Ruben Kretzschmar


Last Name

Kretzschmar

First Name

Ruben

ORCID

0000-0003-2587-2430

Organisational unit

03541 - Kretzschmar, Ruben / Kretzschmar, Ruben

Search Results

Publications 1 - 10 of 337
  • Changes in Fe Speciation during Early Soil Formation in an Alpine Glacier Forefield
    Item type: Report
    Kiczka, Mirjam; Frommer, Jakob; Voegelin, Andreas; et al. (2007)
    Jahresbericht / Hamburger Synchrotronstrahlungslabor HASYLAB am Deutschen Elektronen-Synchrotron DESY
    In this project, we investigate the transformation of Fe during granite weathering and early soil development in the forefield of a retreating glacier (Damma glacier, Central Aare massive, Switzerland). This work is integrated in a multidisciplinary project on the links between climate change, rock weathering, soil formation, and ecosystem evolution. Fe is an essential nutrient and its release from weathering rock is a key factor in initial soil development. To study Fe transformation during early weathering and soil formation, we combine two comparatively new geochemical tools, namely stable Fe isotope studies and X-ray-absorption spectroscopy (XAS). While stable Fe isotope studies provide insight into different physical and chemical weathering mechanisms, XAS allows following the changes in Fe speciation and redox state, as shown in our earlier feasibility study.
  • Hydrogen sulfide reaction with natural organic matter
    Item type: Conference Poster
    Hoffmann, M.; Mikutta, Christian; Kretzschmar, Ruben (2011)
  • Organic matter influences transformation products of ferrihydrite exposed to sulfide
    Item type: Journal Article
    Thomas Arrigo, Laurel K.; Bouchet, Sylvain; Kaegi, Ralf; et al. (2020)
    Environmental Science: Nano
    In redox-dynamic environments, sorption to poorly-crystalline, nanometer-sized Fe(III)-(oxyhydr)oxides like ferrihydrite influences the biogeochemical cycling of nutrients and trace elements. Under sulfate-reducing conditions, the reductive dissolution of ferrihydrite leads to the release of associated constituents, which may be re-immobilized via sorption to secondary Fe minerals. To date, studies following the kinetics and transformation pathways of Fe(III)-(oxyhydr)oxides upon exposure to dissolved sulfide (S(−II)) have largely focused on pure Fe minerals. However, in nature, Fe(III)-(oxyhydr)oxides are often found in association with organic matter (OM). Because ferrihydrite–OM associations exhibit characteristics and biogeochemical reactivity differing from those of pure ferrihydrite, in this study, we compared sulfidization kinetics and transformation pathways of a pure ferrihydrite to those of ferrihydrite coprecipitated with contrasting organic ligands; polygalacturonic acid, galacturonic acid, and citric acid (C/Fe molar ratio ∼0.55). Incorporating aqueous- and solid-phase S and Fe speciation analyses (via wet chemistry techniques and S and Fe X-ray absorption spectroscopy) in addition to X-ray diffraction and electron microscopy, we studied both rapid (<7 days) and long-term (12 months) mineral transformations as well as the impact of varying S(−II)/Fe molar ratios at neutral pH. Our results showed that at low S(−II)/Fe molar ratios (=0.1), poorly-crystalline Fe sulfide minerals (e.g. mackinawite) did not form in any (co)precipitate. In contrast, at higher S(−II)/Fe molar ratios (=0.5), mackinawite rapidly precipitated, with higher contributions detected in the coprecipitates than in the pure ferrihydrite. Aging of the samples led to further mineral transformations, including divergent pyrite and greigite precipitation, and an overall increase in the crystallinity of secondary mineral phases. Still, the fraction of residual ferrihydrite at 12 months was higher in the OM-containing coprecipitates, with the most ferrihydrite preservation observed in coprecipitates comprising carboxyl-poor ligands (galacturonic acid and citric acid). This suggests that the presence of OM inhibited S(−II)-induced ferrihydrite mineral transformations and that the composition of the associated OM influenced mineral transformation pathways. Collectively, these results suggest that further studies regarding sulfidization pathways should include OM in order to better represent environmental conditions.
  • Mn(II) and Cd(II) sorption to synthetic montmorillonite
    Item type: Other Conference Item
    Van Groeningen, Natacha; Christl, Iso; Kretzschmar, Ruben (2017)
    Abstract Volume 15th Swiss Geoscience Meeting
  • The impact of Fe isotope fractionation by plants on the isotopic signature of soils
    Item type: Other Conference Item
    Kiczka, Mirjam; Wiederhold, Jan G.; Kraemer, Stephan M.; et al. (2007)
    Geochimica et Cosmochimica Acta
  • Mechanisms and rates of iron oxide dissolution in biological iron acquisition.
    Item type: Other Conference Item
    Kraemer, Stephan M.; Reichard, P.U.; Kretzschmar, Ruben (2005)
    Abstracts of Papers of the American Chemical Society
  • Bodenchemische Mechanismen der pflanzlichen Eisenakquisition
    Item type: Conference Poster
    Kraemer, S.M.; Reichard, P.U.; Kretzschmar, Ruben (2005)
    Mitteilungen der Deutschen Bodenkundlichen Gesellschaft ~ Referate, Poster : Jahrestagung 2005 der Deutschen Bodenkundlichen Gesellschaft, 02. bis 09. September 2005 in Marburg
  • Reduction and Reoxidation of Humic Acid
    Item type: Journal Article
    Maurer, Felix; Christl, Iso; Hoffmann, Martin; et al. (2012)
    Environmental Science & Technology
  • Interplay of Fe and S biogeochemistry shapes in situ iron mineral transformations in contrasting intertidal sediments
    Item type: Journal Article
    Kubeneck, Luisa Joëlle; Fantappiè, Giulia; Notini de Andrade, Luiza; et al. (2025)
    Environmental Science: Processes & Impacts
    The transformation and stability of iron (Fe) minerals in coastal sediments are closely linked to the sulfur (S) cycle, influencing the fate of nutrients, carbon, and contaminants. However, in situ studies of these interactions in coastal sediments remain limited. We investigated the transformation of lepidocrocite, goethite, and mackinawite in three intertidal field plots with contrasting Fe and S biogeochemistry. Fe minerals were enriched with ⁵⁷Fe and mixed with the sediment, allowing close contact with the other inorganic and organic components of the sediment. After 8 weeks, transformation products were assessed using ⁵⁷Fe Mössbauer spectroscopy. Regular porewater analysis complemented solid-phase analyses, supporting the understanding of transformation pathways and extents. Under low-sulfide, Fe-reducing conditions, lepidocrocite did not transform to more crystalline Fe-oxides such as goethite or magnetite. Instead, ∼20% of the lepidocrocite transformed, mostly into a disordered Fe-phase, due to reductive dissolution and a small extent of sulfidation. Goethite, in contrast, remained apparently unchanged under the same conditions. These results indicate that both Fe-oxides may persist during extended anoxic periods under Fe-reducing conditions in coastal sediments and thus may influence elemental cycles. However, in sulfidic environments, lepidocrocite and goethite transformed into amorphous, nonstoichiometric Fe-sulfide and greigite. We hypothesize that amorphous Fe-sulfide precipitated first, later transforming into greigite; a potential precursor of pyrite formation. This is further supported by the transformation of synthetic mackinawite into greigite under high sulfide conditions, suggesting a sulfidation pathway that may eventually lead to pyrite formation in coastal sediments.
  • Metallic copper and metal sulfide colloid formation in a contaminated riparian soil during flooding at various temperatures
    Item type: Other Conference Item
    Hofacker, Anke Frederike; Voegelin, Andreas; Kägi, Ralf; et al. (2012)
Publications 1 - 10 of 337