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1.
The relationship among H 2S, total organic carbon (TOC), total sulfur (TS) and total nitrogen contents of surface sediments (0–1 cm) was examined to quantify the relationship between H 2S 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 SO 4 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 H 2S production. In portions of the lake where sediment TOC content is less than 3.5 %, H 2S was very low or absent in both bottom and pore waters. However, in areas with TOC >3.5 %, H 2S was correlated with TOC content (pore water H 2S (ppm) = 13.9 × TOC (%) ? 52.1, correlation coefficient: 0.72). H 2S 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, H 2S 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–H 2S relationship at sediment–water interface might be used to infer H 2S production in brackish–lagoonal systems similar to Lake Nakaumi, with readily available SO 4 2? and reactive organic matter. 相似文献
2.
Minerals constitute a primary ecosystem control on organic C decomposition in soils, and therefore on greenhouse gas fluxes to the atmosphere. Secondary minerals, in particular, Fe and Al (oxyhydr)oxides—collectively referred to as “oxides” hereafter—are prominent protectors of organic C against microbial decomposition through sorption and complexation reactions. However, the impacts of Mn oxides on organic C retention and lability in soils are poorly understood. Here we show that hydrous Mn oxide (HMO), a poorly crystalline δ-MnO 2, has a greater maximum sorption capacity for dissolved organic matter (DOM) derived from a deciduous forest composite O i, O e, and O a horizon leachate (“O horizon leachate” hereafter) than does goethite under acidic (pH 5) conditions. Nonetheless, goethite has a stronger sorption capacity for DOM at low initial C:(Mn or Fe) molar ratios compared to HMO, probably due to ligand exchange with carboxylate groups as revealed by attenuated total reflectance-Fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy and scanning transmission X-ray microscopy–near-edge X-ray absorption fine structure spectroscopy coupled with Mn mass balance calculations reveal that DOM sorption onto HMO induces partial Mn reductive dissolution and Mn reduction of the residual HMO. X-ray photoelectron spectroscopy further shows increasing Mn(II) concentrations are correlated with increasing oxidized C (C=O) content (r = 0.78, P < 0.0006) on the DOM–HMO complexes. We posit that DOM is the more probable reductant of HMO, as Mn(II)-induced HMO dissolution does not alter the Mn speciation of the residual HMO at pH 5. At a lower C loading (2 × 10 2 μg C m ?2), DOM desorption—assessed by 0.1 M NaH 2PO 4 extraction—is lower for HMO than for goethite, whereas the extent of desorption is the same at a higher C loading (4 × 10 2 μg C m ?2). No significant differences are observed in the impacts of HMO and goethite on the biodegradability of the DOM remaining in solution after DOM sorption reaches steady state. Overall, HMO shows a relatively strong capacity to sorb DOM and resist phosphate-induced desorption, but DOM–HMO complexes may be more vulnerable to reductive dissolution than DOM–goethite complexes. 相似文献
3.
Dissolved organic matter (DOM) has been shown to be an integral component in biogeochemical electron transfer reactions due to its demonstrated ability to facilitate redox reactions. While the role of DOM as a facilitator of electron transfer processes has been demonstrated, greater knowledge would lead to better understanding of the structural components responsible for redox behavior, such as quinones and nitrogen and sulfur (N/S) functional groups. This investigation uses direct scan voltammetry (DSV) coupled with fluorescence and NMR spectroscopy as well as thermochemolysis gas chromatography mass spectrometry (GC-MS) and X-ray photoelectron spectroscopy (XPS) to elucidate the organic moieties responsible for facilitating electron transfer reactions. We contrast electrochemical properties and structural details of three organic matter isolates from diverse sources; Great Dismal Swamp DOM (terrestrially derived, highly aromatic), Pony Lake DOM (microbially derived, highly aliphatic) and Toolik Lake (terrestrially derived, photochemically and microbially altered) with juglone (a redox-active model quinone). Aromatic and phenolic constituents were detected (by 13C NMR) and recovered (by thermochemolysis GC-MS) from all three fulvic acid samples, highlighting the ubiquity of these compounds and suggesting that the quinone-phenol redox couple is not limited to DOM derived from lignin precursors. The range of hydroxy-benzene and benzoic acid derivatives may explain the lack of a single pair of well-defined oxidation and reduction peaks in the DSV scans. The presence of a wide-range of hydroxylated benzoic acid isomers and other redox-active aromatic residues implies that native DOM possesses overlapping redox potentials analogous to their characteristic range of p Ka values. 相似文献
4.
The primary factors that control the concentration of total reduced (inorganic) sulfide in coastal sediments are believed
to be the availability of reactive iron, dissolved sulfate and metabolizable organic carbon. We selected nine sites in shallow
(<3 m), close to sub-tropical, estuaries and bays along the central Texas coast that represented a range in sediment grain
size (a proxy for reactive iron), salinity (a proxy for dissolved sulfate), and total organic carbon (a proxy for metabolizable
organic carbon). Based on these parameters a prediction was made of which factor was likely to control total reduced sulfide
at each site and what the relative total reduced sulfide concentration was likely to be. To test the prediction, the sediments
were analyzed for total reduced sulfide, acid volatile sulfide, and citrate dithionate-extractable, HCl-extractable and total
Fe in the solid phase. Using solid-state gold–mercury amalgam microelectrodes and voltammetry, we determined pore water depth
profiles of Fe(II) and ΣH 2S and presence or absence of FeS (aq). At five of the nine sites the calculated degree of sufildization of citrate dithionite-reactive-iron was close to or greater
than 1 indicating that rapidly reactive iron was probably the limiting factor for iron sulfide mineral formation. At one site
(salinity = 0.9) dissolved Fe(II) was high, ΣH 2S was undetectable and the total reduced sulfide concentration was low indicating sulfate limitation. At the last three sites
a low degree of sulfidization and modest total reduced (inorganic) sulfide concentrations appeared to be the result of a limited
supply of metabolizable organic carbon. Fe(II)–S(-II) clusters (FeS (aq)) were undetectable in 10 out of 12 bay sediment profiles where ΣH 2S was close to or below detection limits, but was observed in all other porewater profiles. Acid volatile sulfide, but not
total reduced sulfide, was well correlated with total organic carbon and ranged from being undetectable in some cores to representing
a major portion of total reduced sulfide in other cores. Although predicted controls on total reduced sulfide were good for
very low salinity water or sandy sediments, they were only right about half the time for the other sediments. The likely reasons
for the wrong predictions are the poor correlation of total organic carbon with grain size and differing fractions of metabolizable
organic carbon in different sedimentary environments. Differences in sediment accumulation rates may also play a role, but
these are difficult to determine in this region where hurricanes often resuspend and move sediments. This study demonstrates
the need to examine more complex and often difficult to determine parameters in anoxic “normal marine” sediments if we are
to understand what controls the concentration and distribution of sulfides. 相似文献
5.
The effect of organic matter on the sorption of dissolved organic matter (DOM) on lake sediments is critical to understanding
the fate and transport of contaminants at the sediment–water interface in lake ecosystems. Results indicate that DOM sorption
on sediment is largely due to ligand exchange between the DOM and hydroxyl groups, and the amount of DOC sorbed is a linear
function of added DOC. With increasing organic matter content the sediment has lower binding strength, higher releasing ability
for DOM, and the higher amount of DOM sorbed by sediment naturally. There was no clear difference before and after the sediment
was treated with H 2O 2, but the constant b implied that after the sediments were treated DOC release was promoted. Organic matter in the sediment tends to impede the
sorption of DOC and results in a remarkable decrease in DOC sorption rates. 相似文献
7.
Pristine water bodies in the Negro River basin, Brazilian Amazon, show relatively high concentrations of mercury. These waters are characterized by acidic pH, low concentrations of suspended solids, and high amounts of dissolved organic matter and are exposed to intense solar radiation throughout the year. This unique environment creates a very dynamic redox chemistry affecting the mobility of mercury due to the formation of the dissolved elemental species (Hg 0). It has been shown that in this so-called black water, labile organic matter from flooded forest is the major scavenger of photogenerated H 2O 2. In the absence of hydrogen peroxide, these black waters lose their ability to oxidize Hg 0 to Hg 2+, thus increasing Hg 0 evasion across the water/atmosphere interface, with average night time values of 3.80 pmol m ?2 h ?1. When the dry period starts, labile organic matter inputs gradually diminish, allowing the increasing concentration of H 2O 2 to re-establish oxidative water conditions, inhibiting the metal flux across the water/atmosphere interface and contributing to mercury accumulation in the water column. 相似文献
8.
Mid-shelf sediments off the Oregon coast are characterized as fine sands that trap and remineralize phytodetritus leading to the consumption of significant quantities of dissolved oxygen. Sediment oxygen consumption (SOC) can be delayed from seasonal organic matter inputs because of a transient buildup of reduced constituents during periods of quiescent physical processes. Between 2009 and 2013, benthic oxygen exchange rates were measured using the noninvasive eddy covariance (EC) method five separate times at a single 80-m station. Ancillary measurements included in situ microprofiles of oxygen at the sediment–water interface, and concentration profiles of pore water nutrients and trace metals, and solid-phase organic C and sulfide minerals from cores. Sediment cores were also incubated to derive anaerobic respiration rates. The EC measurements were made during spring, summer, and fall conditions, and they produced average benthic oxygen flux estimates that varied between ?2 and ?15 mmol m ?2 d ?1. The EC oxygen fluxes were most highly correlated with bottom-sensed, significant wave heights ( H s). The relationship with H s was used with an annual record of deepwater swell heights to predict an integrated oxygen consumption rate for the mid-shelf of 1.5 mol m ?2 for the upwelling season (May–September) and 6.8 mol m ?2 y ?1. The annual prediction requires that SOC rates are enhanced in the winter because of sand filtering and pore water advection under large waves, and it counters budgets that assume a dominance of organic matter export from the shelf. Refined budgets will require winter flux measurements and observations from cross-shelf transects over multiple years. 相似文献
9.
Manganese oxides, typically similar to δ-MnO 2, form in the aquatic environment at near neutral pH via bacterially promoted oxidation of Mn(II) species by O 2, as the reaction of [Mn(H 2O) 6] 2+ with O 2 alone is not thermodynamically favorable below pH of ~?9. As manganese oxide species are reduced by the triphenylmethane compound leucoberbelein blue (LBB) to form the colored oxidized form of LBB ( λmax?=?623 nm), their concentration in the aquatic environment can be determined in aqueous environmental samples (e.g., across the oxic–anoxic interface of the Chesapeake Bay, the hemipelagic St. Lawrence Estuary and the Broadkill River estuary surrounded by salt marsh wetlands), and their reaction progress can be followed in kinetic studies. The LBB reaction with oxidized Mn solids can occur via a hydrogen atom transfer (HAT) reaction, which is a one-electron transfer process, but is unfavorable with oxidized Fe solids. HAT thermodynamics are also favorable for nitrite with LBB and MnO 2 with ammonia (NH 3). Reactions are unfavorable for NH 4+ and sulfide with oxidized Fe and Mn solids, and NH 3 with oxidized Fe solids. In laboratory studies and aquatic environments, the reduction of manganese oxides leads to the formation of Mn(III)-ligand complexes [Mn(III)L] at significant concentrations even when two-electron reductants react with MnO 2. Key reductants are hydrogen sulfide, Fe(II) and organic ligands, including the siderophore desferioxamine-B. We present laboratory data on the reaction of colloidal MnO 2 solutions ( λmax?~?370 nm) with these reductants. In marine waters, colloidal forms of Mn oxides (<?0.2 µm) have not been detected as Mn oxides are quantitatively trapped on 0.2-µm filters. Thus, the reactivity of Mn oxides with reductants depends on surface reactions and possible surface defects. In the case of MnO 2, Mn(IV) is an inert cation in octahedral coordination; thus, an inner-sphere process is likely for electrons to go into the empty e g * conduction band of its orbitals. Using frontier molecular orbital theory and band theory, we discuss aspects of these surface reactions and possible surface defects that may promote MnO 2 reduction using laboratory and field data for the reaction of MnO 2 with hydrogen sulfide and other reductants. 相似文献
10.
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 (C org = 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 Mn 2+ concentration in the silt water (>500 μM), which causes its flux into the bottom water, oxidation in contact with oxygen,
and the synthesis of MnO 2 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 (MnO 2 and FeOOH) serve as oxidizers of organic matter during anaerobic diagenesis. The calculated diffusion-driven Mn flux from
the sediments (280 μmM/m 2 day) and corresponding amount of forming Mn oxyhydrate as compared to opposite oxygen flux to sediments (1–10 mM/m 2 day) indicates that >10% organic matter in the surface layer of the sediments can be oxidized with the participation of MnO 2. The roles of other oxidizers of organic matter (FeOOH and SO 42−) 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 C org. 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
11.
This study aims to compare the impact of oyster cultures on diagenetic processes and the phosphorus cycle in the sediments of the Aber Benoît and the Rivière d’Auray, estuary of Brittany, France. Our results showed clear evidence of the seasonal impact of oyster cultures on sediment characteristics (grain size and organic matter parameters) and the phosphorus cycle, especially in the Aber Benoît. At this site, seasonal variations in sulfide and Fe concentrations in pore waters, as well as Fe–P concentrations in the solid phase, highlighted a shift from a system governed by iron reduction (Reference) to a system governed by sulfate reduction (beneath oyster). This could be partly explained by the increase in labile organic matter (i.e., biodeposits) beneath oysters, whose mineralization by sulfate led to high sulfide concentrations in pore waters (up to 4,475 µmol l ?1). In turn, sulfide caused an enhanced release of phosphate in the summer, as adsorption sites for phosphate decreased through the formation of iron–sulfide compounds (FeS and FeS 2). In the Aber Benoît, dissolved Fe/PO 4 ratios could be used as an indicator of phosphate release into oxic water. Low Fe/PO 4 ratios in the summer indicated higher effluxes of phosphate toward the water column (up to 47 µmol m ?2 h ?1). At other periods, Fe/PO 4 ratios higher than 2 mol/mol indicated very low phosphate fluxes. In contrast, in the Rivière d’Auray, the occurrence of macroalgae, stranding regularly all over the site, clearly masked the impact of oyster cultures on sediment properties and the phosphorus cycle and made the use of Fe/PO 4 ratios more difficult in terms of indicators of phosphate release. 相似文献
12.
The paper comprises new analytical data on the nature and occurrence of gold in solid pyrobitumen, closely associated with the main gold-bearing sulfide arsenic ores of the Bakyrchik gold deposit (Kazakhstan), related to post-collisional magmatic-hydrothermal origin. Gold mineralization of the deposit occurs mainly in the form of an “invisible” type of gold in the structures of arsenian pyrite and arsenopyrite, and the form of gold-organic compounds of pyrobitumen in carbonaceous-terrigenous sequences of Carboniferous formation. Microscopic and electron microscopic analysis, Raman and FT-Infrared analysis, mineralogical and three-step sequential extraction analysis (NH2OH·HCl, H2O2, HNO3 + HCl) has been carried out using 9 ore samples (from 3 different types of ores) for a comprehensive study of pyrobitumen and sulfide arsenic ores focusing mainly on organic matter. The sequentially extracted precious metal content of pyrobitumen reaches up to 7 ppm gold and other metals like Ag 4 ppm, Pt 31 ppb, and Pd 26 ppb, forming metal–organic compounds, while arsenic sulfide minerals incorporate 11 ppm gold, 39 ppm Ag, 0.49 ppm Pt. The enrichment of gold associating with organic matter and sulfide ore minerals was confirmed in this study. Organic matter was active in the migration of gold and the capture of gold by pyrobitumen. Moreover, the reductive organic matter agent released gold, most likely for the sulfide arsenic ore minerals. Pyrobitumen was a decisive factor in the concentration, transportation, and preservation of gold in the deposit. 相似文献
13.
In the late December of 2006 while Zagros tunnel project in western Iran was advancing according to the schedule, a sudden rush of groundwater accompanied by a nauseating odor similar to that of rotten egg intruded the tunnel. Some workers complained from eye and respiratory tract irritation. The presence of hydrogen sulfide (H 2S) gas as high as 200 ppm was soon tested positive by gas detectors and subsequently the ventilation fans (2*110 kW) speed were boosted to 1,450 rpm in order to dilute the gas concentration to safe levels (10 ppm). Nonetheless, the work continued at a rather moderate pace for another 11 days and 134 more meters excavated in the gas infested grounds before 4 men died during a damage assessment survey of the TBM after a power failure that had forced the tunnel ventilation system to temporarily shut down. This paper is to discuss hazards and geological sources of H 2S gas in of Zagros Water Conveyance Tunnel and to recommend practical solutions to prevent or mitigate the gas destructive effects on human and machinery, as well. 相似文献
14.
Redox properties of humic substances (HS) control important biogeochemical processes. Thus, accurate estimation of redox properties of HS is essential. However, there is no general consensus regarding the best available measurement method of HS redox properties. In this study, we compared several common HS redox property measurement methods using anthraquinone-2,6-disulfonate (AQDS) as model compound, and standard Elliot soil humic acid (1S102H, ESHA), reference Pahokee peat (1R103H, PPHA), and Suwannee River natural organic matter (1R101N, SRNOM) as representative HS. We found that the H 2/Pd reduction method followed by incubation with ferric citrate (FeCit) reagent was incomplete, and the H 2/Pd reduction method followed by incubation with potassium ferricyanide (K 3Fe(CN) 6) was insensitive. Stannous chloride (SnCl 2) reduction followed by titration of excess stannous (Sn 2+) by potassium dichromate (K 2Cr 2O 7) was found to be most accurate. These findings will help in future investigations on detailed characterizations of functional groups of HS responsible for oxidation/reduction reactions. 相似文献
15.
In the aquatic geochemical literature, a redox half-reaction is normally written for a multi-electron process ( n > 2); e.g., sulfide oxidation to sulfate. When coupling two multi-electron half-reactions, thermodynamic calculations indicate possible reactivity, and the coupled half-reactions are considered favorable even when there is a known barrier to reactivity. Thermodynamic calculations should be done for one or two-electron transfer steps and then compared with known reactivity to determine the rate controlling step in a reaction pathway. Here, thermodynamic calculations are presented for selected reactions for compounds of C, O, N, S, Fe, Mn and Cu. Calculations predict reactivity barriers and agree with one previous analysis showing the first step in reducing O 2 to O 2 ? with Fe 2+ and Mn 2+ is rate limiting. Similar problems occur for the first electron transfer step in these metals reducing NO 3 ?, but if reactive oxygen species form or if two-electron transfer steps with O atom transfer occur, reactivity becomes favorable. H 2S and NH 4 + oxidation in a one-electron transfer step by O 2 is also not favorable unless activation of oxygen can occur. H 2S oxidation by Cu 2+, Fe(III) and Mn(III, IV) phases in two-electron transfer steps is favorable but not in one-electron steps indicating that (nano)particles with bands of orbitals are needed to accept two electrons from H 2S. NH 4 + oxidation by Fe(III) and Mn(III, IV) phases is generally not favorable for both one- and two-electron transfer steps, but their reaction with hydroxylamine and hydrazine to form N 2O and N 2, respectively, is favorable. The anammox reaction using hydroxylamine via nitrite reduction is the most favorable for NH 4 + oxidation. Other chemical processes including photosynthesis and chemosynthesis are considered for these element–element transformations. 相似文献
16.
Dissolved organic matter (DOM) in sediment pore water is a complex molecular mixture reflecting various sources and biogeochemical processes. In order to constrain those sources and processes, molecular variations of pore water DOM in surface sediments from the NW Iberian shelf were analyzed by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and compared to river and marine water column DOM. Weighted average molecular element ratios of oxygen to carbon ((O/C) wa) and hydrogen to carbon ((H/C) wa) provided general information about DOM sources. DOM in local rivers was more oxygenated ((O/C) wa 0.52) and contained less hydrogen ((H/C) wa 1.15) than marine pore water DOM (mean (O/C) wa 0.50, mean (H/C) wa 1.26). The relative abundance of specific compound groups, such as highly oxygenated aromatic compounds or nitrogen-bearing compounds with low H/C ratios, correspond to a high concentration of lignin phenols (160 μg/g sediment dry weight) and a high TOC/TN ratio (13.3) in the sedimentary organic matter and were therefore assigned to terrestrial sources. The lower degree of unsaturation and a higher relative abundance of nitrogen-bearing compounds in the pore water DOM reflected microbial activity within the sediment. One sampling site on the shelf with a high sediment accumulation, and a humic-rich river sample showed a wide range of sulfur compounds in the DOM, accompanied by a higher abundance of lipid biomarkers for sulfate-reducing bacteria, probably indicating early diagenetic sulfurization of organic matter. 相似文献
17.
The biogeochemistry of Zn, Cd, Cu, Hg, and Fe in lakes and streams polluted by mine and smelter wastes emitted at Flin Flon,
Canada, was investigated. In Schist Lake, a repository for both tailings-pond drainage and sewage, green algal blooms generated
by nutrients from sewage promote entrapment of metals in sediments by (1) accumulation of metals from solution by algal seston,
with preferential uptake of Zn, the most abundant metal, followed by sinking of the seston; and (2) production of H 2S during decomposition of dead algae, resulting in sulfide precipitation. Metals are partially resolubilized from seston as
it decomposes while sinking. Preferential retention of Cu by sinking seston and by mud promotes Cu enrichment in the mud but
the Cu/Zn ratio of mud varies with the Cu/Zn ratio of surface water seston. In bottom muds, partitioning of a metal between
sulfide and organic matter is strongly dependent on the stability of the metal sulfide as measured by its standard entropy,
the proportion of sulfide-bound metal decreasing in the order Hg>Cd>Cu>Fe>Zn. When sulfide-rich muds were heated under helium,
x-ray diffraction revealed abundant well-crystallized ZnS (sphalerite) containing Cd, Hg, and Fe; only poorly crystallized
traces of the mineral were detected in unheated mud, however. Cu sulfide failed to crystallize, suggesting interference by
sorbed impurities. Metals were concentrated in H 2S-rich muds and extraction of muds with various solvents and by electrodialysis showed that sulfide was much more effective
than organic matter in suppressing remobilization of metals. Remobilized Cu is probably bound to organic complexing agents.
Some extractable complexing agents bind Cu preferentially with respect to Zn and Cd but others preferentially bind Zn and
Cd; the complexes, being stable in the presence of free sulfide, may cause some release of metals from sulfide-rich muds in
nature.
These results indicate that introduction of sewage together with heavy-metal effluents into settling ponds could be an effective
and economic method for limiting heavy-metal pollution of natural waters. 相似文献
18.
Dissolved organic matter (DOM) in leachate from landfills of three different ages (0, 5, and 10?year) was partitioned into hydrophobic acid, hydrophobic neutral, and hydrophilic matter fractions using the fractionation method employing XAD-8 resin. The spectroscopic characteristics of these fractions were determined through constant-wavelength synchronous fluorescence spectrometry (CWSFS). The interaction characteristic of phenanthrene with these fractions was determined through the fluorescence quenching method and CWSFS. The results revealed that the composition of DOM became complex with the increase in landfill age. The partition coefficients ( K doc) for the three DOM samples of different landfill ages are in the order 10?a DOM?>?5?a DOM?>?0?a DOM. The hydrophobic fraction showed the highest K doc value among the DOM fractions. Lower linearity Stern?CVolmer plots were observed in 10?a DOM and its hydrophobic fractions. CWSFS spectra showed that a special site was fully occupied with the addition of the quencher. Desorption was found in some fractions. Therefore, CWSFS is a sensitive tool for the detection of DOM-polycyclic aromatic hydrocarbon interaction. 相似文献
19.
A four month study of a man-made lake used for hydroelectric power generation in northeastern Pennsylvania USA was conducted
to investigate seasonal anoxia and the effects of sulfide species being transported downstream of the power generation equipment.
Water column analyses show that the system is iron-rich compared to sulfide. Total Fe(II) concentrations in the hypolimnion
are typically at least twice the total sulfide levels. In situ voltammetric analyses show that free Fe(II) as [Fe(H 2O) 6] 2+ or free H 2S as H 2S/HS - are either not present or at trace levels and that iron-rich sulfide complexes are present. From the in situ data and total Fe(II) and H 2S measurements, we infer that these iron-rich sulfide complexes may have stoichiometries such as Fe 2SH 3+ (or polymeric forms of this and other stoichiometries). These iron-rich sulfide complexes appear related to dissolution of
the iron-rich FeS mineral, mackinawite, because IAP calculations on data from discrete bottle samples obtained from bottom
waters are similar to the pK sp of mackinawite. Soluble iron-sulfide species are stable in the absence of O 2 (both in lake waters and the pipeline) and transported several miles during power generation. However, iron-sulfide complexes
can react with O 2 to oxidize sulfide and can also dissociate releasing volatile H 2S when the waters containing them are exposed to the atmosphere downstream of the powerplant. Sediment analyses show that
the lake is rich in oxidized iron solids (both crystalline and amorphous). Fe concentrations in FeS solids are low (<5 μmole/gr dry wt) and the pyrite concentration ranges from about equal to the solid FeS to 30 times the solid FeS concentration. The degree
of pyritization is below 0.12 indicating that pyrite formation is limited by free sulfide, which can react with the iron-rich
sulfide complexes. 相似文献
20.
This study examined the dissolved organic matter (DOM) components of cow dung using a combination of fluorescence (excitation–emission matrix, EEM) spectroscopy and parallel factor (PARAFAC) modelling along with eleven trace metals using ICP-MS and nutrients (NH 4+ and NO 3?) using an AA3 auto analyser. EEM–PARAFAC analysis demonstrated that cow dung predominantly contained only one fluorescent DOM component with two fluorescence peaks (Ex/Em = 275/311 nm and Ex/Em = 220/311 nm), which could be denoted as tyrosine by comparison with its standard. Occurrence of tyrosine can be further confirmed by the FTIR spectra. Trace metals analysis revealed that Na, K and Mg were significantly higher than Ca, Fe, Mn, Zn Sr, Cu, Ni and Co. The NH 4+ concentrations were substantially higher than NO 3?. These results thus indicate that the dissolved components of the cow dung could be useful for better understanding its future uses in various important purposes. 相似文献
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