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1.
Concentrations of various sulfur compounds (SO 42−, H 2S, S 0, acid-volatile sulfide, and total sulfur) were determined in the profundal sediments and overlying water column of a shallow eutrophic lake. Low concentrations of sulfate relative to those of acid-volatile sulfide and total sulfur and a decrease in total sulfur with sediment depth implied that the contribution of dissimilatory sulfur reduction to H 2S production was relatively minor. Addition of 1.0 mM Na 235SO 4 to upper sediments in laboratory experiments resulted in the production of H 235S with no apparent lag. Kinetic experiments with 35S demonstrated an apparent Km of 0.068 mmol of SO 42− reduced per liter of sediment per day, whereas tracer experiments with 35S indicated an average turnover time of the sediment sulfate pool of 1.5 h. Total sulfate reduction in a sediment depth profile to 15 cm was 15.3 mmol of sulfate reduced per m 2 per day, which corresponds to a mineralization of 30% of the particulate organic matter entering the sediment. Reduction of 35S 0 occurred at a slower rate. These results demonstrated that high rates of sulfate reduction occur in these sediments despite low concentrations of oxidized inorganic compounds and that this reduction can be important in the anaerobic mineralization of organic carbon. 相似文献
2.
Bacterial sulfate reduction in the surface sediment and the water column of Lake Mendota, Madison, Wis., was studied by using radioactive sulfate ( 35SO 42−). High rates of sulfate reduction were observed at the sediment surface, where the sulfate pool (0.2 mM SO 42−) had a turnover time of 10 to 24 h. Daily sulfate reduction rates in Lake Mendota sediment varied from 50 to 600 nmol of SO 42− cm −3, depending on temperature and sampling date. Rates of sulfate reduction in the water column were 10 3 times lower than that for the surface sediment and, on an areal basis, accounted for less than 18% of the total sulfate reduction in the hypolimnion during summer stratification. Rates of bacterial sulfate reduction in the sediment were not sulfate limited at sulfate concentrations greater than 0.1 mM in short-term experiments. Although sulfate reduction seemed to be sulfate limited below 0.1 mM, Michaelis-Menten kinetics were not observed. The optimum temperature (36 to 37°C) for sulfate reduction in the sediment was considerably higher than in situ temperatures (1 to 13°C). The response of sulfate reduction to the addition of various electron donors metabolized by sulfate-reducing bacteria in pure culture was investigated. The degree of stimulation was in this order: H 2 > n-butanol > n-propanol > ethanol > glucose. Acetate and lactate caused no stimulation. 相似文献
3.
The microbial ecology of anaerobic carbon oxidation processes was investigated in Black Sea shelf sediments from mid-shelf with well-oxygenated bottom water to the oxic-anoxic chemocline at the shelf-break. At all stations, organic carbon (C org) oxidation rates were rapidly attenuated with depth in anoxically incubated sediment. Dissimilatory Mn reduction was the most important terminal electron-accepting process in the active surface layer to a depth of ~1 cm, while SO 42− reduction accounted for the entire C org oxidation below. Manganese reduction was supported by moderately high Mn oxide concentrations. A contribution from microbial Fe reduction could not be discerned, and the process was not stimulated by addition of ferrihydrite. Manganese reduction resulted in carbonate precipitation, which complicated the quantification of C org oxidation rates. The relative contribution of Mn reduction to C org oxidation in the anaerobic incubations was 25 to 73% at the stations with oxic bottom water. In situ, where Mn reduction must compete with oxygen respiration, the contribution of the process will vary in response to fluctuations in bottom water oxygen concentrations. Total bacterial numbers as well as the detection frequency of bacteria with fluorescent in situ hybridization scaled to the mineralization rates. Most-probable-number enumerations yielded up to 10 5 cells of acetate-oxidizing Mn-reducing bacteria (MnRB) cm −3, while counts of Fe reducers were <10 2 cm −3. At two stations, organisms affiliated with Arcobacter were the only types identified from 16S rRNA clone libraries from the highest positive MPN dilutions for MnRB. At the third station, a clone type affiliated with Pelobacter was also observed. Our results delineate a niche for dissimilatory Mn-reducing bacteria in sediments with Mn oxide concentrations greater than ~10 μmol cm −3 and indicate that bacteria that are specialized in Mn reduction, rather than known Mn and Fe reducers, are important in this niche. 相似文献
4.
Microbial Fe reduction in acetate- and succinate-containing enrichment cultures initiated with an estuarine sediment inoculum was studied. Fe reduction was unaffected when SO 42− reduction was inhibited by MoO 42−, indicating that both processes could occur independently. Bacterially produced sulfide precipitated as FeS but was not completely responsible for Fe reduction. The separation of oxidized Fe particles from bacteria by dialysis tubing demonstrated that direct bacterial contact was necessary for Fe reduction. Fe reduction in cultures amended with NO 3− was delayed until NO 3− and NO 2− were removed. However, bacterial attachment to oxidized Fe particles in NO 3−-amended cultures occurred early during growth in a manner similar to NO 3−-free cultures. During late stages of growth, bacteria not attached to Fe particles became pale and swollen, while attached cells remained bright blue when examined by 4′,6-diamidine-2-phenylindole epifluo-rescence microscopy. The presence of added oxidized Mn had no effect on Fe reduction. The results suggested that enzymatic Fe reduction was responsible for reducing Fe in these cultures even in the presence of sulfide and that cells incapable of Fe reduction became unhealthy when Fe(III) was the only available electron acceptor. 相似文献
5.
The addition of 20 mM MoO 42− (molybdate) to a reduced marine sediment completely inhibited the SO 42− reduction activity by about 50 nmol g −1 h −1 (wet sediment). Acetate accumulated at a constant rate of about 25 nmol g −1 h −1 immediately after MoO 42− addition and gave a measure of the preceding utilization rate of acetate by the SO 42−-reducing bacteria. Similarly, propionate and butyrate (including isobutyrate) accumulated at constant rates of 3 to 7 and 2 to 4 nmol g −1 h −1, respectively. The rate of H 2 accumulation was variable, and a range of 0 to 16 nmol g −1 h −1 was recorded. An immediate increase of the methanogenic activity by 2 to 3 nmol g −1 h −1 was apparently due to a release of the competition for H 2 by the absence of SO 42− reduction. If propionate and butyrate were completely oxidized by the SO 42−-reducing bacteria, the stoichiometry of the reactions would indicate that H 2, acetate, propionate, and butyrate account for 5 to 10, 40 to 50, 10 to 20, and 10 to 20%, respectively, of the electron donors for the SO 42−-reducing bacteria. If the oxidations were incomplete, however, the contributions by propionate and butyrate would only be 5 to 10% each, and the acetate could account for as much as two-thirds of the SO 42− reduction. The presence of MoO 42− seemed not to affect the fermentative and methanogenic activities; an MoO 42− inhibition technique seems promising in the search for the natural substrates of SO 42− reduction in sediments. 相似文献
6.
Nitrogen fixation (C 2H 2 reduction) in a sediment-water system was studied under anaerobic incubation conditions. Sodium sulfide at low concentrations stimulated activity, with a twofold increase in C 2H 4 production occurring in the presence of 8 μmol of S 2− per ml of stream water. Sodium sulfide at concentrations of 16 μmol of S 2− per ml or greater inhibited nitrogen fixation, with 64 μmol of S 2− per ml being completely inhibitory. Sulfide at levels of 16 μmol/ml or above inhibited CO 2 production, and the degree of inhibition increased with increasing concentration of sulfide. Titanium (III) citrate (used to modify Eh levels) stimulated both nitrogen fixation and CO 2 production, but could not duplicate, at any concentration tested, the twofold increase in nitrogen fixation caused by 8 μmol of S 2− per ml. Sulfide additions caused pH changes in the sediment, and when the sediment was adjusted and maintained at pH 7.0 all concentrations of sulfide inhibited nitrogen fixation activity. From considerations of the redox equilibria of H 2, H 2S, and other sulfur species at various pH values, it appeared that H 2S was the toxic entity and that HS − was less toxic. The observed stimulation of activity was apparently due to a pH change coupled with the concurrent production of HS − from H 2S. 相似文献
7.
Sulfate reduction and sulfide accumulation were examined in fine-grained sediments from rapidly accreting abandoned channels and mussel culture areas in the Eastern Scheldt, which covered 4 and 5% of the total surface area, respectively.Reduction rates were measured in batch experiments in which the SO 4
2– depletion was measured during anoxic incubation. The reduction rates in summer varied between 14–68 mmol SO 4
2– m –2 day –1 and were related to the sedimentation rate. In the most rapidly accreting channels, SO 4
2– was exhausted below 15–50 cm and methanogenesis became the terminal process of organic carbon oxidationOne-dimensional modelling of sulfate profiles in mussel banks indicated that the subsurface influx of SO 4
2– was almost of the same order as the diffusive flux at the sediment-seawater interface, during the initial stages of the mussel bank accretion. The energy dissipation of waves and tidal currents on the mussel bank surface increased the apparent sediment diffusivity up to 3-fold, especially in the winterThe results indicate that acid volatile sulfide (AVS) was the major, in-situ reduced, sulfur compound in the sediment. The sulfidation of easily extractable iron was nearly complete. Pyrite concentrations (40–80 M S cm –3) were as high as the AVS concentrations, but there was apparently no in-situ transformation of AVS into pyrite. The detrital pyrite originated from eroding marine sediments elsewhere 相似文献
8.
A greatly improved most-probable-number (MPN) method for selective enumeration of sulfate-reducing bacteria (SRB) is described. The method is based on the use of natural media and radiolabeled sulfate ( 35SO 42−). The natural media used consisted of anaerobically prepared sterilized sludge or sediment slurries obtained from sampling sites. The densities of SRB in sediment samples from Kysing Fjord (Denmark) and activated sludge were determined by using a normal MPN (N-MPN) method with synthetic cultivation media and a tracer MPN (T-MPN) method with natural media. The T-MPN method with natural media always yielded significantly higher (100- to 1,000-fold-higher) MPN values than the N-MPN method with synthetic media. The recovery of SRB from environmental samples was investigated by simultaneously measuring sulfate reduction rates (by a 35S-radiotracer method) and bacterial counts by using the T-MPN and N-MPN methods, respectively. When bacterial numbers estimated by the T-MPN method with natural media were used, specific sulfate reduction rates (qSO 42−) of 10 −14 to 10 −13 mol of SO 42− cell −1 day −1 were calculated, which is within the range of qSO 42− values previously reported for pure cultures of SRB (10 −15 to 10 −14 mol of SO 42− cell −1 day −1). qSO 42− values calculated from N-MPN values obtained with synthetic media were several orders of magnitude higher (2 × 10 −10 to 7 × 10 −10 mol of SO 42− cell −1 day −1), showing that viable counts of SRB were seriously underestimated when standard enumeration media were used. Our results demonstrate that the use of natural media results in significant improvements in estimates of the true numbers of SRB in environmental samples. 相似文献
9.
The sulfate kinetics in an anaerobic, sulfate-reducing biofilm were investigated with an annular biofilm reactor. Biofilm growth, sulfide production, and kinetic constants ( Km and Vmax) for the bacterial sulfate uptake within the biofilm were determined. These parameters were used to model the biofilm kinetics, and the experimental results were in good agreement with the model predictions. Typical zero-order volume rate constants for sulfate reduction in a biofilm without substrate limitation ranged from 56 to 93 μmol of SO 24-cm −3 h −1 at 20°C. The temperature dependence (Q 10) of sulfate reduction was equivalent to 3.4 at between 9 and 20°C. The measured rates of sulfate reduction could explain the relatively high sulfide levels found in sewers and wastewater treatment systems. Furthermore, it has been shown that sulfate reduction in biofilms just a few hundred micrometers thick is limited by sulfate diffusion into biofilm at concentrations below 0.5 mM. This observation might, in some cases, be an explanation for the relatively poor capacity of the sulfate-reducing bacteria to compete with the methanogenic bacteria in anaerobic wastewater treatment in submerged filters. 相似文献
10.
Studies were carried out to elucidate the nature and importance of Fe 3+ reduction in anaerobic slurries of marine surface sediment. A constant accumulation of Fe 2+ took place immediately after the endogenous NO 3− was depleted. Pasteurized controls showed no activity of Fe 3+ reduction. Additions of 0.2 mM NO 3− and NO 2− to the active slurries arrested the Fe 3+ reduction, and the process was resumed only after a depletion of the added compounds. Extended, initial aeration of the sediment did not affect the capacity for reduction of NO 3− and Fe 3+, but the treatments with NO 3− increased the capacity for Fe 3+ reduction. Addition of 20 mM MoO 42− completely inhibited the SO 42− reduction, but did not affect the reduction of Fe 3+. The process of Fe 3+ reduction was most likely associated with the activity of facultative anaerobic, NO 3−-reducing bacteria. In surface sediment, the bulk of the Fe 3+ reduction may be microbial, and the process may be important for mineralization in situ if the availability of NO 3− is low. 相似文献
11.
In this paper we investigate the hypothesis that long-term sulphate (SO 4
2−) deposition has made peatlands a larger source of methyl mercury (MeHg) to remote boreal lakes. This was done on experimental plots at a boreal, low sedge mire where the effect of long-term addition of SO 4
2− on peat pore water MeHg concentrations was observed weekly throughout the snow-free portion of 1999. The additions of SO 4
2− started in 1995. The seasonal mean of the pore water MeHg concentrations on the plots with 17 kg ha −1 yr −1 of sulphur (S) addition (1.3±0.08 ng L −1, SE; n = 44) was significantly (p<0.0001) higher than the mean MeHg concentration on the plots with 3 kg ha −1 yr −1 of ambient S deposition (0.6±0.02 ng L −1, SE; n = 44). The temporal variation in pore water MeHg concentrations during the snow free season was larger in the S-addition plots, with an amplitude of >2 ng L −1 compared to +/−0.5 ng L −1 in the ambient S deposition plots. The concentrations of pore water MeHg in the S-addition plots were positively correlated (r 2 = 0.21; p = 0.001) to the groundwater level, with the lowest concentrations of MeHg during the period with the lowest groundwater levels. The pore water MeHg concentrations were not correlated to total Hg, DOC concentration or pH. The results from this study indicate that the persistently higher pore water concentrations of MeHg in the S-addition plots are caused by the long-term additions of SO 4
2− to the mire surface. Since these waters are an important source of runoff, the results support the hypothesis that SO 4
2− deposition has increased the contribution of peatlands to MeHg in downstream aquatic systems. This would mean that the increased deposition of SO 4
2− in acid rain has contributed to the modern increase in the MeHg burdens of remote lakes hydrologically connected to peatlands. 相似文献
12.
Indirect photometric chromatography and microdistillation enabled a simultaneous measurement of sulfate depletion and sulfide production in the top 3 cm of freshwater sediments to be made. The simultaneous measurement of sulfate depletion and sulfide production rates provided added insight into microbial sulfur metabolism. The lower sulfate reduction rates, as derived from the production of acid-volatile 35S 2− only, were explained by a conversion of this pool to an undistillable fraction under acidic conditions during incubation. A mathematical model was applied to calculate sulfate reduction from sulfate gradients at the sediment-water interface. To avoid disturbance of these gradients, the sample volume was reduced to 0.2 g (wet weight) of sediment. Sulfate diffusion coefficients in the model were determined ( Ds = 0.3 × 10 −5 cm 2 s −1 at 6°C). The results of the model were compared with those of radioactive sulfate turnover experiments by assessing the actual turnover rate constants (2 to 5 day −1) and pool sizes of sulfate at different sediment depths. 相似文献
13.
Compartmental analysis of 35SO 42− exchange kinetics is used to obtain SO 42− fluxes and compartment contents in carrot ( Daucus carota L.) storage root cells, where 2 to 5% of the SO 42− taken up is reduced to organic form. The necessary curve fitting is verified by (a) consistency between `content versus time' and `rate versus time' plots of washout data; (b) agreement between loading and washout kinetics; and (c) correct identification of the fastest exchange phase as being from extracellular spaces. Sulfate is actively transported up an electrochemical potential gradient at both plasmalemma and tonoplast. The plasmalemma influx is from 2 to 10 times higher than the tonoplast influx, is much greater than the SO42− reduction rate, and would not limit the rate of either. This is consistent with the finding that the plasmalemma influx is not regulated by internal SO42− or cysteine (Cram 1982 Plant Sci Lett, in press). Both SO42− influxes rise with only limited saturation as the external SO42− concentration increases up to 50 millimolarity. Both effluxes appear to be passive, with extensive recycling in the plasmalemma influx pump. SO42− permeability is about 10−11 meter per second at both membranes. The high, nonlimiting fluxes of SO42− at the plasmalemma relative to the tonoplast (found also in Lemna; Thoiron, Thoiron, Demarty, Thellier 1981 Biochim Biophys Acta 644: 24-35) contrasts with SO42− fluxes in bacteria and with Cl− fluxes in plant cells. Their implications for work on characteristics and regulation of SO42− uptake in roots and tissue cultures are discussed. 相似文献
14.
The sulfate ion (SO 42−) is transported into plant root cells by SO 42− transporters and then mostly reduced to sulfide (S 2−). The S 2− is then bonded to O-acetylserine through the activity of cysteine synthase ( O-acetylserine (thiol)lyase or OASTL) to form cysteine, the first organic molecule of the SO 42− assimilation pathway. Here, we show that a root plasma membrane SO 42− transporter of Arabidopsis, SULTR1;2, physically interacts with OASTL. The interaction was initially demonstrated using a yeast two-hybrid system and corroborated by both in vivo and in vitro binding assays. The domain of SULTR1;2 shown to be important for association with OASTL is called the STAS domain. This domain is at the C terminus of the transporter and extends from the plasma membrane into the cytoplasm. The functional relevance of the OASTL-STAS interaction was investigated using yeast mutant cells devoid of endogenous SO 42− uptake activity but co-expressing SULTR1;2 and OASTL. The analysis of SO 42− transport in these cells suggests that the binding of OASTL to the STAS domain in this heterologous system negatively impacts transporter activity. In contrast, the activity of purified OASTL measured in vitro was enhanced by co-incubation with the STAS domain of SULTR1;2 but not with the analogous domain of the SO 42− transporter isoform SULTR1;1, even though the SULTR1;1 STAS peptide also interacts with OASTL based on the yeast two-hybrid system and in vitro binding assays. These observations suggest a regulatory model in which interactions between SULTR1;2 and OASTL coordinate internalization of SO 42− with the energetic/metabolic state of plant root cells. 相似文献
15.
Interstitial water profiles of SeO 42−, SeO 32−, SO 42−, and Cl − in anoxic sediments indicated removal of the seleno-oxyanions by a near-surface process unrelated to sulfate reduction. In sediment slurry experiments, a complete reductive removal of SeO 42− occurred under anaerobic conditions, was more rapid with H 2 or acetate, and was inhibited by O 2, NO 3−, MnO 2, or autoclaving but not by SO 42− or FeOOH. Oxidation of acetate in sediments could be coupled to selenate but not to molybdate. Reduction of selenate to elemental selenium was determined to be the mechanism for loss from solution. Selenate reduction was inhibited by tungstate and chromate but not by molybdate. A small quantity of the elemental selenium precipitated into sediments from solution could be resolublized by oxidation with either nitrate or FeOOH, but not with MnO 2. A bacterium isolated from estuarine sediments demonstrated selenate-dependent growth on acetate, forming elemental selenium and carbon dioxide as respiratory end products. These results indicate that dissimilatory selenate reduction to elemental selenium is the major sink for selenium oxyanions in anoxic sediments. In addition, they suggest application as a treatment process for removing selenium oxyanions from wastewaters and also offer an explanation for the presence of selenite in oxic waters. 相似文献
16.
In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO 4
2– reduction rates in the sediment, (2) depletion of SO 4
2– in the overlying water column and (3) release of 35S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO 4
2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core 35SO 4
2– injection. Rates of SO 4
2– consumption in the overlying water were estimated by changes in SO 4
2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m –2 d –1. Rates of SO 4
2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m –2 d –1 (November) to 0.43–1.81 mmol m –2 d –1 (July, August and April). Maximum rates of oxidation to SO 4
2– in July 1990 estimated by combination of SO 4
2– reduction rates and rates of in situ SO 4
2– uptake in the enclosed water column were 10.3 and 10.5 mmol m –2 d –1 at an organic rich and at a sandy site respectively.Experiments with 35S 2– and 35SO 4
2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO 4
2– and (2) the presence of mainly non SO 4
2–-S derived from reduced S transported from the sediment into the overlying water. A 35S 2– tracer experiment showed that about 7% of 35S 2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author 相似文献
17.
We measured potential rates of bacterial dissimilatory reduction of 75SeO 42− to 75Se 0 in a diversity of sediment types, with salinities ranging from freshwater (salinity = 1 g/liter) to hypersaline (salinity = 320 g/liter and with pH values ranging from 7.1 to 9.8. Significant biological selenate reduction occurred in all samples with salinities from 1 to 250 g/liter but not in samples with a salinity of 320 g/liter. Potential selenate reduction rates (25 nmol of SeO 42− per ml of sediment added with isotope) ranged from 0.07 to 22 μmol of SeO 42− reduced liter −1 h −1. Activity followed Michaelis-Menten kinetics in relation to SeO 42− concentration ( Km of selenate = 7.9 to 720 μM). There was no linear correlation between potential rates of SeO 42− reduction and salinity, pH, concentrations of total Se, porosity, or organic carbon in the sediments. However, potential selenate reduction was correlated with apparent Km for selenate and with potential rates of denitrification ( r = 0.92 and 0.81, respectively). NO 3−, NO 2−, MoO 42−, and WO 42− inhibited selenate reduction activity to different extents in sediments from both Hunter Drain and Massie Slough, Nev. Sulfate partially inhibited activity in sediment from freshwater (salinity = 1 g/liter) Massie Slough samples but not from the saline (salinity = 60 g/liter) Hunter Drain samples. We conclude that dissimilatory selenate reduction in sediments is widespread in nature. In addition, in situ selenate reduction is a first-order reaction, because the ambient concentrations of selenium oxyanions in the sediments were orders of magnitude less than their Kms. 相似文献
18.
Microbial communities have the potential to control the biogeochemical fate of some radionuclides in contaminated land scenarios or in the vicinity of a geological repository for radioactive waste. However, there have been few studies of ionizing radiation effects on microbial communities in sediment systems. Here, acetate and lactate amended sediment microcosms irradiated with gamma radiation at 0.5 or 30 Gy h −1 for 8 weeks all displayed NO 3− and Fe(III) reduction, although the rate of Fe(III) reduction was decreased in 30-Gy h −1 treatments. These systems were dominated by fermentation processes. Pyrosequencing indicated that the 30-Gy h −1 treatment resulted in a community dominated by two Clostridial species. In systems containing no added electron donor, irradiation at either dose rate did not restrict NO 3−, Fe(III), or SO 42− reduction. Rather, Fe(III) reduction was stimulated in the 0.5-Gy h −1-treated systems. In irradiated systems, there was a relative increase in the proportion of bacteria capable of Fe(III) reduction, with Geothrix fermentans and Geobacter sp. identified in the 0.5-Gy h −1 and 30-Gy h −1 treatments, respectively. These results indicate that biogeochemical processes will likely not be restricted by dose rates in such environments, and electron accepting processes may even be stimulated by radiation. 相似文献
19.
An investigation of the terminal anaerobic processes occurring in polluted intertidal sediments indicated that terminal carbon flow was mainly mediated by sulfate-reducing organisms in sediments with high sulfate concentrations (>10 mM in the interstitial water) exposed to low loadings of nutrient (equivalent to <10 2 kg of N · day −1) and biochemical oxygen demand (<0.7 × 10 3 kg · day −1) in effluents from different pollution sources. However, in sediments exposed to high loadings of nutrient (>10 2 kg of N · day −1) and biochemical oxygen demand (>0.7 × 10 3 kg · day −1), methanogenesis was the major process in the mediation of terminal carbon flow, and sulfate concentrations were low (≤2 mM). The respiratory index [ 14CO 2/( 14CO 2 + 14CH 4)] for [2- 14C]acetate catabolism, a measure of terminal carbon flow, was ≥0.96 for sediment with high sulfate, but in sediments with sulfate as little as 10 μM in the interstitial water, respiratory index values of ≤0.22 were obtained. In the latter sediment, methane production rates as high as 3 μmol · g −1 (dry weight) · h −1 were obtained, and there was a potential for active sulfate reduction. 相似文献
20.
Seasonal variation of dimethylsulfide (DMS) and methane thiol (MSH) concentrations in sediment porewater was determined in a Danish estuary. Dimethylsulfide (DMDS) was never found. Detectable DMS levels of up to 0.1 M were found only in the summer and only within the upper 5 cm of the sediment. The DMS accumulation was probably associated with decomposing fragments of macro-algae in the surface layer. Significant MSH accumulation of up to 1 M was found only in the deep, CH 4-rich sediment below the SO 4
2- zone. With depth, a detectable MSH level could thus be observed below the 1 mM SO 4
2--isopleth which also marked the SO 4
2--CH 4 transition. The transition zone was located deeper in the sediment in winter (20–25 cm depth) than in summer (5–10 cm depth). The absence of MSH in the SO 4
2- zone could be due to rapid utilization of the compound by SO 4
2--reducing bacteria. A possible involvement of MSH in anaerobic CH 4 oxidation at the transition zone is discussed; CH 4 and sulfide (HS - form, pH 7) are proposed to form MSH and H 2 which in turn may be metabolized by, e.g. SO 4
2--reducing bacteria. 相似文献
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