Rate‐limited U(VI) desorption during a small‐scale tracer test in a heterogeneous uranium‐contaminated aquifer

Fox, Patricia; Davis, James A.; Hay, Michael; Conrad, Mark E.; Campbell, Kate M.; Williams, Kenneth H.; Long, Philip E.

doi:10.1029/2011wr011472

Cited by 50 publications

(72 citation statements)

References 45 publications

(91 reference statements)

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“…50,51 This is supported by our results (biotic system) and indicates the effectiveness of biological U reduction in the subsurface in comparison to abiotic pathways if U(VI) is in the aqueous phase. Moreover, microbial metabolic activity can contribute to an increase in the bicarbonate concentration as a result of CO 2 production.…”

Section: Isotopic Measurementssupporting

confidence: 76%

Mechanism of Uranium Reduction and Immobilization in Desulfovibrio vulgaris Biofilms

Stylo

Neubert

Roebbert

et al. 2015

Environ. Sci. Technol.

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The prevalent formation of noncrystalline U(IV) species in the subsurface and their enhanced susceptibility to reoxidation and remobilization, as compared to crystalline uraninite, raise concerns about the long-term sustainability of the bioremediation of U-contaminated sites. The main goal of this study was to resolve the remaining uncertainty concerning the formation mechanism of noncrystalline U(IV) in the environment. Controlled laboratory biofilm systems (biotic, abiotic, and mixed biotic−abiotic) were probed using a combination of U isotope fractionation and X-ray absorption spectroscopy (XAS). Regardless of the mechanism of U reduction, the presence of a biofilm resulted in the formation of noncrystalline U(IV). Our results also show that biotic U reduction is the most effective way to immobilize and reduce U. However, the mixed biotic−abiotic system resembled more closely an abiotic system: (i) the U(IV) solid phase lacked a typically biotic isotope signature and (ii) elemental sulfur was detected, which indicates the oxidation of sulfide coupled to U(VI) reduction. The predominance of abiotic U reduction in our systems is due to the lack of available aqueous U(VI) species for direct enzymatic reduction. In contrast, in cases where bicarbonate is present at a higher concentration, aqueous U(VI) species dominate, allowing biotic U reduction to outcompete the abiotic processes.

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Section: Isotopic Measurementssupporting

confidence: 76%

Mechanism of Uranium Reduction and Immobilization in Desulfovibrio vulgaris Biofilms

Stylo

Neubert

Roebbert

et al. 2015

Environ. Sci. Technol.

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“…Anaerobic Rifle Artificial Groundwater (RAGW) was prepared based on the aqueous geochemical composition of site groundwater [which has been described elsewhere (Williams et al, 2011; Fox et al, 2012)]: 7.7 mM NaHCO 3 , 0.4 mM KCl, 4 mM MgSO 4 .7H 2 O, 4.8 mM CaSO 4 , and 2.6 mM NaCl. As the RAGW did not include a source of N or P, these would have to be provided by the aquifer sediment, as is presumably the case under in situ conditions.…”

Section: Methodsmentioning

confidence: 99%

Metatranscriptomic Analysis Reveals Unexpectedly Diverse Microbial Metabolism in a Biogeochemical Hot Spot in an Alluvial Aquifer

et al. 2017

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Organic matter deposits in alluvial aquifers have been shown to result in the formation of naturally reduced zones (NRZs), which can modulate aquifer redox status and influence the speciation and mobility of metals, affecting groundwater geochemistry. In this study, we sought to better understand how natural organic matter fuels microbial communities within anoxic biogeochemical hot spots (NRZs) in a shallow alluvial aquifer at the Rifle (CO) site. We conducted a 20-day microcosm experiment in which NRZ sediments, which were enriched in buried woody plant material, served as the sole source of electron donors and microorganisms. The microcosms were constructed and incubated under anaerobic conditions in serum bottles with an initial N2 headspace and were sampled every 5 days for metagenome and metatranscriptome profiles in combination with biogeochemical measurements. Biogeochemical data indicated that the decomposition of native organic matter occurred in different phases, beginning with mineralization of dissolved organic matter (DOM) to CO2 during the first week of incubation, followed by a pulse of acetogenesis that dominated carbon flux after 2 weeks. A pulse of methanogenesis co-occurred with acetogenesis, but only accounted for a small fraction of carbon flux. The depletion of DOM over time was strongly correlated with increases in expression of many genes associated with heterotrophy (e.g., amino acid, fatty acid, and carbohydrate metabolism) belonging to a Hydrogenophaga strain that accounted for a relatively large percentage (~8%) of the metatranscriptome. This Hydrogenophaga strain also expressed genes indicative of chemolithoautotrophy, including CO2 fixation, H2 oxidation, S-compound oxidation, and denitrification. The pulse of acetogenesis appears to have been collectively catalyzed by a number of different organisms and metabolisms, most prominently pyruvate:ferredoxin oxidoreductase. Unexpected genes were identified among the most highly expressed (>98th percentile) transcripts, including acetone carboxylase and cell-wall-associated hydrolases with unknown substrates (numerous lesser expressed cell-wall-associated hydrolases targeted peptidoglycan). Many of the most highly expressed hydrolases belonged to a Ca. Bathyarchaeota strain and may have been associated with recycling of bacterial biomass. Overall, these results highlight the complex nature of organic matter transformation in NRZs and the microbial metabolic pathways that interact to mediate redox status and elemental cycling.

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“…25%, and only 38% of the aquifer material is contained in the o2 mm size fraction and the majority is gravel size (Fox et al, 2012).…”

Section: Methodsmentioning

confidence: 99%

Enrichment of specific protozoan populations during in situ bioremediation of uranium-contaminated groundwater

et al. 2013

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The importance of bacteria in the anaerobic bioremediation of groundwater polluted with organic and/or metal contaminants is well recognized and in some instances so well understood that modeling of the in situ metabolic activity of the relevant subsurface microorganisms in response to changes in subsurface geochemistry is feasible. However, a potentially significant factor influencing bacterial growth and activity in the subsurface that has not been adequately addressed is protozoan predation of the microorganisms responsible for bioremediation. In field experiments at a uraniumcontaminated aquifer located in Rifle, CO, USA, acetate amendments initially promoted the growth of metal-reducing Geobacter species, followed by the growth of sulfate reducers, as observed previously. Analysis of 18S rRNA gene sequences revealed a broad diversity of sequences closely related to known bacteriovorous protozoa in the groundwater before the addition of acetate. The bloom of Geobacter species was accompanied by a specific enrichment of sequences most closely related to the ameboid flagellate, Breviata anathema, which at their peak accounted for over 80% of the sequences recovered. The abundance of Geobacter species declined following the rapid emergence of B. anathema. The subsequent growth of sulfate-reducing Peptococcaceae was accompanied by another specific enrichment of protozoa, but with sequences most similar to diplomonadid flagellates from the family Hexamitidae, which accounted for up to 100% of the sequences recovered during this phase of the bioremediation. These results suggest a preypredator response with specific protozoa responding to increased availability of preferred prey bacteria. Thus, quantifying the influence of protozoan predation on the growth, activity and composition of the subsurface bacterial community is essential for predictive modeling of in situ uranium bioremediation strategies.

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Rate‐limited U(VI) desorption during a small‐scale tracer test in a heterogeneous uranium‐contaminated aquifer

Cited by 50 publications

References 45 publications

Mechanism of Uranium Reduction and Immobilization in Desulfovibrio vulgaris Biofilms

Mechanism of Uranium Reduction and Immobilization in Desulfovibrio vulgaris Biofilms

Metatranscriptomic Analysis Reveals Unexpectedly Diverse Microbial Metabolism in a Biogeochemical Hot Spot in an Alluvial Aquifer

Enrichment of specific protozoan populations during in situ bioremediation of uranium-contaminated groundwater

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