Plant Science & Landscape Architecture Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2797

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Subject: search.filters.subject.Chemistry, Agricultural

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    Multi-Scale Pedologic Investigation of Manganiferous Soils in the Maryland Piedmont
    (2008) Bourgault, Rebecca; Rabenhorst, Martin; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Manganese oxides are usually found in trace quantities in soils, but they are important due to their effects on soil chemistry and morphology. There are rare soils in the Maryland Piedmont that have extremely high amounts of manganese oxides that have not been previously studied. These manganiferous soils were examined at multiple scales in order to determine their spatial extent, to characterize their fundamental morphology, mineralogy, and chemical and physical properties, and to better understand their pedogenesis. The soils occupy areas of 1-2 ha in size, within 200 km2 in eastern Frederick County and western Carroll County. The soils can have as much as 140 g kg-1 Mn as oxides, which pigments the entire soil matrix black in subsoil horizons. It appears that the black, porous, Mn-rich material is derived directly from the dissolution of marble bedrock and accumulation of silicate residues plus Mn and Fe from within the rock.
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    Oxidation-Reduction Transformations of Chromium in Aerobic Soils and the Role of Electron-Shuttling Quinones in Chemical and Microbiological Pathways
    (2008-05-05) Brose, Dominic; James, Bruce R; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Soils from three toposequences in Maryland with minimal heavy metal contamination were sampled to investigate oxidation-reduction transformations of chromium in whole soil samples. Chromium (VI) reduction to Cr(III) was observed in all 18 samples, and 11 demonstrated enhanced reduction with the electron shuttle anthraquinone-2,6-disulfonate (AQDS). Oxidation of Cr(III) to Cr(VI) was observed in 12 samples, and 7 samples demonstrated diminished oxidation with AQDS. Lactate was added to the Watchung series to enhance biological activity, and high salt concentration was added to inhibit it. Both treatments reduced Cr(VI) to below detection limits by 11 d, suggesting abiotic reduction. The control treatment demonstrated reduction of Cr(VI) without soil. To further investigate, increasing lactate concentrations were added to Cr(VI) and AQDS. Reduction increased with increasing concentration; 60 mM lactate reduced all Cr(VI) within 1 hr. Other organic acids were tested for similar interactions; tartrate and citrate reduced Cr(VI), which was enhanced with AQDS.