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1.
The ion activity product of Fe and phosphate in interstitial waters from four sediment cores taken from Greifensee, Switzerland indicate the presence of vivianite [Fe3(PO4)2 · 8 H2O] in the solid phase. Analysis of the sediment using an electron microprobe and by electron microscopy revealed P-rich grains to be also enriched in Fe. The combined methods provide strong evidence that vivianite is forming authigenically in the sediments. Thermodynamic stability calculations demonstrate that the most stable Fe and phosphate minerals (pyrite, siderite and apatite) are not the ones controlling the pore water chemistry. The results emphasize the importance of rate processes of mineral formation in early diagenesis.Calculations based on the sediment phosphate concentration, and the degree of supersaturation of Fe and phosphate in the upper portion (0–15 cm) of the pore waters, indicate that the rate of vivianite mineral growth is controlled by a surface reaction rather than a diffusion mechanism. The response time of dissolved phosphate in the sediment pore waters with respect to mineral precipitation is on the order of 1–20 days. Less than 15% of the phosphate released by organic matter degradation at the sediment-water interface and below is retained in the sediments.  相似文献   

2.
Much of the sedimentary geochemistry of iodine has been surmised from analyses of solid phase distributions without direct documentation of reactions or reaction rates. It is shown here that the anoxic production rate of dissolved I in nearshore terrigenous sediments decreases rapidly below the sediment-water interface and is strongly temperature controlled. An apparent activation energy of ~19.3 Kcal/mole comparable to that found for other microbially mediated reactions, describes the temperature dependence of release. Production of dissolved iodide is zeroth order with respect to natural ranges of pore water concentrations and apparently first-order with respect to a reactive I component in the solid phase. First order reaction coefficients in sediments from Mud Bay, South Carolina and Long Island Sound, Connecticut, U.S.A., are strongly depth dependent, varying from ~6.9/yr in the top few centimeters to an average of ~0.011/yr over the upper 70 cm. About 90% of the dissolved I flux comes from the top 10 cm with estimated values of ~ 15 and 29 μmoles/m2/day at 22–23°C in Mud Bay and Long Island Sound, respectively. The I/C net release ratio of decomposing material changes rapidly below the sediment surface. When temperature corrections are made, I remineralization rates from nearshore sediments below the bioturbated zone appear to be similar to those observed in deep water sediments underlying oxygenated waters.  相似文献   

3.
The interstitial waters and the solid phase of a core collected in Lago Maggiore (Italy) were analysed principally for Fe and P. Thermodynamic equilibrium calculations from the data of the pore fluids show that the interstitial waters are oversaturated with respect to vivianite in the upper part of the core. “Vivianite” was detected by optical microscopy as brown-orange concretions at depth below 3 cm and as blue concretions below 5.5 cm. At the 7–8 cm level these concretions were sufficiently large to be separated from the sediment and SEM-EDAX analysis showed the blue and the brown-orange concretions to have similar compositions. X-ray diffraction identified the blue concretions as vivianite, which Mössbauer spectroscopy showed to be partially oxidized. The brown-orange concretions were identified as fully oxidized vivianite. Total P and total Fe profiles in the core together with sedimentation data help to explain the presence of these large concretions at a depth of 7–8 cm.  相似文献   

4.
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5.
The dissolved silica concentration in waters of Lake Superior probably is in a steady state because it is not influenced significantly by man, and the climate, topography and vegetation in the drainage area of the lake have been stable for the past 4000 years. Therefore the rate at which dissolved silica is introduced to the lake should equal the output rate.The primary inputs are: tributaries (4.1–4.6 × 108kgSiO2/yr), diffusion from sediment pore waters (0.21?0.78 × 108kgSiO2/yr) and atmospheric loading (0.26 × 108kgSiO2/yr). Silica is lost from the lake waters by: outflow through the St. Marys River, diatom deposition, adsorption onto particulates in the sediments, and authigenic formation of new silicate minerals. Tributary outflow accounts for less than one half the annual input of silica, and diatom deposition and silica adsorption withdraw less than 10% of the annual input. Therefore the formation of new silicate phases must be the dominant sink for dissolved silica in Lake Superior. The specific phases formed are not identified in the bottom sediments. X-ray diffraction studies suggest that smectite is one product, and amorphous ferroaluminum silicates may be another product.Mathematical modeling of the dissolved silica response to lake eutrophication suggests that the phosphate loading to Lake Superior would have to increase by about 250-fold to cause a silica depletion rate equal to that reported for Lake Michigan, assuming no change in the rate of upwelling of deep waters.  相似文献   

6.
This research tests the hypothesis that trace metals respond to the extent of reducing conditions in a predictable way. We describe pore water and sediment measurements of iron (Fe), manganese (Mn), vanadium (V), uranium (U), rhenium (Re), and molybdenum (Mo) along a transect off Washington State (USA). Sediments become less reducing away from the continent, and the stations have a range of oxygen penetration depths (depth to unmeasurable O2 concentration) varying from a few millimeters to five centimeters. When oxygen penetrates ∼1 cm or less, Fe is reduced in the pore waters but reoxidized near the sediment-water interface, preventing a flux of Fe2+ to overlying waters, whereas Mn oxides are reduced and Mn2+ diffuses to overlying waters. Both Re and U authigenically accumulate in sediments. Only at the most reducing location, where the oxygen penetrates 0.3 cm below the sediment-water interface, does the surface 30 cm of sediments become reducing enough to authigenically accumulate Mo.Stations in close proximity to the Juan de Fuca Ridge crest are enriched in Mn and Fe from hydrothermal plume processes. Both V and Mo clearly associate with Mn cycling, whereas U may be associating with either Mn oxides and/or Fe oxyhydroxides. Rhenium is uncomplicated by adsorption to Mn oxides and/or Fe oxyhydroxides, and Re accumulation in sediments appears to be due solely to the extent of reducing conditions. Therefore, authigenic sediment Re enrichment appears to be the best indicator for intermediate reducing conditions, where oxygen penetrates less than ∼1 cm below the sediment-water interface, when coupled with negligible authigenic Mo enrichment.  相似文献   

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

8.
A 3-m sediment core taken from Lake Suigetsu, in which a shift from fresh to brackish water occurred about three hundred years ago, has been examined for variation with depth of organic carbon and fatty acids. From the difference in total amounts of sulphur between sediments under fresh and brackish water environments, the surface sediments above approximately 35 cm depth were deduced to be accumulated under a brackish water environment. The total contents of organic carbon and fatty acids, and percentage composition of fatty acids gave discontinuous profiles above and below the 35–40 cm sediment layer. At a depth of 12.5 cm, the distribution in chain length of the fatty acids changed from a unimodal (the predominance of C12-C18 over C20-C34) to a bimodal pattern, which was mirrored by the composition diversity index (CDI).Although the fatty acids in the surface sediments (0–40 cm) from Lake Suigetsu seemed to suffer milder degradation through microbial activity than those in a core (0–150 cm) from Lake Suwa, a freshwater eutrophic lake, both lacustrine sediments showed similar trends in the alteration of fatty acid composition with depth.  相似文献   

9.
The effects of freshwater infaunal invertebrates on sediment geochemical properties were studied through an experimental approach using indoor microcosms during a 56-day experiment. The bioturbating organisms were tubificid worms, which consume sediment at depth and deposit undigested material at the sediment?Cwater interface. Bioturbation intensity was determined using fluorescent tracers, and the distribution of redox-sensitive compounds was studied from replicate experimental units handled 7, 14, 21, 28 and 56?days after tubificid colonization. Worm activity transferred reduced particles and pore water at the sediment surface at a rate of 0.14?cm?day?1. Compared to control experimental units, this recycled material represented at the end a several centimetre-thick layer enriched in water content, dissolved nitrate and sulphate, and depleted in oxygen, ammonium and dissolved Mn(II). Tubificids consumed O2 in bottom water, so that the sediment was anoxic, allowing a direct flux of dissolved reduced species into overlying water. Lower ammonium and Mn(II) concentrations and fluxes in anoxic sediment possibly resulted from a decrease in anaerobic microbial metabolism due to competition for labile organic carbon with tubificids. Higher sulphate concentration resulted from burial of surface waters with particle at the sediment surface, but not from bio-irrigation of burrows. Nitrate was produced in anoxic condition, as observed in almost every mixed modern sediments.  相似文献   

10.
 The study of water chemistry and sediment core samples from Udaisagar lake in Rajasthan has revealed high phosphate contents; 186 and 236 μg/l in surface and sub-surface waters and in core samples 0.157 wt % P2O5, low D.O. 4.61 and 3.50 mg/l on average in surface and depth waters and high E.C. 1316 and 1395 μs/cm and higher sedimentation rate 8.90 mm/year in this lake compared to other lakes in the vicinity. The enormous and wide-spread growth of algal bloom in lake water and Ahar river and occasional fish mortality are indications of eutrophic conditions prevailing in the lake. Such a situation is developing due to the discharge of pollutants from phosphorite mines, chemical factories, distillary, sewage and domestic waste from settlements, hotels throughout the length of River Ahar which during its journey receives and finally discharges pollution in this lake. This renders the water unhygenic for human consumption and deleterious to aquatic life. Received: 27 January 1998 · Accepted: 28 September 1998  相似文献   

11.
Lake Turkana, in northwestern Kenya, is a closed-basin, alkaline (pH = 9.2) lake of moderate salinity (TDS = 2500 ppm). Principal ions are Na+, HCO?3 and CI?. The lake is essentially polymictic in the northern basin and little compositional variation occurs in surface waters. The Omo River is the principal influent, providing some 80–90% of water input to the lake. Chloride has an apparent accumulation time of about 2500 years after accounting for burial of interstitial water.The bottom sediments are predominantly detrital and fine-grained, yet mineral-water reactions are very important for the geochcmical budget. Ca2+ is precipitated as calcite; Na+ is removed as an exchangeable cation on smectite; Mg2+ is probably incorporated into a Mg-silicate phase, most likely poorlycrystalline smectite, as it enters the lake water; K+ may be used in illite regradation. Cation exchange is a very important process in the mass balance of this lake. Over 40% of incoming Na is removed as an exchangeable cation. After cation exchange and interstitial water burial, Na has a response time of 2650 years, which compares favorably with that of chloride. These processes seem to occur rapidly within the water mass of the lake: other reactions may be important in regulating interstitial water compositions.Several changes occur in the upper 3m of sediment: interstitial-water pH drops to 8.3 and alkalinity increases slightly with depth, SO2?4 decreases slightly, and amorphous silica saturation is approached. These changes are a response to organic matter oxidation and the dissolution of unstable silicates rather than a reversal of reactions occurring in the lake water. High rates of sedimentation (up to 1 cm per year) may minimize the effects of diffusion between the interstitial waters and the lake water, although burial of interstitial water assumes considerable importance.  相似文献   

12.
Intense primary biologic productivity in the surface waters of the Benguela upwelling system provides a high supply of organic matter to the sea floor at the continental slope off Namibia and sustains extreme concentrations of magnetite producing bacteria in the top sediment layers. Biogenic magnetite is thus by far the dominant carrier of the magnetic signal in these deposits also because of a very minor input of terrigenous ferrimagnetic minerals. Reducing conditions in the sediment column cause a selective dissolution of the bacterial magnetite fraction just a few centimeters below the main mineralization horizon. This diagenetic process is documented in detail by high-resolution rock magnetic analyses and transmission electron microscopy. Concentration dependent and grain-size sensitive magnetic parameters, such as susceptibility, laboratory imparted remanences, and hysteresis data, reveal a significant drop in ferrimagnetic mineral content within the upper 10 cm of the sediments accompanied by a gradual downward coarsening of the ferrimagnetic mineral assemblage from primarily magnetic single-domain particles in the top centimeters to multi-domain grains in deeper strata. Electron microscope observations enable both an unequivocal identification of bacterial magnetite on the basis of shape and grain-size and to trace dissolution effects on the biogenic magnetic mineral component to depth. Received: 9 November 1998 / Accepted: 10 October 1999  相似文献   

13.
As a consequence of the 1969–1970 flooding of normally dry Owens Lake, a 2.4-m-deep lake formed and 20% of the 2-m-thick salt bed dissolved in it. Its desiccation began August 1969, and salts started crystallizing September 1970, ending August 1971. Mineralogic, brine-composition, and stable-isotope data plus field observations showed that while the evolving brine composition established the general crystallization timetable and range of primary and secondary mineral assemblages, it was the daily, monthly, and seasonal temperature changes that controlled the details of timing and mineralogy during this depositional process. Deuterium analyses of lake brine, interstitial brine, and hydrated saline phases helped confirm the sequence of mineral crystallizations and transformations, and they documented the sources and temperatures of waters involved in the reactions.Salts first crystallized as floating rafts on the lake surface. Natron and mirabilite, salts whose solubilities decrease greatly with lowering temperatures, crystallized late at night in winter, when surface-water temperatures reached their minima; trona, nahcolite, burkeite, and halite, salts with solubilities less sensitive to temperature, crystallized during the afternoon in summer, when surface salinities reached their maxima. However, different temperatures were generally associated with crystallization (at the surface) and accumulation (on the lake floor) because short-term temperature changes were transmitted to surface and bottom waters at different rates. Consequently, even when solubilities were exceeded at the surface, salts were preserved or not as a function of bottom-water temperatures. Halite, a nearly temperature-insensitive salt, was always preserved.Monitoring the lake-brine chemistry and mineralogy of the accumulating salts shows: (1) An estimated 0.9 × 106 tons of CO2 was released to the atmosphere or consumed by the lake's biomass prior to most salt crystallization. (2) After deposition, some salts reacted in situ to form other minerals in less than one month, and all salts (except halite) decomposed or recrystallized at least once in response to seasons. (3) Warming in early 1971 caused solution of all the mirabilite and some of the natron deposited a few months earlier, a deepening of the lake (though the lake-surface lowered), and an increase in dissolved solids. (4) Phase and solubility-index data suggest that at the close of desiccation, Na2CO3·7H2O, never reported as a mineral, could have been the next phase to crystallize.  相似文献   

14.
Apparent overall equilibrium constants for the adsorption of Cd, Cu, Ni, Pb and Zn onto natural iron oxyhydroxides have been calculated from the partitioning of these trace metals in oxic lake sediments and the in situ measurement of trace metal concentrations in the associated pore waters. Such values obtained from lakes of various pH located on the Precambrian Shield, in the area of Sudbury, Ontario, are compared with equilibrium constants obtained for the adsorption of the trace metals onto iron oxyhydroxides in well-defined media.The field data are consistent with laboratory experiments reported in the literature and with theory. Both the influence of pH upon adsorption and the binding strength sequence observed for the field data agree with theory. At high sediment pH values, the partitioning of Cd, Ni and Zn between the pore waters and the natural iron oxyhydroxides is similar to those reported in the literature for the adsorption of these metals at low surface coverage onto amorphous iron oxyhydroxides in a NaNO3 medium; deviation from this simple model is however observed for Cu and Pb, presumably due to the competitive action of dissolved ligands. At low sediment pH values, the adsorption is much higher than predicted by the simple model and can be explained by the formation of ternary complexes with the iron oxyhydroxide surface.  相似文献   

15.
The vertical distribution of dissolved Al in interstitial waters of recent marine sediments has been determined using a fluorimetric analytical method adapted for interstitial water analysis. The results suggest that diagenetic reactions occur in the sediment soon after deposition. A narrow depth zone acting as a source of dissolved Al is found in each core. Outside this zone Al appears to be removed from solution and its concentration decreases to values of 1.5 μgAl/l or less, comparable to those of open ocean waters. Dissolved Al and SiO2 concentrations in interstitial waters close to the sediment-seawater interface are linearly correlated in most cases, suggesting that the geochemistry of Al may be related to the behaviour of biogenic silica in marine sediments.  相似文献   

16.
 The concentrations of N, P and Fe in surface sediments and interstitial and overlying (bottom and surface) waters of the Ashtamudi estuary located in the southwest coast of India are reported along with the various chemical species of N (NO2–N, NO3–N, NH3–N and total N) and P (organic P, inorganic P and total P) in interstitial and overlying waters and discussed in terms of the physico-chemical environment of the system. The interstitial water exhibits higher salinity values compared to bottom and surface waters, indicating the coupled effects of salt-wedge phenomena and gravitational convection of more saline-denser marine water downward through surface sediments. N, P and Fe as well as their chemical forms are enriched in the interstitial water compared to bottom and surface waters. However, the dissolved oxygen (DO) shows an opposite trend. The marked enrichment of NH3–N in the interstitial water and its marginal presence in bottom and surface waters, together with the substantial decrease in the DO concentrations of bottom water and consequent increase in the concentrations of NO2–N and NO3–N in interstitial and bottom waters, points to the nitrification process operating in the sediment-water interface of the Ashtamudi estuary. The enrichment of total N, P and Fe in the interstitial water compared to the overlying counterparts and the positive correlation of sediment N, P and Fe with mud contents as well as organic carbon indicate that these elements are liberated during the early diagenetic decomposition of organic matter trapped in estuarine muds. Received: 5 Oktober 1998 · Accepted: 9 February 1999  相似文献   

17.
The brackish Bafa Lake located in the southwestern part of Turkey is under stress because of both natural and untreated wastewater effluents. The purpose of this research is to determine spatiotemporal distributions of some physicochemical variables in water column (temperature, salinity, pH, conductivity, dissolved oxygen, NH4–N, NO2–N, NO3–N, oPO4–P, TPO4–P, chlorophyll-a, total suspended solids) and sediment (TN, TC, TOC, TP) and their relationships at coastal stations. In the water column, nitrate and phosphate concentrations showed seasonal variations with high values recorded in winter period. Ammonium was determined as a main source of TIN component. During summer period, a large amount of total phosphorus was found as dissolved organic form. However, in the winter period, inorganic phosphate levels increased at sampling stations. N limitation was a common feature throughout the lake where P-limitation was only observed in summer period. The total phosphorus levels which showed hypereutrophic condition at the western part of the lake changed between 1.55 and 4.99 μM and did not remain in the range for uncontaminated condition. In the lake sediment, a strong relationship was found between TOC and TC levels. Generally, the mean TOC concentrations constitute small amount of TC values in the sampling stations. The results also indicated that a strong correlation exists between TOC and TN values, and TN was greatly regulated by organic sources. In the lake, TOC:TN ratios changed between 5 and 13; the ratio greater than 10 could be an indicator of algal and land plant sources mixing as an organic matter.  相似文献   

18.
A new sediment profile imaging (SPI) instrument, CHEM-SPI, was developed for in situ two-dimensional measurements of biogeochemical solutes using fluorosensor foils in sediments and overlying waters. The CHEM-SPI system was used to simultaneously measure vertical sections of pH, O2, and pCO2 distributions in subtidal, surface deposits of Long Island Sound, NY. Images are readily obtained in 5?C15 min with inexpensive LED excitation and commercial grade digital cameras having typical pixel resolution of ~50?C100 ??m over areas >150 cm2 sediment. Seasonal examples of in situ deployments of the instrument revealed extensive horizontal and vertical heterogeneity of pH distributions. pH dynamics were associated with complex biogenic structures in the upper few centimeters of marine sediment and the pulsed input of organic matter during the spring bloom period. The pH beneath the sediment?Cwater interface was dramatically depressed by the bloom input of organic matter but macrofaunal activity otherwise dominated pH variations in the bioturbated zone. The CHEM-SPI system allows direct quantitative confirmation of biogeochemical patterns previously inferred qualitatively from color patterns in visible SPI images. The instrument is sufficiently adaptable in design to accommodate new optical sensor foils for other chemical variables.  相似文献   

19.
《Applied Geochemistry》2003,18(1):25-36
The controls on the internal neutralization of low productivity, highly acidified waters by sulfide accumulation in sediments are yet poorly understood. It is demonstrated that the neutralization process is constrained by organic matter quality and thermodynamic effects which control the relative rates of SO4 and Fe reduction, and the fate of the reduced Fe and S in the sediments. The investigated sediments were rich in dissolved Fe(II) (0.005–12 mmol l−1) and SO4 (1.3–22 mmol l−1). The pH ranged from 3.0 to 6.8. Contents of reduced inorganic S (0.1–9.5%), molar C/N ratios of the organic matter (12–80) and metabolic turnover rates (1–110 μeq cm−3 a−1) varied strongly. Substantial amounts of Fe sulfides were only found at a simultaneous partial thermodynamic and solubility equilibrium of the involved biogeochemical processes. Sulfide oxidation was apparently inhibited, and SO4 and Fe reduction coexisted. In this type of sediment increases in C availability cause enhanced neutralization rates. In the absence of a partial equilibrium, the sediments were in a sulfide oxidizing and Fe reducing state, and did not accumulate Fe sulfides. The latter type of sediment will increase neutralization rates in response to decreasing deposition of reactive Fe oxides but not necessarily in response to increases in lake productivity by e.g. fertilization measures.  相似文献   

20.
Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition (δ13C) values of the carbonate sediment (?1‰ to ?2‰) have no relation to the oxygen isotope composition of the carbonate (δ18O) values (?7‰ to ?8‰), with both isotopes showing a low variability. The carbonate content is low (<20%). Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with δ13C values between approximately +0.5‰ and +3‰, and δ18O values between ?1‰ and ?5‰. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg–calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg–calcite. Evaporation and biological processes are the main reasons for the salinity and carbonate mineralogy influence of the surface-sediment carbonate in Bosten Lake. The lake water residence time and the CO2 exchange between the atmosphere and the water body control the carbon and oxygen isotope composition of the carbonate sediment. In addition, organic matter pollution and decomposition result in the abnormally low carbon isotope values of the lake surface-sediment carbonate.  相似文献   

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