scholarly journals Microbial methanogenesis in the sulfate-reducing zone of sediments in the Eckernförde Bay, SW Baltic Sea

2018 ◽  
Vol 15 (1) ◽  
pp. 137-157 ◽  
Author(s):  
Johanna Maltby ◽  
Lea Steinle ◽  
Carolin R. Löscher ◽  
Hermann W. Bange ◽  
Martin A. Fischer ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Sulfate Reduction ◽  
Water Column ◽  
Methane Emissions ◽  
Potential Contribution ◽  
Reduction Zone ◽  
Sulfate Reducers ◽  
Sulfate Reducing ◽  
Hydrogenotrophic Methanogenesis ◽  
Environmental Controls

Abstract. Benthic microbial methanogenesis is a known source of methane in marine systems. In most sediments, the majority of methanogenesis is located below the sulfate-reducing zone, as sulfate reducers outcompete methanogens for the major substrates hydrogen and acetate. The coexistence of methanogenesis and sulfate reduction has been shown before and is possible through the usage of noncompetitive substrates by methanogens such as methanol or methylated amines. However, knowledge about the magnitude, seasonality, and environmental controls of this noncompetitive methane production is sparse. In the present study, the presence of methanogenesis within the sulfate reduction zone (SRZ methanogenesis) was investigated in sediments (0–30 cm below seafloor, cm b.s.f.) of the seasonally hypoxic Eckernförde Bay in the southwestern Baltic Sea. Water column parameters such as oxygen, temperature, and salinity together with porewater geochemistry and benthic methanogenesis rates were determined in the sampling area Boknis Eck quarterly from March 2013 to September 2014 to investigate the effect of seasonal environmental changes on the rate and distribution of SRZ methanogenesis, to estimate its potential contribution to benthic methane emissions, and to identify the potential methanogenic groups responsible for SRZ methanogenesis. The metabolic pathway of methanogenesis in the presence or absence of sulfate reducers, which after the addition of a noncompetitive substrate was studied in four experimental setups: (1) unaltered sediment batch incubations (net methanogenesis), (2) 14C-bicarbonate labeling experiments (hydrogenotrophic methanogenesis), (3) manipulated experiments with the addition of either molybdate (sulfate reducer inhibitor), 2-bromoethanesulfonate (methanogen inhibitor), or methanol (noncompetitive substrate, potential methanogenesis), and (4) the addition of 13C-labeled methanol (potential methylotrophic methanogenesis). After incubation with methanol, molecular analyses were conducted to identify key functional methanogenic groups during methylotrophic methanogenesis. To also compare the magnitudes of SRZ methanogenesis with methanogenesis below the sulfate reduction zone (> 30 cm b.s.f.), hydrogenotrophic methanogenesis was determined by 14C-bicarbonate radiotracer incubation in samples collected in September 2013.SRZ methanogenesis changed seasonally in the upper 30 cm b.s.f. with rates increasing from March (0.2 nmol cm−3 d−1) to November (1.3 nmol cm−3 d−1) 2013 and March (0.2 nmol cm−3 d−1) to September (0.4 nmol cm−3 d−1) 2014. Its magnitude and distribution appeared to be controlled by organic matter availability, C / N, temperature, and oxygen in the water column, revealing higher rates in the warm, stratified, hypoxic seasons (September–November) compared to the colder, oxygenated seasons (March–June) of each year. The majority of SRZ methanogenesis was likely driven by the usage of noncompetitive substrates (e.g., methanol and methylated compounds) to avoid competition with sulfate reducers, as was indicated by the 1000–3000-fold increase in potential methanogenesis activity observed after methanol addition. Accordingly, competitive hydrogenotrophic methanogenesis increased in the sediment only below the depth of sulfate penetration (> 30 cm b.s.f.). Members of the family Methanosarcinaceae, which are known for methylotrophic methanogenesis, were detected by PCR using Methanosarcinaceae-specific primers and are likely to be responsible for the observed SRZ methanogenesis.The present study indicates that SRZ methanogenesis is an important component of the benthic methane budget and carbon cycling in Eckernförde Bay. Although its contributions to methane emissions from the sediment into the water column are probably minor, SRZ methanogenesis could directly feed into methane oxidation above the sulfate–methane transition zone.

scholarly journals Microbial methanogenesis in the sulfate-reducing zone in sediments from Eckernförde Bay, SW Baltic Sea

2017 ◽  
Author(s):  
Johanna Maltby ◽  
Lea Steinle ◽  
Carolin R. Löscher ◽  
Hermann W. Bange ◽  
Martin A. Fischer ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Water Column ◽  
Environmental Changes ◽  
Sea Water ◽  
Fold Increase ◽  
Potential Contribution ◽  
Sulfate Reducers ◽  
Sulfate Reducing ◽  
Hydrogenotrophic Methanogenesis ◽  
Competitive Substrate

Abstract. The presence of surface methanogenesis, located within the sulfate-reducing zone (0–30 centimeters below seafloor, cmbsf), was investigated in sediments of the seasonally hypoxic Eckernförde Bay, southwestern Baltic Sea. Water column parameters like oxygen, temperature and salinity together with porewater geochemistry and benthic methanogenesis rates were determined in the sampling area ''Boknis Eck'' quarterly from March 2013 to September 2014, to investigate the effect of seasonal environmental changes on the rate and distribution of surface methanogenesis and to estimate its potential contribution to benthic methane emissions. The metabolic pathway of methanogenesis in the presence or absence of sulfate reducers and after the addition of a non-competitive substrate was studied in four experimental setups: 1) unaltered sediment batch incubations (net methanogenesis), 2) 14C-bicarbonate labeling experiments (hydrogenotrophic methanogenesis), 3) manipulated experiments with addition of either molybdate (sulfate reducer inhibitor), 2-bromoethane-sulfonate (methanogen inhibitor), or methanol (non-competitive substrate, potential methanogenesis), 4) addition of 13C-labeled methanol (potential methylotrophic methanogenesis). After incubation with methanol in the manipulated experiments, molecular analyses were conducted to identify key functional methanogenic groups. Hydrogenotrophic methanogenesis in sediments below the sulfate-reducing zone (> 30 cmbsf) was determined by 14C-bicarbonate radiotracer incubation in samples collected in September 2013. Surface methanogenesis changed seasonally in the upper 30 cmbsf with rates increasing from March (0.2 nmol cm−3 d−1) to November (1.3 nmol cm−3 d−1) 2013 and March (0.2 nmol cm−3 d−1) to September (0.4 nmol cm−3 d−1) 2014, respectively. Its magnitude and distribution appeared to be controlled by organic matter availability, C / N, temperature, and oxygen in the water column, revealing higher rates in warm, stratified, hypoxic seasons (September/November) compared to colder, oxygenated seasons (March/June) of each year. The majority of surface methanogenesis was likely driven by the usage of non-competitive substrates (e.g., methanol and methylated compounds), to avoid competition with sulfate reducers, as it was indicated by the 1000–3000-fold increase in potential methanogenesis activity observed after methanol addition. Accordingly, competitive hydrogenotrophic methanogenesis increased in the sediment only below the depth of sulfate penetration (> 30 cmbsf). Members of the family Methanosarcinaceae, which are known for methylotrophic methanogenesis, were detected by PCR using Methanosarcinaceae-specific primers and are likely to be responsible for the observed surface methanogenesis. The present study indicated that surface methanogenesis makes an important contribute to the benthic methane budget of Eckernförde Bay sediments as it could directly feed into methane oxidation above the sulfate-methane transition zone.

scholarly journals Anaerobic Benzene Degradation in Petroleum-Contaminated Aquifer Sediments after Inoculation with a Benzene-Oxidizing Enrichment

1998 ◽  
Vol 64 (2) ◽  
pp. 775-778 ◽  
Author(s):  
Jonathan M. Weiner ◽  
Derek R. Lovley
Keyword(s):  
Sulfate Reduction ◽  
Environmental Conditions ◽  
Reduction Zone ◽  
Contaminated Aquifer ◽  
Sulfate Reducers ◽  
Sulfate Reducing ◽  
Benzene Degradation ◽  
Anaerobic Benzene Degradation ◽  
Aquifer Sediments ◽  
Over Time

ABSTRACT Sediments from the sulfate-reduction zone of a petroleum-contaminated aquifer, in which benzene persisted, were inoculated with a benzene-oxidizing, sulfate-reducing enrichment from aquatic sediments. Benzene was degraded, with apparent growth of the benzene-degrading population over time. These results suggest that the lack of benzene degradation in the sulfate-reduction zones of some aquifers may result from the failure of the appropriate benzene-degrading sulfate reducers to colonize the aquifers rather than from environmental conditions that are adverse for anaerobic benzene degradation.

Microbial ecology of sulfate-reducing bacteria in wastewater biofilms analyzed by microelectrodes and fish (fluorescent in situ hybridization) technique

1999 ◽  
Vol 39 (7) ◽  
pp. 41-47 ◽  
Author(s):  
Satoshi Okabe ◽  
Hisashi Satoh ◽  
Tsukasa Itoh ◽  
Yoshimasa Watanabe
Keyword(s):  
In Situ Hybridization ◽  
Sulfate Reduction ◽  
Sulfate Reducing Bacteria ◽  
Hybridization Technique ◽  
Concentration Profiles ◽  
Reduction Zone ◽  
Sulfate Reducing ◽  
Reducing Bacteria ◽  
Culture Dependent

The vertical distribution of sulfate-reducing bacteria (SRB) in microaerophilic wastewater biofilms grown on fully submerged rotating disk reactors (RDR) was determined by the conventional culture-dependent MPN method and in situ hybridization of fluorescently-labelled 16S rRNA-targeted oligonucleotide probes for SRB in parallel. Chemical concentration profiles within the biofilm were also measured using microelectrodes for O2, S2-, NO3- and pH. In situ hybridization revealed that the SRB probe-stained cells were distributed throughout the biofilm even in the oxic surface zone in all states from single scattered cells to clustered cells. The higher fluorescence intensity and abundance of SRB probe-stained cells were found in the middle part of the biofilm. This result corresponded well with O2 and H2S concentration profiles measured by microelectrodes, showing sulfate reduction was restricted to a narrow anaerobic zone located about 500 μm below the biofilm surface. Results of the MPN and potential sulfate reducing activity (culture-dependent approaches) indicated a similar distribution of cultivable SRB in the biofilm. The majority of the general SRB probe-stained cells were hybridized with SRB 660 probe, suggesting that one important member of the SRB in the wastewater biofilm could be the genus Desulfobulbus. An addition of nitrate forced the sulfate reduction zone deeper in the biofilm and reduced the specific sulfate reduction rate as well. The sulfate reduction zone was consequently separated from O2 and NO3- respiration zones. Anaerobic H2S oxidation with NO3- was also induced by addition of nitrate to the medium.

scholarly journals Butyrate Conversion by Sulfate-Reducing and Methanogenic Communities from Anoxic Sediments of Aarhus Bay, Denmark

2020 ◽  
Vol 8 (4) ◽  
pp. 606
Author(s):  
Derya Ozuolmez ◽  
Elisha K. Moore ◽  
Ellen C. Hopmans ◽  
Jaap S. Sinninghe Damsté ◽  
Alfons J. M. Stams ◽  
...  
Keyword(s):  
Sulfate Reduction ◽  
Marine Sediments ◽  
Relative Abundance ◽  
Archaeal Community ◽  
Community Analysis ◽  
Sulfate Concentration ◽  
Vertical Separation ◽  
Sulfate Reducers ◽  
Sulfate Reducing ◽  
Initial Zone

The conventional perception that the zone of sulfate reduction and methanogenesis are separated in high- and low-sulfate-containing marine sediments has recently been changed by studies demonstrating their co-occurrence in sediments. The presence of methanogens was linked to the presence of substrates that are not used by sulfate reducers. In the current study, we hypothesized that both groups can co-exist, consuming common substrates (H2 and/or acetate) in sediments. We enriched butyrate-degrading communities in sediment slurries originating from the sulfate, sulfate–methane transition, and methane zone of Aarhus Bay, Denmark. Sulfate was added at different concentrations (0, 3, 20 mM), and the slurries were incubated at 10 °C and 25 °C. During butyrate conversion, sulfate reduction and methanogenesis occurred simultaneously. The syntrophic butyrate degrader Syntrophomonas was enriched both in sulfate-amended and in sulfate-free slurries, indicating the occurrence of syntrophic conversions at both conditions. Archaeal community analysis revealed a dominance of Methanomicrobiaceae. The acetoclastic Methanosaetaceae reached high relative abundance in the absence of sulfate, while presence of acetoclastic Methanosarcinaceae was independent of the sulfate concentration, temperature, and the initial zone of the sediment. This study shows that there is no vertical separation of sulfate reducers, syntrophs, and methanogens in the sediment and that they all participate in the conversion of butyrate.

scholarly journals Diversity of Sulfur Isotope Fractionations by Sulfate-Reducing Prokaryotes

2001 ◽  
Vol 67 (2) ◽  
pp. 888-894 ◽  
Author(s):  
Jan Detmers ◽  
Volker Brüchert ◽  
Kirsten S. Habicht ◽  
Jan Kuever
Keyword(s):  
Sulfate Reduction ◽  
Isotope Fractionation ◽  
Sulfur Isotope ◽  
Reduction Rate ◽  
Sulfate Reduction Rate ◽  
Dissimilatory Sulfate Reduction ◽  
Systematic Effect ◽  
Sulfate Reducers ◽  
Sulfate Reducing ◽  
Sulfur Isotope Fractionation

ABSTRACT Batch culture experiments were performed with 32 different sulfate-reducing prokaryotes to explore the diversity in sulfur isotope fractionation during dissimilatory sulfate reduction by pure cultures. The selected strains reflect the phylogenetic and physiologic diversity of presently known sulfate reducers and cover a broad range of natural marine and freshwater habitats. Experimental conditions were designed to achieve optimum growth conditions with respect to electron donors, salinity, temperature, and pH. Under these optimized conditions, experimental fractionation factors ranged from 2.0 to 42.0‰. Salinity, incubation temperature, pH, and phylogeny had no systematic effect on the sulfur isotope fractionation. There was no correlation between isotope fractionation and sulfate reduction rate. The type of dissimilatory bisulfite reductase also had no effect on fractionation. Sulfate reducers that oxidized the carbon source completely to CO2 showed greater fractionations than sulfate reducers that released acetate as the final product of carbon oxidation. Different metabolic pathways and variable regulation of sulfate transport across the cell membrane all potentially affect isotope fractionation. Previous models that explained fractionation only in terms of sulfate reduction rates appear to be oversimplified. The species-specific physiology of each sulfate reducer thus needs to be taken into account to understand the regulation of sulfur isotope fractionation during dissimilatory sulfate reduction.

scholarly journals Microbial methanogenesis in the sulfate-reducing zone of surface sediments traversing the Peruvian margin

2015 ◽  
Vol 12 (17) ◽  
pp. 14869-14910 ◽  
Author(s):  
J. Maltby ◽  
S. Sommer ◽  
A. W. Dale ◽  
T. Treude
Keyword(s):  
Sulfate Reduction ◽  
Surface Sediments ◽  
Carbon Export ◽  
Labile Organic Matter ◽  
Methanogenic Activity ◽  
Sulfate Reducing ◽  
Hydrogenotrophic Methanogenesis ◽  
Minimum Zone ◽  
Shelf Station ◽  
The Relationship

Abstract. We studied the concurrence of methanogenesis and sulfate reduction in surface sediments (0–25 cm below sea floor, cmbsf) at six stations (70, 145, 253, 407, 770 and 1024 m) along the Peruvian margin (12° S). This oceanographic region is characterized by high carbon export to the seafloor, creating an extensive oxygen minimum zone (OMZ) on the shelf, both factors that could favor surface methanogenesis. Sediments sampled along the depth transect traversed areas of anoxic and oxic conditions in the bottom-near water. Net methane production (batch incubations) and sulfate reduction (35S-sulfate radiotracer incubation) were determined in the upper 0–25 cmbsf of multicorer cores from all stations, while deep hydrogenotrophic methanogenesis (> 30 cmbsf, 14C-bicarbonate radiotracer incubation) was determined in two gravity cores at selected sites (78 and 407 m). Furthermore, stimulation (methanol addition) and inhibition (molybdate addition) experiments were carried out to investigate the relationship between sulfate reduction and methanogenesis. Highest rates of methanogenesis and sulfate reduction in the surface sediments, integrated over 0–25 cmbsf, were observed on the shelf (70–253 m, 0.06–0.1 and 0.5–4.7 mmol m−2 d−1, respectively), while lowest rates were discovered at the deepest site (1024 m, 0.03 and 0.2 mmol m−2 d−1, respectively). The addition of methanol resulted in significantly higher surface methanogenesis activity, suggesting that the process was mostly based on non-competitive substrates, i.e., substrates not used by sulfate reducers. In the deeper sediment horizons, where competition was probably relieved due to the decline of sulfate, the usage of competitive substrates was confirmed by the detection of hydrogenotrophic activity in the sulfate-depleted zone at the shallow shelf station (70 m). Surface methanogenesis appeared to be correlated to the availability of labile organic matter (C / N ratio) and organic carbon degradation (DIC production), both of which support the supply of methanogenic substrates. A negative correlation of methanogenesis rates with dissolved oxygen in the bottom-near water was not obvious, however, anoxic conditions within the OMZ might be advantageous for methanogenic organisms at the sediment–water interface. Our results revealed a high relevance of surface methanogenesis on the shelf, where the ratio between surface to deep (below sulfate penetration) methanogenic activity ranged between 0.13 and 105. In addition, methane concentration profiles indicate a partial release of surface methane into the water column as well as a partial consumption of methane by anaerobic methane oxidation (AOM) in the surface sediment. The present study suggests that surface methanogenesis might play a greater role in benthic methane budgeting than previously thought, especially for fueling AOM above the sulfate-methane transition zone.

Sulfate-reducing bacterial communities in the water column of the Gdansk Deep (Baltic Sea)

Microbiology ◽  
2015 ◽  
Vol 84 (2) ◽  
pp. 268-277 ◽  
Author(s):  
V. A. Korneeva ◽  
N. V. Pimenov ◽  
A. V. Krek ◽  
T. P. Tourova ◽  
A. L. Bryukhanov
Keyword(s):  
Baltic Sea ◽  
Water Column ◽  
Bacterial Communities ◽  
Sulfate Reducing ◽  
Gdansk Deep

Competition for H2 between sulfate reducers, methanogens and homoacetogens in a gas-lift reactor

2002 ◽  
Vol 45 (10) ◽  
pp. 75-80 ◽  
Author(s):  
J. Weijma ◽  
F. Gubbels ◽  
L.W. Hulshoff Pol ◽  
A.J.M. Stams ◽  
P. Lens ◽  
...  
Keyword(s):  
Kinetic Parameters ◽  
Sulfate Reduction ◽  
Growth Kinetic ◽  
Settling Velocity ◽  
Sulfate Reducing Bacteria ◽  
Anaerobic Sludge ◽  
Sulfate Reducers ◽  
Sulfate Reducing ◽  
Reducing Bacteria ◽  
Gas Lift

Reported values for growth kinetic parameters show an order in competitivity of heterotrophic sulfate reducing bacteria>methanogens>homoacetogens for the substrate hydrogen. This order suggests that methanogens can succesfully compete with consortia of heterotrophic SRB and homoacetogens when H2/CO2 is present as sole substrate. However, we found in experiments using gas-lift reactors inoculated with anaerobic sludge and fed with H2/CO2 and sulfate, that heterotrophic sulfate reduction rapidly and completely outcompeted methanogenesis, whereas a low amount of acetate was formed. Thus, in disagreement with the above competitivity order, hydrogen is more readily consumed by homoacetogenesis than by methanogenesis, indicating that the competition is not kinetically determined. The superior settling velocity of sulfidogenic-acetogenic sludge compared to that of methanogenic sludge suggests that the former sludge is better retained, which can explain the predominance of sulfate reduction/homoacetogenesis over methanogenesis.

scholarly journals Microbial methanogenesis in the sulfate-reducing zone of surface sediments traversing the Peruvian margin

2016 ◽  
Vol 13 (1) ◽  
pp. 283-299 ◽  
Author(s):  
J. Maltby ◽  
S. Sommer ◽  
A. W. Dale ◽  
T. Treude
Keyword(s):  
Sulfate Reduction ◽  
Surface Sediments ◽  
Carbon Export ◽  
Labile Organic Matter ◽  
Methanogenic Activity ◽  
Sulfate Reducing ◽  
Hydrogenotrophic Methanogenesis ◽  
Multiple Cores ◽  
Minimum Zone ◽  
Shelf Station

Abstract. We studied the concurrence of methanogenesis and sulfate reduction in surface sediments (0–25 cm below sea floor) at six stations (70, 145, 253, 407, 990 and 1024 m) along the Peruvian margin (12° S). This oceanographic region is characterized by high carbon export to the seafloor creating an extensive oxygen minimum zone (OMZ) on the shelf, both factors that could favor surface methanogenesis. Sediments sampled along the depth transect traversed areas of anoxic and oxic conditions in the bottom-near water. Net methane production (batch incubations) and sulfate reduction (35S-sulfate radiotracer incubation) were determined in the upper 0–25 cm b.s.f. of multiple cores from all stations, while deep hydrogenotrophic methanogenesis (> 30 cm b.s.f., 14C-bicarbonate radiotracer incubation) was determined in two gravity cores at selected sites (78 and 407 m). Furthermore, stimulation (methanol addition) and inhibition (molybdate addition) experiments were carried out to investigate the relationship between sulfate reduction and methanogenesis.Highest rates of methanogenesis and sulfate reduction in the surface sediments, integrated over 0–25 cm b.s.f., were observed on the shelf (70–253 m, 0.06–0.1 and 0.5-4.7 mmol m−2 d−1, respectively), while lowest rates were discovered at the deepest site (1024 m, 0.03 and 0.2 mmol m−2 d−1, respectively). The addition of methanol resulted in significantly higher surface methanogenesis activity, suggesting that the process was mostly based on non-competitive substrates – i.e., substrates not used by sulfate reducers. In the deeper sediment horizons, where competition was probably relieved due to the decrease of sulfate, the usage of competitive substrates was confirmed by the detection of hydrogenotrophic activity in the sulfate-depleted zone at the shallow shelf station (70 m).Surface methanogenesis appeared to be correlated to the availability of labile organic matter (C ∕ N ratio) and organic carbon degradation (DIC production), both of which support the supply of methanogenic substrates. A negative correlation between methanogenesis rates and dissolved oxygen in the bottom-near water was not obvious; however, anoxic conditions within the OMZ might be advantageous for methanogenic organisms at the sediment-water interface.Our results revealed a high relevance of surface methanogenesis on the shelf, where the ratio between surface to deep (below sulfate penetration) methanogenic activity ranged between 0.13 and 105. In addition, methane concentration profiles indicated a partial release of surface methane into the water column as well as consumption of methane by anaerobic methane oxidation (AOM) in the surface sediment. The present study suggests that surface methanogenesis might play a greater role in benthic methane budgeting than previously thought, especially for fueling AOM above the sulfate–methane transition zone.

Effect of nitrite and nitrate on biogenic sulfide production in sewer biofilms determined by the use of microelectrodes

2003 ◽  
Vol 47 (11) ◽  
pp. 281-288 ◽  
Author(s):  
S. Okabe ◽  
T. Ito ◽  
H. Satoh ◽  
Y. Watanabe
Keyword(s):  
Sulfate Reduction ◽  
Reduction Rate ◽  
Rotating Disk ◽  
Sulfate Reduction Rate ◽  
Reduction Zone ◽  
Sulfate Reducing ◽  
H2s Oxidation ◽  
Rotating Disk Reactors ◽  
Microelectrode Measurements

The effects of O2 and NO3− concentrations on in situ sulfate reduction and sulfide reoxidation in microaerophilic wastewater biofilms grown on rotating disk reactors were investigated by the use of microelectrodes for O2, S2−, NO3−, NO2−, and pH. Microelectrode measurements showed the vertical microzonation of O2 respiration, NO3− respiration, H2S oxidation and SO42− reduction in the biofilms. The microelectrode measurements indicate that sulfate reducing activity was largely restricted to a narrow anaerobic zone located about 500 μm below the biofilm surface. An addition of nitrate forced the sulfate reduction zone deeper in the biofilm and reduced the specific sulfate reduction rate as well. The sulfate reduction zone was consequently separated from the O2 and NO3− respiration zones. Anaerobic H2S oxidation with NO3− was also induced by addition of nitrate to the medium. Measurements of the reduced inorganic sulfur compounds (FeS, FeS2 and S0), total-Mn and total-Fe in the biofilm indicated that the produced H2S became immediately oxidized with O2, NO3− and other oxidants, mainly ferric/ferrous hydrates. On the basis of the present results, it was estimated that of all sulfide produced, 13% of the sulfide was precipitated by metal ions as FeS and S0 just above the sulfate reduction zone, 65% was anaerobically oxidized to SO42− with NO3− as an electron acceptor and 22% was aerobically oxidized within the biofilm incubated in 70 μmol l−1 of DO and 280 μmol l−1 of NO3−.

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