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Bill Batchelor - One of the best experts on this subject based on the ideXlab platform.

  • reductive capacity of natural reductants
    Environmental Science & Technology, 2003
    Co-Authors: Woojin Lee, Bill Batchelor
    Abstract:

    Reductive capacities of Soil Minerals and Soil for Cr(VI) and chlorinated ethylenes were measured and characterized to provide basic knowledge for in-situ and ex-situ treatment using these natural reductants. The reductive capacities of iron-bearing sulfide (pyrite), hydroxide (green rust; GR(SO4)), and oxide (magnetite) Minerals for Cr(VI) and tetrachloroethylene (PCE) were 1-3 orders of magnitude greater than those of iron-bearing phyllosilicates (biotite, vermiculite, and montmorillonite). The reductive capacities of surface Soil collected from the plains of central Texas were similar and slightly greater than those of iron-bearing phyllosilicates. The reductive capacity of iron-bearing Soil Minerals for Cr(VI) was roughly 3-16 times greater than that for PCE, implying that Cr(VI) is more susceptible to being reduced by Soil Minerals than is PCE. GR(SO4) has the greatest reductive capacity for both Cr(VI) and PCE followed by magnetite, pyrite, biotite, montmorillonite, and vermiculite. This order was the same for both target compounds, which indicates that the relative reductive capacities of Soil Minerals are consistent. The reductive capacities of pyrite and GR(SO4) for chlorinated ethylenes decreased in the order: trichloroethylene (TCE) > PCE > cis-dichloroethylene (c-DCE) > vinyl chloride (VC). Fe(II) content in Soil Minerals was directly proportional to the reductive capacity of Soil Minerals for Cr(VI) and PCE, suggesting that Fe(II) content is an important factor that significantly affects reductive transformations of target contaminants in natural systems.

  • abiotic reductive dechlorination of chlorinated ethylenes by iron bearing Soil Minerals 2 green rust
    Environmental Science & Technology, 2002
    Co-Authors: Woojin Lee, Bill Batchelor
    Abstract:

    Abiotic reductive dechlorination of chlorinated ethylenes by the sulfate form of green rust (GR(SO4)) was examined in batch reactors. Dechlorination kinetics were described by a modified Langmuir-Hinshelwood model. The rate constant for reductive dechlorination of chlorinated ethylenes at reactive GR(SO4) surfaces was in the range of 0.592 (+/-4.4%) to 1.59 (+/-6.3%) day(-1). The specific reductive capacity of GR(SO4) for target organics was in the range of 9.86 (+/-10.1%) to 18.0 (+/-4.3%) microM/g and sorption coefficient was in the range of 0.53 (+/-2.4%) to 1.22 (+/-4.3%) mM(-1). Surface area-normalized pseudo-first-order initial rate constants for chlorinated ethylenes by GR(SO4) were 3.4 to 8.2 times greater than those by pyrite. Chlorinated ethylenes were mainly transformed to acetylene, and no detectable amounts of chlorinated intermediates were observed. The rate constants for the reductive dechlorination of trichloroethylene (TCE) increased as pH increased (6.8 to 10.1) but were independent of solid concentration and initial TCE concentration. Magnetite and/or maghemite were produced by the oxidation of GR(SO4) by TCE. These findings are relevant to the understanding of the role of abiotic reductive dechlorination during natural attenuation in environments that contain GR(SO4).

  • abiotic reductive dechlorination of chlorinated ethylenes by iron bearing Soil Minerals 1 pyrite and magnetite
    Environmental Science & Technology, 2002
    Co-Authors: Woojin Lee, Bill Batchelor
    Abstract:

    Abiotic reductive dechlorination of chlorinated ethylenes (tetrachloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (cis-DCE), and vinyl chloride (VC)) by pyrite and magnetite was c...

  • abiotic reductive dechlorination of chlorinated ethylenes by iron bearing Soil Minerals 1 pyrite and magnetite
    Environmental Science & Technology, 2002
    Co-Authors: Woojin Lee, Bill Batchelor
    Abstract:

    Abiotic reductive dechlorination of chlorinated ethylenes (tetrachloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (cis-DCE), and vinyl chloride (VC)) by pyrite and magnetite was characterized in a batch reactor system. Dechlorination kinetics was adequately described by a modified Langmuir−Hinshelwood model that includes the effect of a decreasing reductive capacity of Soil mineral. The kinetic rate constant for the reductive dechlorination of target organics at reactive sites of Soil Minerals was in the range of 0.185 (±0.023) to 1.71 (±0.06) day-1. The calculated specific reductive capacity of Soil Minerals for target organics was in the range of 0.33 (±0.02) to 2.26 (±0.06) μM/g and sorption coefficient was in the range of 0.187 (±0.006) to 0.7 (±0.022) mM-1. Surface area-normalized pseudo-first-order initial rate constants for target organics by pyrite were found to be 23.5 to 40.3 times greater than those by magnetite. Target organics were mainly transformed to acetylene and small a...

Steven D Allison - One of the best experts on this subject based on the ideXlab platform.

  • controls on the temperature sensitivity of Soil enzymes a key driver of in situ enzyme activity rates
    2010
    Co-Authors: Steven D Allison, Megan J Steinweg, Matthew D Wallenstein, Jessica G Ernakovich, Robert L Sinsabaugh
    Abstract:

    Enzyme activities are commonly measured in lab assays at a single standard temperature, which does not provide any information on their temperature sensitivity. Temperature is one of the primary controls on enzyme activities, yet few studies have explored how temperature drives enzyme activities in the environment. The temperature sensitivity of enzyme activity is controlled by the structure and conformation of the isoenzymes that constitute an environmental enzyme pool as well as physical and chemical interactions with Soil Minerals, clays, and organic matter. Yet, these complex relationships are typically represented by a simple Q 10 of 2. There is sufficient evidence to suggest that even for the same enzyme class, temperature sensitivities vary between Soils, and even seasonally in a single site. We will explore the controls on enzyme temperature sensitivity and their importance for understanding seasonal patterns in Soil processes and their potential responses to global change.

  • Soil Minerals and humic acids alter enzyme stability implications for ecosystem processes
    Biogeochemistry, 2006
    Co-Authors: Steven D Allison
    Abstract:

    In most ecosystems, the degradation of complex organic material depends on extracellu- lar enzymes produced by microbes. These en- zymes can exist in bound or free form within the Soil, but the dynamics of these different enzyme pools remain uncertain. To address this uncer- tainty, I determined rates of enzyme turnover in a volcanic Soil with and without added enzymes. I also tested whether or not Soil Minerals and hu- mic acids would alter enzyme activity. In Soils that were gamma-irradiated to stop enzyme produc- tion, 35-70% of the enzyme activity was stable throughout the 21-day incubation. The remaining enzyme fraction decayed at rates ranging from - 0.032 to - 0.628 day -1 . In both the irradiated Soils and in Soils with added enzymes, addition of the mineral allophane had a strong positive effect on most enzyme activities. Another added mineral, ferrihydrite, had a weak positive effect on some enzymes. Added humic acids strongly inhibited enzyme activity. These findings suggest that Minerals, especially allophane, enhance potential enzyme activities in young volcanic Soils. How- ever, the actual activity and function of these enzymes may be low under field conditions if stabilization results in less efficient enzyme-sub- strate interactions. If this is the case, then much of the measured enzyme activity in bulk Soil may be stabilized but unlikely to contribute greatly to ecosystem processes.

Thea Whitman - One of the best experts on this subject based on the ideXlab platform.

  • microbial community assembly differs across Minerals in a rhizosphere microcosm
    Environmental Microbiology, 2018
    Co-Authors: Thea Whitman, R Neurath, Adele Perera, Daliang Ning, Jizhong Zhou, P S Nico, Ilexis Chujacoby, Jennifer Pettridge
    Abstract:

    Mineral-associated microbes drive many critical Soil processes, including mineral weathering, Soil aggregation and cycling of mineral-sorbed organic matter. To investigate the interactions between Soil Minerals and microbes in the rhizosphere, we incubated three types of Minerals (ferrihydrite, kaolinite and quartz) and a native Soil mineral fraction near roots of a common Californian annual grass, Avena barbata, growing in its resident Soil. We followed microbial colonization of these Minerals for up to 2.5 months - the plant's lifespan. Bacteria and fungi that colonized mineral surfaces during this experiment differed across mineral types and differed from those in the background Soil, implying that microbial colonization was the result of processes in addition to passive movement with water to mineral surfaces. Null model analysis revealed that dispersal limitation was a dominant factor structuring mineral-associated microbial communities for all mineral types. Once bacteria arrived at a mineral surface, capacity for rapid growth appeared important, as ribosomal copy number was significantly correlated with relative enrichment on Minerals. Glomeromycota (a phylum associated with arbuscular mycorrhizal fungi) appeared to preferentially associate with ferrihydrite surfaces. The mechanisms enabling the colonization of Soil Minerals may be foundational in shaping the overall Soil microbiome composition and development of persistent organic matter in Soils.

  • microbial community assembly differs by mineral type in the rhizosphere
    bioRxiv, 2017
    Co-Authors: Thea Whitman, R Neurath, Adele Perera, Daliang Ning, Jizhong Zhou, P S Nico, Jennifer Pettridge, Mary K Firestone
    Abstract:

    Inputs of root carbon (C) fuel growth of nearby Soil microorganisms. If these microbes associate with Soil Minerals, then mineral-microbiome complexes near roots could be a gateway towards stabilization of Soil carbon and may influence the quantity and quality of persistent SOM. To investigate the interactions between roots, Soil Minerals, and microbes, we incubated three types of Minerals (ferrihydrite, kaolinite, quartz) and a native Soil mineral fraction near roots of a common Californian annual grass, Avena barbata, growing in its resident Soil. We followed microbial colonization of these Minerals for 2.5 months - the plant9s lifespan. Bacteria and fungi that colonized mineral surfaces during this experiment differed across mineral types and differed from those in the background Soil, implying microbial colonization was the result of processes in addition to passive movement with water to mineral surfaces. Null model analysis revealed that dispersal limitation was a dominant factor structuring mineral-associated microbial communities for all mineral types. Once bacteria arrived at a mineral surface, capacity for rapid growth appeared important, as ribosomal copy number was significantly correlated with relative enrichment on Minerals. Glomeromycota (a phylum associated with arbuscular mycorrhizal fungi) appeared to preferentially associate with ferrihydrite surfaces. The mechanisms enabling colonization of Soil Minerals may be foundational to the overall Soil microbiome composition and partially responsible for the persistence of C entering Soil via plant roots.

Markus Kleber - One of the best experts on this subject based on the ideXlab platform.

  • Mineral Surfaces as Agents of Environmental Proteolysis: Mechanisms and Controls
    2019
    Co-Authors: Stephany S. Chacon, Patrick N. Reardon, Christopher J. Burgess, Samuel Purvine, Rosalie K. Chu, Therese R. Clauss, Eric Walter, David D. Myrold, Nancy Washton, Markus Kleber
    Abstract:

    We investigated the extent to which contact with mineral surfaces affected the molecular integrity of a model protein, with an emphasis on identifying the mechanisms (hydrolysis, oxidation) and conditions leading to protein alteration. To this end, we studied the ability of four mineral surface archetypes (negatively charged, positively charged, neutral, redox-active) to abiotically fragment a well-characterized protein (GB1) as a function of pH and contact time. GB1 was exposed to the Soil Minerals montmorillonite, goethite, kaolinite, and birnessite at pH 5 and pH 7 for 1, 8, 24, and 168 h and the supernatant was screened for peptide fragments using Tandem Mass Spectrometry. To distinguish between products of oxidative and hydrolytic cleavage, we combined results from the SEQUEST algorithm, which identifies protein fragments that were cleaved hydrolytically, with the output of a deconvolution algorithm (DECON-Routine) designed to identify oxidation fragments. All four Minerals were able to induce protein cleavage. Manganese oxide was effective at both hydrolytic and oxidative cleavage. The fact that phyllosilicateswhich are not redox activeinduced oxidative cleavage indicates that surfaces acted as catalysts and not as reactants. Our results extend previous observations of proteolytic capabilities in Soil Minerals to the groups of phyllosilicates and Fe-oxides. We identified structural regions of the protein with particularly high susceptibility to cleavage (loops and β strands) as well as regions that were entirely unaffected (α helix)

  • persistence of Soil organic matter in eroding versus depositional landform positions
    Journal of Geophysical Research, 2012
    Co-Authors: Asmeret Asefaw Berhe, Markus Kleber, Jennifer W Harden, Margaret S Torn, Sarah D Burton, John Harte
    Abstract:

    Soil organic matter (SOM) processes in dynamic landscapes are strongly influenced by Soil erosion and sedimentation. We determined the contribution of physical isolation of organic matter (OM) inside aggregates, chemical interaction of OM with Soil Minerals, and molecular structure of SOM in controlling storage and persistence of SOM in different types of eroding and depositional landform positions. By combining density fractionation with elemental and spectroscopic analyses, we showed that SOM in depositional settings is less transformed and better preserved than SOM in eroding landform positions. However, which environmental factors exert primary control on storage and persistence of SOM depended on the nature of the landform position considered. In an annual grassland watershed, protection of SOM by physical isolation inside aggregates and chemical association of organic matter (complexation) with Soil Minerals, as assessed by correlation with radiocarbon concentration, were more effective in the poorly drained, lowest-lying depositional landform positions, compared to well-drained landform positions in the upper parts of the watershed. Results of this study demonstrated that processes of Soil erosion and deposition are important mechanisms of long-term OM stabilization.

  • poorly crystalline mineral phases protect organic matter in acid subSoil horizons
    European Journal of Soil Science, 2005
    Co-Authors: Markus Kleber, Robert Mikutta, M S Torn, Reinhold Jahn
    Abstract:

    Summary Soil Minerals are known to influence the biological stability of Soil organic matter (SOM). Our study aimed to relate properties of the mineral matrix to its ability to protect organic C against decomposition in acid Soils. We used the amount of hydroxyl ions released after exposure to NaF solution to establish a reactivity gradient spanning 12 subSoil horizons collected from 10 different locations. The subSoil horizons represent six Soil orders and diverse geological parent materials. Phyllosilicates were characterized by X-ray diffraction and pedogenic oxides by selective dissolution procedures. The organic carbon (C) remaining after chemical removal of an oxidizable fraction of SOM with NaOCl solution was taken to represent a stable organic carbon pool. Stable organic carbon was confirmed as older than bulk organic carbon by a smaller radiocarbon (14C) content after oxidation in all 12 Soils. The amount of stable organic C did not depend on clay content or the content of dithionite–citrate-extractable Fe. The combination of oxalate-extractable Fe and Al explained the greatest amount of variation in stable organic C (R2 = 0.78). Our results suggest that in acid Soils, organic matter is preferentially protected by interaction with poorly crystalline Minerals represented by the oxalate-soluble Fe and Al fraction. This evidence suggests that ligand exchange between mineral surface hydroxyl groups and negatively charged organic functional groups is a quantitatively important mechanism in the stabilization of SOM in acid Soils. The results imply a finite stabilization capacity of Soil Minerals for organic matter, limited by the area density of reactive surface sites.

Rota Wagai - One of the best experts on this subject based on the ideXlab platform.

  • climate and parent material controls on organic matter storage in surface Soils a three pool density separation approach
    Geoderma, 2008
    Co-Authors: Kanehiro Kitayama, Lawrence M Mayer, Rota Wagai, Heike Knicker
    Abstract:

    article Physically- and biochemically-distinct fractions of Soil organic matter (SOM) can be separated by density to yield: (i) low-density plant detritus fraction easily separable from Soil Minerals (f-LF), (ii) low-density materials strongly associated with Minerals (m-LF), and (iii) high-density fraction (HF) rich in microbially- processed organic matter strongly associated with Minerals. The factors controlling the pool size and chemistry in these fractions, especially those in m-LF, are unclear. We examined the influence of climate and parent material on SOM in these fractions using two sets of forest Soils (0-10 cm mineral horizon) developed from contrasting parent materials (metasedimentary vs. ultrabasic igneous rock) along an altitudinal gradient in Mt. Kinabalu, Borneo. From 700 m to upper altitudes (1700, 2700 m), where mean annual temperature decreases from 24 to 12 °C with roughly constant rainfall, surface Soil C stocks on both parent