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  • Chorover, Jon  (16)
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  • 1
    Language: English
    In: Geology, Feb, 2005, Vol.33(2), p.117(4)
    Description: Considerable mobilization of Fe without mobilization of Al in Precambrian paleosols has been documented and attributed to either anoxic- or ligand-promoted dissolution. To elucidate these mechanisms, basalt was dissolved under oxic and anoxic conditions with and without citrate, and the mobility of several elements was analyzed. The extent of release of Fe and P was minor (in citrate-free conditions) or considerable (with citrate) regardless of oxygen pressure. Release of AI was minor in all cases, whereas release of Cu was minor (in anoxic conditions) or considerable (in oxic conditions). Release of Cu was enhanced by citrate. In comparison, in the weathered surface of two of the oldest-known basalt-derived paleosols--the Mount Roe (2.76 Ga) and the Hekpoort (2.25 Ga)--Fe and P were considerably depleted and Al retained, consistent with the presence of organic ligands. Cu, retained in the Mount Roe paleosol but considerably mobilized in the Hekpoort paleosol, documents formation under an anoxic atmosphere and an oxic atmosphere, respectively, as inferred by others on the basis of Fe mobility. The immobility of AI in both paleosols is consistent with formation under conditions in which the annual volume of rainwater was lower than the topsoil pore volume. Mobilization of P in such paleosols developed under low-rainfall conditions provides a new proxy for identification of ligands secreted by terrestrial organisms on early Earth. Keywords: Precambrian paleosols, organic ligands, basalt, element mobility, dissolution, early Earth.
    Keywords: Iron Compounds -- Research ; Precambrian Era -- Natural History ; Organic Compounds -- Research ; Organic Compounds -- Environmental Aspects
    ISSN: 0091-7613
    E-ISSN: 19432682
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  • 2
    Language: English
    In: Chemical Geology, 2010, Vol.278(1), pp.1-14
    Description: The primary objective of this research was to investigate the effects of aliphatic and aromatic low molecular weight organic acids (LMWOAs) on rare earth element and yttrium (REY) release from the phosphate minerals apatite and monazite. Since prior studies have shown that redox status can affect REY partitioning during incongruent dissolution, a secondary objective was to assess the influence of dissolved O concentration. Increasing LMWOA concentrations from 0 to 10 mM resulted in enhanced REY release. In general, REY release increased in the order: no ligand ≈ salicylate 〈 phthalate ≈ oxalate 〈 citrate. REY–ligand stability constants were only useful for predicting REY release for oxalate reacted with apatite and phthalate reacted with monazite. The role of dissolved oxygen in dissolution of the phosphate minerals was mixed and inconsistent. Mineral type was observed to significantly affect REY pattern development. REY release patterns for apatite range from nearly flat to those exhibiting the lanthanide contraction effect (radius-dependent fractionation); whereas, monazite REY release patterns are best described as exhibiting an M-type lanthanide tetrad effect (radius-independent fractionation). Weathering of apatite in the presence of aliphatic LMWOAs resulted in development of the lanthanide contraction effect fractionation pattern, and the aliphatic LMWOAs further developed MREE and radius-independent fractionation during monazite dissolution. Geochemical and mineral-specific REY signatures may, therefore, have utility for distinguishing the impacts of biota on soil weathering processes on early Earth. The development of such signatures may be mitigated, in part, by accessory mineral composition, the types and concentration of LMWOAs present, and precipitation of secondary minerals.
    Keywords: Apatite ; Dissolution ; Monazite ; Organic Acids ; Rare Earth Elements ; Yttrium ; Geology
    ISSN: 0009-2541
    E-ISSN: 1872-6836
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  • 3
    Language: English
    In: American Journal of Science, June, 2006, Vol.306(6), p.451-473
    Description: A study was conducted on Yosemite granite from the Tuolumne River series by dissolving under oxic and anoxic conditions in the presence and absence of organic ligands in batch experiments at pH 6. It was found that the release of all elements from granite was enhanced considerably in the presence of 0.001M and 0.01M organic ligands in comparison to ligand-free dissolution experiments emphasizing the importance of low-molecular weight organic acids in weathering of primary minerals.
    Keywords: Granite -- Chemical Properties ; Granite -- Environmental Aspects ; Ligands (Chemistry)
    ISSN: 0002-9599
    E-ISSN: 1945452X
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  • 4
    Language: English
    In: American Journal of Science, Feb, 2005, Vol.305(2), p.147-185
    Description: The contribution of ligands during weathering on Earth is discussed. The effects of the ligands generally followed trends in cation-ligand, stability constants, but aromatic ligands are less effective in element mobilization than aliphatic ligands.
    Keywords: Basalt -- Environmental Aspects ; Ligands (Chemistry) -- Research ; Organic Acids -- Environmental Aspects
    ISSN: 0002-9599
    E-ISSN: 1945452X
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  • 5
    Language: English
    In: Journal of Colloid And Interface Science, 2005, Vol.283(1), pp.160-170
    Description: Mesoporous and nonporous SiO and Al O adsorbents were reacted with the fluoroquinolone carboxylic acid ofloxacin over a range of pH values (2–10) and initial concentrations (0.03–8 mM) to investigate the effects of adsorbent type and intraparticle mesopores on adsorption/desorption. Maximum ofloxacin adsorption to SiO surfaces occurs slightly below the p (pH 8.28) of the antibiotic and sorption diminishes rapidly at pH 〉 p . For Al O , maximum sorption is observed at pH values slightly higher than the adsorbent's point of zero net charge (p.z.n.c.) and less than midway between the p values of ofloxacin. The effects of pH on adsorption and ATR–FTIR spectra suggest that the zwitterionic compound adsorbs to SiO solids through the protonated N in the piperazinyl group and, possibly, a cation bridge; whereas the antibiotic sorbs to Al O solids through the ketone and carboxylate functional groups via a ligand exchange mechanism. Sorption edge and isotherm experiments show that ofloxacin exhibits a higher affinity for mesoporous SiO and nonporous Al O , relative to their counterparts. It is hypothesized that decreased ofloxacin sorption to mesoporous Al O occurs due to electrostatic repulsion within pore confines. In contrast, it appears that the environment within SiO mesopores promotes sorption by inducing formation of ofloxacin–Ca complexes, thus increasing electrostatic attraction to SiO surfaces.
    Keywords: Ofloxacin ; Fluoroquinolone Carboxylic Acid ; Mesoporosity ; Sorption Edge ; Adsorption/Desorption Isotherms ; Atr–Ftir Spectroscopy ; Molecular Modeling ; Mineral–Organic Interactions ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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  • 6
    Language: English
    In: Journal of Colloid And Interface Science, 2004, Vol.272(1), pp.10-20
    Description: Two SiO 2 and three Al 2 O 3 adsorbents with varying degrees of mesoporosity (pore diameter 2–50 nm) were reacted with 2,4-dichlorophenoxyacetic acid (2,4-D) at pH 6 to investigate the effects of intraparticle mesopores on adsorption/desorption. Anionic 2,4-D did not adsorb onto either SiO 2 solid, presumably because of electrostatic repulsion, but it did adsorb onto positively charged Al 2 O 3 adsorbents, resulting in concave isotherms. The Al 2 O 3 adsorbent of highest mesoporosity consistently adsorbed more 2,4-D per unit surface area than did the nonporous and less mesoporous Al 2 O 3 adsorbents over a range of initial 2,4-D solution concentrations (0.025–2.5 mM) and reaction times (30 min–55 d). Differences in adsorption efficiency were observed despite equivalent surface site densities on the three Al 2 O 3 adsorbents. Hysteresis between the adsorption/desorption isotherms was not observed, indicating that adsorption is reversible. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy studies confirm that 2,4-D adsorption does not occur via ligand exchange, but rather via electrostatic interaction. The results indicate that adsorbent intraparticle mesopores can result in consistently greater 2,4-D adsorption, but the amount adsorbed is dependent upon surface charge and the presence of adsorbent mesoporosity. The data also suggest that when mineral pores are significantly larger than the adsorbate, they do not contribute to diffusion-limited adsorption/desorption hysteresis. Adsorbent transformations through time are discussed.
    Keywords: Mesoporosity ; X-Ray Diffraction ; Mineral Transformation ; 2,4-D ; Adsorption/Desorption Isotherms ; Freundlich Isotherm ; Frumkin–Fowler–Guggenheim Isotherm ; Atr-Ftir Spectroscopy ; Mineral–Organic Interactions ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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  • 7
    Language: English
    In: Earth Surface Dynamics Discussions, 06/19/2017, pp.1-30
    Description: The critical zone (CZ), the dynamic living skin of the Earth, extends from the top of the vegetation canopy through the soil and down to fresh bedrock and the bottom of groundwater. All humans live in and depend on the critical zone. This zone has three co-evolving surfaces: the top of the vegetation canopy, the ground surface, and a deep subsurface below which Earth’s materials are unweathered. The US National Science Foundation supported network of nine critical zone observatories has made advances in three broad critical zone research areas. First, monitoring has revealed how natural and anthropogenic inputs at the vegetation canopy and ground surface cause subsurface responses in water, regolith structure, minerals, and biotic activity to considerable depths. This response in turn impacts above-ground biota and climate. Second, drilling and geophysical imaging now reveal how the deep subsurface of the CZ varies across landscapes, which in turn influences above-ground ecosystems. Third, several mechanistic models providing quantitative predictions of the spatial structure of the subsurface of the CZ have been proposed. 〈br〉〈br〉 Many countries now fund networks of critical zone observatories (CZOs) to measure the fluxes of solutes, water, energy, gas, and sediments in the CZ and some relate these observations to the histories of those fluxes recorded in landforms, biota, soils, sediments, and rocks. Each U.S. observatory has succeeded in synthesizing observations across disciplines; providing long-term measurements to compare across sites; testing and developing models; collecting and measuring baseline data for comparison to catastrophic events; stimulating new process-based hypotheses; catalyzing development of new techniques and instrumentation; informing the public about the CZ; mentoring students and teaching about emerging multi-disciplinary CZ science; and discovering new insights about the CZ. Many of these activities can only be accomplished with observatories. Here we review the CZO experiment in the US and identify how such a network could evolve in the future. Specifically, we recognize the need for the network to study network-level questions, expand the environments under investigation, accommodate both hypothesis testing and monitoring, and involve more stakeholders. We propose a 〈q〉hubs-and-campaigns〈/q〉 model that promotes study of the CZ as one unit. Only with such integrative efforts will we learn to steward the life-sustaining critical zone now and into the future.
    ISSN: Earth Surface Dynamics Discussions
    ISSN: 2196632X
    E-ISSN: 2196-6338
    Source: CrossRef
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  • 8
    Language: English
    In: Earth Surface Dynamics, Dec 18, 2017, Vol.5(4), p.841
    Description: The critical zone (CZ), the dynamic living skin of the Earth, extends from the top of the vegetative canopy through the soil and down to fresh bedrock and the bottom of the groundwater. All humans live in and depend on the CZ. This zone has three co-evolving surfaces: the top of the vegetative canopy, the ground surface, and a deep subsurface below which Earth's materials are unweathered. The network of nine CZ observatories supported by the US National Science Foundation has made advances in three broad areas of CZ research relating to the co-evolving surfaces. First, monitoring has revealed how natural and anthropogenic inputs at the vegetation canopy and ground surface cause subsurface responses in water, regolith structure, minerals, and biotic activity to considerable depths. This response, in turn, impacts aboveground biota and climate. Second, drilling and geophysical imaging now reveal how the deep subsurface of the CZ varies across landscapes, which in turn influences aboveground ecosystems. Third, several new mechanistic models now provide quantitative predictions of the spatial structure of the subsurface of the CZ.Many countries fund critical zone observatories (CZOs) to measure the fluxes of solutes, water, energy, gases, and sediments in the CZ and some relate these observations to the histories of those fluxes recorded in landforms, biota, soils, sediments, and rocks. Each US observatory has succeeded in (i) synthesizing research across disciplines into convergent approaches; (ii) providing long-term measurements to compare across sites; (iii) testing and developing models; (iv) collecting and measuring baseline data for comparison to catastrophic events; (v) stimulating new process-based hypotheses; (vi) catalyzing development of new techniques and instrumentation; (vii) informing the public about the CZ; (viii) mentoring students and teaching about emerging multidisciplinary CZ science; and (ix) discovering new insights about the CZ. Many of these activities can only be accomplished with observatories. Here we review the CZO enterprise in the United States and identify how such observatories could operate in the future as a network designed to generate critical scientific insights. Specifically, we recognize the need for the network to study network-level questions, expand the environments under investigation, accommodate both hypothesis testing and monitoring, and involve more stakeholders. We propose a driving question for future CZ science and a hubs-and-campaigns model to address that question and target the CZ as one unit. Only with such integrative efforts will we learn to steward the life-sustaining critical zone now and into the future.
    Keywords: Terrestrial Planets – Analysis ; Vegetation Management – Analysis
    ISSN: 2196-6311
    E-ISSN: 2196632X
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  • 9
    Language: English
    In: Chemical Geology, 2006, Vol.234(1), pp.28-45
    Description: We have previously suggested that mobility patterns of P and Y in paleosols could serve as “organomarkers” to denote the presence of organic ligands secreted by terrestrial organisms on early Earth. In addition, our data indicate that Cu depletion may provide a viable oxymarker for determining the presence of atmospheric oxygen during soil weathering processes. In this research, we continue pursuing the potential for utilizing these elements as markers by investigating dissolution of Durango apatite (Ca (PO ) (F,Cl,OH) ) and Messina chalcopyrite (CuFeS ) reacted under batch conditions in the presence and absence of two aliphatic and aromatic organic acids under oxic and anoxic conditions. In general, results show that organic acids enhance element release from apatite (Ca, P and Y) and chalcopyrite (Cu, Fe, and Y), and increasing organic acid concentrations from 1 to 10 mM results in greater dissolution. The aliphatic organic acid citrate enhances mineral dissolution to the greatest extent and dissolution in the presence of aromatic salicylate or absence of ligand is lowest. Release of Ca, P, and Y from apatite was not impacted by dissolved O (g) while release of Cu from chalcopyrite was impacted. Aqueous Cu concentrations at the end of batch experiments with chalcopyrite are four orders of magnitude greater under oxic conditions, whereas Fe concentrations are substantially higher under anoxic conditions. These data support the hypothesis that release of P and Y from apatite is enhanced by organic acids and that Cu release is impacted significantly by dissolved O (g) and, to a lesser extent, organic acids. Thus, it seems plausible that geochemical and mineralogical signatures of P, Y, and Cu may have utility for distinguishing the presence of terrestrial organisms and atmospheric conditions during soil weathering processes on early Earth.
    Keywords: Apatite ; Chalcopyrite ; Organic Acids ; Dissolution ; Organomarker ; Oxymarker ; Geology
    ISSN: 0009-2541
    E-ISSN: 1872-6836
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  • 10
    Language: English
    In: Developments in Earth Surface Processes, pp.15-78
    Description: The US National Science Foundation (NSF) has pioneered an integrated approach to the study of Earth’s Critical Zone by supporting a network of Critical Zone Observatories (CZOs). The CZOs are intensively studied and monitored sites with a focus on a range of Critical Zone processes that are well represented at the various sites. The initial network (beginning in 2007) consisted of 3 CZOs, expanded to 6 in 2009, and is currently expanding to a total of 10 in 2014. The investment in financial and human resources into the CZOs has enabled a range of new scientific investigations that were not accessible under traditional funding mechanisms, and this is leading to novel and exciting advances in scientific understanding of a fundamentally important part of the Earth system.
    Keywords: Critical Zone ; Critical Zone Observatories ; watershed ; CZO network ; Anthropocene
    ISBN: 978-0-444-63369-9
    ISSN: 0928-2025
    Source: ScienceDirect (Elsevier B.V.)
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