌、霉菌、变色菌等有害真菌的有效杀菌剂,并在国外已有大量商品化的产品。随着人们环保意识的增强,以有机杀菌剂为主剂的木竹材保护剂最终将在中国木竹材保护领域占据重要地位。从木竹材保护常用有机杀菌剂种类、作用效果、作用机制、检测方法及有机杀菌剂对环境影响等方面对有机杀菌剂在木竹材保护中的应用进行了阐述,进而提出有机杀菌剂将成为未来木竹材保护剂研究和发展的重要领域之一。参62 相似文献
14.
Headlands, islands, and reefs generate complex three-dimensional secondary flows that result in physical and biological fronts. Mixing and diffusion processes near these reefs and headlands are quite different from these processes in the open sea, and classical advection-diffusion models that were developed for the open sea are not valid near shore. Topographically generated fronts affect the distribution of sediments, and they aggregate waterborne eggs, larvae, and plankton. This aggregation influences the distribution and density of benthic assemblages and of pelagic secondary and tertiary predators. 相似文献
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磷在不同类型湖泊沉积物上的吸附特征及形态再分布研究 总被引：2，自引：0，他引：2
以乌梁素海和岱海表层沉积物为吸附剂,开展了磷在沉积物上的吸附动力学和等温吸附实验研究,采用交叉型Langmuir模型描述了磷在2个湖泊沉积物上的吸附行为,并分析测定了等温吸附后沉积物中磷的形态分布。结果表明,不同浓度条件下沉积物对磷的吸附动力学过程基本相似,Elovich方程能较好地描述2个湖泊沉积物对磷酸盐的吸附动力学过程;Langmuir交叉型吸附等温式能较好地描述磷在岱海和乌梁素海沉积物上的等温吸附行为(R2=0.990),模型中的k、Qm、EPC0、NAP等参数较好地反映了2个湖泊沉积物在成因、粒度及矿物组成等方面的差异;吸附磷的形态再分布揭示颗粒物所吸附的水相磷主要分布于Ex-P,且Or-P是沉积物中重要的潜在生物有效性磷源,对湖泊富营养化的作用不容忽视。 相似文献
16.
The ecological role and biogeochemical relevance of extracellular DNA in the oceanic sediments are unknown. Our global estimates indicate that up to 0.45 gigatons of extracellular DNA are present in the top 10 centimeters of deep-sea sediments, representing the largest reservoir of DNA in the world oceans. We demonstrate that extracellular DNA accounts for about one fifth of the total organic phosphorus regeneration and provides almost half of the prokaryotic demand for organic phosphorus. It therefore plays a key role in deep-sea ecosystem functioning on a global scale. 相似文献
17.
为揭示高原湖泊流域农村沟渠底泥氮、磷和有机质的分布特征,以云南省4种典型农村(畜禽养殖型、生态休闲型、集镇型和传统型)为研究对象,分析其全氮(TN)、全磷(TP)和有机质(OM)的含量,并应用有机指数法和单因子评价法评价底泥的污染程度。结果表明,不同类型农村之间w(TN)、w(TP)和w(OM)的空间分布差异显著,w(TN)和w(TP)均表现为畜禽养殖型集镇生态休闲型传统型,w(OM)表现为畜禽养殖型生态休闲型集镇型传统型。TN与TP呈极显著正相关,说明氮磷元素在底泥累积过程中有着较高的同步性;TP与OM呈极显著正相关,说明OM是磷元素的重要载体;TN与OM的相关性不显著,表明农村沟渠底泥氮的主要来源并不是OM的矿化与分解。各村沟渠底泥氮和有机质污染均达到了重度污染状态,磷污染程度相对较低,畜禽养殖型农村属于中度污染,集镇型和生态休闲型农村属于轻度污染,传统型农村属于清洁型。畜禽养殖业是高原湖泊流域典型农村沟渠底泥氮、磷和有机质污染的主要来源。 相似文献
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黄海表层沉积物中重金属的分布特征与生态风险评价 总被引：2，自引：0，他引：2
[目的]研究黄海表层沉积物中重金属的分布特征,评价其生态风险。[方法]对黄海海域表层沉积物中重金属（Cu、Mn、Pb、Zn、Cr、Fe、Hg和Cd）的含量分布和富集状况进行了调查,分析了重金属之间以及重金属与有机碳（TOC）含量之间的相关性,并采用Hakan-son的潜在生态危害指数法评价了该海域重金属污染的程度及其潜在的生态危害。[结果]在南黄海中部和威海以北的北黄海西部海域表层沉积物中Cu、Pb、Zn、Cr、Fe和Hg的含量偏高,海州湾和北黄海北部含量偏低,Mn、Cd的分布较不均匀,离散程度较大;黄海表层沉积物中各项重金属含量均存在正相关性,Pb与Zn、Zn与Cr、Pb与Cr的相关系数分别达到0.97、0.96和0.94。Cd和Cu呈显著相关,但Cd与其他重金属无显著相关关系,重金属与TOC之间也存在正相关。潜在生态危害评价结果表明,黄海表层沉积物只有部分站点处于生态危害的中等级别,大多站点生态危害轻微,各个重金属元素的潜在生态风险程度由强到弱依次为Cd〉Hg〉Cu〉Pb〉Cr〉Zn,对黄海表层沉积物具有潜在影响的重金属主要是Cd;底质环境质量评价显示,南黄海中部的泥质沉积区域环境质量较差,应予以重视。[结论]该研究为黄海环境保护和生态系统的可持续发展提供了理论依据。 相似文献
20.
江苏海岸带的重金属特征及生态风险分析 总被引：13，自引：0，他引：13
通过测定水体和沉积物重金属含量,分析了江苏海岸带的重金属水平。结果表明,江苏沿海水体中Hg、Pb超过标准值,沉积物中Cd样品超过背景值。重金属元素与有机质、铝元素的关系显示:Cu、Zn、Hg和有机质的相关性较好,表明该地区的Cu、Zn、Hg有人为污染成分;Cr和铝元素的相关性较好,说明Cr主要是陆地碎屑成分。重金属潜在生态风险分析显示:江苏海岸带的生态风险程度以启东最低,其他地区较高,其中灌云沿海最高。粒度分析显示:重金属元素与粘粒有较好的正相关性,而与砂粒呈负相关性。 相似文献