Aqueous- and solid-phase molybdenum geochemistry of oil sands fluid petroleum coke deposits, Alberta, Canada

Robertson, Jared; Nesbitt, Jake A.; Lindsay, Matthew B.J.

doi:10.1016/j.chemosphere.2018.11.064

Cited by 13 publications

(9 citation statements)

References 33 publications

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“…These results imply that the reliance of boreal ecosystems on V-Nase N input would have been higher in preindustrial times when atmospheric deposition of metals and fixed N, which increase with anthropogenic activities (40, 41), were lower. Recent increases in anthropogenic pollutants enriched in Mo and/or V, such as tar sands (41, 42), could provide new fluxes of Mo and V to natural environments. Conversely, successful pollution control policies (e.g., the Clean Air Act in the United States), which have led to recent declines in atmospheric deposition of heavy metal pollutants and reactive N (43), may help to maintain Mo limitation of BNF in high latitude N-limited forests and increase the need for V-Nase BNF.…”

Section: Resultsmentioning

confidence: 99%

Molybdenum threshold for ecosystem scale alternative vanadium nitrogenase activity in boreal forests

Darnajoux

Magain

Renaudin

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

163

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Biological nitrogen fixation (BNF) by microorganisms associated with cryptogamic covers, such as cyanolichens and bryophytes, is a primary source of fixed nitrogen in pristine, high-latitude ecosystems. On land, low molybdenum (Mo) availability has been shown to limit BNF by the most common form of nitrogenase (Nase), which requires Mo in its active site. Vanadium (V) and iron-only Nases have been suggested as viable alternatives to countering Mo limitation of BNF; however, field data supporting this long-standing hypothesis have been lacking. Here, we elucidate the contribution of vanadium nitrogenase (V-Nase) to BNF by cyanolichens across a 600-km latitudinal transect in eastern boreal forests of North America. Widespread V-Nase activity was detected (∼15–50% of total BNF rates), with most of the activity found in the northern part of the transect. We observed a 3-fold increase of V-Nase contribution during the 20-wk growing season. By including the contribution of V-Nase to BNF, estimates of new N input by cyanolichens increase by up to 30%. We find that variability in V-based BNF is strongly related to Mo availability, and we identify a Mo threshold of ∼250 ng·glichen−1 for the onset of V-based BNF. Our results provide compelling ecosystem-scale evidence for the use of the V-Nase as a surrogate enzyme that contributes to BNF when Mo is limiting. Given widespread findings of terrestrial Mo limitation, including the carbon-rich circumboreal belt where global change is most rapid, additional consideration of V-based BNF is required in experimental and modeling studies of terrestrial biogeochemistry.

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Section: Resultsmentioning

confidence: 99%

Molybdenum threshold for ecosystem scale alternative vanadium nitrogenase activity in boreal forests

Darnajoux

Magain

Renaudin

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

163

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“…We interpret the apparent Mo incorporation in all columns as occurring during Fe(II)-induced mineral transformation. Coordination changes can result from decreasing pH, 3,47 reduction, 7 or polymerization. 90 Effluent pH did not decrease in Fh-L or Gt-L columns, but local pH decreases cannot be ruled out, as equilibrium between tetrahedral and octahedral coordinated Mo(VI) occurs at pH 4 under oxic conditions and increases to pH 6 under anoxic conditions.…”

Section: ■ Resultsmentioning

confidence: 99%

“…For Phase I, 0.1 mM of Mo(VI) was added to the influent by dissolving Na 2 MoO 4 •2H 2 O (≥99.5%, Sigma-Aldrich, U.S.A.) in the artificial groundwater. This Mo concentration was chosen based on previous studies and to mimic concentrations previously reported for mine waters, 7 while also minimizing potential for the formation of aqueous polynuclear Mo species at concentrations >1 mM. 55 S1).…”

Section: ■ Methodsmentioning

confidence: 99%

Structural Incorporation of Sorbed Molybdate during Iron(II)-Induced Transformation of Ferrihydrite and Goethite under Advective Flow Conditions

Schoepfer

Qin

Robertson³

et al. 2020

ACS Earth Space Chem.

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Aqueous Fe(II) can induce recrystallization of ferrihydrite and goethite [α-FeOOH] to their more crystalline or molecularly homogeneous counterparts. Despite common association with these and other Fe(III) (oxyhydr)oxides, relationships between Fe(II)-induced transformation and Mo mobility remain poorly constrained. We conducted laboratory column experiments to examine repartitioning of sorbed Mo during Fe(II)-induced transformation of ferrihydrite and goethite under advective flow conditions. We first pumped (∼0.25 L d–1) artificial groundwater containing 0.1 mM MoO4 2– and buffered to pH 6.5 through columns packed with ferrihydrite- and goethite-coated sand until >90% Mo breakthrough was observed. Extended X-ray absorption fine structure (EXAFS) spectroscopy shows that initial Mo attenuation resulted from inner sphere complexation of MoO4 tetrahedra at ferrihydrite and goethite surfaces. We then pumped Mo-free anoxic artificial groundwater containing 0.2 mM or 2.0 mM Fe(II) through the columns until effluent Mo concentrations remained <0.005 mM. Raman spectroscopy shows that Fe(II) introduction induced transformation of both ferrihydrite and goethite to lepidocrocite. Additionally, Fe(II) introduction mobilized 4–34% of sorbed Mo and total mass release was greater for (i) ferrihydrite compared to goethite columns and (ii) low Fe(II) compared to high Fe(II) influent. Effluent pH decreased to ∼5.8 for columns receiving the high Fe(II) influent and returned to pH 6.5 after 5–10 pore volumes. EXAFS spectroscopy indicates that structural incorporation of MoO6 octahedra into neoformed phases contributes to Mo retention during Fe(II)-induced transformation. Our results offer new insight into Mo repartitioning during Fe(II)-induced transformation of Fe(III) (oxyhydr)oxides and, more generally, controls on Mo mobility in geohydrologic systems.

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“…Other regions that may be similarly sensitive to anthropogenic perturbations of the Mo cycle are regions where N limitation is strong and new inputs of Mo from weathering or natural atmospheric deposition are low. These areas include North American boreal forests, which may be affected by tar sands (Robertson et al., 2019), recovering Neotropical tropical forests (Batterman et al., 2013; Davidson et al., 2007) and savannas, which may be affected by biomass burning and agricultural dust, and recovering Asian tropical forests, which may be affected by combustion.…”

Section: Discussionmentioning

confidence: 99%

Anthropogenic Perturbations to the Atmospheric Molybdenum Cycle

Wong

Rathod

Marino

et al. 2021

Global Biogeochemical Cycles

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Molybdenum (Mo) is a key cofactor in enzymes used for nitrogen (N) fixation and nitrate reduction, and the low availability of Mo can constrain N inputs, affecting ecosystem productivity. Natural atmospheric Mo aerosolization and deposition from sources such as desert dust, sea‐salt spray, and volcanoes can affect ecosystem function across long timescales, but anthropogenic activities such as combustion, motor vehicles, and agricultural dust have accelerated the natural Mo cycle. Here we combined a synthesis of global atmospheric concentration observations and modeling to identify and estimate anthropogenic sources of atmospheric Mo. To project the impact of atmospheric Mo on terrestrial ecosystems, we synthesized soil Mo data and estimated the global distribution of soil Mo using two approaches to calculate turnover times. We estimated global emissions of atmospheric Mo in aerosols (<10 μm in diameter) to be 23 Gg Mo yr−1, with 40%–75% from anthropogenic sources. We approximated that for the top meter of soil, Mo turnover times range between 1,000 and 1,000,000 years. In some industrialized regions, anthropogenic inputs have enhanced Mo deposition 100‐fold, lowering the soil Mo turnover time considerably. Our synthesis of global observational data, modeling, and a mass balance comparison with riverine Mo exports suggest that anthropogenic activity has greatly accelerated the Mo cycle, with potential to influence N‐limited ecosystems.

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Aqueous- and solid-phase molybdenum geochemistry of oil sands fluid petroleum coke deposits, Alberta, Canada

Cited by 13 publications

References 33 publications

Molybdenum threshold for ecosystem scale alternative vanadium nitrogenase activity in boreal forests

Molybdenum threshold for ecosystem scale alternative vanadium nitrogenase activity in boreal forests

Structural Incorporation of Sorbed Molybdate during Iron(II)-Induced Transformation of Ferrihydrite and Goethite under Advective Flow Conditions

Anthropogenic Perturbations to the Atmospheric Molybdenum Cycle

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