Arne Sturm - Academia.edu (original) (raw)
Papers by Arne Sturm
Seafloor hydrothermal activity at mid-ocean ridges (MOR) is one of the fundamental processes cont... more Seafloor hydrothermal activity at mid-ocean ridges (MOR) is one of the fundamental processes controlling the exchange of heat and chemical species between seawater and ocean rocks and there is increasing evidence that off-axis vent fields may significantly affect biogeochemical cycles and oceanic elemental budgets. Active hydrothermal venting associated with volcanic seamounts has been well documented, in particular at Loihi Seamount, Hawaii and Vailulu`u Seamount, Samoa, but the degree to which diffuse venting and subsurface processes occur at hot-spot volcanoes is not known. Loihi Seamount offers at least three distinct microbial habitats that support a biogeochemically-significant class of microorganisms – iron oxidizing bacteria. These habitats include sites of warm, iron-rich hydrothermal vents at the volcano’s summit (1,000m depth), sites of cold, ultra-diffuse iron-rich hydrothermal fluids at 5,000m, and bare basalts with no localized active hydrothermal fluids. Here, we prov...
Geochemistry Exploration Environment Analysis
A microorganism of the Marinobacter genus capable of Fe-oxidation at near-neutral pH, both in the... more A microorganism of the Marinobacter genus capable of Fe-oxidation at near-neutral pH, both in the presence and absence of oxygen, was found at a depth of 1.4 km in proximity to a Cu-Zn Volcanogenic Massive Sulphide (VMS) deposit, within the Triple 7 mine, Flin Flon, Manitoba, Canada. The microorganism was isolated from saline groundwater emanating from boreholes at that depth, which contained a small microbial community consisting of only two organisms. To examine biogeochemical trace metal cycling in this deep subsurface setting, incubation experiments were carried out with the Marinobacter isolate and mineralized (metal-containing ore) material in batch and column flow-through settings. The activity of the Marinobacter isolate resulted in an increase in the mobilization of major elements (Fe, S) and trace metals (Cu, Zn) from the solid ore material. These results indicate that Fe-oxidation may be an important biogeochemical process in the deep subsurface, which affects the mobiliz...
Geobiology, 2014
Ferruginous Lake Matano, Indonesia hosts one of the deepest anoxygenic photosynthetic communities... more Ferruginous Lake Matano, Indonesia hosts one of the deepest anoxygenic photosynthetic communities on Earth. This community is dominated by low-light adapted, BChl e-synthesizing green sulfur bacteria (GSB), which comprise ~25% of the microbial community immediately below the oxic-anoxic boundary (OAB; 115-120 m in 2010). The size of this community is dependent on the mixing regime within the lake and the depth of the OAB-at ~117 m, the GSB live near their low-light limit. Slow growth and C-fixation rates suggest that the Lake Matano GSB can be supported by sulfide even though it only accumulates to scarcely detectable (low μm to nm) concentrations. A model laboratory strain (Chlorobaculum tepidum) is indeed able to access HS- for oxidation at nm concentrations. Furthermore, the GSB in Lake Matano possess a full complement of S-oxidizing genes. Together, this physiological and genetic information suggests that deep-water GSB can be supported by a S-cycle, even under ferruginous condi...
A Modern Analog Technique (MAT 5 201/31) has been applied to fossil diatom assemblages to provide... more A Modern Analog Technique (MAT 5 201/31) has been applied to fossil diatom assemblages to provide down-core estimates of February sea-surface temperatures (SSTs) and of sea ice duration over the past 220 000 years at 56 ‡40PS, 160 ‡14PE. At the core location, sea ice progression lagged the SST drop by V1 ka at interglacial^glacial transitions, and sea ice retreat was almost synchronous to the SST increase at glacial^interglacial terminations. Sea ice increased continuously during glacial periods to reach its maximum extent at the end of glacial times, although SSTs were almost constant during glacials. This indicates that SSTs are the major parameter determining the advance and retreat of sea ice at transitions, but that the sea ice advance during glacial conditions may be related to positive feedbacks of the ice on albedo, air temperature and meridional wind stress. The strong correlation (r = 0.75) between sea ice duration at the core location and the Vostok CO 2 record argues for a control of Antarctic sea ice extent on atmospheric CO 2 concentration via the modification of the ocean-to-atmosphere gas balance. ß
Proceedings of the National Academy of Sciences, 2008
Considerable discussion surrounds the potential role of anoxygenic phototrophic Fe(II)-oxidizing ... more Considerable discussion surrounds the potential role of anoxygenic phototrophic Fe(II)-oxidizing bacteria in both the genesis of Banded Iron Formations (BIFs) and early marine productivity. However, anoxygenic phototrophs have yet to be identified in modern environments with comparable chemistry and physical structure to the ancient Fe(II)-rich (ferruginous) oceans from which BIFs deposited. Lake Matano, Indonesia, the eighth deepest lake in the world, is such an environment. Here, sulfate is scarce (<20 mol⅐liter ؊1 ), and it is completely removed by sulfate reduction within the deep, Fe(II)-rich chemocline. The sulfide produced is efficiently scavenged by the formation and precipitation of FeS, thereby maintaining very low sulfide concentrations within the chemocline and the deep ferruginous bottom waters. Low productivity in the surface water allows sunlight to penetrate to the >100-m-deep chemocline. Within this sulfide-poor, Fe(II)-rich, illuminated chemocline, we find a populous assemblage of anoxygenic phototrophic green sulfur bacteria (GSB). These GSB represent a large component of the Lake Matano phototrophic community, and bacteriochlorophyll e, a pigment produced by low-light-adapted GSB, is nearly as abundant as chlorophyll a in the lake's euphotic surface waters. The dearth of sulfide in the chemocline requires that the GSB are sustained by phototrophic oxidation of Fe(II), which is in abundant supply. By analogy, we propose that similar microbial communities, including populations of sulfate reducers and photoferrotrophic GSB, likely populated the chemoclines of ancient ferruginous oceans, driving the genesis of BIFs and fueling early marine productivity.
Marine Micropaleontology, 2004
A Modern Analog Technique (MAT 5 201/31) has been applied to fossil diatom assemblages to provide... more A Modern Analog Technique (MAT 5 201/31) has been applied to fossil diatom assemblages to provide down-core estimates of February sea-surface temperatures (SSTs) and of sea ice duration over the past 220 000 years at 56 ‡40PS, 160 ‡14PE. At the core location, sea ice progression lagged the SST drop by V1 ka at interglacial^glacial transitions, and sea ice retreat was almost synchronous to the SST increase at glacial^interglacial terminations. Sea ice increased continuously during glacial periods to reach its maximum extent at the end of glacial times, although SSTs were almost constant during glacials. This indicates that SSTs are the major parameter determining the advance and retreat of sea ice at transitions, but that the sea ice advance during glacial conditions may be related to positive feedbacks of the ice on albedo, air temperature and meridional wind stress. The strong correlation (r = 0.75) between sea ice duration at the core location and the Vostok CO 2 record argues for a control of Antarctic sea ice extent on atmospheric CO 2 concentration via the modification of the ocean-to-atmosphere gas balance. ß
![Research paper thumbnail of Erratum to “Room-temperature magnetic properties of ferrihydrite: A potential magnetic remanence carrier?”[Earth Planet. Sci. Lett. 236 (2005) 856–870]](https://attachments.academia-assets.com/42477743/thumbnails/1.jpg)
](Earth and Planetary Science Letters, 2005
Earth and Planetary Science Letters, 2005
Room-temperature magnetic techniques are rapidly becoming an important tool for the discriminatio... more Room-temperature magnetic techniques are rapidly becoming an important tool for the discrimination and quantification of minerals in a broad range of geological, environmental and extraterrestrial materials. The utility of these techniques is dependent upon the comprehensiveness and consistency of data describing the magnetic characteristics of individual mineral phases. In this regard, there is a paucity of data pertaining to the magnetic properties of ferrihydrite. This paper reports room-temperature magnetic properties of ferrihydrite that are relevant to studies concerning geological and environmental materials under surficial conditions. Synthetic ferrihydrite, both 2-and 6-line varieties, exhibit a susceptibility of~2.7 Â 10 À 6 m 3 kg À 1 at 298 K. Significantly, at 298 K synthetic ferrihydrite exhibits a saturation remanent magnetization (r RS ) of 1.19 and 0.86 Â 10 À 4 A m 2 kg À 1 for 2-and 6-line ferrihydrite, respectively. These observations suggest that ferrihydrite is a potential magnetic remanence carrier under ambient environmental conditions. Measurements of mineral mixtures show that magnetic techniques can discriminate between ferrihydrite and goethite at low concentrations. Natural samples of ferrihydrite exhibit magnetic properties that are consistent with those obtained for synthetic ferrihydrite. Thus, magnetic techniques using room-temperature magnetic properties may find important applications in studies of the biogeochemical cycling of Fe in dynamic settings. D
Chemical Geology, 2008
Dissimilatory Iron Reduction (DIR) is often implicated in both the remobilization of trace metals... more Dissimilatory Iron Reduction (DIR) is often implicated in both the remobilization of trace metals from sediments, and in the sequestration of trace metals into secondary mineral products. However, the factors controlling the extent of dissolution versus solid-phase redistribution have been elusive. We have made the following observations after incubating pure and Pb-substituted Fe (hydr)oxides with Shewanella putrefaciens 200R over 1200 h: 1) Pb substitution at a molar ratio of Pb:Fe = 5.19 × 10 − 4 inhibited Fe reduction; 2) the presence of Pb enhanced Fe dissolution and inhibited biologically induced magnetite formation; 3) Pb dissolved incongruently with Fe and accumulated to 190 nmol l − 1 in the aqueous phase; and 4) the residual solid-phase Pb was partitioned between an unresolved poorly reducible phase and weak acid extractable (surface sorbed or carbonate) phases. The presence of trace metals and Pb in soils and sediments could partially explain the apparent absence of magnetite in many Fe-reducing environments and its paucity in the sedimentary record. Organic matter degradation rates in Pb contaminated ecosystems may be reduced because of the inhibition of DIR by Pb. We assert that Pb should be largely immobile under Fe-reducing conditions due to its incorporation into refractory secondary minerals.
Biogeosciences, 2011
This study explores Mn biogeochemistry in a stratified, ferruginous lake, a modern analogue to fe... more This study explores Mn biogeochemistry in a stratified, ferruginous lake, a modern analogue to ferruginous oceans. Intense Mn cycling occurs in the chemocline where Mn is recycled at least 15 times before sedimentation. The product of biologically catalyzed Mn oxidation in Lake Matano is birnessite. Although there is evidence for abiotic Mn reduction with Fe(II), Mn reduction likely occurs through
ABSTRACT In surface and subsurface environments native microbial communities influence the mobili... more ABSTRACT In surface and subsurface environments native microbial communities influence the mobility and distribution of trace elements. Understanding how microbial metabolic activities and cell surfaces influnce the behavior of trace elements is integral to successful remediation programs in modern systems and the correct interpretation of diagenetic signatures preserved in sedimentary rocks. Ferric iron oxides and oxyhydroxides are ubiquitous in surficial environments where they often control the cycling of heavy metals. It is well established that the use of Fe(III) as a terminal electron acceptor by dissimilatory iron reducing bacteria (DIRB), causes the reductive dissolution of iron oxide minerals and leads to the release of Fe2+ and the oxidation of organic matter. In this study we examine the fate of Pb associated with Fe oxyhydroxides during DIR. We synthesized Pb-bearing and Pb-free Fe oxyhydroxides and incubated them anaerobically with Shewanella putrefaciens 200R and lactate as the sole electron donor. The extent of Fe reduction was determined using 0.5 mol L-1 HCl extractions and was equivalent in incubations containing either Pb-bearing or Pb-free Fe oxyhydroxides. During the 2 month experiment aqueous Pb concentrations increased with progressive Fe reduction from 1 nmol L-1 to >150 nmol L-1. Aqueous Fe(II) concentrations in incubations with Pb-bearing Fe oxyhydroxides were significantly higher than those in reactors containing Pb-free Fe oxyhydroxides . This suggests that the secondary mineralization is different in Pb-bearing systems and results in less incorporation of Fe(II) into the solid phase. This was confirmed using x- ray diffraction analysis and a suite of sequential extractions. Intriguingly our sequential extraction data reveal a highly refractory phase (extractable only by 6N HCl), which formed during the DIR in the incubations with Pb- bearing Fe oxyhydroxides. This refractory phase is responsible for the sequestration of approximately 80% of the total solid Fe and between 20 and 30% of the solid Pb. Although bacterial Fe reduction induces the remobilization of some Pb associated with Fe oxyhydroxides, more Pb is sequestered into an unknown refractory, solid phase. The identity of this phase remains unknown and should be elucidated in future studies.
Lakes are test tubes of oceans, Jun 1, 2008
6.1 Abstract Organic carbon is oxidized by microorganisms that use a series of terminal electron ... more 6.1 Abstract Organic carbon is oxidized by microorganisms that use a series of terminal electron acceptors defined by free energy yield and availability. Methanogenesis by highly specialized Archea occurs once the availability of these electron acceptors is diminished beyond a thermodynamic threshold which renders the energy yield to low to sustain microbial respiration. In the deep waters of the persistently stratified and Fe-rich Lake Matano, Indonesia, authigenic organic matter is largely degraded through ...
Geobiology, 2011
In Lake Matano, Indonesia, the world's largest known ferruginous basin, more than 50% of authigen... more In Lake Matano, Indonesia, the world's largest known ferruginous basin, more than 50% of authigenic organic matter is degraded through methanogenesis, despite high abundances of Fe (hydr)oxides in the lake sediments. Biogenic CH 4 accumulates to high concentrations (up to 1.4 mmol L )1 ) in the anoxic bottom waters, which contain a total of 7.4 · 10 5 tons of CH 4 . Profiles of dissolved inorganic carbon (RCO 2 ) and carbon isotopes (d 13 C) show that CH 4 is oxidized in the vicinity of the persistent pycnocline and that some of this CH 4 is likely oxidized anaerobically. The dearth of NO 3 ) and SO 4 2) in Lake Matano waters suggests that anaerobic methane oxidation may be coupled to the reduction of Fe (and ⁄ or Mn) (hydr)oxides. Thermodynamic considerations reveal that CH 4 oxidation coupled to Fe(III) or Mn(III ⁄ IV) reduction would yield sufficient free energy to support microbial growth at the substrate levels present in Lake Matano. Flux calculations imply that Fe and Mn must be recycled several times directly within the water column to balance the upward flux of CH 4 . 16S gene cloning identified methanogens in the anoxic water column, and these methanogens belong to groups capable of both acetoclastic and hydrogenotrophic methanogenesis. We find that methane is important in C cycling, even in this very Fe-rich environment. Such Fe-rich environments are rare on Earth today, but they are analogous to conditions in the ferruginous oceans thought to prevail during much of the Archean Eon. By analogy, methanogens and methanotrophs could have formed an important part of the Archean Ocean ecosystem.
Seafloor hydrothermal activity at mid-ocean ridges (MOR) is one of the fundamental processes cont... more Seafloor hydrothermal activity at mid-ocean ridges (MOR) is one of the fundamental processes controlling the exchange of heat and chemical species between seawater and ocean rocks and there is increasing evidence that off-axis vent fields may significantly affect biogeochemical cycles and oceanic elemental budgets. Active hydrothermal venting associated with volcanic seamounts has been well documented, in particular at Loihi Seamount, Hawaii and Vailulu`u Seamount, Samoa, but the degree to which diffuse venting and subsurface processes occur at hot-spot volcanoes is not known. Loihi Seamount offers at least three distinct microbial habitats that support a biogeochemically-significant class of microorganisms – iron oxidizing bacteria. These habitats include sites of warm, iron-rich hydrothermal vents at the volcano’s summit (1,000m depth), sites of cold, ultra-diffuse iron-rich hydrothermal fluids at 5,000m, and bare basalts with no localized active hydrothermal fluids. Here, we prov...
Geochemistry Exploration Environment Analysis
A microorganism of the Marinobacter genus capable of Fe-oxidation at near-neutral pH, both in the... more A microorganism of the Marinobacter genus capable of Fe-oxidation at near-neutral pH, both in the presence and absence of oxygen, was found at a depth of 1.4 km in proximity to a Cu-Zn Volcanogenic Massive Sulphide (VMS) deposit, within the Triple 7 mine, Flin Flon, Manitoba, Canada. The microorganism was isolated from saline groundwater emanating from boreholes at that depth, which contained a small microbial community consisting of only two organisms. To examine biogeochemical trace metal cycling in this deep subsurface setting, incubation experiments were carried out with the Marinobacter isolate and mineralized (metal-containing ore) material in batch and column flow-through settings. The activity of the Marinobacter isolate resulted in an increase in the mobilization of major elements (Fe, S) and trace metals (Cu, Zn) from the solid ore material. These results indicate that Fe-oxidation may be an important biogeochemical process in the deep subsurface, which affects the mobiliz...
Geobiology, 2014
Ferruginous Lake Matano, Indonesia hosts one of the deepest anoxygenic photosynthetic communities... more Ferruginous Lake Matano, Indonesia hosts one of the deepest anoxygenic photosynthetic communities on Earth. This community is dominated by low-light adapted, BChl e-synthesizing green sulfur bacteria (GSB), which comprise ~25% of the microbial community immediately below the oxic-anoxic boundary (OAB; 115-120 m in 2010). The size of this community is dependent on the mixing regime within the lake and the depth of the OAB-at ~117 m, the GSB live near their low-light limit. Slow growth and C-fixation rates suggest that the Lake Matano GSB can be supported by sulfide even though it only accumulates to scarcely detectable (low μm to nm) concentrations. A model laboratory strain (Chlorobaculum tepidum) is indeed able to access HS- for oxidation at nm concentrations. Furthermore, the GSB in Lake Matano possess a full complement of S-oxidizing genes. Together, this physiological and genetic information suggests that deep-water GSB can be supported by a S-cycle, even under ferruginous condi...
A Modern Analog Technique (MAT 5 201/31) has been applied to fossil diatom assemblages to provide... more A Modern Analog Technique (MAT 5 201/31) has been applied to fossil diatom assemblages to provide down-core estimates of February sea-surface temperatures (SSTs) and of sea ice duration over the past 220 000 years at 56 ‡40PS, 160 ‡14PE. At the core location, sea ice progression lagged the SST drop by V1 ka at interglacial^glacial transitions, and sea ice retreat was almost synchronous to the SST increase at glacial^interglacial terminations. Sea ice increased continuously during glacial periods to reach its maximum extent at the end of glacial times, although SSTs were almost constant during glacials. This indicates that SSTs are the major parameter determining the advance and retreat of sea ice at transitions, but that the sea ice advance during glacial conditions may be related to positive feedbacks of the ice on albedo, air temperature and meridional wind stress. The strong correlation (r = 0.75) between sea ice duration at the core location and the Vostok CO 2 record argues for a control of Antarctic sea ice extent on atmospheric CO 2 concentration via the modification of the ocean-to-atmosphere gas balance. ß
Proceedings of the National Academy of Sciences, 2008
Considerable discussion surrounds the potential role of anoxygenic phototrophic Fe(II)-oxidizing ... more Considerable discussion surrounds the potential role of anoxygenic phototrophic Fe(II)-oxidizing bacteria in both the genesis of Banded Iron Formations (BIFs) and early marine productivity. However, anoxygenic phototrophs have yet to be identified in modern environments with comparable chemistry and physical structure to the ancient Fe(II)-rich (ferruginous) oceans from which BIFs deposited. Lake Matano, Indonesia, the eighth deepest lake in the world, is such an environment. Here, sulfate is scarce (<20 mol⅐liter ؊1 ), and it is completely removed by sulfate reduction within the deep, Fe(II)-rich chemocline. The sulfide produced is efficiently scavenged by the formation and precipitation of FeS, thereby maintaining very low sulfide concentrations within the chemocline and the deep ferruginous bottom waters. Low productivity in the surface water allows sunlight to penetrate to the >100-m-deep chemocline. Within this sulfide-poor, Fe(II)-rich, illuminated chemocline, we find a populous assemblage of anoxygenic phototrophic green sulfur bacteria (GSB). These GSB represent a large component of the Lake Matano phototrophic community, and bacteriochlorophyll e, a pigment produced by low-light-adapted GSB, is nearly as abundant as chlorophyll a in the lake's euphotic surface waters. The dearth of sulfide in the chemocline requires that the GSB are sustained by phototrophic oxidation of Fe(II), which is in abundant supply. By analogy, we propose that similar microbial communities, including populations of sulfate reducers and photoferrotrophic GSB, likely populated the chemoclines of ancient ferruginous oceans, driving the genesis of BIFs and fueling early marine productivity.
Marine Micropaleontology, 2004
A Modern Analog Technique (MAT 5 201/31) has been applied to fossil diatom assemblages to provide... more A Modern Analog Technique (MAT 5 201/31) has been applied to fossil diatom assemblages to provide down-core estimates of February sea-surface temperatures (SSTs) and of sea ice duration over the past 220 000 years at 56 ‡40PS, 160 ‡14PE. At the core location, sea ice progression lagged the SST drop by V1 ka at interglacial^glacial transitions, and sea ice retreat was almost synchronous to the SST increase at glacial^interglacial terminations. Sea ice increased continuously during glacial periods to reach its maximum extent at the end of glacial times, although SSTs were almost constant during glacials. This indicates that SSTs are the major parameter determining the advance and retreat of sea ice at transitions, but that the sea ice advance during glacial conditions may be related to positive feedbacks of the ice on albedo, air temperature and meridional wind stress. The strong correlation (r = 0.75) between sea ice duration at the core location and the Vostok CO 2 record argues for a control of Antarctic sea ice extent on atmospheric CO 2 concentration via the modification of the ocean-to-atmosphere gas balance. ß
Earth and Planetary Science Letters, 2005
Earth and Planetary Science Letters, 2005
Room-temperature magnetic techniques are rapidly becoming an important tool for the discriminatio... more Room-temperature magnetic techniques are rapidly becoming an important tool for the discrimination and quantification of minerals in a broad range of geological, environmental and extraterrestrial materials. The utility of these techniques is dependent upon the comprehensiveness and consistency of data describing the magnetic characteristics of individual mineral phases. In this regard, there is a paucity of data pertaining to the magnetic properties of ferrihydrite. This paper reports room-temperature magnetic properties of ferrihydrite that are relevant to studies concerning geological and environmental materials under surficial conditions. Synthetic ferrihydrite, both 2-and 6-line varieties, exhibit a susceptibility of~2.7 Â 10 À 6 m 3 kg À 1 at 298 K. Significantly, at 298 K synthetic ferrihydrite exhibits a saturation remanent magnetization (r RS ) of 1.19 and 0.86 Â 10 À 4 A m 2 kg À 1 for 2-and 6-line ferrihydrite, respectively. These observations suggest that ferrihydrite is a potential magnetic remanence carrier under ambient environmental conditions. Measurements of mineral mixtures show that magnetic techniques can discriminate between ferrihydrite and goethite at low concentrations. Natural samples of ferrihydrite exhibit magnetic properties that are consistent with those obtained for synthetic ferrihydrite. Thus, magnetic techniques using room-temperature magnetic properties may find important applications in studies of the biogeochemical cycling of Fe in dynamic settings. D
Chemical Geology, 2008
Dissimilatory Iron Reduction (DIR) is often implicated in both the remobilization of trace metals... more Dissimilatory Iron Reduction (DIR) is often implicated in both the remobilization of trace metals from sediments, and in the sequestration of trace metals into secondary mineral products. However, the factors controlling the extent of dissolution versus solid-phase redistribution have been elusive. We have made the following observations after incubating pure and Pb-substituted Fe (hydr)oxides with Shewanella putrefaciens 200R over 1200 h: 1) Pb substitution at a molar ratio of Pb:Fe = 5.19 × 10 − 4 inhibited Fe reduction; 2) the presence of Pb enhanced Fe dissolution and inhibited biologically induced magnetite formation; 3) Pb dissolved incongruently with Fe and accumulated to 190 nmol l − 1 in the aqueous phase; and 4) the residual solid-phase Pb was partitioned between an unresolved poorly reducible phase and weak acid extractable (surface sorbed or carbonate) phases. The presence of trace metals and Pb in soils and sediments could partially explain the apparent absence of magnetite in many Fe-reducing environments and its paucity in the sedimentary record. Organic matter degradation rates in Pb contaminated ecosystems may be reduced because of the inhibition of DIR by Pb. We assert that Pb should be largely immobile under Fe-reducing conditions due to its incorporation into refractory secondary minerals.
Biogeosciences, 2011
This study explores Mn biogeochemistry in a stratified, ferruginous lake, a modern analogue to fe... more This study explores Mn biogeochemistry in a stratified, ferruginous lake, a modern analogue to ferruginous oceans. Intense Mn cycling occurs in the chemocline where Mn is recycled at least 15 times before sedimentation. The product of biologically catalyzed Mn oxidation in Lake Matano is birnessite. Although there is evidence for abiotic Mn reduction with Fe(II), Mn reduction likely occurs through
ABSTRACT In surface and subsurface environments native microbial communities influence the mobili... more ABSTRACT In surface and subsurface environments native microbial communities influence the mobility and distribution of trace elements. Understanding how microbial metabolic activities and cell surfaces influnce the behavior of trace elements is integral to successful remediation programs in modern systems and the correct interpretation of diagenetic signatures preserved in sedimentary rocks. Ferric iron oxides and oxyhydroxides are ubiquitous in surficial environments where they often control the cycling of heavy metals. It is well established that the use of Fe(III) as a terminal electron acceptor by dissimilatory iron reducing bacteria (DIRB), causes the reductive dissolution of iron oxide minerals and leads to the release of Fe2+ and the oxidation of organic matter. In this study we examine the fate of Pb associated with Fe oxyhydroxides during DIR. We synthesized Pb-bearing and Pb-free Fe oxyhydroxides and incubated them anaerobically with Shewanella putrefaciens 200R and lactate as the sole electron donor. The extent of Fe reduction was determined using 0.5 mol L-1 HCl extractions and was equivalent in incubations containing either Pb-bearing or Pb-free Fe oxyhydroxides. During the 2 month experiment aqueous Pb concentrations increased with progressive Fe reduction from 1 nmol L-1 to >150 nmol L-1. Aqueous Fe(II) concentrations in incubations with Pb-bearing Fe oxyhydroxides were significantly higher than those in reactors containing Pb-free Fe oxyhydroxides . This suggests that the secondary mineralization is different in Pb-bearing systems and results in less incorporation of Fe(II) into the solid phase. This was confirmed using x- ray diffraction analysis and a suite of sequential extractions. Intriguingly our sequential extraction data reveal a highly refractory phase (extractable only by 6N HCl), which formed during the DIR in the incubations with Pb- bearing Fe oxyhydroxides. This refractory phase is responsible for the sequestration of approximately 80% of the total solid Fe and between 20 and 30% of the solid Pb. Although bacterial Fe reduction induces the remobilization of some Pb associated with Fe oxyhydroxides, more Pb is sequestered into an unknown refractory, solid phase. The identity of this phase remains unknown and should be elucidated in future studies.
Lakes are test tubes of oceans, Jun 1, 2008
6.1 Abstract Organic carbon is oxidized by microorganisms that use a series of terminal electron ... more 6.1 Abstract Organic carbon is oxidized by microorganisms that use a series of terminal electron acceptors defined by free energy yield and availability. Methanogenesis by highly specialized Archea occurs once the availability of these electron acceptors is diminished beyond a thermodynamic threshold which renders the energy yield to low to sustain microbial respiration. In the deep waters of the persistently stratified and Fe-rich Lake Matano, Indonesia, authigenic organic matter is largely degraded through ...
Geobiology, 2011
In Lake Matano, Indonesia, the world's largest known ferruginous basin, more than 50% of authigen... more In Lake Matano, Indonesia, the world's largest known ferruginous basin, more than 50% of authigenic organic matter is degraded through methanogenesis, despite high abundances of Fe (hydr)oxides in the lake sediments. Biogenic CH 4 accumulates to high concentrations (up to 1.4 mmol L )1 ) in the anoxic bottom waters, which contain a total of 7.4 · 10 5 tons of CH 4 . Profiles of dissolved inorganic carbon (RCO 2 ) and carbon isotopes (d 13 C) show that CH 4 is oxidized in the vicinity of the persistent pycnocline and that some of this CH 4 is likely oxidized anaerobically. The dearth of NO 3 ) and SO 4 2) in Lake Matano waters suggests that anaerobic methane oxidation may be coupled to the reduction of Fe (and ⁄ or Mn) (hydr)oxides. Thermodynamic considerations reveal that CH 4 oxidation coupled to Fe(III) or Mn(III ⁄ IV) reduction would yield sufficient free energy to support microbial growth at the substrate levels present in Lake Matano. Flux calculations imply that Fe and Mn must be recycled several times directly within the water column to balance the upward flux of CH 4 . 16S gene cloning identified methanogens in the anoxic water column, and these methanogens belong to groups capable of both acetoclastic and hydrogenotrophic methanogenesis. We find that methane is important in C cycling, even in this very Fe-rich environment. Such Fe-rich environments are rare on Earth today, but they are analogous to conditions in the ferruginous oceans thought to prevail during much of the Archean Eon. By analogy, methanogens and methanotrophs could have formed an important part of the Archean Ocean ecosystem.