湿地土壤和沉积物异化铁还原过程研究进展

异化铁还原是湿地土壤和沉积物中重要的生物地球化学过程,也是有机质矿化的主要途径之一。湿地干湿交替等过程会使土壤的氧化还原状态发生改变,影响铁元素及与其相关的元素的迁移和转化。总结了湿地土壤和沉积物中异化铁还原过程及其与碳、磷、硫等元素在生物地球化学循环关键过程中的相互作用,阐述了湿地土壤和沉积物中异化铁还原过程对微量金属元素迁移和转化的影响,分析了影响湿地土壤和沉积物异化铁还原过程的主要环境因子。未来相关研究应集中于湿地土壤和沉积物中异化铁还原微生物分析和纯化、不同有机质形式对异化铁还原过程的影响以及异化铁还原对土壤有机质矿化的贡献。     

排污活动对长江口滨岸潮滩营养元素N累积运移的影响及作用机制

选择长江口滨岸潮滩作为典型研究区,研究了排污活动对潮滩营养盐N环境地球化学过程的影响。结果发现排污口滨岸潮滩上覆水、表层沉积物孔隙水和表层沉积物中的NH₄⁺-N、TIN等都有显著累积效应,而NO_x^--N在长江口滨岸潮滩上覆水、表层沉积物孔隙水和表层沉积物中并未出现累积高峰值,表明外源输入不是潮滩环境中NO_x^--N主要来源。分析结果还显示,排污口潮滩沉积物-水界面间N分子扩散通量明显大于非排污口,表明排污活动加剧了潮滩沉积物-水界面间营养盐N的扩散过程。     

BP神经网络模型在表层沉积物及其非残渣态组分吸附双酚A研究中的应用

应用沉积物吸附双酚A(BPA)BP神经网络模型,模拟了松花江表层沉积物的不同泥水比、非残渣态组分(有机质、铁氧化物、锰氧化物)和BPA初始浓度对BPA吸附量的影响。所建BP神经网络模型相关系数R²为0.9665,校正集均方差(MSE_c)、验证集均方差(MSE_v)和预测集均方差(MSE_p)分别为0.0068、0.0596和0.1285;利用遗传算法优化估算了基于BP神经网络模型的沉积物吸附BPA的最大吸附量,优化值与实验值的相对偏差为0.96%~8.21%。此外,利用BP神经网络模型预测了沉积物非残渣态组分(有机质、铁氧化物、锰氧化物)质量百分比及摩尔含量变化与BPA吸附量的关系,经分析可知,铁氧化物和有机质对沉积物吸附BPA起着促进作用,沉积物非残渣态组分吸附BPA的相对贡献(K)为K_Fe>K_OMs>K_Mn,即沉积物中铁氧化物是BPA的主要吸附位,而Mn氧化物则对沉积物吸附BPA起着抑制作用。     

冲绳海槽DGKS9604孔酸不溶相中常量元素组成及环境指示意义

运用1N HCl对冲绳海槽中部西陆坡DGKS9604孔沉积物样品进行预处理得到酸不溶相组分,利用ICP-AES分析常量元素的含量.结果显示主要氧化物与Al<,2>O<,3>的比值以及氧化物通量在垂向上呈规律性变化,反映了近30ka以来的元素地层以及沉积古环境对沉积地球化学组成的影响.30～22 ka、17.8～11.8 ka、7～3.5 ka和2ka B.P.以来氧化物通量高于末次冰盛期和全新世早期.主要氧化物组成记录了7.4 Cal ka和25.8 Cal ka B.P.两次火山事件;因子分析揭示钻孔中主要氧化物含量在垂向上的变化主要受沉积物源、热液活动、沉积动力环境及火山活动等多因素影响.     

北极巴罗AB-67钻孔岩芯的沉积过程分析

对巴罗ＡＢ－６７钻孔岩芯的粒度分析资料和地球化学分析资料进行了系统的多变量沉积过程分析。结果表明,３２～６０ｃｍ岩芯段为陆相沉积,该段沉积环境和沉积过程都较为稳定;２０～３２ｃｍ岩芯段为由陆相向海相转换的过渡时期,此时粗粒的含Ｃｒ磁性矿物由峰值跌入谷值,硅、钙质氧化物减少,钛、铁质氧化物增加,有机质成分增加;０～２０ｃｍ岩芯段为海相沉积,本段沉积粗粒成分很少,氧化物、粘土、有机质和吸附成分波动很大,表层淋溶残余成分迅速增加,物源环境稳定,但动力条件变化较大     

淮南潘一矿塌陷水域沉积物磷吸附特征分析

本文选取淮南潘一矿—20年左右的塌陷水域为研究对象,研究区域水化学环境对沉积物磷吸附特征的影响。以纯水(Pure water)体系及弱碱性NaHCO3体系为参照,研究NaHCO3+CaCl2综合体系下磷的吸附特征,并分析了磷赋存形态、有机质环境、铁氧化物和粘土含量等对吸附特征参数的影响。研究结果表明,水化学条件对沉积物P吸附特征具有重要影响,对比纯水组,弱碱性(NaHCO3组)环境对磷的吸附具有减弱作用,而Ca2+离子的存在能显著增强沉积物对磷的吸附,同时泥质湖相沉积—淹水土层二元结构也会导致磷吸附特征的差异。     

盐尘暴及其生态效应

总结了盐尘暴的概念及其一般特征,系统分析了盐尘暴的发生条件、分布、扩散沉积和生态效应。盐尘暴是由干旱、半干旱地区干涸湖底蒸发盐风蚀所致的一种化学尘暴;大面积松散富盐沉积物和频繁的大风天气是其发生的基本条件;盐尘暴扩散过程中沉积通量和化学组分随迁移距离表现出明显的分异规律;盐尘暴扩散导致干旱区“盐随风来”,致使土壤盐渍化,加剧冰雪消融,抑制植物叶片对营养元素的正常吸收。系统认识盐尘暴对干旱区灾害防治和生态建设具有重要指导意义。     

兰州市城区河道表层沉积物地球化学元素分布特征

通过对兰州市河道表层沉积物地球化学元素分析发现,兰州市河道表层沉积物41种地球化学元素富集因子多小于1,Cl、S、P、Bi、Cr、Cu、Pb、Sn、U、W、Zn富集因子值均大于2,显示了较高的污染水平。对单个采样点总富集因子的分析研究发现,R值均大于2,显示出较多的富集。其中水磨沟下游和鱼儿沟下游富集因子出现高值,显示出严重污染。元素来源研究结果显示,兰州市河道表层沉积物地球化学元素的来源可分为3类:①生活污水排放以及雨水对地面或街道的冲刷作用;②工业污染,包括冶金、电镀、农药和化肥等污水的排放;③本地土壤类型灰钙土中元素的贡献。通过粒度与元素相关性分析可知,元素P、Cl主要分布于细颗粒物质中,反映了兰州市河道表层沉积物污染物质在细颗粒中有较大量的富集。     

沼泽学

X142 20030429‘9向海湿地元素地球化学特征与离分辨沉积记录=Chatacter-isties of element geochemistry and high一r即lution sedimenta-tion records in Xia雌hai wetlands/王国平,刘景双//地理科学.一2003,23(2)卜一208一212 以内流河下游漫流区—向海沼泽湿地为研究对象,对其典型剖面沉积物柱状样以厘米级间距采样,在多元统计分析基础上,结合‘3,CS、“10Pb测年数据对其进行高分辨率元素地球化学特征解析,以获取现代沉积记录及其与流域环境变化的关系.研究区沼泽湿地沉积物表层沉积序列内已明显富集了重金属元素,近年霍林河流域上游…     

湘江河流沉积物重金属的形态类型及其形成因素

进入河水中的重金属离子,在一定的条件下,由于吸附、络合、絮凝、离子交换和共沉淀等作用,最终绝大部分将进入河流沉积物中。当水环境理化条件变化时,一部分重金属又可通过扩散、解吸、溶解、氧化还原和络合等作用从沉积物重返水相。这些作用通常是     

REMOBILIZATION AND ACCUMULATION OF IODINE IN MARINE SEDIMENTS, WESTERN ANTARCTIC OCEAN

Remobilization and accumulation mechanisms of iodine in marine sediments, which are divided into several geochemical environment, are studied. The result shows that iodine is characteristically rich in organic fractions of the sediments on the bottom of bay and pelagic sediments. However, it may be associated with oxyhydroxide and adsorptive phase in a highter percentage at the continental shelf and hemipelagic sediments. The environmental characteristics of remobilization of iodine in surficial sediments are similar to that of iron, that is, it is remobilized on anoxic conditions and converted into solid phases when it is in oxic environments, though the iodine does not act as the electron acceptor. The processes of adsorption and oxidation are responsible for the value of I_t/C_(org) in excess of that of planktonic materials other than the organic fraction in surficial sediments. It is a comprehensive effect of organism decomposition, oxyhydroxide reduction, particulate adsorption and pore water diffu     

Soil Iodine Determination in Deccan Syneclise,India: Implications for Near Surface Geochemical Hydrocarbon Prospecting

The association of iodine with organic matter in sedimentary basins is well documented. High iodine concentration in soils overlying oil and gas fields and areas with hydrocarbon microseepage has been observed and used as a geochemical exploratory tool for hydrocarbons in a few studies. In this study, we measure iodine concentration in soil samples collected from parts of Deccan Syneclise in the west central India to investigate its potential application as a geochemical indicator for hydrocarbons. The Deccan Syneclise consists of rifted depositional sites with Gondwana–Mesozoic sediments up to 3.5 km concealed under the Deccan Traps and is considered prospective for hydrocarbons. The concentration of iodine in soil samples is determined using ICP-MS and the values range between 1.1 and 19.3 ppm. High iodine values are characteristic of the northern part of the sampled region. The total organic carbon (TOC) content of the soil samples range between 0.1 and 1.3%. The TOC correlates poorly with the soil iodine (r ² < 1), indicating a lack of association of iodine with the surficial organic matter and the possibility of interaction between the seeping hydrocarbons and soil iodine. Further, the distribution pattern of iodine compares well with two surface geochemical indicators: the adsorbed light gaseous hydrocarbons (methane through butane) and the propane-oxidizing bacterial populations in the soil. The integration of geochemical observations show the occurrence of elevated values in the northern part of the study area, which is also coincident with the presence of exposed dyke swarms that probably serve as conduits for hydrocarbon microseepage. The corroboration of iodine with existing geological, geophysical, and geochemical data suggests its efficacy as one of the potential tool in surface geochemical exploration of hydrocarbons. Our study supports Deccan Syneclise to be promising in terms of its hydrocarbon prospects.     

A simple and effective method for preserving the sediment–water interface of sediment cores during transport

We describe a method for preserving the upper sediments of fragile sediment cores during transport from field sites and assess potential effects on subsequent laboratory analyses. This method addresses the need to minimize disturbance to the surfaces of unfrozen sediment cores used for paleoenvironmental or other high-resolution sedimentological analyses during transport. A polymer gel (sodium polyacrylate) applied above the sediment surface acts as a barrier to movement while also preserving surface undulations. The gel seal can preserve even exceptionally fine sedimentary structures (<0.2 mm) in the upper sediments of lacustrine and fiord sediment cores, but may react with organic material (e.g. algal mats) present on some sediment surfaces. This reaction creates an adhesive layer at the gel’s base but it can be handled effectively during sampling. The gel seal minimizes surface deformation and preserves surficial sediments better than traditional seals made of water-absorbent floral foam, wax or paper towel. In addition to permitting detailed sedimentary and subfossil investigations of the sediment–water interface, this method shows no detectable effects on measurements of total organic carbon or total nitrogen values in the sediment. This method is inexpensive, non-hazardous and applicable to many coring systems and sediment types.     

Relationship between C:N ratios of lake sediments, organic matter sources, and historical deforestation in Lake Pleasant, Massachusetts, USA

The C:N ratios of lake sediments may reflect proportions of terrestrial and algal carbon contributing to accumulation of sediment. This possibility was tested in Lake Pleasant, Massachussetts, USA which underwent watershed deforestation in about 1780 A.D. The C:N profile of a 70-cm sediment core clearly reflected deforestation through a rise in C:N ratio caused by an increase in watershed contributions to sedimentary carbon. Spatial variability of C:N in modern surficial sediments is small compared to the change caused by deforestation.     

察尔汗盐湖区线形沙丘下伏湖相地层的释光年代及其环境意义

本研究尝试使用钾长石多步升温红外后红外法(MET-pIRIR)对察尔汗盐湖北侧线形沙丘下伏古湖相沉积物进行年代测定,并初步探讨其古环境意义.结果表明:钾长石MET-pIRIR250法能够得到等效剂量坪区,说明长石信号能够充分晒退并且异常衰减对测年结果的影响可以忽略,从而保证了测年结果的可靠性;古湖相沉积顶部200-18...     

Porewater geochemistry and solute flux from bottom sediments,Devils Lake,North Dakota

Sediment cores were collected for pore-water analysis from the eastern end of Devils Lake, located in northeastern North Dakota, to determine diagenetic reactions occurring in surficial bottom sediments and to evaluate the impact of these reactions on chemical concentrations in the overlying lake water. Sediment pore waters are enriched in major ions and nutrients relative to lake water. The principal sources of major ions to pore water are saline sediments located in the upper 1 m of bottom sediment. The principal source of titration alkalinity and nutrients to pore water is microbial decomposition of sedimentary organic matter by sulfate reduction. Sediment pore waters in the eastern part of Devils Lake have higher major-ion concentrations and solute-flux rates than the sediment pore waters in the central part of the lake. In contrast, sediment pore waters in the central part of Devils Lake have significantly higher nutrient concentrations and solute-flux rates. Major-ion concentrations and solute-flux rates in sediment pore water increase from west to east. These trends indicate that bottom-sediment diagenetic processes are, in part, responsible for the observed concentration gradient in the lake. The higher nutrient concentrations and the higher nutrient diffusional-flux rates in Main Bay are the result of more labile sedimentary organic matter and the occurrence of sulfate reduction. Environmentally-reactive trace-metal concentrations (Cu, Pb, Zn, and Fe) in bottom sediments decrease from west to east with distance from the surface-water sources and with increasing surface-water salinity.     

Delivery and deposition of organic matter in surface sediments of Lagoa do Caçó (Brazil)

Elemental and isotopic compositions of organic matter in surficial sediments from five transects across Lagoa do Caçó (Brazil) were analyzed to identify the depth-related processes that affect the production and deposition of sedimentary organic matter in this shallow tropical lake. Each of four transverse transects began at a margin dominated by aquatic macrophytes (Eleocharis), crossed the central deep part of the lake, and terminated in the opposite, macrophyte-dominated margin. In each transect, TOC concentrations, C/N ratios, and δ¹³C values decreased between 0 and 4 m, whereas δ¹⁵N values increased. The variables remained stable in sediment from 4 m water depth to the center of the lake at 10 m. The depth-related patterns reflect differences in both the delivery and the deposition of organic matter in the lake. Organic matter is produced in abundance in the marginal area by emersed and submerged macrophyte vegetation that diminishes with depth and disappears at 4 meters. After the disappearance of macrophytes, organic matter is produced at low rates principally by open-lake phytoplankton. Drawdown of dissolved oxygen is high in the lake margins, but it is low in the oligotrophic open waters of the lake. Preservation of organic matter is consequently better in sediments of the lake margins than in deep waters. The depth-related pattern of organic matter delivery and deposition in the sediments of Lagoa do Caçó, in which water levels are sensitive to groundwater fluctuations, shows that the elemental and isotopic compositions of sediment organic matter can provide a record of changes in the paleohydrology of this and other similar shallow lake systems.     

Geochemical effects of rapid sedimentation in aquatic systems: minimal diagenesis and the preservation of historical metal signatures

Rapid sedimentation exerts a pronounced influence on early sedimentary diagenesis in that there is insufficient time for a sediment particle to equilibrate in any one sediment layer before that layer may be displaced vertically by another layer. These sedimentation patterns are common in surface-water reservoirs whose sedimentation rates (1-10 cm yr^-1) are several orders of magnitude greater than those for natural lakes (0.01-0.5 cm yr^-1).Two examples of the effects of rapid sedimentation on geochemical metal signatures are presented here. Interstitial-water data (Fe) from two sites in the Cheyenne River Embayment of Lake Oahe on the Missouri River illustrate the effects of changing sedimentation rates on dissolved species. Rapid burial during high-flow yrs appears to limit early sedimentary diagenesis to aerobic respiration. Solid-phase metal data (Pb) from a site in Pueblo Reservoir on the upper Arkansas River in Colorado appear to record historical releases by flooding of abandoned mine sites upstream in Leadville, Colorado. Interstitial-water ammonia and ferrous Fe data indicate that at least one interval at depth in the sediment where solid metal concentrations peak is a zone of minimal diagenesis.The principal diagenetic reactions that occur in these sediments are aerobic respiration and the reduction of Mn and Fe oxides. Under slower sedimentation conditions, there is sufficient time for particulate organic matter to decompose and create a diagenetic environment where metal oxides may not be stable. The quasi-steady-state interstitial Fe profiles from Tidal Potomac River sediments are an example of such a situation. This occurs primarily because the residence time of particles in the surficial sediment column is long enough to allow benthic organisms and bacteria to perform their metabolic functions. When faster sedimentation prevails, there is less time for these metabolic reactions to occur since the organisms do not occupy a sediment layer for any length of time. Also, the quantity and quality of the organic matter input to the sediment layer is important in that reservoirs often receive more terrestrial organic matter than natural lakes and this terrestrial organic matter is generally more refractory than autochthonous aquatic organic matter.     

Highly variable sediment distribution in shallow, wind-stressed lakes: a case for sediment-mapping surveys in paleolimnological studies

We examine sediment distribution patterns in seven Florida lakes and discuss implications for paleolimnological studies of shallow, subtropical lakes. The study lakes are highly productive and should exhibit thick organic sediment deposits, but organic sediments are often grossly lacking because basins are shallow, and frequent mixing, lack of stratification, and warm temperatures lead to breakdown of organic material.Organic sediment distribution patterns are highly variable. We observe three types of distribution patterns. When organic sediments are abundant, there may be (1) uniform sediment distribution. In lakes lacking organic sediments, there are (2) distribution to deeper areas if present, or (3) distribution to peripheral areas and embayments when deep waters are absent. We advocate the use of systematic mapping surveys to locate optimal coring sites for paleolimnological studies of shallow, wind-stressed lakes. Because numerous factors affect diagenesis and sediment redistribution, sediment abundance and location are not predictable. Sediment chronologies may be discontinuous and disturbed even in accumulation zones. The extent to which sedimentary records are discontinuous or disturbed is not quantifiable in any practical manner. ²¹⁰Pb and ¹³⁷Cs radioisotopic profiles provide qualitative evidence of the degree of stratigraphic disturbance. Total excess ²¹⁰Pb inventories show that sediments are focused into depositional zones when sediment distribution is uneven. Excess ²¹⁰Pb inventories are not informative about the completeness of sedimentary profiles unless small inventories suggest discontinuous sedimentation or erosional events. We present examples of disturbed and undisturbed profiles, and discuss how we use radioisotopic and geochemical evidence, and multiple cores to assess stratigraphic continuity.Journal Series No. R-04815 of the Florida Agricultural Experiment Station.     

Modern and historic accumulation rates of phosphorus in Lake Okeechobee, Florida

Phosphorus accumulation rates in depositional zone sediments of Lake Okeechobee were determined in 11 mud-zone cores and two peat-zone cores dated by ²¹⁰Pb. Although difficulties were encountered in interpreting ²¹⁰Pb data from some sites, reliable dating of sediments from the mud zone of this shallow lake is possible. Sediment accumulation rates in this zone have increased during the present century by an average of about twofold, and accumulation of organic sediments in the lake during pre-settlement times apparently was much slower than during the past century. Concentrations of all forms of sedimentary P but especially nonapatite inorganic-P and organic-P also have increased since pre-settlement times and especially since about 1940. Annual P accumulation rates in the lake's sediments have increased about fourfold during the 1900s, with most of the increase occurring in the past 40–50 years. The recent accumulation rate of sedimentary P (past ~ 10 years) agrees within a factor of 1.5 with the net retention of P in the lake calculated from published input-output mass balances.