Publications (13) View all
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Article: Podzolisation and exportation of organic matter in black waters of the Rio Negro (upper Amazon basin, Brazil)
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ABSTRACT: In the Rio Negro basin, podzols develop at the expense of clay-depleted laterites through localized and spectacular weathering fronts. This natural process leads to the remobilization of previously accumulated organic matter (OM) which is redistributed within soil profiles and exported towards rivers, hence their typical black coloration. We investigate the fate of OM in the soil–water continuum in the Rio Negro basin through description of the composition of OM potentially mobile at different stages of podzol development and exploration of evidence for contributions from different soil horizons to the exportation of OM into waters. OM was water-extracted from seven key soil samples from a sequence representative of the transition between latosol and podzol on the low elevation plateaux of the Rio Negro basin, thus enabling following both vertical and lateral differentiations. The chemical structure of freeze-dried samples, investigated using 13C nuclear magnetic resonance and thermally assisted hydrolysis and methylation (THM), shows contrasting features depending on the horizon considered. The bulk features of water extracts were first compared with samples collected in the water-tables and rivers draining the soil sequence. A molecular level comparison was then performed with groundwater draining the well-developed podzol. This approach evidenced a contribution from deep horizons of well-developed podzols. It highlights that OM is certainly remobilised after being accumulated in Bh horizons during the development of podzols through accumulation of OM redistributed from surface horizons. The identification of specific compounds opens new perspective to trace a “podzolic origin” of OM in drainage networks. KeywordsAmazon basin–Black waters–Podzols–Water-extractable organic matterBiogeochemistry 04/2012; 106(1):71-88. · 3.07 Impact Factor -
Article: Dissolved organic matter dynamic in the Amazon basin: Sorption by mineral surfaces
Chemical Geology. 12/2010; -
Article: Radiation-stability of smectite.
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ABSTRACT: The safety assessment of geological repositories for high-level nuclear waste and spent nuclear fuel requires an understanding of the response of materials to high temperatures and intense radiation fields. Clays, such as smectite, have been proposed as backfill material around waste packages, but their response to intense radiation from short-lived fission products and alpha decay of sorbed actinides remains poorly understood. Cumulative doses may amorphize clays and may alter their properties of sorption, swelling, or water retention. We describe the amorphization of smectites induced by electron and heavy ion irradiations to simulate ionizing radiation and alpha recoil nuclei, respectively. A new "bell-shaped" evolution of the amorphization dose with temperature has been determined. The maximum dose for amorphization occurs at about 300-400 degrees C, showing that temperature-induced dehydroxylation enhances amorphization. The exact shape of the bell-shaped curves depends on the interlayer cation. At ambient temperature, ionizing radiation and alpha-decay events do not show the same efficiency. The former results in amorphization at doses between 10(10)-10(11) Gy which are greater than the total radiation dose expected for radioactive waste over 10(6) years. In contrast, alpha-decay events amorphize clays at doses as low as 0.13-0.16 displacements per atom, i.e. doses consistent with nuclear waste accumulated over approximately 1000 yrs. However, the limited penetration of alpha particles and recoil nuclei, in the 100 nm - 20 microm range, will minimize damage. Clays will not be amorphized unless the waste package is breached and released actinides are heavily sorbed onto the clay overpack.Environmental Science and Technology 12/2008; 42(22):8407-11. · 5.23 Impact Factor -
Article: Alteration geochemistry of the Nopal I uranium deposit (Sierra Peña Blanca, Mexico), a natural analogue for a radioactive waste repository in volcanic tuffs
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ABSTRACT: Natural analogues provide an approach to characterize and test the long-term modelling of a repository performance. This article presents geochemical information about the alteration conditions of the Nopal I uranium deposit, Mexico, an analogue for the proposed Yucca Mountain radioactive waste repository. Mineralization and hydrothermal alteration of volcanic tuffs are contemporaneous, according to petrographic observations. Trace element geochemistry (U, Th, REE) provides evidence for local mobilization of uranium under oxidizing conditions and further precipitation under reducing conditions. O- and H-isotope geochemistry of kaolinite, smectite, opal and calcite suggests that argillic alteration proceeded at shallow depth with meteoric water at 25–75 °C, a low-temperature context, unusual for volcanic-hosted uranium deposits. This temperature range is compatible with some post-closure evolution models of the proposed Yucca Mountain repository.Terra Nova 05/2008; 20(3):206 - 212. · 2.34 Impact Factor -
Article: Modeling iron binding to organic matter.
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ABSTRACT: The aim of the present work is to model iron speciation during its interaction with natural organic matter. Experimental data for iron speciation were achieved with an insolubilised humic acid used as an organic matter analogue for 30microM to 1.8 mM total iron concentrations and 2< or = pH< or = 5.5. IHA was found to be able to impose its redox potential to the solution and therefore the Fe(ll)/Fe(lll) ratio. Model VI and the NICA-Donnan model have been adjusted to experimental results of acid-base titrations, total iron measurements, and redox speciation in solution. They both describe well pH and concentration dependence of iron adsorption. For high iron concentration, Fe(lll) solution activity is limited by precipitation of a poorly ordered Fe oxyhydroxide with a higher solubility (log Ks = 5.6-5.7) than ferryhydrite described in the litterature.Environmental Science and Technology 01/2007; 40(24):7488-93. · 5.23 Impact Factor
