Publications by authors named "Kurt O Konhauser"

38 Publications

Reusable magnetite nanoparticles-biochar composites for the efficient removal of chromate from water.

Sci Rep 2020 11 4;10(1):19007. Epub 2020 Nov 4.

Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Alberta, T6G 2E3, Canada.

Biochar (BC) and magnetite (FeO) nanoparticles (MNP) have both received considerable recent attention in part due to their potential use in water treatment. While both are effective independently in the removal of a range of anionic metals from aqueous solution, the efficacy of these materials is reduced considerably at neutral pH due to decreased metal adsorption and MNP aggregation. In addition to synthetic metal oxide-biochar composites for use in treatment and remediation technologies, aggregates may also occur in nature when pyrolytic carbon is deposited in soils. In this study, we tested whether magnetite synthesized in the presence of biochar leads to increased removal efficiency of hexavalent chromium, Cr(VI), at the mildly acidic to neutral pH values characteristic of most natural and contaminated aqueous environments. To do so, magnetite nanoparticles and biochar produced from ground willow were synthesized to form composites (MNP-BC). Batch studies showed that MNP-BC markedly enhanced both adsorption and reduction of Cr(VI) from aqueous solution at acidic to neutral pH as compared to MNP and BC separately, suggesting a strong synergetic effect of hybridizing FeO with BC. Mechanistically, the Cr(VI) removal processes occurred through both adsorption and intraparticle diffusion followed by reduction to Cr(III). Synchrotron-based X-ray absorption spectroscopy analyses confirmed that Cr(VI) was reduced at the surface of MNP-BC, with electrons derived directly from both biochar and magnetite at low pH, while at near-neutral pH, biochar increased Cr(VI) reduction by inhibiting MNP aggregation. Extended X-ray absorption fine structure fitting results confirmed that the Cr(III) precipitates consist of Cr(OH) and chromite (CrFeO) nanoparticles. Our results demonstrate that MNP-BC composites have great potential as a material for the treatment of chromate-containing aqueous solutions across a wide range of pH values, and provide information valuable broadly relevant to soils and sediments that contain biochar.
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http://dx.doi.org/10.1038/s41598-020-75924-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7642354PMC
November 2020

Shedding light on manganese cycling in the early oceans.

Proc Natl Acad Sci U S A 2020 10 12;117(42):25960-25962. Epub 2020 Oct 12.

Department of Earth & Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada.

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http://dx.doi.org/10.1073/pnas.2016447117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7584896PMC
October 2020

Clay minerals as a source of cadmium to estuaries.

Sci Rep 2020 06 26;10(1):10417. Epub 2020 Jun 26.

Department of Earth & Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada.

Given the high surface reactivity of clay minerals, it is assumed that flocculation will lead to metal accumulation in marginal marine settings. However, the degree of metal sorption to clays is impacted by solution pH and ionic strength, and it remains unknown whether riverine clays indeed serve as a metal sink once they encounter seawater where pH and ionic strength markedly increase. Here, we conducted cadmium (Cd) adsorption experiments to three types of common clay minerals - kaolinite, illite and montmorillonite. We found that 20-30% of Cd from illite and montmorillonite surfaces were desorbed when transitioning from freshwater to seawater pH and ionic strength conditions, while kaolinite showed no discernible differences. Synchrotron X-ray adsorption spectroscopy confirmed that Cd release corresponded to a change in bonding from outer- to inner-sphere complexes when clays encountered seawater pH and ionic strength conditions. If other trace nutrients (such as Cu, Zn, Co) adsorbed onto riverine clay minerals behave in a similar manner to Cd, we speculate that their desorption in marginal marine settings should exert a significant impact on the productivity of the biosphere.
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http://dx.doi.org/10.1038/s41598-020-67279-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7320025PMC
June 2020

Competitive adsorption of heavy metals by anaerobic ammonium-oxidizing (anammox) consortia.

Chemosphere 2020 Nov 6;258:127289. Epub 2020 Jun 6.

State Key Laboratory of Water and Sediment Sciences (Ministry of Education), College of Environmental Science & Engineering, Peking University, Beijing, 100871, China. Electronic address:

Anammox-based processes and microbial consortia have drawn extensive attention for their use in high-efficiency wastewater treatment technologies. Metals substantially affect the activity of anammox consortia and the quality of wastewater treatment plant effluent. Here, we explored the role of anammox consortia in terms of metals complexation in both single and multi-metal systems. Adsorption edges of single metal cations indicate that the adsorption preference was in the order: Pb(II) > Cd(II) > Cr(VI). A competitive effect was observed in multi-metal cations systems, with Pb(II) being preferably adsorbed and the degree of adsorption somewhat reduced in the presence of either Cd(II) or Cr(VI), while Cd(II) and Cr(VI) were easily exchanged and substituted by other metals. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) further suggest that the adsorption of Pb(II) and Cd(II) are as inner-sphere ion-exchange mechanisms, while Cr(VI) adsorption is mainly by outer-sphere complexation. Density functional theory (DFT) calculations highlight that Cd(II) and Pb(II) have different binding sites compared to Cr(VI), and the order of binding energy (E) of three metal cations were Pb(II) > Cd(II) > Cr(VI). These calculations support the adsorption data in that Pb forms more stable complexes with anammox bacterial surface ligands. Surface complexation modelling (SCM) further predicted both the sorption of single metal cations and competitive adsorption of the three metals to anammox consortia, the exception being Cd at higher loadings. The results of this study highlight the potential role of anammox consortia in removing metal cations from wastewater in treatment systems.
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http://dx.doi.org/10.1016/j.chemosphere.2020.127289DOI Listing
November 2020

Photoferrotrophy, deposition of banded iron formations, and methane production in Archean oceans.

Sci Adv 2019 11 27;5(11):eaav2869. Epub 2019 Nov 27.

Departments of Microbiology and Immunology and Earth, Ocean, and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, Canada.

Banded iron formation (BIF) deposition was the likely result of oxidation of ferrous iron in seawater by either oxygenic photosynthesis or iron-dependent anoxygenic photosynthesis-photoferrotrophy. BIF deposition, however, remains enigmatic because the photosynthetic biomass produced during iron oxidation is conspicuously absent from BIFs. We have addressed this enigma through experiments with photosynthetic bacteria and modeling of biogeochemical cycling in the Archean oceans. Our experiments reveal that, in the presence of silica, photoferrotroph cell surfaces repel iron (oxyhydr)oxides. In silica-rich Precambrian seawater, this repulsion would separate biomass from ferric iron and would lead to large-scale deposition of BIFs lean in organic matter. Excess biomass not deposited with BIF would have deposited in coastal sediments, formed organic-rich shales, and fueled microbial methanogenesis. As a result, the deposition of BIFs by photoferrotrophs would have contributed fluxes of methane to the atmosphere and thus helped to stabilize Earth's climate under a dim early Sun.
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http://dx.doi.org/10.1126/sciadv.aav2869DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6881150PMC
November 2019

How did the evolution of oxygenic photosynthesis influence the temporal and spatial development of the microbial iron cycle on ancient Earth?

Free Radic Biol Med 2019 08 16;140:154-166. Epub 2019 Jul 16.

Geomicrobiology, Center for Applied Geosciences, University of Tübingen, 72076, Tübingen, Germany. Electronic address:

Iron is the most abundant redox active metal on Earth and thus provides one of the most important records of the redox state of Earth's ancient atmosphere, oceans and landmasses over geological time. The most dramatic shifts in the Earth's iron cycle occurred during the oxidation of Earth's atmosphere. However, tracking the spatial and temporal development of the iron cycle is complicated by uncertainties about both the timing and location of the evolution of oxygenic photosynthesis, and by the myriad of microbial processes that act to cycle iron between redox states. In this review, we piece together the geological evidence to assess where and when oxygenic photosynthesis likely evolved, and attempt to evaluate the influence of this innovation on the microbial iron cycle.
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http://dx.doi.org/10.1016/j.freeradbiomed.2019.07.014DOI Listing
August 2019

Potential of asphalt concrete as a source of trace metals.

Environ Geochem Health 2020 Feb 15;42(2):397-405. Epub 2019 Jul 15.

Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, T6G 2E3, Canada.

Asphalt concrete is one of the most important building materials in the modern world, but the leaching potential of metals from this composite material to the environment is poorly understood. In this study, metals leaching from four hot-mix asphalt samples were analyzed: two fresh samples of low-traffic and high-traffic composition and their weathered equivalents collected from roads in the city of Edmonton, Alberta, Canada. A sequential extraction, based on the Community Bureau of Reference method, was applied to study the speciation and potential mobility of metals and metalloids in those samples. Major trace metals identified in all four samples were Mn, P, Ba, Sr, Zn, V, and Ni, with the highest metals concentrations generally found in weathered asphalt concrete. Of the major trace metals, P, Mn, Sr, and Zn were relatively mobile, having large portions of their total concentrations in the exchangeable/acid-soluble and reducible fractions. When considering the most mobile fraction (exchangeable/acid soluble) and using Canada as a model country, up to 180 t P, 440 t Mn, 50 t Ba, 36 t Sr, 11 t Zn, and 0.11-3.2 t of other metals and metalloids (including Cr, Ni, Cu, As, and Pb) could potentially leach from the top layer of Canada's total of paved public roads. To place these amounts into perspective, they were estimated to make up to 22‰ of Canada's annual release numbers into soil, water and air for these same metals and metalloids. However, they are concentrated in a small area around roads and highways, creating the potential for localized soil and groundwater contamination.
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http://dx.doi.org/10.1007/s10653-019-00370-yDOI Listing
February 2020

Author Correction: Microbially induced potassium enrichment in Paleoproterozoic shales and implications for reverse weathering on early Earth.

Nat Commun 2019 Jun 27;10(1):2922. Epub 2019 Jun 27.

Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, T6G 2E3, Canada.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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http://dx.doi.org/10.1038/s41467-019-11042-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6597704PMC
June 2019

Microbially induced potassium enrichment in Paleoproterozoic shales and implications for reverse weathering on early Earth.

Nat Commun 2019 06 17;10(1):2670. Epub 2019 Jun 17.

Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada.

Illitisation requires potassium incorporation into a smectite precursor, a process akin to reverse weathering. However, it remains unclear whether microbes facilitate K uptake to the sediments and whether illitisation was important in the geological past. The 2.1 billion-year-old Francevillian Series of Gabon has been shown to host mat-related structures (MRS) and, in this regard, these rocks offer a unique opportunity to test whether ancient microbes induced illitisation. Here, we show high K content confined to illite particles that are abundant in the facies bearing MRS, but not in the host sandstone and black shale. This observation suggests that microbial biofilms trapped K from the seawater and released it into the pore-waters during respiration, resulting in illitisation. The K-rich illite developed exclusively in the fossilized MRS thus provides a new biosignature for metasediments derived from K-feldspar-depleted rocks that were abundant crustal components on ancient Earth.
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http://dx.doi.org/10.1038/s41467-019-10620-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6572813PMC
June 2019

Cell surface characterization and trace metal adsorptive properties of anaerobic ammonium-oxidizing (anammox) consortia.

Chemosphere 2019 Apr 6;221:11-20. Epub 2019 Jan 6.

Key Lab of Water & Sediment Sciences (Ministry of Education), College of Environmental Science & Engineering, Peking University, Beijing 100871, China. Electronic address:

Interactions between metals and anaerobic ammonium oxidizing consortia substantially affect the quality of wastewater treatment plant effluent. In this study, we conducted acid-base titrations to ascertain the surface reactivity and proton adsorptive capacity of anammox consortia. A combination of titration data modeling and infrared spectroscopy suggested the presence of carboxyl, amine, and hydroxyl groups. Cd adsorption experiments demonstrate that 1 g of dry biomass could bind an equivalent of 7.12 × 10 mol/L of Cd. Density functional theory calculations further reveal that carboxyl and hydroxyl groups are able to form stable Cd complexes. Furthermore, considerable carboxyl and hydroxyl groups promote bacterial aggregation, and thus solid-liquid separation. The results of this study highlight the potential role of anammox consortia in adsorbing metal cations, and thus help to improve the understanding of the universally significant contribution of anammox consortia at the detoxification of metal cations in wastewater treatment systems.
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http://dx.doi.org/10.1016/j.chemosphere.2019.01.025DOI Listing
April 2019

Characterization and implications of solids associated with hydraulic fracturing flowback and produced water from the Duvernay Formation, Alberta, Canada.

Environ Sci Process Impacts 2019 Feb;21(2):242-255

School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.

Public concern is heightened around flowback and produced water (FPW) generated by the hydraulic fracturing process. FPW is a complex mix of organic and inorganic solutes derived from both the injected hydraulic fracturing fluid and interactions with the subsurface lithology. Few studies to date have systematically investigated the composition of FPW or its individual components. Here, we provide the first systematic characterization of the composition of the solids associated with FPW by analyzing samples from three wells drilled into the Duvernay Formation in Alberta, Canada. The FPW initially returned to the surface with high total dissolved solids (greater than 170 000 mg L-1) and enriched with Fe(ii), silica, sulfate, barium, and strontium. The solids form two distinct phases once the FPW reached the surface: (1) silica-enriched Fe(iii) oxyhydroxides, and (2) a barite-celestine solid solution. We hypothesize that the precipitation of the amorphous silica-enriched Fe(iii) oxyhydroxide is a two-step process, where first the silica precipitates as a function of the cooling of the FPW from elevated subsurface temperatures to ambient surface temperatures. Next, the silica acts as a template for the precipitation of Fe(iii) oxyhydroxide as the diffusion of oxygen into the subsurface causes oxidation of aqueous Fe(ii). The barite-celestine solid solution precipitates solely as a function of cooling. Elevated dissolved Fe concentrations in FPW and modeled saturation indices from five North American shale plays (Marcellus, Fayetteville, Barnett, Bakken, and Denver-Julesburg) indicate that solids similar to those found in Duvernay FPW, specifically Fe(iii) oxyhydroxides, barite and quartz, are likely to occur. With the solids known to carry a significant portion of FPW's toxicity and organic contaminant load, the development of new treatment technologies, such as the oxidation of the Fe(ii) in FPW, may increase FPW reuse and reduce the environmental risk posed by FPW.
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http://dx.doi.org/10.1039/c8em00404hDOI Listing
February 2019

Mechanisms of the Removal of U(VI) from Aqueous Solution Using Biochar: A Combined Spectroscopic and Modeling Approach.

Environ Sci Technol 2018 11 1;52(22):13057-13067. Epub 2018 Nov 1.

Department of Earth and Atmospheric Sciences , University of Alberta , 1-26 Earth Sciences Building , Alberta , T6G 2E3 , Canada.

Biochar has been touted as a promising sorbent for the removal of inorganic contaminants, such as uranium (U), from water. However, the molecular-scale mechanisms of aqueous U(VI) species adsorption to biochar remain poorly understood. In this study, two approaches, grounded in equilibrium thermodynamics, were employed to investigate the U(VI) adsorption mechanisms: (1) batch U(VI) adsorption experiments coupled to surface complexation modeling (SCM) and (2) isothermal titration calorimetry (ITC), supported by synchrotron-based X-ray absorption spectroscopy (XAS) analyses. The biochars tested have considerable proton buffering capacity and most strongly adsorb U(VI) between approximately pH 4 and 6. FT-IR and XPS studies, along with XAS analyses, show that U(VI) adsorption occurs primarily at the proton-active carboxyl (-COOH) and phenolic hydroxyl (-OH) functional groups on the biochar surface. The SCM approach is able to predict U(VI) adsorption behavior across a wide range of pH and at varying initial U(VI) and biochar concentrations, and U adsorption is strongly influenced by aqueous U(VI) speciation. Supporting ITC measurements indicate that the calculated enthalpies of protonation reactions of the studied biochar, as well as the adsorption of U(VI), are consistent with anionic oxygen ligands and are indicative of both inner- and outer-sphere complexation. Our results provide new insights into the modes of U(VI) adsorption by biochar and more generally improve our understanding of its potential to remove radionuclides from contaminated waters.
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http://dx.doi.org/10.1021/acs.est.8b01715DOI Listing
November 2018

UV radiation limited the expansion of cyanobacteria in early marine photic environments.

Nat Commun 2018 08 6;9(1):3088. Epub 2018 Aug 6.

Earth and Atmospheric Sciences, University of Alberta, Edmonton, T6G 2E3, AB, Canada.

Prior to atmospheric oxygenation, ecosystems were exposed to higher UV radiation fluxes relative to modern surface environments. Iron-silica mineral coatings have been evoked as effective UV radiation shields in early terrestrial settings. Here we test whether similar protection applied to planktonic cyanobacteria within the Archean water column. Based on experiments done under Archean seawater conditions, we report that Fe(III)-Si-rich precipitates absorb up to 70% of incoming UV-C radiation, with a reduction of <20% in photosynthetically active radiation flux. However, we demonstrate that even short periods of UV-C irradiation in the presence of Fe(III)-Si precipitates resulted in high mortality rates, and suggest that these effects would have persisted throughout much of the photic zone. Our findings imply that despite the shielding properties of Fe(III)-Si-rich precipitates in the early water column, UV radiation would continue to limit cyanobacterial expansion and likely had a greater effect on Archean ecosystem structure before the formation of an ozone layer.
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http://dx.doi.org/10.1038/s41467-018-05520-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6079077PMC
August 2018

Authigenesis of biomorphic apatite particles from Benguela upwelling zone sediments off Namibia: The role of organic matter in sedimentary apatite nucleation and growth.

Geobiology 2018 11 30;16(6):640-658. Epub 2018 Jul 30.

Department of Geology, University of Tartu, Tartu, Estonia.

Sedimentary phosphorites comprise a major phosphorus (P) ore, yet their formation remains poorly understood. Extant polyphosphate-metabolizing bacterial communities are known to act as bacterial phosphate-pumps, leading to episodically high dissolved phosphate concentrations in pore waters of organic-rich sediment. These conditions can promote the precipitation of amorphous precursor phases that are quickly converted to apatite-usually in carbonate fluorapatite form [Ca (PO ,CO ) F ]. To assess the mechanisms underpinning the nucleation and growth of sedimentary apatite, we sampled P-rich sediments from the Namibian shelf, a modern environment where phosphogenesis presently occurs. The P-rich fraction of the topmost centimetres of sediment mainly consists of pellets about 50-400 μm in size, which in turn are comprised of micron-sized apatite particles that are often arranged into radial structures with diameters ranging from 2 to 4 μm, and morphologies that range from rod-shapes to dumbbells to spheres that resemble laboratory-grown fluorapatite-gelatin nanocomposites known from double-diffusion experiments in organic matrices. The nucleation and growth of authigenic apatite on the Namibian shelf is likely analogous to these laboratory-produced precipitates, where organic macromolecules play a central role in apatite nucleation and growth. The high density of apatite nucleation sites within the pellets (>10 particles per cm ) suggests precipitation at high pore water phosphate concentrations that have been reported from the Namibian shelf and may be attributed to microbial phosphate pumping. The intimate association of organic material with the apatite could suggest a possible role of biological substrata, such as exopolymeric substances (EPS), in the nucleation of apatite precursors. Importantly, we do not observe any evidence that the apatite particles are actual phosphatized microbes, contradicting some earlier studies. Nevertheless, these results further evidence the potential importance of microbially derived (extracellular) organic matter as a template for phosphatic mineral nucleation in both recent and ancient phosphorites.
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http://dx.doi.org/10.1111/gbi.12309DOI Listing
November 2018

Electron donor-driven bacterial and archaeal community patterns along forest ring edges in Ontario, Canada.

Environ Microbiol Rep 2018 12 9;10(6):663-672. Epub 2018 Sep 9.

University of Alberta, Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, Edmonton, Alberta, T6G 2E3, Canada.

Forest rings are 50-1600 m diameter circular structures found in boreal forests around the globe. They are believed to be chemically reducing chimney features, having an accumulation of reduced species in the middle of the ring and oxidation processes occurring at the ring's edges. It has been suggested that microorganisms could be responsible for charge transfer from the inside to the outside of the ring. To explore this, we focused on the changes in bacterial and archaeal communities in the ring edges of two forest rings, the 'Bean' and the 'Thorn North' ring, in proximity to each other in Ontario, Canada. The drier samples from the methane-sourced Bean ring were characterized by the abundance of bacteria from the classes Deltaproteobacteria and Gemmatimonadetes. Geobacter spp. and methanotrophs, such as Candidatus Methylomirabilis and Methylobacter, were highly abundant in these samples. The Thorn North ring, centred on an H S accumulation in groundwater, had wetter samples and its communities were dominated by the classes Alphaproteobacteria and Anaerolineae. This ring's microbial communities showed an overall higher microbial diversity supported by higher available free energy. For both rings, the species diversity was highest near the borders of the 20-30 m broad ring edges.
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http://dx.doi.org/10.1111/1758-2229.12678DOI Listing
December 2018

Earth's youngest banded iron formation implies ferruginous conditions in the Early Cambrian ocean.

Sci Rep 2018 07 2;8(1):9970. Epub 2018 Jul 2.

Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada.

It has been proposed that anoxic and iron-rich (ferruginous) marine conditions were common through most of Earth history. This view represents a major shift in our understanding of the evolution of marine chemistry. However, thus far, evidence for ferruginous conditions comes predominantly from Fe-speciation data. Given debate over these records, new evidence for Fe-rich marine conditions is a requisite if we are to shift our view regarding evolution of the marine redox landscape. Here we present strong evidence for ferruginous conditions by describing a suite of Fe-rich chemical sedimentary rocks-banded iron formation (BIF)--deposited during the Early Cambrian in western China. Specifically, we provide new U-Pb geochronological data that confirm a depositional age of ca. 527 Ma for this unit, as well as rare earth element (REE) data are consistent with anoxic deposition. Similar to many Algoma-type Precambrian iron formations, these Early Cambrian sediments precipitated in a back-arc rift basin setting, where hydrothermally sourced iron drove the deposition of a BIF-like protolith, the youngest ever reported of regional extent without direct links to volcanogenic massive sulphide (VMS) deposits. Their presence indicates that marine environments were still characterized by chemical- and redox-stratification, thus supporting the view that-despite a dearth of modern marine analogues-ferruginous conditions continued to locally be a feature of early Phanerozoic seawater.
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http://dx.doi.org/10.1038/s41598-018-28187-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6028650PMC
July 2018

Unusual microbial mat-related structural diversity 2.1 billion years ago and implications for the Francevillian biota.

Geobiology 2018 09 20;16(5):476-497. Epub 2018 Jun 20.

Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada.

The 2.1-billion-year-old (Ga) Francevillian series in Gabon hosts some of the oldest reported macroscopic fossils of various sizes and shapes, stimulating new debates on the origin, evolution and organization of early complex life. Here, we document ten representative types of exceptionally well-preserved mat-related structures, comprising "elephant-skin" textures, putative macro-tufted microbial mats, domal buildups, flat pyritized structures, discoidal microbial colonies, horizontal mat growth patterns, wrinkle structures, "kinneyia" structures, linear patterns and nodule-like structures. A combination of petrographic analyses, scanning electron microscopy, Raman spectroscopy and organic elemental analyses of carbon-rich laminae and microtexture, indicate a biological origin for these structures. The observed microtextures encompass oriented grains, floating silt-sized quartz grains, concentrated heavy minerals, randomly oriented clays, wavy-crinkly laminae and pyritized structures. Based on comparisons with modern analogues, as well as an average δ C organic matter (C ) composition of -32.94 ± 1.17‰ (1 standard deviation, SD) with an outlier of -41.26‰, we argue that the mat-related structures contain relicts of multiple carbon pathways including heterotrophic recycling of photosynthetically derived C . Moreover, the relatively close association of the macroscopic fossil assemblages to the microbial mats may imply that microbial communities acted as potential benthic O oases linked to oxyphototrophic cyanobacterial mats and grazing grounds. In addition, the mat's presence likely improved the preservation of the oldest large colonial organisms, as they are known to strongly biostabilize sediments. Our findings highlight the oldest community assemblage of microscopic and macroscopic biota in the aftermath of the "Great Oxidation Event," widening our understanding of biological organization during Earth's middle age.
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http://dx.doi.org/10.1111/gbi.12296DOI Listing
September 2018

A case study for late Archean and Proterozoic biogeochemical iron- and sulphur cycling in a modern habitat-the Arvadi Spring.

Geobiology 2018 07 9;16(4):353-368. Epub 2018 Jun 9.

Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Tuebingen, Germany.

As a consequence of Earth's surface oxygenation, ocean geochemistry changed from ferruginous (iron(II)-rich) into more complex ferro-euxinic (iron(II)-sulphide-rich) conditions during the Paleoproterozoic. This transition must have had profound implications for the Proterozoic microbial community that existed within the ocean water and bottom sediment; in particular, iron-oxidizing bacteria likely had to compete with emerging sulphur-metabolizers. However, the nature of their coexistence and interaction remains speculative. Here, we present geochemical and microbiological data from the Arvadi Spring in the eastern Swiss Alps, a modern model habitat for ferro-euxinic transition zones in late Archean and Proterozoic oceans during high-oxygen intervals, which enables us to reconstruct the microbial community structure in respective settings for this geological era. The spring water is oxygen-saturated but still contains relatively elevated concentrations of dissolved iron(II) (17.2 ± 2.8 μM) and sulphide (2.5 ± 0.2 μM) with simultaneously high concentrations of sulphate (8.3 ± 0.04 mM). Solids consisting of quartz, calcite, dolomite and iron(III) oxyhydroxide minerals as well as sulphur-containing particles, presumably elemental S , cover the spring sediment. Cultivation-based most probable number counts revealed microaerophilic iron(II)-oxidizers and sulphide-oxidizers to represent the largest fraction of iron- and sulphur-metabolizers in the spring, coexisting with less abundant iron(III)-reducers, sulphate-reducers and phototrophic and nitrate-reducing iron(II)-oxidizers. 16S rRNA gene 454 pyrosequencing showed sulphide-oxidizing Thiothrix species to be the dominating genus, supporting the results from our cultivation-based assessment. Collectively, our results suggest that anaerobic and microaerophilic iron- and sulphur-metabolizers could have coexisted in oxygenated ferro-sulphidic transition zones of late Archean and Proterozoic oceans, where they would have sustained continuous cycling of iron and sulphur compounds.
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http://dx.doi.org/10.1111/gbi.12293DOI Listing
July 2018

Tracking the rise of eukaryotes to ecological dominance with zinc isotopes.

Geobiology 2018 07 5;16(4):341-352. Epub 2018 Jun 5.

Geology and Geophysics, Yale University, New Haven, Connecticut.

The biogeochemical cycling of zinc (Zn) is intimately coupled with organic carbon in the ocean. Based on an extensive new sedimentary Zn isotope record across Earth's history, we provide evidence for a fundamental shift in the marine Zn cycle ~800 million years ago. We discuss a wide range of potential drivers for this transition and propose that, within available constraints, a restructuring of marine ecosystems is the most parsimonious explanation for this shift. Using a global isotope mass balance approach, we show that a change in the organic Zn/C ratio is required to account for observed Zn isotope trends through time. Given the higher affinity of eukaryotes for Zn relative to prokaryotes, we suggest that a shift toward a more eukaryote-rich ecosystem could have provided a means of more efficiently sequestering organic-derived Zn. Despite the much earlier appearance of eukaryotes in the microfossil record (~1700 to 1600 million years ago), our data suggest a delayed rise to ecological prominence during the Neoproterozoic, consistent with the currently accepted organic biomarker records.
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http://dx.doi.org/10.1111/gbi.12289DOI Listing
July 2018

Thermodynamic Analysis of Nickel(II) and Zinc(II) Adsorption to Biochar.

Environ Sci Technol 2018 06 21;52(11):6246-6255. Epub 2018 May 21.

Department of Earth & Atmospheric Sciences , 1-26 Earth Sciences Building, University of Alberta , Edmonton , Alberta T6G 2E3 , Canada.

While numerous studies have investigated metal uptake from solution by biochar, few of these have developed a mechanistic understanding of the adsorption reactions that occur at the biochar surface. In this study, we explore a combined modeling and spectroscopic approach for the first time to describe the molecular level adsorption of Ni(II) and Zn(II) to five types of biochar. Following thorough characterization, potentiometric titrations were carried out to measure the proton (H) reactivity of each biochar, and the data was used to develop protonation models. Surface complexation modeling (SCM) supported by synchrotron-based extended X-ray absorption fine structure (EXAFS) was then used to gain insights into the molecular scale metal-biochar surface reactions. The SCM approach was combined with isothermal titration calorimetry (ITC) data to determine the thermodynamic driving forces of metal adsorption. Our results show that the reactivity of biochar toward Ni(II) and Zn(II) directly relates to the site densities of biochar. EXAFS along with FT-IR analyses, suggest that Ni(II) and Zn(II) adsorption occurred primarily through proton-active carboxyl (-COOH) and hydroxyl (-OH) functional groups on the biochar surface. SCM-ITC analyses revealed that the enthalpies of protonation are exothermic and Ni(II) and Zn(II) complexes with biochar surface are slightly exothermic to slightly endothermic. The results obtained from these combined approaches contribute to the better understanding of molecular scale metal adsorption onto the biochar surface, and will facilitate the further development of thermodynamics-based, predictive approaches to biochar removal of metals from contaminated water.
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http://dx.doi.org/10.1021/acs.est.7b06261DOI Listing
June 2018

Modified sequential extraction for biochar and petroleum coke: Metal release potential and its environmental implications.

Bioresour Technol 2017 Jul 29;236:106-110. Epub 2017 Mar 29.

Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton T6G 2E3, Canada.

A modified Community Bureau of Reference (CBR) sequential extraction method was tested to assess the composition of untreated pyrogenic carbon (biochar) and oil sands petroleum coke. Wood biochar samples were found to contain lower concentrations of metals, but had higher fractions of easily mobilized alkaline earth and transition metals. Sewage sludge biochar was determined to be less recalcitrant and had higher total metal concentrations, with most of the metals found in the more resilient extraction fractions (oxidizable, residual). Petroleum coke was the most stable material, with a similar metal distribution pattern as the sewage sludge biochar. The applied sequential extraction method represents a suitable technique to recover metals from these materials, and is a valuable tool in understanding the metal retaining and leaching capability of various biochar types and carbonaceous petroleum coke samples.
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http://dx.doi.org/10.1016/j.biortech.2017.03.162DOI Listing
July 2017

Evolution of the global phosphorus cycle.

Nature 2017 01 21;541(7637):386-389. Epub 2016 Dec 21.

Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada.

The macronutrient phosphorus is thought to limit primary productivity in the oceans on geological timescales. Although there has been a sustained effort to reconstruct the dynamics of the phosphorus cycle over the past 3.5 billion years, it remains uncertain whether phosphorus limitation persisted throughout Earth's history and therefore whether the phosphorus cycle has consistently modulated biospheric productivity and ocean-atmosphere oxygen levels over time. Here we present a compilation of phosphorus abundances in marine sedimentary rocks spanning the past 3.5 billion years. We find evidence for relatively low authigenic phosphorus burial in shallow marine environments until about 800 to 700 million years ago. Our interpretation of the database leads us to propose that limited marginal phosphorus burial before that time was linked to phosphorus biolimitation, resulting in elemental stoichiometries in primary producers that diverged strongly from the Redfield ratio (the atomic ratio of carbon, nitrogen and phosphorus found in phytoplankton). We place our phosphorus record in a quantitative biogeochemical model framework and find that a combination of enhanced phosphorus scavenging in anoxic, iron-rich oceans and a nutrient-based bistability in atmospheric oxygen levels could have resulted in a stable low-oxygen world. The combination of these factors may explain the protracted oxygenation of Earth's surface over the last 3.5 billion years of Earth history. However, our analysis also suggests that a fundamental shift in the phosphorus cycle may have occurred during the late Proterozoic eon (between 800 and 635 million years ago), coincident with a previously inferred shift in marine redox states, severe perturbations to Earth's climate system, and the emergence of animals.
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http://dx.doi.org/10.1038/nature20772DOI Listing
January 2017

No evidence for high atmospheric oxygen levels 1,400 million years ago.

Proc Natl Acad Sci U S A 2016 May 20;113(19):E2550-1. Epub 2016 Apr 20.

Department of Earth Science, University of California, Riverside, CA 92521;

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http://dx.doi.org/10.1073/pnas.1601925113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4868423PMC
May 2016

Cu isotopes in marine black shales record the Great Oxidation Event.

Proc Natl Acad Sci U S A 2016 May 18;113(18):4941-6. Epub 2016 Apr 18.

Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada T6G 2EG.

The oxygenation of the atmosphere ∼2.45-2.32 billion years ago (Ga) is one of the most significant geological events to have affected Earth's redox history. Our understanding of the timing and processes surrounding this key transition is largely dependent on the development of redox-sensitive proxies, many of which remain unexplored. Here we report a shift from negative to positive copper isotopic compositions (δ(65)CuERM-AE633) in organic carbon-rich shales spanning the period 2.66-2.08 Ga. We suggest that, before 2.3 Ga, a muted oxidative supply of weathering-derived copper enriched in (65)Cu, along with the preferential removal of (65)Cu by iron oxides, left seawater and marine biomass depleted in (65)Cu but enriched in (63)Cu. As banded iron formation deposition waned and continentally sourced Cu became more important, biomass sampled a dissolved Cu reservoir that was progressively less fractionated relative to the continental pool. This evolution toward heavy δ(65)Cu values coincides with a shift to negative sedimentary δ(56)Fe values and increased marine sulfate after the Great Oxidation Event (GOE), and is traceable through Phanerozoic shales to modern marine settings, where marine dissolved and sedimentary δ(65)Cu values are universally positive. Our finding of an important shift in sedimentary Cu isotope compositions across the GOE provides new insights into the Precambrian marine cycling of this critical micronutrient, and demonstrates the proxy potential for sedimentary Cu isotope compositions in the study of biogeochemical cycles and oceanic redox balance in the past.
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http://dx.doi.org/10.1073/pnas.1523544113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4983842PMC
May 2016

The Archean Nickel Famine Revisited.

Astrobiology 2015 Oct 1;15(10):804-15. Epub 2015 Oct 1.

5 CNRS-UMR6538 Laboratoire Domaines Océaniques, European Institute for Marine Studies , Technopôle Brest-Iroise, Plouzané, France .

Iron formations (IF) preserve a history of Precambrian oceanic elemental abundance that can be exploited to examine nutrient limitations on early biological productivity. However, in order for IF to be employed as paleomarine proxies, lumped-process distribution coefficients for the element of interest must be experimentally determined or assumed. This necessitates consideration of bulk ocean chemistry and which authigenic ferric iron minerals controlled the sorption reactions. It also requires an assessment of metal mobilization reactions that might have occurred in the water column during particle descent and during post-depositional burial. Here, we summarize recent developments pertaining to the interpretation and fidelity of the IF record in reconstructions of oceanic trace element evolution. Using an updated compilation, we reexamine and validate temporal trends previously reported for the nickel content in IF (see Konhauser et al., 2009 ). Finally, we reevaluate the consequences of methanogen Ni starvation in the context of evolving views of the Archean ocean-climate system and how the Ni famine may have ultimately facilitated the rise in atmospheric oxygen.
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http://dx.doi.org/10.1089/ast.2015.1301DOI Listing
October 2015

Benthic perspective on Earth's oldest evidence for oxygenic photosynthesis.

Proc Natl Acad Sci U S A 2015 Jan 12;112(4):995-1000. Epub 2015 Jan 12.

Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, T6G 2E3, Canada.

The Great Oxidation Event (GOE) is currently viewed as a protracted process during which atmospheric oxygen increased above ∼10(-5) times the present atmospheric level (PAL). This threshold represents an estimated upper limit for sulfur isotope mass-independent fractionation (S-MIF), an Archean signature of atmospheric anoxia that begins to disappear from the rock record at 2.45 Ga. However, an increasing number of papers have suggested that the timing for oxidative continental weathering, and by conventional thinking the onset of atmospheric oxygenation, was hundreds of million years earlier than previously thought despite the presence of S-MIF. We suggest that this apparent discrepancy can be resolved by the earliest oxidative-weathering reactions occurring in benthic and soil environments at profound redox disequilibrium with the atmosphere, such as biological soil crusts and freshwater microbial mats covering riverbed, lacustrine, and estuarine sediments. We calculate that oxygenic photosynthesis in these millimeter-thick ecosystems provides sufficient oxidizing equivalents to mobilize sulfate and redox-sensitive trace metals from land to the oceans while the atmosphere itself remained anoxic with its attendant S-MIF signature. As continental freeboard increased significantly between 3.0 and 2.5 Ga, the chemical and isotopic signatures of benthic oxidative weathering would have become more globally significant from a mass-balance perspective. These observations help reconcile evidence for pre-GOE oxidative weathering with the history of atmospheric chemistry, and support the plausible antiquity of a terrestrial biosphere populated by cyanobacteria well before the GOE.
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http://dx.doi.org/10.1073/pnas.1415718112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4313849PMC
January 2015

Potential role of nitrite for abiotic Fe(II) oxidation and cell encrustation during nitrate reduction by denitrifying bacteria.

Appl Environ Microbiol 2014 Feb 22;80(3):1051-61. Epub 2013 Nov 22.

Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Tuebingen, Germany.

Microorganisms have been observed to oxidize Fe(II) at neutral pH under anoxic and microoxic conditions. While most of the mixotrophic nitrate-reducing Fe(II)-oxidizing bacteria become encrusted with Fe(III)-rich minerals, photoautotrophic and microaerophilic Fe(II) oxidizers avoid cell encrustation. The Fe(II) oxidation mechanisms and the reasons for encrustation remain largely unresolved. Here we used cultivation-based methods and electron microscopy to compare two previously described nitrate-reducing Fe(II) oxidizers ( Acidovorax sp. strain BoFeN1 and Pseudogulbenkiania sp. strain 2002) and two heterotrophic nitrate reducers (Paracoccus denitrificans ATCC 19367 and P. denitrificans Pd 1222). All four strains oxidized ∼8 mM Fe(II) within 5 days in the presence of 5 mM acetate and accumulated nitrite (maximum concentrations of 0.8 to 1.0 mM) in the culture media. Iron(III) minerals, mainly goethite, formed and precipitated extracellularly in close proximity to the cell surface. Interestingly, mineral formation was also observed within the periplasm and cytoplasm; intracellular mineralization is expected to be physiologically disadvantageous, yet acetate consumption continued to be observed even at an advanced stage of Fe(II) oxidation. Extracellular polymeric substances (EPS) were detected by lectin staining with fluorescence microscopy, particularly in the presence of Fe(II), suggesting that EPS production is a response to Fe(II) toxicity or a strategy to decrease encrustation. Based on the data presented here, we propose a nitrite-driven, indirect mechanism of cell encrustation whereby nitrite forms during heterotrophic denitrification and abiotically oxidizes Fe(II). This work adds to the known assemblage of Fe(II)-oxidizing bacteria in nature and complicates our ability to delineate microbial Fe(II) oxidation in ancient microbes preserved as fossils in the geological record.
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http://dx.doi.org/10.1128/AEM.03277-13DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3911208PMC
February 2014

Response to comment on "Bilaterian burrows and grazing behavior at >585 million years ago".

Science 2013 Feb;339(6122):906

Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada.

Gaucher et al. suggest that their field observations and petrographic analysis of one thin section do not support an Ediacaran age for the trace fossils-bearing strata of the Tacuarí Formation. We have strengthened our conclusion of an Ediacaran age for the Tacuarí Formation based on reassessment of new and previously presented field and petrographic evidence.
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http://dx.doi.org/10.1126/science.1230677DOI Listing
February 2013

Biological carbon precursor to diagenetic siderite with spherical structures in iron formations.

Nat Commun 2013 ;4:1741

Geomicrobiology Group, Center for Applied Geoscience, University of Tuebingen, Sigwartstrasse 10, 72076 Tuebingen, Germany.

During deposition of Precambrian iron formation, the combined sedimentation of ferrihydrite and phytoplankton biomass should have facilitated Fe(III) reduction during diagenesis. However, the only evidence for this reaction in iron formations is the iron and carbon isotope values preserved in the authigenic ferrous iron-containing minerals. Here we show experimentally that spheroidal siderite, which is preserved in many iron formation and could have been precursor to rhombohedral or massive siderite, forms by reacting ferrihydrite with glucose (a proxy for microbial biomass) at pressure and temperature conditions typical of diagenesis (170 °C and 1.2 kbar). Depending on the abundance of siderite, we found that it is also possible to draw conclusions about the Fe(III):C ratio of the initial ferrihydrite-biomass sediment. Our results suggest that spherical to rhombohedral siderite structures in deep-water, Fe-oxide iron formation can be used as a biosignature for photoferrotrophy, whereas massive siderite reflects high cyanobacterial biomass loading in highly productive shallow-waters.
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http://dx.doi.org/10.1038/ncomms2770DOI Listing
November 2013