BER Research Highlights

Search Date: June 27, 2017

16 Records match the search term(s):


December 22, 2016

Metagenomics Leads to New CRISPR-Cas Systems

Researchers discover the first CRISPR-Cas9 system in archaea.

The Science
Using large amounts of metagenomic data generated by the Department of Energy’s Joint Genome Institute (DOE JGI), researchers analyzed 155 million protein coding genes from uncultivated microbial communities. This work led to the discovery of the first CRISPR- (clustered regularly interspaced short palindromic repeats) Cas9 protein in the archaeal domain, as well as two previously unknown simple bacterial CRISPR-Cas systems.

The Impact
Microbes play key roles in the planet’s cycles, and characterizing them helps researchers work toward solutions for energy and environmental challenges. Examining environmental microbial communities has enabled access to an unprecedented diversity of genomes and CRISPR-Cas systems that have many applications, including biological research. The combined computational-experimental approach that was successful in this study can be used to investigate nearly all environments where life exists.

Summary
Microbes heavily influence the planet’s cycles, but only a fraction have been identified. Characterizing the abundant but largely unknown extent of microbial diversity can help researchers develop solutions to energy and environmental challenges. In microbes, CRISPR-Cas systems provide a form of adaptive immunity, and these gene-editing tools are the foundation of versatile technologies revolutionizing research. Thus far, CRISPR-Cas technology has been based only on systems from isolated bacteria. In a study led by longtime DOE JGI collaborator Jill Banfield of the University of California, Berkeley, researchers discovered, for the first time, a CRISPR-Cas9 system in archaea, as well as simple CRISPR-Cas systems in uncultivable bacteria. To identify these new CRISPR-Cas systems, the team harnessed more than a decade’s worth of metagenomic data from samples sequenced and analyzed by DOE JGI, a DOE Office of Science user facility. The CasX and CasY proteins were found in bacteria from groundwater and sediment samples. The archaeal Cas9 was identified in samples taken from the Iron Mountain Superfund site as part of Banfield’s pioneering metagenomics work with DOE JGI. Both CasX and CasY are among some of the most compact systems ever identified. This application of metagenomics validates studies of CRISPR-Cas proteins using living organisms.

Contacts
Daniel Drell, Ph.D.
Program Manager
Biological Systems Science Division
Office of Biological and Environmental Research
Office of Science
U.S. Department of Energy
daniel.drell@science.doe.gov

David Lesmes, Ph.D.
Program Manager
Climate and Environmental Sciences Division
Office of Biological and Environmental Research
Office of Science
U.S. Department of Energy
david.lesmes@science.doe.gov

Jill Banfield
University of California, Berkeley
jbanfield@berkeley.edu

Funding
DOE Office of Science, National Science Foundation, EMBO, German Science Foundation, Paul Allen Institute, and Howard Hughes Medical Institute 

Publication
Burstein, D., et al., “New CRISPR-Cas systems from uncultivated microbes.” Nature (2016). [DOI: 10.1038/nature21059] (Reference link)

Related Links

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER,SC-23.2 Biological Systems Science Division, BER



An artistic representation of the Tree of Life, with the many groups of bacteria and archaea at the upper left and eukaryotes, which include humans, at the lower right. Department of Energy Joint Genome Institute scientists are using gene-editing tools to explore microbial “dark matter.” [Artistic representation of Fig. 1 from Hug et al., “A new view of the tree of life.” Nature Microbiology 1 (2016). DOI: 10.1038/nmicrobiol.2016.48. Courtesy of Jill Banfield, University of California, Berkeley]



December 14, 2016

Clay Minerals and Metal Oxides Can Change How Uranium Travels Through Sediments

The molecular form of reduced uranium in the subsurface is affected by common sediment constituents.

The Science 
Clay minerals are ubiquitous native components of sediments and soils, as well as a material used in the engineered barriers of spent nuclear fuel storage facilities. A recent study examined the molecular form of uranium(IV) in the presence of montmorillonite clays and found that they can inhibit the predicted precipitation of the mineral uraninite.

The Impact
The effect of environmental surfaces on the form of reduced uranium is currently not accounted for in computational models. This study used state-of-the-art spectroscopy techniques to provide the molecular-level information needed for accurate prediction of uranium transport in subsurface environments.

Summary
Uranium mobility in the subsurface depends strongly on its oxidation state, with U(IV) being significantly less soluble than U(VI). However, solubility also depends on the contaminant’s molecular form, which can be affected by adsorption to the surface of minerals, bacterial membranes, and other constituents in the surrounding environment. Researchers examined the ability of montmorillonite clay minerals to adsorb U(IV) resulting from the reduction of U(VI) and compared it to that of iron and titanium oxide surfaces. The valence and molecular structure of U was tracked by synchrotron x-ray absorption spectroscopy. Findings showed that at low clay surface:U ratios, the reduction of U(VI) in the presence of SYn-1 montmorillonite leads to the formation of the mineral uraninite (UO2). However, at high clay surface:U ratios (more typical of environmental conditions), a significant fraction of the resulting U(IV) is present as adsorbed U(IV) ions (up to 50% of total U). The threshold U(IV) surface coverage above which uraninite formation begins was determined to be significantly lower for montmorillonite than for iron or titanium oxides, suggesting that metal oxides may play a more important role than clay minerals in stabilizing the nonuraninite species observed in natural sediments.

Contacts (BER PM)
Dr. Roland F. Hirsch
Program Officer, U.S. DOE Office of Science
roland.hirsch@science.doe.gov; (301) 903-9009

(PI Contact)
Dr. Kenneth M. Kemner
Argonne National Laboratory
kemner@anl.gov; (630) 252-1163

Funding
This research is part of the Subsurface Science Scientific Focus Area at Argonne National Laboratory (ANL), which is supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, Subsurface Biogeochemical Research program. Use of the Electron Microscopy Center at ANL and the Advanced Photon Source is supported by DOE’s Office of Science, Office of Basic Energy Sciences. MRCAT/EnviroCAT operations are supported by DOE and the MRCAT/EnviroCAT member institutions. All work at ANL was under contract DE-AC02-06CH11357.

Publication
M. I. Boyanov, D. E. Latta, M. M. Scherer, E. J. O’Loughlin, and K. M. Kemner, “Surface area effects on the reduction of UVI in the presence of synthetic montmorillonite.” Chemical Geology (2017). [DOI: 10.1016/j.chemgeo.2016.12.016] (Reference link)

Related Links
Subsurface Science Scientific Focus Area at Argonne National Laboratory

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Redox transformations that affect the environmental mobility of metal or radionuclide contaminants typically occur in the presence of mineral or biological surfaces. [Image courtesy of Argonne National Laboratory]



October 25, 2016

Future Climate Warming Induces Emergence of New Hydrologic Regimes of Surface Water Resources in the Conterminous United States

Global warming poses great challenges to the future U.S. surface water supply.

The Science  
Future climate change projections often focus on average trends over time, or zero in on changes in extreme events. When evaluating climate change impacts, however, it is often important to consider additional parameters, such as changes in the seasonality of runoff. This study evaluates whether the overall pattern of surface water supply in a given watershed has shifted significantly away from historical conditions—that is, when it is projected to enter a new “hydrological regime”— using a statistical technique, and finds that more than 40% of the continental United States land area is likely to experience a significant hydrological regime shift by the end of the 21st century.

The Impact
Many human and natural systems have evolved in the context of a relatively stable climate, so it is important to understand when and where climate change could push systems across thresholds that would result in rapid, nonlinear changes. This study assessed changes in the probability distributions of surface water resources in large (HUC-4) sub-basins across the United States under a range of future climate projections. The research found that each 1°C increase in global mean temperature was associated with an 11-17% increase in land area experiencing a new hydrologic regime, which could pose significant challenges to water resource managers. Northern California and the Pacific Northwest are projected to experience these regime shifts by 2030, earlier than other US regions.

Summary
Researchers at the Department of Energy’s Pacific Northwest National Laboratory (PNNL) analyzed runoff projections from the Variable Infiltration Capacity (VIC) hydrological model which was driven by 97 downscaled and bias-corrected Coupled Model Intercomparison Project Phase 5 (CMIP5) climate projections over the conterminous United States (CONUS). A statistical technique based on the two-sample Kolmogorov-Smirnov test was used to determine the year in which the summer and winter surface runoff in each sub-basin shifted to a new regime in each of these projections, compared to the simulated historical hydroclimate from 1970-1999. They found that the overall land area experiencing a significant hydrologic regime shift followed a linear relationship with respect to global mean temperature, with 11-17% more lands experiencing statistically significant changes in winter and summer runoff across all scenarios and models considered. Further decomposition showed that the emergence of new runoff regimes is typically dominated by changes in variability, rather than shifts in average runoff, and that these runoff regime shifts are driven by an increase in the year-to-year variability of precipitation across many future climate scenarios.

Contacts (BER PM)
Robert Vallario
Integrated Assessment Research Program
Bob.Vallario@science.doe.gov

David Lesmes and Paul Bayer
Subsurface Biogeochemical Research
David.Lesmes@science.doe.gov and Paul.Bayer@science.doe.gov

(PI Contacts)
Maoyi Huang
Pacific Northwest National Laboratory
Maoyi.Huang@pnnl.gov

Funding
This study was conducted with support from the US Department of Energy’s Office of Science, Office of Biological and Environmental Research (BER) for the Subsurface Biogeochemical Research (SBR) program through the PNNL SBR SFA, and the BER’s Integrated Assessment Research Program for the Regional Integrated Assessment Modeling project (RIAM).

Publications
Leng, G., et al., “Emergence of new hydrologic regimes of surface water resources in the conterminous United States under future warming,” Environmental Research Letters, 11(11):114003, (2016). DOI:10.1088/1748-9326/11/11/114003 (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 24, 2016

Metabolic Handoffs Among Microbial Community Members Drive Biogeochemical Cycles

Thousands of microbial genomes shed light on interconnected biogeochemical processes in an aquifer system.

The Science
2,540 genomes that represent the majority of known bacterial phyla and 47 new phylum-level lineages were reconstructed from sediment and groundwater collected from a semi-arid floodplain near Rifle, CO. Analyses showed that inter-organism interactions are required to turn the carbon, sulfur and nitrogen biogeochemical cycles and revealed that complex patterns of community assembly are likely key to ecosystem functioning and resilience.

The Impact
The research almost doubled the number of major bacterial groups and provided detailed information about the ecosystem roles of organisms from these groups. The research dramatically increased understanding of subsurface biology and motivates new approaches to ecosystem modeling. The genomes represent a treasure-trove that will be mined for biotechnology.

Summary
The subterranean world hosts up to one fifth of all biomass, including microbial communities that drive transformations central to Earth’s biogeochemical cycles. However, little is known about how complex microbial communities in such environments are structured, and how inter-organism interactions shape ecosystem function. Terabase-scale cultivation-independent metagenomics was applied to aquifer sediments and groundwater and 2,540 high-quality near-complete and complete strain-resolved genomes that represent the majority of known bacterial phyla were constructed.  Some of these genomes derive from 47 newly discovered phylum-level lineages. Metabolic analyses spanning this vast phylogenetic diversity and representing up to 36% of organisms detected in the system were used to document the distribution of pathways in coexisting organisms. Consistent with prior findings indicating metabolic handoffs in simple consortia, it was shown that few organisms within the community conduct multiple sequential redox transformations. As environmental conditions change, different assemblages of organisms are selected for, altering linkages among the major biogeochemical cycles.

BER PM Contact
David Lesmes, SC-23.1, 301-903-2977

Contact
Susan Hubbard
Lawrence Berkeley National Laboratory
sshubbard@lbl.gov

Funding: This work was supported by Lawrence Berkeley National Laboratory’s Sustainable Systems Scientific Focus Area funded by the US Department of Energy, Office of Science, Office of Biological and Environmental Research.  Terabase-scale sequencing critical for this work was provided by the Joint Genome Institute via Community Science Program allocations.

Publication
K. Anantharaman, C. T. Brown, L. A. Hug, I.Sharon, C. J. Castelle, A. J. Probst, B. C. Thomas, A. Singh, M. J. Wilkins, U. Karaoz, E. L. Brodie, K. H. Williams, S. S. Hubbard, and J. F. Banfield. “Thousands of microbial genomes shed light on interconnected biogeochemical processes in an aquifer system”. Nature Communications 7, ncomms13219 (2016). [DOI: 10.1038/ncomms13219]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Tree showing all of bacterial diversity that is now represented by genomes, with the major lineages indicated by wedges. Research on the microbiology of the Rifle aquifer has provided new genomic information within previously identified groups (black wedges). In addition, many major bacterial groups were first identified and via study of the Rifle site (red and purple wedges). Red wedges indicate many major lineages that were first identified in the current study. Colored dots indicate the genomically predicted roles of members of these newly defined bacterial lineages in geochemical cycling. Remarkably, few major bacterial lineages have not been genomically sampled at this site (olive green wedges). [Image courtesy of Anantharaman et al. 2016. DOI: 10.1038/ncomms13219. Reprinted under CC by 4.0.]



October 12, 2016

Unraveling the Molecular Complexity of Cellular Machines and Environmental Processes

State-of-the-art mass spectrometer delivers unprecedented capability to users.

The Science
Two recent studies demonstrate the enormous potential for scientists to explore extremely complex molecular mixtures and systems frequently encountered in environmental, biological, atmospheric, and energy research.

The Impact
The Environmental Molecular Sciences Laboratory (EMSL), a Department of Energy Office of Science user facility, has an unprecedented ability to routinely analyze large intact proteins, precisely measure the fine structure of isotopes, and extract more information from complex natural organic matter mixtures. One of the world’s most powerful mass spectrometry instruments, a 21 Tesla Fourier transform ion cyclotron resonance mass spectrometer (21T FTICR MS), is now available to the scientific community. Illustrating the power of this new instrument for biogeochemical research, EMSL scientists were able to make over 8,000 molecular formula assignments from dissolved organic matter mixtures using the 21T FTICR MS. In another study, EMSL users rapidly identified and discovered new types of metal-binding molecules known as siderophores, which are produced by bacterial cells.

Summary
As the highest-performance mass spectrometry technique, the FTICR MS has become increasingly valuable in recent years for various research applications. The FTICR MS determines the mass-to-charge ratio of ions by measuring the frequency at which ions rotate in a magnetic field, providing ultra-high resolution and mass measurement accuracy. The 21T FTICR MS, which is one of only two in the world with this high magnetic field strength, went online at EMSL in 2015. In a recent study, a team of EMSL scientists evaluated performance gains produced by this high magnetic field strength. They found this next-generation instrument empowers routine analysis of large intact proteins, precisely measures the fine structure of isotopes, and elicits more information than ever before from complex natural organic matter mixtures. The initial performance characterization of the 21T FTICR MS demonstrates enormous potential for future applications to extremely complex molecular mixtures and systems frequently encountered in environmental, biological, atmospheric, and energy research. Moreover, this unprecedented level of mass resolution and accuracy will help promote widespread use of top-down proteomics—an approach that enables accurate characterization of different protein variants with different biological activity. As a result, this transformative instrument will enable users from around the world to tackle previously intractable questions related to atmospheric, terrestrial, and subsurface processes; microbial communities; biofuel development; and environmental remediation.

BER PM Contact
Paul Bayer, SC-23.1, 301-903-5324

PI Contact
Ljiljana Paša-Tolic
Environmental Molecular Sciences Laboratory
ljiljana.pasatolic@pnnl.gov

Funding
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, including support of the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science user facility, and the "High Resolution and Mass Accuracy Capability" development project at EMSL.

Publications
J. B. Shaw, T.-Y. Lin, F. E Leach III, A. V. Tolmachev, N. Tolic, E. W. Robinson, D. W. Koppenaal, and L. Paša-Tolic, “21 Tesla Fourier transform ion cyclotron resonance mass spectrometer greatly expands mass spectrometry toolbox.” Journal of the American Society for Mass Spectrometry 27(12), 1929-36 (2016). DOI: 10.1007/s13361-016-1507-9. (Reference link)

L. R. Walker, M. M. Tfaily, J. B. Shaw, N. J. Hess, L. Pasa-Tolic, and D. W. Koppenaal, “Unambiguous identification and discovery of bacterial siderophores by direct injection 21 Tesla Fourier transform ion cyclotron resonance mass spectrometry.” Metallomics (2017). DOI: 10.1039/c6mt00201c. (Reference link)

Related Links
Unraveling Molecular Complexity of Natural Systems
Top-down Proteomics: Onward and Upward

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



The 21 Tesla Fourier transform ion cyclotron resonance mass spectrometer will propel the future direction of environmental, biological, atmospheric, and energy research. [Image courtesy Pacific Northwest National Laboratory]



September 01, 2016

Reconciling Observations and Global Models of Terrestrial Water Fluxes

Water table depth and groundwater flow are key to understanding the amount of water that plants transmit to the atmosphere.

The Science
Plants are one of the largest water users on land, and, through transpiration, they move more water into the atmosphere than streams or rivers move across the landscape. Unlike stream flow, which can be easily observed, measuring and simulating the amount of water plants transmit to the atmosphere is a significant challenge. A new modeling study using high-performance computers (HPCs) shows that lateral groundwater flow, not included in previous modeling approaches, may be the missing link to predicting how important plant water use is to the total hydrologic system.

The Impact
The relative importance of plant transpiration remains one of the largest uncertainties in balancing water at continental scales. Improving the large-scale simulation of plant transpiration will enable scientists to better predict hydrologic response and manage water resources, as well as predict and understand how much freshwater is available globally.

Summary
Using integrated hydrologic simulations that couple vegetation and land-energy processes with surface and subsurface hydrology, the researchers studied the relative importance of transpiration as a fraction of all of the water moving from the land surface to the atmosphere (commonly referred to as transpiration partitioning) at the continental scale. They found that both the total flux of water and transpiration partitioning are connected to water table depth. Because of this connection, including groundwater flow in the model increases transpiration partitioning from 47±13% to 62±12%. This finding suggests that groundwater flow, which is generally simplified or excluded from other continental-scale simulations, may provide a missing link to reconciling observations and global models of terrestrial water fluxes.

BER PM Contact
David Lesmes, SC-23.1, 301-903-2977
Paul Bayer, SC-23.1, 301-903-5324

Contact
Reed Maxwell
Colorado School of Mines
Rmaxwell@mines.edu

Laura Condon
Syracuse University
lecondon@syr.edu

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research and Office of Advanced Scientific Computing through the Interoperable Design of Extreme-scale Application Software (IDEAS) project. Simulations were made possible through support from Yellowstone at the National Center for Atmospheric Research Computational and Information Systems Laboratory.

Publication
Maxwell, R. M., and L. E. Condon. 2016. “Connections Between Groundwater Flow and Transpiration Partitioning,” Science, DOI: 10.1126/science.aaf7891. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Modeling Water Movement. This conceptual diagram compares two approaches for modeling water movement above and below the land surface. Traditional land surface models simplify the system by solving it as a set of discrete columns without lateral groundwater flow, while integrated hydrologic models connect three-dimensional flow in the subsurface with processes at the land surface. [Image courtesy Laura Condon, Syracuse University; Mary Michael Forrester and Reed Maxwell, Colorado School of Mines]



Connecting Water, Plant Function, and Scale. A mosaic of plant and water images making up a single leaf overlaid on the continental United States illustrates the connection between water, plant function, and scale. Continental-scale simulations reconcile previous stand and global scale approaches and link lateral groundwater flow to transpiration partitioning. [Image courtesy Mary Michael Forrester, Colorado School of Mines]



August 26, 2016

A Novel Iron-Loving Bacterium from the Deep Subsurface

New research has uncovered the bacterium Orenia metallireducens, a microorganism from 2 km deep underground capable of reducing iron.

The Science                       
A novel microorganism capable of withstanding high temperatures and briny water was isolated from a geological formation located two kilometers deep within the Illinois Basin. This bacterium, dubbed Orenia metallireducens, has many distinctive properties that allow it to reduce iron minerals such as goethite and hematite. These findings expand current knowledge of how bacteria survive in the deep, hostile environments of the terrestrial subsurface and provide further insights into how life might exist on other planetary bodies.

The Impact
The discovery of O. metallireducens expands current knowledge of the metabolic diversity of bacteria that inhabit the subsurface. Previously thought to be largely sterile, researchers now know that microbial life dwells deep within the fractures and pore spaces of rocks that make up Earth’s crust. These bacteria drive many of the biogeochemical cycles that occur within the subsurface, driving the dissolution and precipitation of minerals as well as the breakdown of organic matter. Understanding the microbially driven mechanisms behind these geochemical transformations is essential for parameterizing Earth system models that seek to quantify the flux of carbon between the atmosphere, soil, and subsurface.

Summary
The microbial reduction of ferric iron minerals is widespread in both terrestrial and marine environments and is potentially one of the earliest forms of metabolisms to evolve on Earth. Due to the abundance of ferric minerals in Earth’s crust, Fe(III) reduction is of global environmental significance, particularly in the subsurface where it contributes to water quality, contaminant fate and transport, and the biogeochemical cycling of carbon. Taking groundwater that was sampled from two kilometers deep underground, researchers isolated a novel member of the phylum Firmicutes, named Orenia metallireducens strain Z6. They found O. metallireducens to have numerous unique properties, including the ability to reduce ferric iron minerals across a broad range of temperature, pH, and salinity. O. metallireducens also lacks the c-type cytochromes that are typically present in bacteria capable of reducing ferric iron such as Geobacter and Shewanella species. The researchers also found that O. metallireducens is the only member of the order Halanaerobiales capable of reducing crystalline iron minerals such as goethite and hematite. This study’s results significantly expand the scope of phylogenetic affiliations, metabolic capabilities, and catalytic mechanisms that are known for iron-reducing microorganisms.

Contacts (BER PM)
Dr. Roland F. Hirsch
Program Manager, U.S. Department of Energy Office of Science
roland.hirsch@science.doe.gov; 301-903-9009

(PI Contact)
Dr. Kenneth M. Kemner
Argonne National Laboratory
kemner@anl.gov; 630-252-1163

Funding
This research is part of the Subsurface Science Scientific Focus Area at Argonne National Laboratory (ANL), which is supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, Subsurface Biogeochemical Research program. Use of the Electron Microscopy Center at Argonne and the Advanced Photon Source is supported by DOE’s Office of Science, Office of Basic Energy Sciences. MRCAT/EnviroCAT operations are supported by DOE and the MRCAT/EnviroCAT member institutions. All work at ANL was performed under contract DE-AC02-06CH11357. This work, including the efforts of Y. Dong, R.A. Sanford, R. A. Locke, Jr., and B. W. Fouke, was funded under DE-FC26-05NT42588. Parts of this work, including the efforts of Y. Dong, R. A. Sanford, J. Y. Chang, and B. W. Fouke, was also funded by National Aeronautics and Space Administration (NNA13AA91A).

Publication
Dong, Y., R. A. Sanford, M. I. Boyanov, K. M. Kemner, T. M. Flynn, E. J. O’Loughlin, Y.-J. Chang, R. A. Locke Jr., J. R. Weber, S. M. Egan, R. I. Mackie, I. Cann, and B. W. Fouke. 2016. “Orenia metallireducens sp. nov. strain Z6, a Novel Metal-Reducing Member of the Phylum Firmicutes from the Deep Subsurface,” Applied and Environmental Microbiology 82(21), 6440-453. DOI:10.1128/aem.02382-16. (Reference link)

Related Links
Subsurface Science Scientific Focus Area at Argonne National Laboratory

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Photo Micrograph of Orenia metallireducens Strain Z6. Inset focus shows peritrichous pili produced by the organism. This bacterium was isolated from groundwater sampled from 2 km deep within the Illinois Basin and can reduce crystalline forms of ferric iron such as goethite and hematite. [Image courtesy Yiran Dong, University of Illinois at Urbana-Champaign]



July 28, 2016

Microbial Respiration in Deep Subsurface Contributes Significant Greenhouse Gas Fluxes to Atmosphere

CO2 production from soils between 2 m and 3.5 m in depth contributes ˜17% of total gas fluxes in a semiarid floodplain.

The Science
Most carbon dioxide (CO2) fluxes leaving the soil surface are commonly attributed to root and microbial respiration occurring at shallow depths (< 1 m). Less understood are respiration rates in the deeper subsurface (> 1-m depth), which contains a large inventory of organic carbon and supports an abundance of microorganisms. In this study, vertical profiles of CO2 concentrations in pore gases, measured from the soil surface down to the water table in a semiarid floodplain, were shown to have significant contributions from microbial respiration in the deeper subsurface or vadose zone, well below the rooting depth and above the water table.

The Impact
The deeper vadose zone was shown to contribute a significant amount of CO2 to the total floodplain—approximately 17% of the surface CO2 flux originates from depths between 2 m and 3.5 m. These contributions are not typically accounted for in Earth system models.

Summary
CO2 fluxes from soils are often assumed to originate within shallow soil horizons (< 1-m depth), whereas relatively little is known about respiration rates at greater depths. Scientists compared measured and calculated CO2 fluxes at the Rifle floodplain along the Colorado River, and measured CO2 production rates of floodplain sediments to determine the relative importance of deeper vadose zone respiration. Calculations based on measured CO2 gradients and estimated effective diffusion coefficients yielded fluxes that are generally consistent with measurements obtained at the soil surface (326 g C m-2 yr-1). CO2 production from the 2 to 3.5-m depth interval was calculated to contribute 17% of the total floodplain respiration, with rates that were larger than some parts of the shallower vadose zone and underlying aquifer. Microbial respiration rates determined from laboratory incubation tests of the sediments support this conclusion. The deeper unsaturated zone typically maintains intermediate water and air saturations, lacks extreme temperatures and salinities, and is annually resupplied with organic carbon from snowmelt-driven recharge and by water table decline. This combination of favorable conditions supports deeper unsaturated zone microbial respiration throughout the year.

BER PM Contact
David Lesmes, SC-23.1, 301-903-2977

PI Contact
Susan Hubbard
Lawrence Berkeley National Laboratory
sshubbard@lbl.gov

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Subsurface Biogeochemical Research program.

Publication
T. K. Tokunaga, Y. Kim, M. E. Conrad, M. Bill, C. Hobson, K. H. Williams, W. Dong, J. Wan, M. J. Robbins, P. E. Long, B. Faybishenko, J. N. Christensen, and S. S. Hubbard, “Deep vadose zone respiration contributions to carbon dioxide fluxes from a semiarid floodplain,” Vadose Zone Journal 15(7) (2016). [DOI: 10.2136/vzj2016.02.0014]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Left: Rifle, Colorado, floodplain vadose zone profile. Middle: Instrumentation for monitoring pore water and gas profiles down to 3.5-m depth. Right: Respiration profiles sustained by organic carbon carried in infiltration water. [Image courtesy Tokunaga, T. K., et al. 2016. Vadose Zone Journal. [DOI: 10.2136/vzj2016.02.0014]



July 27, 2016

Mercury Methylation Genes involved in Additional Microbial Metabolic Pathways

The work supports the hypothesis that the function of HgcA and HgcB is linked to one-carbon metabolism of the acetyl-CoA pathway.

The Science
Comparative proteomics of the global response of Geobacter sulfurreducens PCA following the deletion of mercury methylation genes demonstrates that these genes are involved in other cellular metabolic pathways.

The Impact
This study is the first to compare differences in the proteomes of several strains of G. sulfurreducens PCA, demonstrating that the deletion of the genes for mercury methylation leads to impacts on other key metabolic processes in these strains. This work supports the hypothesis that the function of HgcA and HgcB is linked to one-carbon (C1) metabolism through the folate branch of the acetyl-CoA pathway by providing methyl groups required for mercury methylation.

Summary
In this study, shotgun proteomics was used to compare global proteome profiles between wild-type G. sulfurreducens PCA and two mutant strains in which DhgcAB is deficient in two genes known to be essential for the biosynthesis of methylmercury toxin, and DomcBESTZ is deficient in five outer membrane c-type cytochromes and thus impaired in its ability for dissimilatory metal ion reduction. The team delineated the global response of G. sulfurreducens PCA in both mutants and identified cellular networks and metabolic pathways that were affected by the loss of these genes. Deletion of hgcAB increased the relative abundances of proteins implicated in extracellular electron transfer, including most of the c-type cytochromes, PilA-C and OmpB, whereas deletion of omcBESTZ significantly increased relative abundances of various methyltransferases, suggesting that a loss of dissimilatory reduction capacity results in elevated activity among C1 metabolic pathways. These results support the hypothesis that the function of HgcA and HgcB is linked to C1 metabolism through the folate branch of the acetyl-CoA pathway by providing methyl groups required for mercury methylation.

Contact (BER PM)
Paul Bayer
DOE Office of Biological and Environmental Research
Paul.Bayer@science.doe.gov (301-903-5324)

(PI Contact)
Baohua Gu
Oak Ridge National Laboratory
gub1@ornl.gov (865-574-7286)

Funding
This research was funded by the Office of Biological and Environmental Research within the U.S. Department of Energy’s Office of Science, as part of the Mercury Science Focus Area project at Oak Ridge National Laboratory.

Publication
Qian, C., A. Johs, H. Chen, B. F. Mann, X. Lu, P.E. Abraham, R. L. Hettich, and B. Gu. 2016. “Global Proteome Response to Deletion of Genes Related to Mercury Methylation and Dissimilatory Metal Reduction Reveals Changes in Respiratory Metabolism in Geobacter sulfurreducens PCA,” Journal of Proteome Research 15(10), 3340-49. DOI: 10.1021/acs.jproteome.6b00263. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 15, 2016

Molecular Probes Developed for Mercury Methylating Genes

The new tools will enable researchers to more quickly detect and quantify microbes with these genes in the environment.

The Science
Researchers have developed deoxyribonucleic acid (DNA) and messenger ribonucleic acid (mRNA) probes to not only identify microbes that carry the genes for mercury (Hg) methylation, but also to quantify the extent to which specific types of microbes contribute to the methylation process.

The Impact
The neurotoxin methylmercury (MeHg) poses a serious risk to human health. MeHg production in nature is associated with anaerobic microbes. The development of DNA and mRNA probes represents a substantial improvement over previous work to develop both qualitative and quantitative primers for Hg-methylating genes. These new primers take into consideration the different degrees of methylation potential for specific types of microbes, which ranges from ~10% in the Archaea to ~90% in some Deltaproteobacterial species. These findings will enable a more realistic understanding of possible MeHg generation levels that may occur in a given environment, with the resulting data enabling more accurate risk management assessments.

Summary
Two genes, hgcA and hgcB, are essential for microbial Hg methylation. Detecting and estimating their abundance in microbes in conjunction with quantifying Hg species and other geochemical factors is critical in determining potential hotspots of MeHg generation in at-risk environments. Scientists at Oak Ridge National Laboratory led a team that identified a broad range of degenerate polymerase chain reaction (PCR) primers spanning known hgcAB genes to determine the presence of both genes in diverse environments. These broad-range primers were tested against an extensive set of pure cultures with published genomes that are known to methylate mercury, including 13 Deltaproteobacteria, nine Firmicutes, and nine methanogenic Archaea. For all these types of microbes, the primers not only consistently identified the methylating genes, but they enabled the team to quantify the extent to which each type of microbe methylates Hg. Environmental samples were further used to validate the primers and determine corrective calculations for DNA extraction and PCR amplification efficiencies. Taken together, these findings will enable a more realistic picture of possible MeHg generation levels that may occur in a given environment.

Contact (BER PM)
Paul Bayer
DOE Office of Biological and Environmental Research
Paul.Bayer@science.doe.gov (301-903-5324)

(PI Contact)
Dwayne Elias
Oak Ridge National Laboratory
eliasda@ornl.gov (865-574-0956)

Funding
This research was funded by the Office of Biological and Environmental Research within the U.S. Department of Energy’s Office of Science, as part of the Mercury Science Focus Area project at Oak Ridge National Laboratory.

Publication
G. A. Christensen, A. M. Wymore, A. J. King, M. Podar, R. A. Hurt Jr., E. U. Santillan, A. Soren, C. C. Brandt, S. D. Brown, A. V. Palumbo, J. D. Wall, C. C. Gilmour, and D. A. Elias, “Development and validation of broad-range qualitative and clade-specific quantitative molecular probes for assessing mercury methylation in the environment.” Applied and Environmental Microbiology (2016). DOI:10.1128/ AEM.01271-16. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



New molecular tool probes for genes linked to toxic methylmercury. [Image courtesy Oak Ridge National Laboratory]



June 18, 2016

How Wetlands Naturally Clean Up Contaminants

Highly ordered iron nanoparticles found closely associated with wetland plant roots in the rhizosphere may be key to immobilizing uranium in wetlands.

The Science
Wetland environments are effective at mitigating migration of many groundwater contaminants because of their unique combination of geochemistry, microbiology, and hydrology. A recent study showed iron nanoparticles enriched near wetland plants roots bind natural organic matter to greatly immobilize uranium and possibly other contaminants.

The Impact
This study provides a new perspective on geochemical processes responsible for the observed enrichment of uranium in wetlands. Moreover, the findings shed light on a natural process of environmental remediation that potentially could be harnessed for strategies aimed at immobilizing a wide variety of groundwater contaminants.

Summary
Wetlands inhibit migration of groundwater contaminants through a series of biogeochemical processes that enhance the soil’s capacity to immobilize toxic metals. Past evidence has suggested that the root-impacted soil zone, known as the rhizosphere, might play an important role in contaminant immobilization in wetlands. Plants have adapted to grow in these waterlogged environments by transporting oxygen into the rhizosphere, thereby promoting oxidation of dissolved ferrous iron (Fe(II)) to form ferric iron (Fe(III)) oxyhydroxide and soluble uranium ( precipitates on the root surface, referred to as plaques). A recent study examined whether this type of Fe(II)/Fe(III) cycling in wetlands could participate in immobilizing U(VI)—a highly soluble form of uranium. To explore this possibility, researchers from Savannah River National Laboratory, Environmental Molecular Sciences Laboratory (EMSL), University of Georgia, U.S. Environmental Protection Agency, and Princeton University collected soil samples containing roots from the Tims Branch wetland on the Savannah River Site, a nuclear processing facility in South Carolina. The team characterized subsamples near and far from the roots using wet chemistry and various types of spectroscopy and microscopy. Mössbauer spectroscopy, X-ray computed tomography, transmission electron microscopy, helium ion microscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy were conducted at EMSL, a Department of Energy user facility. The analysis revealed wetland rhizosphere soil is enriched in Fe(III) nanoparticles. Moreover, U(VI) is concentrated in root plaques containing Fe(III)-oxyhydroxide precipitates. These results suggest dissolved Fe(II) from the wetland environment enters the rhizosphere and precipitates as Fe(III) nanoparticles capable of binding U(VI). Taken together, the findings suggest plant roots create biogeochemical conditions conducive to the formation of iron nanoparticles, which, in turn, play an important role in uranium enrichment and contaminant immobilization in wetlands.

BER PM Contact
Paul Bayer, SC-23.1, 301-903-5324

PI Contacts
Daniel Kaplan
Savannah River National Laboratory
daniel.kaplan@srnl.doe.gov

Ravi Kukkadapu
Environmental Molecular Sciences Laboratory
Ravi.Kukkadapu@pnnl.gov

Funding
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Offices of Basic Energy Sciences and Biological and Environmental Research, including support of the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility, and Subsurface Biogeochemical Research program; and Princeton University.

Publication
Kaplan, D. I., R. Kukkadapu, J. C. Seaman, B. W. Arey, A. C. Dohnalkova, S. Buettner, D. Li, T. Varga, K. G. Scheckel, and P. R. Jaffé. 2016. “Iron Mineralogy and Uranium-Binding Environment in the Rhizosphere of a Wetland Soil,” Science of the Total Environment 569-570, 53-64. DOI: 10.1016/j.scitotenv.2016.06.120. (Reference link)

Related Links
EMSL News

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 11, 2016

Snowmelt-Induced Hydrologic Perturbations Drive Dynamic Biogeochemical Behavior in a Shallow Aquifer

Shallow riparian aquifers represent hotspots of biogeochemical activity in the arid western United States.

The Science                                              
Researchers used a high-resolution sampling approach to track subsurface biogeochemical shifts during an annual period of water table fluctuation in a riparian aquifer near Rifle, Colorado. This work provided the first description of microbiological and geochemical responses to increased dissolved oxygen concentrations within the aquifer across a six-month period, revealing how local sediment heterogeneity was responsible for dramatically different shifts in both groundwater chemistry and microbial community structures. Simultaneously, the implementation of a computational framework for predicting biogeochemical behavior throughout the site indicated that seasonal “background” subsurface processes and responses could be successfully modeled.

The Impact
This work resulted in a new understanding of how biogeochemical processes in riparian zones may respond to seasonal hydrologic fluctuations linked to snowmelt discharge. While subsurface regions previously were assumed to be relatively stable ecosystems, the new data indicated that dynamic geochemical and microbiological shifts occur on annual cycles, with implications for carbon cycling, metal mobility, and contaminant sequestration. Additionally, the aquifer site near Rifle is a potential template for riparian aquifers throughout the semi-arid inner mountain western United States, allowing these results to be extrapolated across larger scales. The successful implementation of a modeling framework offers one such approach for this up-scaling and will enable a greater understanding of potential shifts in biogeochemical processes under future climate change scenarios.

Summary
Various regions of the aquifer responded differently to the snowmelt-driven hydrologic perturbation based on redox state, with dissolved oxygen penetrating deeply into oxidized regions, and being rapidly consumed via abiotic reactions in naturally reduced regions, liberating Fe2+ and U6+ species. Microbial community composition varied across spatial and temporal scales. During periods of elevated river stage associated with increasing dissolved oxygen concentrations in the aquifer, microbial community composition favored putative chemolithoautotrophs and heterotrophs, while putative fermenters within the candidate phyla radiation (CPR) were greatly enriched (e.g., members of the Microgenomates and Parcubacteria) during water table fall. Reactive transport modeling was able to capture the dynamic behavior of both the geochemistry and microbiology at the site during the fluctuating hydrology, suggesting that a predictive framework can be developed to better understand biogeochemical responses to future hydrologic dynamics.

Contacts
(BER PM)
David Lesmes, SC-23.1, 301-903-2977
Paul Bayer, SC-23.1, 301-903-5324

(PI Contact)
Michael J. Wilkins
The Ohio State University
wilkins.231@osu.edu

Funding
This work was supported as part of the Genomes to Watershed Scientific Focus Area at Lawrence Berkeley National Laboratory, which is funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under Award Number DEAC02-05CH11231.

Publications
Danczak, R. E., S. B. Yabusaki, K. H. Williams, Y. Fang, C. Hobson, and M. J. Wilkins. 2016. “Snowmelt Induced Hydrologic Perturbations Drive Dynamic Microbiological and Geochemical Behaviors Across a Shallow Riparian Aquifer,” Frontiers in Earth Science 4(57). DOI: 10.3389/feart.2016.00057. (Reference link).

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 11, 2016

A New View of the Tree of Life

Access to a wealth of environments and the ability to reconstruct genomes for previously unknown and uncultured lineages has greatly expanded understanding of the diversity of life on earth.

The Science
A comprehensive three domain tree of life was constructed from all lineages for which sequenced genomes are available. The tree highlights the diversity contained in candidate phyla: lineages with no cultivated representatives for which genome sequences are derived from environmental surveys.

The Impact
The tree of life is one of the most important organizing principles in biology. The new depiction will be useful not only to biologists who study microbial ecology, but also to biochemists searching for novel genes and researchers studying evolution and earth history. This updated view highlights the weight of diversity found within the bacteria and within lineages with no cultured representatives.

Summary
This tree presents a new view of the diversity of life from a genome perspective. Exploration of new environments and deeper sequencing of well-studied systems continue to uncover new organisms and lineages on the tree. To construct a comprehensive tree of life, researchers gathered 3,085 genomes representing all genera for which genomes are available and including over 1,000 newly reconstructed genomes targeting candidate phyla representatives. Sample sites for new genomes included extreme environments like Chile’s Atacama Desert salt flats and Yellowstone National Park hot springs, but also more common environments such as groundwater, estuarine sediment, meadow soil, and dolphin oral microbiomes. The tree inferred from this genomic perspective shows the predominance of bacterial diversity compared to the divergence seen in the Archaea and Eukarya.  Collapsing the tree based on sequence divergence rather than taxonomy highlighted the amount of diversity found within candidate phyla, emphasizing the importance of environmental surveys for discovery of organisms not tractable in laboratory experiments.

Contacts (BER PM)
Todd Anderson
Todd.Anderson@science.doe.gov

David Lesmes
David.Lesmes@science.doi.gov

(PI Contact)
Jillian Banfield
University of California Berkeley
jbanfield@berkeley.edu

Funding
This research was largely supported by Lawrence Berkeley National Laboratory’s (LBNL) Genomes to Watershed Scientific Focus Area funded by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research (BER) under contract DE-AC02-05CH11231. Additional support was provided by LBNL EFRC award DE-AC02-05CH11231; National Aeronautics and Space Administration NESSF grant 12 PLANET12R-0025 and National Science Foundation DEB grant 1406956; DOE BER grant DOE-SC10010566; Office of Naval Research grants N00014-07-1-0287, N00014-10-1-0233, and N00014-11-1-0918; and the Thomas C. and Joan M. Merigan Endowment at Stanford University. In addition, funding was provided by the Ministry of Economy, Trade, and Industry of Japan, and metagenome sequence was generated by DOE’s Joint Genome Institute via the Community Science Program.

Publication
Hug, L. A., B. J. Baker, K. Anantharaman, C. T. Brown, A. J. Probst, C. J. Castelle, C. N. Butterfield, A. W. Hernsdorf, Y. Amano, K. Ise, Y. Suzuki, N. Dudek, D. A. Relman, K. M. Finstad, R. Amundson, B. C. Thomas, and J. F. Banfield. 2016. “A New View of the Tree of Life,” Nature Microbiology 1(16048), DOI: 10.1038/nmicrobiol.2016.48. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 01, 2016

Managing Complexity in Simulations of Land-Surface and Near-Surface Processes

New multiphysics software framework facilitates more realistic, process-based simulations of environmental systems.

The Science  
A new approach has been developed and demonstrated for managing the rapidly increasing complexity of simulations of environmental systems in the critical zone near the land surface. The multiphysics Arcos framework combines modern software design principles in a novel way to create flexibly configured simulators, thus enabling significantly more complex and realistic simulations that combine many individual ecohydrological and biogeochemical processes.

The Impact
As simulations of environmental systems grow in complexity by incorporating more and more ecohydrological and biogeochemical process representations, adding new process understanding while ensuring that individual and coupled-process simulations are reliable has become increasingly difficult. A new multiphysics framework helps tame this runaway complexity, making process-rich simulations easier to develop, test, combine with data, and reconfigure for different numerical experiments. This approach to developing models provides a more natural way for scientists to collaborate on increasingly complex models and helps build confidence in the resulting simulations.

Summary
The Arcos system is based on two graph representations that interact to provide a flexible and extensible framework. The first graph is a process tree representation that defines the coupling among various environmental process representations denoted as process kernels (PKs). Two or more PKs are coupled together through multiprocess coordinators. The second graph defines how the mass and energy balances depend on primary variables (unknowns to be solved for) through a series of intermediate variables. Formal representation of these dependencies in a graph structure makes it easier to substitute new constitutive models and ensures that intermediate variables are always current and consistent among different PKs. Taken together, these two graphs make it possible to define which PKs are to be used and how they are to be coupled at run time. Such a flexibly configured and hierarchical structure is critical to systematically building up complexity supported by rigorous testing and evaluation against observations.

Contacts (BER PM)
David Lesmes and Paul Bayer
SC-23.1
David.Lesmes@science.doe.gov, 301-903-0289; and Paul.Bayer@science.doe.gov, 301-903-1678

(PI Contact)
Ethan T. Coon
Los Alamos National Laboratory
ecoon@lanl.gov; 505-665-8289

Funding
This research was supported by the Interoperable Design of Extreme-scale Application Software (IDEAS) project funded by the U.S. Department of Energy, Office of Science. This work was also supported by Los Alamos National Laboratory’s Laboratory Directed Research and Development Predicting Climate Impacts and Feedbacks in the Terrestrial Arctic project (LDRD201200068DR).

Publication
Coon, E. T., J. D. Moulton, and S. L. Painter. 2016. “Managing Complexity in Simulations of Land Surface and Near-Surface Processes,” Environmental Modelling and Software 78(C), 134-49. DOI: 10.1016/j.envsoft.2015.12.017. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 31, 2016

Mercury and Methylmercury Dynamics in an Industrially Contaminated Stream

Algal biofilms found to be major generators of toxic methylmercury in streams.

The Science
Detailed monitoring of changing mercury (Hg) and methylmercury (MeHg) concentrations in a creek during baseflow and flood events indicates that MeHg is produced within the stream and further suggests that algal biofilms, also called periphyton, are major sources of MeHg production.

The Impact
These findings may explain why past improvements in overall stream water quality have not resulted in concomitant improvements in MeHg concentrations in water and in fish. Additionally, future alterations to stream management practices or climate that alter periphyton abundance, activity, or composition may have unintended negative consequences that could influence MeHg production within the creek.

Summary
Sediments and floodplain soils in the East Fork Poplar Creek (EFPC) watershed in Oak Ridge, Tennessee, are contaminated with high levels of Hg from an industrial source at the headwaters. While baseflow conditions have been monitored, concentrations of Hg and MeHg during high-flow storm events (when the stream is more hydrologically connected to the floodplain) had not yet been assessed. This study evaluates EFPC baseflow and event-driven Hg and MeHg dynamics 5 km upstream of the confluence with Poplar Creek to determine the importance of hydrology to instream concentrations and downstream loads, and to ascertain if dynamics are comparable to systems without an industrial Hg source. Particulate Hg (HgP) and MeHg were positively correlated with discharge (r2=0.64 and 0.58, respectively) and total suspended sediment (r2=0.97 and 0.89, respectively). Dissolved Hg (HgD) also increased with increasing flow (r2=0.18) and was associated with increases in dissolved organic carbon (DOC; r2=0.65) similar to dynamics observed in uncontaminated systems. Dissolved MeHg (MeHgD) decreased with increases in discharge (r2=0.23) and was not related to DOC concentrations (p=0.56), dynamics comparable to relatively uncontaminated watersheds with a small percentage of wetlands (<10%). While stormflows exert a dominant control on HgP, MeHgP, and HgD concentrations and loads, baseflows were associated with the highest MeHgD concentration (0.38 ng/L) and represented the majority of the annual MeHgD load.

BER PM Contact
Paul Bayer, SC-23.1, 301-903-5324

PI Contact
Scott C. Brooks
Oak Ridge National Laboratory
brookssc@ornl.gov

Funding
This work was supported by the U.S. Department of Energy’s (DOE) Subsurface Biogeochemical Research program within DOE’s Office of Science Office of Biological and Environmental Research. The isotope(s) used in this research were supplied by DOE’s Isotope Program within DOE’s Office of Science Office of Nuclear Physics.

Publication
Riscassi, A., C. Miller, and S. Brooks. “Seasonal and flow-driven dynamics of particulate and dissolved mercury and methylmercury in a stream impacted by an industrial mercury source.” Environ. Toxicol. Chem. (2015). [DOI:10.1002/etc.3310]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Dissolved mercury increases during high flow events in streams. [Image courtesy Oak Ridge National Laboratory]



February 02, 2016

Metal Monouranates Found to be Highly Stable

A less common form of uranium may hold the key to remediation efforts.

The Science
A recent study examined in unprecedented detail the structural and thermodynamic properties of uranium (U(V))-containing compounds called metal monouranates. Metal monouranates are of considerable interest because of their relevance to nuclear technology.

The Impact
The new findings on this understudied form of uranium help complete the picture of uranium solid-state chemistry and could improve models of and strategies for minimizing the environmental impact of uranium contamination.

Summary
Uranium poses a serious risk to groundwater contamination at the Department of Energy’s (DOE) Hanford Site and other locations worldwide. Its chemistry is complex because uranium can exist in several different oxidation states, each having different properties. Remediation strategies have focused on developing approaches for converting the highly soluble U(VI) form of uranium into the less soluble U(IV) form, which poses less risk of contamination due to its lower mobility in groundwater and soil. While much research has focused on these two forms of uranium, remediation efforts have been limited by the lack of knowledge about the intermediate U(V) form. To address this question, a team of researchers recently examined in unprecedented detail the structural and thermodynamic properties of U(V)-containing compounds called metal monouranates. U(V)-containing monouranates allow in-depth structural and stability investigations. The research team used a variety of advanced structural and spectroscopic techniques combined with calorimetric measurements and computational modeling. Mossbauer and X-ray photoelectron spectroscopy (XPS) analyses were performed at the RadEMSL radiochemistry facility at the Environmental Molecular Sciences Laboratory (EMSL), a DOE national scientific user facility. This project received major support from the DOE Energy Frontier Research Center, “Materials Science of Actinides.” It was led by the University of California, Davis, and included participation by a team of scientists from Pacific Northwest National Laboratory; Los Alamos National Laboratory; Argonne National Laboratory; and Lawrence Berkeley National Laboratory; as well as the Nuclear Energy Center of the Negev, Israel; University of California, Berkeley; University of Michigan; and University of Chicago. The research team confirmed the presence of U(V) in the thermodynamically stable metal monouranates CrUO4 and FeUO4. The structural and thermodynamic behavior of U5+ elucidated in this work is relevant to applications in the nuclear industry and radioactive waste disposal. For example, the thermodynamic studies suggest these compounds are highly stable, making them potentially useful in precipitating uranium from oxidizing aqueous environments.

BER PM Contact
Paul Bayer, SC-23.1, 301-903-5324

PI Contact
Alexandra Navrotsky
University of California, Davis
anavrotsky@ucdavis.edu

Funding
This work was supported by DOE’s Office of Science, Office of Biological and Environmental Research, including support of EMSL, a DOE Office of Science user facility. Major funding was provided by the DOE Energy Frontier Research Center, Materials Science of Actinides, under DOE’s Office of Basic Energy Sciences. This work also was supported by the National Science Foundation, DOE GeoSciences program, and the Laboratory-Directed Research and Development Program at Los Alamos National Laboratory.

Publication
Guo, X., et al. “U(V) in metal urinates: a combined experimental and theoretical study of MgUO4, CrUO4 and FeUO4.” Dalton Trans. 45, 4622–32 (2016). [DOI: 10.1039/c6dt00066e]. (Reference link)

Related Links
EMSL website

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER