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1.
Iron and manganese in bottom sediments studied along the sublatitudinal transect from Kandalaksha to Arkhangelsk are characterized by various contents and forms depending on sedimentation environments, grain size of sediments, and diagenetic processes. The latter include redistribution of reactive forms leading to enrichment in Fe and Mn of the surface sediments, formation of films, incrustations, and ferromanganese nodules. Variations in the total Fe content (2–8%) are accompanied by changes in the concentration of its reactive forms (acid extraction) and the concentration of dissolved Fe in the interstitial water (1–14 μM). Variations in the Mn content in sediments (0.03–3.7%) and the interstitial water (up to 500 μM) correspond to a high diagenetic mobility of this element. Changes in the valence of chemical elements results in the redox stratification of sediment strata with maximum concentrations of Fe, Mn, and sulfides. Organic matter of sediments with a considerable terrestrial constituent is oxidized by bottom water oxygen mainly at the sediment surface or in anaerobic conditions within the sediment strata. The role of inorganic components in organic matter oxidation changes from surface sediments, where manganese oxyhydroxide dominates among oxidants, to deeper layers, where sulfate of interstitial water serves as the main oxidant. Differences in river runoff and hydrodynamics are responsible for geochemical asymmetry of the transect. The deep Kandalaksha Bay serves as a sediment trap for manganese (Mn content in sediments varies within 0.5–0.7%), whereas the sedimentary environment in the Dvina Bay promotes its removal from sediments (Mn 0.05%).  相似文献   

2.
Bulk chemical, mineralogical and selective leach analyses have been made on a suite of abyssal ferromanganese nodules and associated sediments from the S.W. equatorial Pacific Ocean. Compositional relations between nodules, sediment oxyhydroxides and nearby ferromanganese encrustations are drawn assuming that the crusts represent purely hydrogenetic ferromanganese material. Crusts, δMnO2-rich nodules and sediment oxyhydroxides are compositionally similar and distinct from diagenetic todorokitebearing nodules. Compared to Fe-Mn crusts, sediment oxyhydroxides are however slightly enriched, relative to Mn and Ni, in Fe, Cu, Zn, Ti and Al, and depleted in Co and Pb, reflecting processes of non-hydrogenous element supply and diagenesis. δMnO2 nodules exhibit compositions intermediate between Fe-Mn crusts and sediment oxyhydroxides and thus are considered to accrete oxides from both the water column and associated sediments.Deep ocean vertical element fluxes associated with large organic aggregates, biogenic calcite, silica and soft parts have been calculated for the study area. Fluxes associated with organic aggregates are one to three orders of magnitude greater than those associated with the other phases considered, are in good agreement with element accumulation rates in sediments, and are up to four orders of magnitude greater than element accumulation rates in nodules. Metal release from labile biogenic material in surface sediments can qualitatively explain the differences between the composition of Fe-Mn crusts and sediment oxyhydroxides.Todorokite-rich diagenetic nodules are confined to an eastwards widening equatorial wedge. It is proposed that todorokite precipitates directly from interstitial waters. Since the transition metal chemistry of interstitial waters is controlled dominantly by reactions involving the breakdown of organic carbon, the supply and degradation rate of organic material is a critical factor in the formation of diagenetic nodules. The wide range of (trace metal/Mn) ratios observed in marine todorokite reflects a balance between the release of trace metals from labile biogenic phases and the reductive remobilisation of Mn oxide, both of which are related to the breakdown of organic carbon.  相似文献   

3.
The adsorption of phosphorus on natural diagenetic iron (Feox) and manganese (Mnox) oxyhydroxides was studied in deep and littoral zone sediments of mesotrophic Lac Saint-Charles (46°56 N, 71°23 W), using a Teflon sheet technique for collecting diagenetically produced metal oxyhydroxides. Collected metal oxide amounts were greater at the deep-water station, relative to littoral zone stations reflecting sediment and local diagenetic differences. Two-layer surface complexation modeling on iron oxyhydroxide was consistent with the measured total P/Fe molar ratios except for the upper mixed Mn–Fe oxide layer from the littoral stations, where measured phosphorus exceeded the modeled phosphorus by more than fivefold. Soluble reactive phosphorus (SRP) exchange between oxyhydroxide samples and natural lake water in the laboratory revealed a labile phosphorus pool. Phosphorus determined on the Teflon sheets from the littoral zone stations appears to be related to a distinct non-humic organic carbon pool that readily exchanges SRP, while little exchange was observed from material collected from the deep-water station. We suggest that the enhanced SRP release from littoral zone sediments is due to an organic carbon and/or metal oxide-impoverished sediment matrix, limiting microbial oxide reduction and allowing phosphorus to be rapidly recycled at the sediment–water interface, instead of being slowly incorporated into humic material. The SRP fluxes revealed in our study, which originate from the solid phase at the sediment–water interface, would be difficult to resolve using interstitial pore-water samplers and might be a quantitatively important source of inorganic phosphorus in Shield lakes.  相似文献   

4.
Samples of authigenic material, sediment overlying water and oxic surface sediment (0–0.5-cm depth) from a perennially oxygenated lacustrine basin were analysed to investigate which solid phases are important for binding a suite of trace elements (Ag, As, Ca, Cd, Cu, Hg, In, methylmercury (MeHg), Mg, Mo, Pb, Sb and Zn). The authigenic material, which was collected with inert Teflon sheets deployed for several years across the sediment–water interface, contained mainly poorly crystallized Fe oxyhydroxides and natural organic matter, presumably humic substances derived from the watershed. Manganese oxyhydroxides were not present in the collected authigenic material due to the slightly acidic condition (pH = 5.6) of the lake that prevents the formation and recycling of these compounds. Conditional equilibrium constants for the adsorption of cationic (KFe–M) and anionic (KFe–A) trace elements onto the authigenic Fe oxyhydroxides were estimated from their concentrations in the authigenic material and in bottom water samples. These field-derived values of KFe–M and KFe–A were compared with those predicted by the surface complexation model, using laboratory-derived intrinsic adsorption constants and the water composition at the study site. Equilibrium constants (KPOM–M) were also calculated for the adsorption of the cationic trace elements onto the humic substances contained in the diagenetic material. The field-derived values of KPOM–M were compared to those predicted by the speciation code WHAM 6 for the complexation of the trace elements by dissolved humic substances in the lake. Combining the results of the present study with those on the distributions of trace elements in the porewater and solid-phase sediments reported in previous studies at the same site, it was determined whether the trace elements bind preferentially to Fe oxyhydroxides or natural organic matter in oxic sediments. The main inferences are that the anionic trace elements As, Mo and Sb, as well as the cationic metal Pb are preferentially bound to the authigenic Fe oxyhydroxides whereas the other trace elements, and especially Hg and MeHg, are preferentially bound to the humic substances.  相似文献   

5.
 Sediment and its associated pore water were collected from a zoned, freshwater, riparian wetland, located in the Talladega National Forest, northeastern Hale County, Alabama, to study the porewater chemistry and its spatial changes within and between the wetland ecological zones. Obvious changes in pH, Eh and element concentrations were observed between the different wetland ecological zones. Major cations (Ca, Mg, and Na) and trace elements (B, Ba, Sr, and Mn) have very good spatial correlation with Fe and Mn distributions, both in the pore water and the sediment, suggesting that adsorption on, and desorption from, iron and manganese oxyhydroxides are important processes controlling the distributions of these elements in the wetland sediment. However, an equilibrium adsorption model is not able to explain the distribution of trace elements between the pore water and sediment. A redox kinetic model gives similar vertical profiles for iron and the correlated elements as those measured in the field and thus suggests that the relative rates of ferrous iron oxidation and the reductive dissolution of ferric iron in the sediment are important variables determining the distributions of these elements in the wetland pore waters. Received: 31 October 1996 · Accepted: 27 May 1997  相似文献   

6.
The formation of iron sulphide minerals exerts significant control on the behaviour of trace elements in sediments. In this study, three short sediment cores, retrieved from the remote Antinioti lagoon (N. Kerkyra Island, NW Greece), are investigated concerning the solid phase composition, distribution, and partitioning of major (Al, Fe) and trace elements (Cd, Cu, Mn, Pb, and Zn). According to 210Pb, the sediments sampled correspond to depositions of the last 120 years. The high amounts of organic carbon (4.1–27.5%) result in the formation of Fe sulphides, predominantly pyrite, already at the surface sediment layers. Pyrite morphologies include monocrystals, polyframboids, and complex FeS–FeS2 aggregates. According to synchrotron-generated micro X-ray fluorescence and X-ray absorption near-edge structure spectra, authigenically formed, Mn-containing, Fe(III) oxyhydroxides (goethite type) co-exist with pyrite in the sediments studied. Microscopic techniques evidence the formation of galena, sphalerite and CuS, whereas sequential extractions show that carbonates are important hosts for Mn, Cd, and Zn. However, significant percentages of non-lattice held elements are bound to Fe/Mn oxyhydroxides that resist reductive dissolution (on average 60% of Pb, 46% of Cd, 43% of Zn and 9% of Cu). The partitioning pattern changes drastically in the deeper part of the core that is influenced by freshwater inputs. In these sediments, the post-depositional pyritization mechanism, illustrated by overgrowths of Fe monosulphides on pre-existing pyrite grains, results in relatively high degree of pyritization that reaches 49% for Cd, 66% for Cu, 32% for Zn and 7% for Pb.  相似文献   

7.
Indicator role of trace elements in sedimentation and ore formation is considered for sediments from Station 2182 in the Angola Basin. It is shown that pelagic sediments were formed from two main sources: biogenic calcium carbonate and lithogenic sediment component compositionally similar to the miopelagic clay. Increase of the Mn/Al ratio, Ce anomaly in the REE composition, Co/Ni and Mo/W ratios, and anomalous accumulation of Tl, Pb, Bi and other microelements indicate that sediments from horizons 15–20 and 30–35 cm contain significant amounts of hydrogenic material as Fe-Mn oxyhydroxides. Manganese micronodules (MN) were extracted from different horizons (10–15, 15–20, and 30–35 cm) and analyzed to study the hydrogenic component. Their development is related to retardation of biogenic and lithogenic sedimentation. The studied manganese micronodules are represented by the hydrogenic-diagenetic formations >100 μm in size with Mn/Fe = 2.0–2.8, Co/Ni = 0.2–0.4, Ce an = 4.2–5.7, and Mo/W = 5.2–7.9. The MN content is too low to affect the major and trace element composition of sediments. The main part of Fe and Mn is confined to fraction <10 μm.  相似文献   

8.
Processes governing the formation of rare earth elements (REE) composition are considered for ferromanganese deposits (nodules, separate parts of nodules, and micronodules of different fractions) within the Clarion–Clipperton ore province in the Pacific Ocean. It is shown that ferromanganese oxyhydroxide deposits with different chemical compositions can be produced in sediments under similar sedimentation conditions. In areas with high bioproductivity, the size of micronodules has a positive correlation with the Mn content and Mn/Fe and P/Fe ratios and a negative correlation with Fe, P, REE, and Ce anomaly. The behavior of REE in micronodules from sediments within bioproductive zones is related to increase of the influence of diagenetic processes in sediments as a response to the growth of the size of micronodules. Distinctions in the chemical composition of micronodules and nodules are related to their interrelations with associated sediments. Micronodules grow in sediments using hydrogenous ferromanganese oxyhydroxides. As they grow, micronodules are enriched in the labile fraction of sediments reworked during diagenesis. Sources of the material of ferromanganese nodules are governed by their formation at the water bottom interface. Their upper part is formed by direct settling of iron oxyhydroxides from the bottom water, whereas the lower part is accumulated due to diagenetic processes in sediments. Differences of REE compositions in ferromanganese deposits are caused by the reduction of manganese during diagenesis and its separation from iron. Iron oxyhydroxides form a sorption complex due to the sorption of phosphate-ion from bottom and pore waters. The sorption of phosphate-ion results in an additional sorption of REE.  相似文献   

9.
Uranium geochemistry has been investigated in three acid lakes located on the Canadian Shield and one circumneutral lake in the Appalachian Region of Eastern Canada. In all Shield lakes, dissolved U concentrations were higher in the porewater than in the overlying water. In one of them, whose hypolimnion is perennially oxic, U released to porewater at depths of Fe remobilization was removed from the porewater at depths of Fe oxyhydroxides precipitation; these similarities in the U and Fe profiles indicate that part of the U becomes associated to Fe oxyhydroxides. The dissolved U and Fe profiles in the other two Shield lakes, whose hypolimnions were anoxic when sampled, did not show any significant recycling of these elements in the vicinity of the sediment-water interface and both elements diffused from the sediment to the overlying water. In contrast, in the Appalachian Lake, dissolved U concentrations were higher in the overlying water than in porewater, strongly decreased at the vicinity of the sediment-water interface and then remained relatively constant with sediment depth. Diagenetic modeling of the porewater U profiles, assuming steady-state, reveals that authigenic U always represented ?3% of the total U concentration in the sediments of all lakes. This observation indicates that diagenetic reactions involving U are not quantitatively important and that most of the U was delivered to the sediments at our study sites as particulate U and not through diffusion across the sediment-water interface, as is seen in continental margin sediments. Comparison of the U:Corg and U:Fe molar ratios in diagenetic material collected across the sediment-water interface with Teflon sheets and in surface sediments (0-0.5 cm) of the lake having a perennially oxic hypolimnion suggest that solid phase U was mainly bound to organic matter originating from the watershed; a strong statistical correlation between sediment non-lithogenic U and Corg in the Appalachian Lake supports this contention. Thermodynamic calculations of saturation states suggest that dissolved U was not removed from porewater through precipitation of UO2(s), U3O7(s) and U3O8(s) as previously proposed in the literature.  相似文献   

10.
A sedimentological study of two dimitic lakes in North-Eastern Germany provided a record of anthropogenic impacts and historical changes of water quality. The upper 50 cm sediment profiles were compared for major nutrients and selected major trace elements. The sediments were dated by 210Pb and 137Cs measurement. The upper 50 cm sediment profiles represent approximately the last 100 years of history in both lakes. Element analyses show different characteristic stratigraphic patterns in both lakes. Based on the nutrient and metal stratification, three characteristic time periods can be documented for both lakes. In addition to agricultural use of the catchment area, atmospheric pollution greatly influenced the metal concentration in the sediment layers. Variation in the external loading and redox conditions in the hypolimnion explain the variation in the composition and accumulation of metals in the sediment stratigraphy. No increases or changes in the trophic level of either lake could be documented based on the accumulation of the nutrients C, N and P. The ratio of Fe/Mn and Fe/Ca characterized the changing redox conditions. The stratigraphy of Pb and Zn agrees with the historical variation in atmospheric pollution and confirms literature values for Central and North Europe. The drop in Pb and Zn over the last 10–15 years is a regional effect in North-Eastern Germany.  相似文献   

11.
Arsenic species including arsenite, arsenate, and organic arsenic were measured in the porewaters collected from Poyang Lake, the largest freshwater lake of China. The vertical distributions of dissolved arsenic species and some diagenetic constituents [Fe(II), Mn(II), S(−II)] were also obtained in the same porewater samples in summer and winter. In sediments the concentration profiles of total As and As species bound to Fe–Mn oxyhydroxides and to organic matter were also determined along with the concentrations of Fe, Mn and S in different extractable fractions. Results indicate that, in the summer season, the concentrations of total dissolved As varying from 3.9 to 55.8 μg/L in sediments were higher than those (5.3–15.7 μg/L) measured in the winter season, while the concentrations of total As species in the solid phase varied between 10.97 and 25.32 mg/kg and between 7.84 and 30.52 mg/kg on a dry weight basis in summer and winter, respectively. Seasonal profiles of dissolved As suggest downward and upward diffusion, and the flux of dissolved As across the sediment–water interface (SWI) in summer and winter were estimated at 3.88 mg/m2 a and 0.79 mg/m2 a, respectively. Based on porewater profiles and sediment phase data, the main geochemical behavior of As was controlled by adsorption/desorption, precipitation and molecular diffusion. The solubility and migration of inorganic As are controlled by Fe–Mn oxyhydroxides in summer whereas they appear to be more likely controlled by both amorphous Fe–Mn oxyhydroxides and sulfides in winter. A better knowledge of the cycle of As in Poyang Lake is essential to a better management of its hydrology and for the environmental protection of biota in the lake.  相似文献   

12.
沉积物微量金属元素在重建水体环境变化中的意义   总被引：7，自引：0，他引：7  
沉积物所记录的微量金属含量与形态的变化是指示人类活动影响下水体环境变化的有效指标,主要用于指示沉积物重金属污染、水体初级生产力变化和氧化还原条件等方面的水体环境状况。总体而言,沉积物中微量金属含量在近一个世纪以来显著上升,反映了采矿、冶金、污水排放、化肥使用、煤炭和石油燃烧等各种人类活动造成水体和沉积物重金属污染的记录作为浮游植物微量营养元素,Cu、Zn、Ni、Ba、Cd等在沉积物中的记录可以指示水体初级生产力水平。U、Mo、V、Cu、Cd、Mn等氧化还原敏感元素在沉积物中的富集或贫化,及其比值(如Re/Mo、Cd/U、Th/U和V/Sc)的变化,是指示水体和沉积物氧化还原环境的有效指标。但需要指出的是,在受人类活动影响的水体中,这些生产力和氧化还原指标很少能指示水体生产力或氧化还原状况,可能主要与人类活动同时造成这些金属元素大量污染输入而掩盖了其自生来源和内在变化的沉积记录有关。所以,对沉积物中微量金属元素来源的判别(陆源碎屑输入、人为输入和水体自生来源)是重建水体环境变化的重要前提。本文总结了多种化学和统计学方法(包括同位素示踪法、化学提取法、富集因子法和主成分分析法等)在沉积物金属来源判别中的应用另外,成岩作用等多种因素会干扰沉积物金属记录对环境变化的指示作用,所以构建多元素指标来综合判断沉积物记录所反映的环境信息是今后的研究所必须关注的  相似文献   

13.
The major and minor element composition of ferromanganese nodules from DOMES Site A has been determined by X-ray fluorescence methods. Three phases appear to control the bulk compositions: Mn and Fe oxyhydroxides and aluminosilicates. Relatively wide compositional variations are evident throughout the area. Nodules with high Mn/Fe ratios, high Cu, Mg, Mo, Ni and Zn concentrations and high todorokite/δ-MnO2 ratios have granular surface textures and are confined to an east-west trending depression with thin Quaternary sediment cover. Nodules with low Mn/Fe ratios, high concentrations of As, Ca, Ce, Co, La, P, Sr, Ti, V, Y and Zr and low todorokite/δ-MnO2 ratios have smooth surfaces and are confined to shallower areas with relatively thick Quaternary sediment to the north and south of the depression.All nodules in the area have compositions which are influenced by diagenesis, but those with the most marked diagenetic signature (high Mn/Fe and Cu/Ni ratios, low Ce/La ratios and more todorokite) are found in areas of very slow or non-existent sedimentation; many of these nodules are actually in contact with outcropping Tertiary sediment. This paradox may be resolved by postulating, by analogy with some shallow-water occurrences, that the nodules accrete from bottom waters which have enhanced particulate and dissolved metal contents derived from diagenetic reaction in areas remote from the site of nodule formation. The metals are supplied in a bottom flow (probably Antarctic Bottom Water) which also erodes, or prevents modern sedimentation in, the depression. Nodules on the flanks of the depression are not evidently affected by this flow and derive at least pan of their constituent metals from diagenetic reaction in the underlying Quaternary sediment.Apparently, abyssal diagenetic nodules can have an immediate and a remote diagenetic metal source. Metal fluxes derived from pore water dissolved metal gradients may not be relevant to particular accreting nodules if a significant fraction of their metals is derived from outside the area in which they form.  相似文献   

14.
Monthly sampling of slightly alkaline arsenic-rich stream in the Mokrsko gold deposit revealed seasonal variations in dissolved Zn, Cu, As and Mo. Concentrations of trace metal cations (Zn, Cu) increased as much as 330 and 178%, respectively, from minimum mean values at autumn to maximum mean values at spring. In contrast, concentrations of trace element oxyanions (As, Mo) revealed opposite seasonal pattern with increase to 189% (As) and 123% (Mo) during summer–autumn, indicating that in-stream biogeochemical process(es) played the main role in controlling the seasonal variations of these trace elements. The trace elements were mainly scavenged by low crystalline Mn oxyhydroxide and Fe oxyhydroxide (ferrihydrite). Results are consistent with sorption and coprecipitation processes controlling seasonal variations of dissolved Zn and Cu, while As and Mo dynamics appear linked to Mn redox reactions. The sorption processes and Mn redox processes are attributed to the changes of pH and oxic/anoxic conditions on the surface of oxyhydroxides, respectively, which are themselves controlled by the balance between photosynthesis and respiration. Under the geochemical conditions of the stream, inferred Mn redox reactions can only be explained by microbial activity.  相似文献   

15.
The early diagenetic environment of intertidal sandy sediments (sands) and muddy sediments (muds) is described and compared from two cores taken from an unpolluted part of the Manukau Harbour, New Zealand. Extraction techniques characterized the form of the trace elements (Fe, Mn, S, C, Pb, Zn, Cu) at different depths in the sediment. Dissolved forms of Fe, Mn, and S were measured in interstitial water. Nonresidual metal concentrations, humic acid, FeS, and FeS2 are an order of magnitude higher in the muds than in the sands because of dilution by unreactive sand particles. Muds contain a larger proportion of metals in the mobile fractions; exchangeable (Mn), carbonate (Mn, Fe, Zn), and easily-reducible oxide (Fe, Mn, Zn, Pb). This is due to greater surface area (for Mn adsorption); the favorable conditions for MnCO3, FeCO3, and FeS precipitation; and higher concentrations of easily reducible iron oxide and humic acid. Therefore, compared to the sands, muds are more important as reservoirs for toxic metals, both in terms of quantity and availability. At either site there was very little difference between the forms of Zn, Pb or Cu identified by sequential extraction as sediments changed from oxic to anoxic conditions. One reason for this is that the amounts and proportions of some of the important components that bind metals, viz., amorphous iron hydrous oxides, humic acids, and FeS2, do not change much. Other components that do change with redox conditions, for example, manganese phases and FeS, are only minor components of the sediment. Redox conditions, then, have relatively little effect on trace-metal partitioning in the sediment matrix of these unpolluted sediments.  相似文献   

16.
The Sr isotope stratigraphy of the biogenic apatite was used to determine the age of pelagic sediments in the Brazil Basin (Station 1541) that contain ferromanganese micronodules, nodules, and coatings on the weathered volcanic rocks. The age of sediments at horizons 0–5 and 86–90 cm was estimated at 24.1 ± 0.2 Ma and 24.8 ± 0.2 Ma, respectively. The average sedimentation rate in the Late Oligocene was about 13 mm/ka. The hydrogenous Fe–Mn nodule on the sediment surface with the Mn/Fe value of 1.05–1.95 was formed at a rate of 1.2–2.4 mm/Ma, which is 1000 times lower than the growth rate of buried nodule (Mn/Fe 0.4) at depth of 83 cm. Diagenesis provoked changes in the mineral composition of the buried nodule (asbolane-buserite partially replaced by goethite), leading to the loss of a part of Mn, Ni, Li, and Tl but accumulation of trace elements linked with iron oxyhydroxides (Ce, Th, Be, As, and V) were retained. The composition of manganese micronodules at two studied depths in sediments evolved in the course of two stages of ore formation: related to the oxic and suboxic diagenesis. The Sr isotopic composition in manganese micronodules from both horizons do not differ from that of dissolved Sr in the ocean water. The 143Nd/144Nd ratio, which reflects the Nd isotopic composition in the paleocean during the micronodule formation, varies in manganese micronodules from different horizons and is constant in different size fractions.  相似文献   

17.
The heavy metal contents of Mn, Ni, Cu, Zn, Cr, Co, Pb, Cd, Fe, and V in the surface sediments from five selected sites of El Temsah Lake was determined by graphite furnace atomic absorption spectrophotometer. Geochemical forms of elements were investigated using four-step sequential chemical extraction procedure in order to identify and evaluate the mobility and the availability of trace metals on lake sediments, in comparison with the total element content. The operationally defined host fractions were: (1) exchangeable/bound to carbonate, (2) bound to Fe/Mn oxide, (3) bound to organic matter/sulfides, and (4) acid-soluble residue. The speciation data reveals that metals Zn, Cd, Pb, Ni, Mn, Cu, Cr, Fe, and V are sink primarily in organic and Fe–Mn oxyhydroxides phases. Co is mainly concentrated in the active phase. This is alarming because the element is enriched in Al Sayadin Lagoon which is still the main site of open fishing in Ismailia. Average concentration of the elements is mostly above the geochemical background and pristine values of the present study. There is a difference on the elemental composition of the sediment collected at the western lagoon (Al Sayadin Lagoon), junction, the shoreline shipyard workshops, and eastern beach of the lake. Depending upon the nature of elements and local pollution source, high concentration of Zn, Pb, and Cu are emitted by industrial wastewater flow (shoreline workshops), while sanitary and agricultural wastewater (El Bahtini and El Mahsama Drains) emit Co and Cd in Al Sayadin Lagoon. On the other hand, there is a marked decrease in potentially toxic heavy metal concentrations in the sediments at the most eastern side of the lake, probably due to the successive sediment dredging and improvements in water purification systems for navigation objective. These result show that El Temsah receives concentrations in anthropogenic metals that risk provoking more or less important disruptions, which are harmful and irreversible on the fauna and flora of this lake and on the whole ecobiological equilibrium.  相似文献   

18.
We measured the vertical distributions of Mo, Fe, Mn, sulfide, sulfate, organic carbon, major ions, and pH in sediment porewater from one perennially oxic and three seasonally anoxic lacustrine basins in Eastern Canada, as well as those of Mo, acid volatile sulfide, Fe, Mn, Al, organic C, 210Pb and 137Cs in sediment cores from the same sites. The only input of anthropogenic Mo to these lakes comes from atmospheric deposition.The relatively monotonous distribution of Mo in the porewater of three seasonally anoxic basins suggests that Mo is not redistributed in the sedimentary column during periods of anoxia. In contrast, porewater Mo profiles obtained at three sampling dates in a perennially oxic basin display sharp Mo peaks below the sediment-water interface, indicating redistribution subsequent to deposition. Modeling of these latter porewater Mo profiles with a diagenetic reaction-transport equation coupled to comparisons among the various porewater and solid phase profiles reveal that Mo is released at 1-2 cm depth as a consequence of the reductive dissolution of Fe oxyhydroxides and scavenged both at the vicinity of the sediment-water interface, by re-adsorption onto authigenic Fe oxyhydroxides, and deeper in the sediments where dissolved sulfide concentrations are higher. The estimated rate constant for the adsorption of Mo onto Fe oxyhydroxides is 36 ± 45 cm3 mol−1 s−1.Diagenetic modeling indicates that authigenic Mo in sediments of the perennially oxic basin represents about one-third of the total solid phase Mo in the first cm below the sediment-water interface and only one tenth below this horizon. If we assume that no authigenic Mo is accumulated in the seasonally anoxic lake sediments we conclude that the sediment Mo concentrations, which are up to 3-16 times higher than the average lithogenic composition, depending on the lake, are mainly due to atmospheric deposition of anthropogenic Mo and not to the formation of authigenic Mo phases. Reconstructed historical records of the atmospheric Mo deposition indicate maximum values in the 1970s and 1980s and significant decreases since then. Emissions to the atmosphere associated with the smelting of non-ferrous ores and coal combustion appear to be the most important sources of anthropogenic Mo.  相似文献   

19.
We analyzed 77 surface sediment samples collected in the southwestern East/Japan Sea from the Korea Strait through the Ulleung Basin and the Korea Plateau for grain size, calcium carbonate, organic carbon, and major (Na, Mg, Al, Fe, K, Ca, and Ti) and trace elements (P, Mn, Sr, Li, Sc, V, Cr, Co, Ni, Zn, Cu, and Pb).The chemical composition of the surface sediments was found to be highly variable spatially. Cluster analysis of surface sediment chemical compositions indicated five major geochemical sedimentary environments: basin, lower slope, coast and upper slope, inner shelf, and outer shelf. Continental-shelf sediments were rich in shell fragments and had relict and coarse-grained characteristics. Recent fine-grained sediments were only distributed in coastal, slope, and basin areas. Concentrations of Al, K, Ca, Ti, Cr, and Sc were highest in the coastal and upper slope areas and decreased with water depth. Elemental ratios using major and trace elements indicated that coastal and upper slope detrital sediments were mixtures of sediments derived from the Changjiang (Yangtze) and Nakdong Rivers. Although the concentrations of organic carbon, P, Mn, V, Co, Ni, Cu, and Pb increased with water depth, their distribution patterns indicated authigenic (V, Cu, and Pb) and diagenetic (Fe, P, Mn, Co, and Ni) origins. The distribution pattern with water depth suggested that the chemical composition of surface sediment was determined by sedimentologic and geochemical processes, such as the supply of detrital and biogenic materials, and authigenic and post-depositional diagenetic processes in sediments.  相似文献   

20.
The redox stratification of bottom sediments in Kandalaksha Bay, White Sea, is characterized by elevated concentrations of Mn (3–5%) and Fe (7.5%) in the uppermost layer, which is two orders of magnitude and one and a half times, respectively, higher than the average concentrations of these elements in the Earth’s crust. The high concentrations of organic matter (Corg = 1–2%) in these sediments cannot maintain (because of its low reaction activity) the sulfate-reducing process (the concentration of sulfide Fe is no higher than 0.6%). The clearest manifestation of diagenesis is the extremely high Mn2+ concentration in the silt water (>500 μM), which causes its flux into the bottom water, oxidation in contact with oxygen, and the synthesis of MnO2 oxyhydroxide enriching the surface layer of the sediments. Such migrations are much less typical of Fe. Upon oxygen exhaustion in the uppermost layer of the sediments, the synthesized oxyhydroxides (MnO2 and FeOOH) serve as oxidizers of organic matter during anaerobic diagenesis. The calculated diffusion-driven Mn flux from the sediments (280 μmM/m2 day) and corresponding amount of forming Mn oxyhydrate as compared to opposite oxygen flux to sediments (1–10 mM/m2 day) indicates that >10% organic matter in the surface layer of the sediments can be oxidized with the participation of MnO2. The roles of other oxidizers of organic matter (FeOOH and SO42−) becomes discernible at deeper levels of the sediments. The detailed calculation of the balance of reducing processes testifies to the higher consumption of organic matter during the diagenesis of surface sediments than it follows from the direct determination of Corg. The most active diagenetic redox processes terminate at depths of 25–50 cm. Layers enriched in Mn at deeper levels are metastable relicts of its surface accumulation and are prone to gradual dissemination  相似文献   

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