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1.
A total of 49 elements have been identified in 338 coastal sea sediment samples collected from an area situated off the Ise-Tokai region of Japan for a nationwide marine geochemical mapping project. The spatial distribution patterns of the elemental concentrations in coastal seas along with the existing geochemical maps in terrestrial areas were used to define the natural geochemical background variation, mass transport, and contamination processes. The elemental concentrations of coastal sea sediments are determined primarily by particle size and regional differences. Most elemental concentrations increase with a decrease in particle size. Some elements such as Ca, Mn, and Yb are found to exist in large quantities in coarse particles containing calcareous shells, Fe–Mn oxides, and felsic volcanic sediments. Regional differences reflect the mass transfer process from terrestrial areas to coastal seas and the influence of the local marine geology. An analysis of variance (ANOVA) reveals that for many elements, the particle size effect is predominant over regional difference. The mean chemical compositions of coastal sea sediments are similar to those of stream sediments in adjacent terrestrial areas and in the upper crust of Japan. This observation supports the fact that coastal sea sediments have certainly originated from terrestrial materials. However, the spatial distributions of elemental concentrations are not always continuous between the land and coastal seas. The scale of mass movement observed in marine geochemical maps occurs at a distance of 20 km from the river mouth. A detailed examination of the spatial distribution patterns of K (K2O) and Cr concentrations suggests that terrestrial materials supplied through rivers are deposited near the shore initially, and then gravity-driven processes shift the sediments deeper into the basin. Contamination with heavy metals such as Zn, Cd and Pb was observed in coastal bays surrounded by urban and industrial areas. It is noteworthy that the areas with the highest concentration of these elements usually do not occur near the shore (not near the contamination source) but at the center of the bay. Unexpected low concentrations of Zn, Cd and Pb near shore may either be due to a decreased anthropogenic load in the most recent sediments or to dilution by unpolluted flood sediments.  相似文献   

2.
Formation of iron sulfide nodules during anaerobic oxidation of methane   总被引：1，自引：0，他引：1  
The biomarker compositions of iron sulfide nodules (ISNs; upper Pliocene Valle Ricca section near Rome, Italy) that contain the ferrimagnetic mineral greigite (Fe3S4) were examined. In addition to the presence of specific terrestrial and marine biomarkers, consistent with formation in coastal marine sediments, these ISNs contain compounds thought to originate from sulfate reducing bacteria (SRB). These compounds include a variety of low-molecular-weight and branched alkanols and several non-isoprenoidal dialkyl glycerol diethers (DGDs). In addition, archaeal biomarkers, including archaeol, macrocyclic isoprenoidal DGDs and isoprenoidal glycerol dialkyl glycerol tetraethers are also present. Both SRB and archaeal lipid δ13C values are depleted in 13C (δ13C values are typically less than −50‰), which suggests that the SRB and archaea consumed 13C depleted methane. These biomarker and isotopic signatures are similar to those found in cold seeps and marine sediments where anaerobic oxidation of methane (AOM) occurs with sulfate serving as the terminal electron acceptor. Association of AOM with formation of greigite-containing ISNs could provide an explanation for documented remagnetization of the Valle Ricca sediments. Upward migration of methane, subsequent AOM and associated authigenic greigite formation are widespread processes in the geological record that have considerable potential to compromise paleomagnetic records.  相似文献   

3.
潮滩盐沼物理过程的研究进展综述   总被引：9，自引：2，他引：9  
综述了本世纪国外潮滩盐沼堆积、侵蚀机制的研究进展，主要包括潮滩盐沼的粘性泥沙沉积动力机制的分析、对潮滩盐沼的物理过程的详细观测研究、沉积模式研究，以及潮滩盐沼物理过程的知识在海岸防护和其它方面的应用。  相似文献   

4.
Denitrification in continental shelf sediments has been estimated to be a significant sink of oceanic fixed nitrogen (N). The significance and mechanisms of denitrification in organic-poor sands, which comprise 70% of continental shelf sediments, are not well known. Core incubations and isotope tracer techniques were employed to determine processes and rates of denitrification in the coarse-grained, sandy sediments of the Georgia continental shelf. In these sediments, heterotrophic denitrification was the dominant process for fixed N removal. Processes such as coupled nitrification-denitrification, anammox (anaerobic ammonium oxidation), and oxygen-limited autotrophic nitrification-denitrification were not evident over the 24 and 48 h time scale of the incubation experiments. Heterotrophic denitrification processes produce 22.8–34.1 μmole N m-2 d-1 of N2 in these coarse-grained sediments. These denitrification rates are approximately two orders of magnitude lower than rates determined in fine-grained shelf sediments. These lower rates may help reconcile unbalanced marine N budgets which calculate global N losses exceeding N inputs.  相似文献   

5.
The Nuclear Waste Management Organization (NWMO) is developing a Deep Geological Repository (DGR) to contain and isolate used nuclear fuel in a suitable rock formation at a depth of approximately 500 m. The design concept employs a multibarrier system, including the use of copper-coated used fuel containers, surrounded by a low-permeability, swelling clay buffer material within a low permeability, stable host rock environment. The natural organic matter (NOM) composition of the bentonite clays being considered for the buffer material is largely uncharacterized at the molecular-level. To gain a better understanding of the NOM in target clays from Wyoming and Saskatchewan, molecular-level methods (biomarker analysis, solid-state 13C NMR and solution-state 1H nuclear magnetic resonance (NMR)) were used to elucidate the structure and sources of NOM. Organic carbon content in three commercially available bentonites analyzed was low (0.11–0.41%). The aliphatic lipid distribution of the clay samples analyzed showed a predominance of higher concentration of lipids from vascular plants and low concentrations of lipids consistent with microbial origin. The lignin phenol vanillyl acid to aldehyde ratio (Ad/Al) for the National sample indicated an advanced state of lignin oxidation and NOM diagenesis. The 13C NMR spectra were dominated by signals in the aromatic and aliphatic regions. The ratio of alkyl/O-alkyl carbon ranged from 7.6 to 9.7, indicating that the NOM has undergone advanced diagenetic alteration. The absence lignin-derived phenols commonly observed in CuO oxidation extracts from contemporary soils and sediments as well as the lack of amino acids suggests that the material corresponding to the aromatic signal is not composed of lignin or proteins but may be derived from another source such as black carbon or some other non-extractable aromatic-rich NOM. The aliphatic signal appears to correspond to long-chain compounds with little side branching based on the results of the one-dimensional (1D) and two-dimensional (2D) solution-state 1H NMR analyses. Overall, the organic geochemical analyses suggest that the NOM is composed mainly of plant-derived waxes and highly aromatic carbon with low contributions from small molecules. The compounds identified by the molecular-level analysis of NOM in the clay samples are hypothesized to be recalcitrant but future studies should examine if these compounds may serve as a microbial substrate to further test the observations of this study. Furthermore, our study suggests that the NOM has undergone diagenesis and that marine NOM signatures are no longer recognizable or detectable. As such, future work may also examine the diagenesis of these deposits to further understand the NOM geochemistry and paleoenvironmental conditions in bentonite deposits.  相似文献   

6.
Systematic positive anomalies of Ce, where Ce/Ce* spans 2.1 to 11.4, are present in basalts and rhyolites of a 2.96 Ga submarine volcanic sequence of the Murchison Province, Western Australia. This volcanic sequence is host to a stratabound Cu–Zn deposit that formed on the seafloor from a seawater hydrothermal system. These are true Ce anomalies as Pr/Pr* < 1. In modern oxygenated marine water Ce is sequestered by Mn-oxides and hydroxides, which coprecipitate with Fe-oxides and hydroxides as nodules and crusts on the ocean floor, as well as Fe–Mn chemical sediments from hydrothermal systems at ocean spreading centers. Fe–Mn sediments have positive Ce anomalies and marine water complementary negative anomalies. Such Ce anomalies have not formerly been reported for Archean hydrothermally altered volcanic rocks. These extreme anomalies are attributed to Mn-transport in shallow-circulating oxygenated marine bottom waters peripheral to the deeper, hotter, hydrothermal system from which the Cu–Zn deposit formed, and record an oxygenated marine environment ~ 500 Ma before the so-called great oxidation event at ~ 2.4 Ga. Results for positive Ce anomalies in the Golden Grove volcanic sequence are complementary to negative anomalies in Archean BIF, collectively stemming from particulate scavenging of Ce+ 3 in an oxic water column.  相似文献   

7.
In all, 53 elements were analyzed in 1406 coastal sea sediment samples collected from an area off Hokkaido and the Tohoku region of Japan during a nationwide marine geochemical mapping project. The spatial distribution patterns of the elemental concentrations in coastal seas along with the existing geochemical maps in terrestrial areas were used to define natural geochemical background variation and mass transport processes. The terrestrial area is covered by mafic volcanic rocks and accretionary complexes associated with ophiolite, which has small amounts of felsic volcanic rocks and granite. The spatial distribution patterns of elements enriched in mafic lithologies such as Fe (Total Fe2O3) and Sc in marine environments are influenced by adjoining terrestrial materials. The spatial distribution patterns of Cr and Ni concentrations, which are highly abundant in ultramafic rocks on land, are used to evaluate the mass transport from land to the sea and the dispersive processes caused by oceanic currents. The scale of mass transport by oceanic currents occurs up to a distance of 100–200 km from the coast along the coastal areas. The regional differences of elements rich in felsic lithologies such as K (K2O), Nb and La in marine sediments are determined mainly by the relative proportion of minerals and lithic fragments enriching felsic materials to those associated with mafic materials. The spatial distribution of elemental concentration is not always continuous between the land areas and coastal sea areas. That difference is interpreted as resulting from (1) transportation of marine sediments by oceanic currents and storm waves, (2) contribution of volcanic materials such as tephra, (3) occurrence of shell fragments and foraminifera tests and (4) distribution of relict sediments of the last glacial age and early transgression age. Contamination with Cu, Zn, Cd, As, Mo, Sn, Sb, Hg, Pb and Bi was not observed in marine environments because the study area has little anthropogenic activity. Terrestrial materials are the dominant source for these metals. The Mo, Cd, Sn, Sb, Hg, Pb and Bi are abundant in silty and clayey sediments locally because of early diagenetic processes, authigenic precipitation and organic substances associated with these elements. The spatial distribution of As concentration shows exceptions: it is concentrated in some coarse and fine sands on the shelf. The enrichment is explained by adsorption of As, sourced from a coal field, to Fe hydroxide.  相似文献   

8.
Large and complete glaciotectonic sequences formed by marine‐terminating glaciers are rarely observed on land, hampering our understanding of the behaviour of such glaciers and the processes operating at their margins. During the Late Weichselian in western Iceland, an actively retreating marine‐terminating glacier resulted in the large‐scale deformation of a sequence of glaciomarine sediments. Due to isostatic rebound since the deglaciation, these formations are now exposed in the coastal cliffs of Belgsholt and Melabakkar‐Ásbakkar in the Melasveit district, and provide a detailed record of past glacier dynamics and the inter‐relationships between glaciotectonic and sedimentary processes at the margin of this marine‐terminating glacier. A comprehensive study of the sedimentology and glaciotectonic architecture of the coastal cliffs reveals a series of subaquatic moraines formed by a glacier advancing from Borgarfjörður to the north of the study area. Analyses of the style of deformation within each of the moraines demonstrate that they were primarily built up by ice‐marginal/proglacial thrusting and folding of marine sediments, as well as deposition and subsequent deformation of ice‐marginal subaquatic fans. The largest of the moraines exposed in the Melabakkar‐Ásbakkar section is over 1.5 km wide and 30 m high and indicates the maximum extent of the Borgarfjörður glacier. Generally, the other moraines in the series become progressively younger towards the north, each designating an advance or stillstand position as the glacier oscillated during its overall northward retreat. During this active retreat, glaciomarine sediments rapidly accumulated in front of the glacier providing material for new moraines. As the glacier finally receded from the area, the depressions between the moraines were infilled by continued glaciomarine sedimentation. This study highlights the dynamics of marine‐terminating glaciers and may have implications for the interpretation of their sedimentological and geomorphological records.  相似文献   

9.
A total of 402 coastal sea-sediment samples were collected from the continental shelf, slope, and basin off Tsushima Island in the western Sea of Japan, and were analyzed for 51 elements as part of a nationwide marine geochemical mapping project. The samples were compared to potentially related sample sets, and the results were considered from the viewpoint of the origin of marine surface sediments in the western Sea of Japan. The spatial distribution of elemental concentrations in the coastal sea sediments correspond to texture, grain size, the presence of shells and foraminifera, and the mud content of surface marine sediments. Most elemental concentrations increased with increasing mud content. Some samples located in littoral areas included sediment particles apparently supplied from nearby rivers, but their contribution was limited. Overall, the mean chemical compositions of clastic material in coastal sea sediments appear to differ from those of stream sediments in adjacent terrestrial areas. In addition, the geochemistry of the coastal sea sediments cannot be fully explained by the mixing of the material supplied from Korean and Chinese stream sediments, which are the most feasible sources. Coastal sea sediments in the study area are well mixed by transportation processes; therefore, elemental abundances in these marine sediments may be homogenized to such an extent that it is not possible to determine their origin. Alternatively, most of the clastics in the sediment may actually represent relict reworked material, originally formed in the Yellow Sea and Tsushima Strait during the last glacial stage and subsequent transgression.  相似文献   

10.
《Organic Geochemistry》1999,30(8):937-945
The anaerobic degradation of the polycyclic aromatic hydrocarbons (PAHs) naphthalene and phenanthrene was investigated in several marine harbor sediments. In sediments from Boston Harbor that were heavily contaminated with petroleum, [14C]-naphthalene and [14C]-phenanthrene were oxidized to 14CO2 without a lag, suggesting that the microbial community was adapted for anaerobic PAH oxidation in situ. The addition of molybdate, a specific inhibitor of sulfate-reducing microorganisms, inhibited PAH mineralization which suggested that sulfate reducers were involved in the anaerobic oxidation of the PAHs. PAHs were also anaerobically oxidized at another site in Boston Harbor that was less heavily contaminated, but at a slower rate than in the most heavily contaminated sediments. Sediments not contaminated with petroleum did not significantly oxidize the PAHs. A similar correspondence between rates of anaerobic PAH oxidation and the degree of PAH contamination was observed in sediments from Tampa Bay and San Diego Bay. When relatively pristine sediments from San Diego Bay that did not have a significant capacity for anaerobic PAH oxidation were exposed to high concentrations of naphthalene, they developed a potential for naphthalene degradation that was comparable to that in sediments that had a history of PAH contamination. The increase in potential for naphthalene degradation in the sediments exposed to naphthalene was associated with an increase in naphthalene-degrading microorganisms. These results suggest that many marine harbor sediments contain microorganisms capable of anaerobically oxidizing PAHs under sulfate-reducing conditions and that these microorganisms will respond with an increase in their activity when PAHs are introduced into the sediments. Thus, if PAH inputs into harbor sediments from petroleum can be reduced there may be a widespread potential for microorganisms to remove this PAH contamination from the sediments, despite anaerobic conditions.  相似文献   

11.
The lowermost Carboniferous rocks in the Cockburnspath area of east Berwickshire (southern Scotland) are interpreted as coastal floodplain sediments. A lower mudstone-dominated unit is composed of silty mudstones and shales with subordinate sandstones and argillaceous ferroan dolomites (cementstones). These are interpreted as distal floodplain sediments with periodic crevasse-splay deposition. The dark grey colour of the mudrocks suggests deposition in reducing conditions, probably in floodplain lakes. Most of the cementstones are concretionary, some with septarian cracks, suggesting an early diagenetic origin. An immature palaeosol suggests periodic pedogenesis under improved drainage. A synsedimentary erosion surface indicates incision of a valley into the floodplain, presumably in response to base-level lowering. An upper sandstone-dominated unit starts with fine-grained rippled sandstones, cut by small channel sandstones. These are interpreted as floodplain lake deposits fed by crevasse channels. A distinctive conglomerate with cementstone clasts, wood fragments and fish remains is interpreted as a major overbank deposit, dumped into a pre-existing floodplain lake. A bivalve fauna was established in the overlying mudstones, followed by a thin limestone with a restricted marine fossil assemblage, showing that seawater flooding of the lakes occurred at times. Mudrocks throughout the sequence contain no pyrite, except for the marine band which has an organic-carbon/sulphur ratio and degree of pyritization value typical of marine sediments. The concretionary cementstones have δ13C values around —4 to —6%0/00 PDB which are interpreted as indicative of anaerobic oxidation of organic matter. The combined geochemical data suggest a significant involvement of iron reduction in cementstone formation, although the δ13C values are ambiguous in assessing the relative involvement of methanogenesis and methane oxidation. Limited seawater inundation of the floodplains might have supplied magnesium and calcium ions for dolomite formation assuming that any H2S derived as a result of sulphate reduction was oxidized by iron reduction. Alternatively a weathering source for solutes might have been involved.  相似文献   

12.
The C and N stable isotope compositions of some flora of East Africa from coastal Tanzania and Amboseli National Park (Kenya) are used to assess if they can be used as a terrestrial end member during the estimation of terrestrial fraction in coastal marine sediments. The results of C isotope composition of various tree leaves, which average −29.3 ± 1.4%, indicate that these tropical higher land plant species follow a Calvin-Benson or non-Kranz (C3) type of metabolism. The results for grass species, which average −13.2 ± 2.4%, indicate that most of them follow a Hatch-Slack or Kranz (C4) type of metabolism. However, some of the succulent plants from the Amboseli National Park have δ13C values that average −14.7%, an indication that they follow a CAM (Crassulacean Acid Metabolism) type of metabolism. The N isotope values are relatively higher than expected for the terrestrial organic material. The average δ15N values for both tree and grass samples are higher than 5% and fall within the range normally considered to be marine. The high enrichment in 15N may be related to the environmental conditions in which plants thrive. Plants growing in sandy, dry and overgrazed environments are expected to be enriched in 15N owing to full utilisation of all available N species, regardless of their isotopic compositions. Other processes which may cause an enrichment in 15N include adsorption by various types of clay minerals, supply of 15N-enriched nitrate through sea-spray, and local denitrification, especially in swampy and lake margins where the input of organic matter may be higher than the rate of decomposition.The stable isotopic composition of organic C and N for surficial organic matter for the coastal marine sediments averages −17.0 ± 0.9% and 5.4 ± 1.1%, respectively. These values indicate a substantial contribution of C4 plants and sea grasses. However, contribution of C4 relative to that of sea grasses can not be evaluated owing to the fact that there is no significant difference in the isotopic compositions between the two groups.In the savannah environment, where a contribution from the C4 types of plants might be substantial, the δ13C value for a terrestrial end member needs to be established prior to evaluation of the terrestrially derived organic matter in the marine environment. Owing to a significant contribution of sea grasses to the total organic matter preserved in coastal marine sediments, the stable isotopes of organic C seem to have a limited applicability as source indicators in the East African coastal waters. Furthermore, the results indicate that N stable isotopes seem to have a limited applicability as source indicators in coastal waters of East Africa. However, more work needs to be conducted to determine the terrestrial and sea grass end member values for the coastal areas.  相似文献   

13.
Quaternary sediment deposits are well exposed along the eastern coastal margin of Sri Lanka. Systematic trace fossil studies along with sediment characteristics have been carried out for the first time to interpret the paleoenvironment that prevailed during Quaternary sedimentation in eastern Sri Lanka. The trace fossils Thalassinoides, Skolithos and Polykladichnus have been recognized about 5m above the present mean sea level. Features of the major trace fossil, Thalassinoides, indicate that it was formed by Thalassinidean shrimp Calianassa. Isolated, vertical to steeply inclined, cylindrical to sub cylindrical tubes with thin internal wall lining and inner wall striations of Skolithos and Polykladichnus show that they were formed by polychaetes. The typical characteristic of Polykladichnus isY-shaped branching with slight enlargement at junctions. Morphology and association of burrows as well as mineralogy, grain size and roundness of sediments indicate that the environment prevailed was marine soft grounds of the intertidal zone. Presence of preserved fine-scale features of burrows indicate that the bioturbated sandy tidal flat was suddenly exposed to the tropical environment due to sea level regression in Quaternary periods. Due to the microbial activities of wall linings, burrows were preserved and it was supported by other microbial activities that produced secondary iron bearing minerals that suffered subsequent oxidation. The bio-origination of red sediments of eastern coastal area of the present study can be used to interpret the debatable origin of the red beds found in northwestern and southeastern coastal areas of the island.  相似文献   

14.
Thermal stability of ladderane lipids as determined by hydrous pyrolysis   总被引：1，自引：0，他引：1  
Anaerobic ammonium oxidation (anammox) has been recognized as a major process resulting in loss of fixed inorganic nitrogen in the marine environment. Ladderane lipids, membrane lipids unique to anammox bacteria, have been used as markers for the detection of anammox in marine settings. However, the fate of ladderane lipids after sediment burial and maturation is unknown. In this study, anammox bacterial cell material was artificially matured by hydrous pyrolysis at constant temperatures ranging from 120 to 365 °C for 72 h to study the stability of ladderane lipids during progressive dia- and catagenesis. HPLC-MS/MS analysis revealed that structural alterations of ladderane lipids already occurred at 120 °C. At temperatures >140 °C, ladderane lipids were absent and only more thermally stable products could be detected, i.e., ladderane derivatives in which some of the cyclobutane rings were opened. These diagenetic products of ladderane lipids were still detectable up to temperatures of 260 °C using GC-MS. Thus, ladderane lipids are unlikely to occur in ancient sediments and sedimentary rocks, but specific diagenetic products of ladderane lipids will likely be present in sediments and sedimentary rocks of relatively low maturity (i.e., C31 hopane 22S/(22S + 22R) ratio <0.2 or ββ/(αβ + βα + ββ) ratio of >0.5).  相似文献   

15.
The results of a study of the contribution of microbial metabolic products to total dissolved organic carbon (DOC) levels in coastal sediments are presented. The data indicate that acidic volatile compounds make up a substantial fraction of pore water DOC's in both oxic and anoxic pore waters of coastal marine sediments. Formic, acetic and butyric acids are the principal volatile species identified at levels exceeding 10 μM. Acid concentrations are up to five times higher in anoxic pore waters than in oxic waters. Volatile organic acids show promise as indicators of diagenetic processes in marine sediments and of the ecological succession of microorganisms, in particular.  相似文献   

16.
Indian coastal waters are subjected to considerable pressure from sewage and industrial wastes, which are responsible for the contamination of the coastal sediments with consequent loss in biosphere. The present investigation attempts to study the significance of coarse material (Sand fraction) in the distribution of metals in polluted marine sediments. The study revealed that coarse Sand component contains a relatively significant proportion of the anthropogenic metals (Cd, Cu, Pb and Zn) and therefore it cannot be neglected in metal pollution studies of coastal sediments. Further, the distribution of anthropogenic metals in both Silt + Clay and Sand fraction follow the same suit indicating similar pollution sources. From the total sediment type (Silt + Clay and Sand fraction) all anthropogenic metals had a noticeable amount (>50%) in the acid extractable (and potentially bio-available) fraction. This article stresses the importance of coarse fraction in metal pollution studies in Indian coastal system.  相似文献   

17.
《Quaternary Science Reviews》2007,26(7-8):1106-1128
The coastal geomorphology of the northeastern Raukumara Peninsula, New Zealand, is examined with the aim of determining the mechanisms of Holocene coastal uplift. Elevation and coverbed stratigraphic data from previously interpreted coseismic marine terraces at Horoera and Waipapa indicate that, despite the surface morphology, there is no evidence that these terraces are of marine or coseismic origin. Early Holocene transgressive marine deposits at Hicks Bay indicate significant differences between the thickness of preserved intertidal infill sediments and the amount of space created by eustatic sea level rise, therefore uplift did occur during early Holocene evolution of the estuary. The palaeoecology and stratigraphy of the sequence shows no evidence of sudden land elevation changes. Beach ridge sequences at Te Araroa slope gradually toward the present day coast with no evidence of coseismic steps. The evolution of the beach ridges was probably controlled by sediment supply in the context of a background continuous uplift rate. No individual dataset uniquely resolves the uplift mechanism. However, from the integration of all evidence we conclude that Holocene coastal uplift of this region has been driven by a gradual, aseismic mechanism. An important implication of this is that tectonic uplift mechanisms do vary along the East Coast of the North Island. This contrasts with conclusions of previous studies, which have inferred Holocene coastal uplift along the length of the margin was achieved by coseismic events. This is the first global example of aseismic processes accommodating uplift at rates of >1 mm yr−1 adjacent to a subduction zone and it provides a valuable comparison to subduction zones dominated by great earthquakes.  相似文献   

18.
《Applied Geochemistry》1999,14(6):735-745
In the Lower Andarax river basin 3 aquifer units have been defined, namely the Carbonate Aquifer, the Deep Aquifer and the Detrital Aquifer, which between them contain a wide variety of water types. Identification of hydrogeochemical processes has been performed by studying a series of ionic ratios, comprising the principal constituents together with B and Li (Cl vs SO4, Cl vs Mg, Cl vs Li, B vs Li). Among the processes detected, the circulation of groundwaters with high concentrations of SO4 was found to have significant effects. Moreover, in the coastal region, naturally occurring processes related to the flushing of saline waters from sediments of marine origin occur in conjunction with others, clearly of human origin, that are related to saltwater intrusion. A further factor is the entry, from overlying deposits, of waters with a high saline content; this salinity is related to the flushing of sediments of marine origin. The use of B and Li together enables waters in which salinity is related to seawater to be distinguished from others in which salinity is related to evaporitic layers or to thermal areas. The concentration of Li is directly related to water temperature, while that of B is greater in the most saline sectors, of gypsiferous and/or seawater origin.  相似文献   

19.
The respiratory reduction of nitrate (denitrification) is acknowledged as the most important process that converts biologically available nitrogen to gaseous dinitrogen (N2) in marine ecosystems. Recent findings, however, indicate that anaerobic ammonium oxidation by nitrite (anammox) may be an important pathway for N2 formation and N removal in coastal marine sediments and in anoxic water columns of the oceans. In the present study, we explored this novel mechanism during N mineralization by 15N amendments (single and coupled additions of 15NH4+, 14NO3− and 15NO3−) to surface sediments with a wide range of characteristics and overall reactivity. Patterns of 29/30N2 production in the pore water during closed sediment incubations demonstrated anammox at all 7 of the investigated sites. Stoichiometric calculations revealed that 4% to 79% of total N2 production was due to this novel route. The relative importance of anammox for N2 release was inversely correlated with remineralized solute production, benthic O2 consumption, and surface sediment Chl a. The observed correlations indicate competition between reductants for pore water nitrite during early diagenesis and that additional factors (e.g. availability of Mn-oxides), superimposed on overall patterns of diagenetic activity, are important for determining absolute and relative rates of anammox in coastal marine sediments.  相似文献   

20.
海洋环境中的厌氧铵氧化过程作为实现固定态氮从海洋生态系统中移除的一个新途径,广泛地存在于各种海洋环境中,包括永久性缺氧水体、沉积物、海冰甚至海底热液,是海洋氮循环过程中一个非常重要的环节。开展海洋环境中厌氧铵氧化过程的研究可以更好地量化海洋氮循环过程中的收支,而这一收支在很大程度上影响着全球的气候变化。介绍了海洋环境中厌氧铵氧化过程研究历史,并分别讨论了在大洋缺氧水体和沉积物中厌氧铵氧化速率的分布情况,同时还总结了海洋环境因子如温度、氧气、硫化氢、NO3-/NO2-、NH4+以及有机物等对厌氧铵氧化的影响。最后探讨了该领域研究中所存在的问题并指出了亟待开展的工作:特定大洋缺氧水体中厌氧铵氧化与反硝化的争议以及近岸缺氧水体中厌氧铵氧化的研究;陆架及深海大洋沉积物中厌氧铵氧化的深入研究;对于全球海洋氮循环收支的重新评估。  相似文献   

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