Browsing by Author "Sullivan, LA"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Iron-monosulfide oxidation in natural sediments: resolving microbially mediated S transformations using XANES, electron microscopy, and selective extractions
    (American Chemical Society, 2009-05-01) Burton, ED; Bush, RT; Sullivan, LA; Hocking, RK; Mitchell, DRG; Johnston, SG; Fitzpatrick, RW; Raven, M; McClure, S; Jang, LY
    Iron-monosulfide oxidation and associated S transformations in a natural sediment were examined by combining selective extractions, electron microscopy and S K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The sediment examined in this study was collected from a waterway receiving acid−sulfate soil drainage. It contained a high acid-volatile sulfide content (1031 μmol g−1), reflecting an abundance of iron-monosulfide. The iron-monosulfide speciation in the initial sediment sample was dominated by nanocrystalline mackinawite (tetragonal FeS). At near-neutral pH and an O2 partial pressure of 0.2 atm, the mackinawite was found to oxidize rapidly, with a half-time of 29 ± 2 min. This oxidation rate did not differ significantly (P < 0.05) between abiotic versus biotic conditions, demonstrating that oxidation of nanocrystalline mackinawite was not microbially mediated. The extraction results suggested that elemental S (S08) was a key intermediate S oxidation product. Transmission electron microscopy showed the S08 to be amorphous nanoglobules, 100−200 nm in diameter. The quantitative importance of S08 was confirmed by linear combination XANES spectroscopy, after accounting for the inherent effect of the nanoscale S08 particle-size on the corresponding XANES spectrum. Both the selective extraction and XANES data showed that oxidation of S08 to SO42− was mediated by microbial activity. In addition to directly revealing important S transformations, the XANES results support the accuracy of the selective extraction scheme employed here. © 2009, American Chemical Society
  • No Thumbnail Available
    Item
    Mobilisation, alternation, and redistribution of monosulfidic sediments in inland river systems
    (Academic Press Ltd- Elsevier Science Ltd, 2012-12-15) Cheetham, MD; Wong, VN; Bush, RT; Sullivan, LA; Ward, NJ; Zawadzki, AW
    The accumulation of monosulfidic sediments in inland waterways is emerging as a major environmental issue. Mobilisation and suspension of monosulfidic sediments can result in deoxygenation, acidification of the water column and mobilisation of trace metals. The controls on monosulfidic sediment mobilisation and the critical thresholds for its scour and entrainment have not been established. This study examines the effect of a minor flood event (average return interval of 5 years) on sulfidic sediment scour in the Wakool River in southern NSW, Australia. Five profiles were sampled within a small (similar to 300 m) reach before and after a minor flood event to determine the degree of sediment scour and transport. The results indicate substantial scour of both monosulfidic sediments and underlying bed sediments (approximately 2100 m(3)). Changes in the sediment geochemistry suggest large concentrations of monosulfidic sediments had been suspended in the water column, partially-oxidised and redeposited. This is supported by Pb-210 results from one of the profiles. These results suggest that these monosulfidic sediments can move as bed load during minor flood events. (C) 2012 Elsevier Ltd. All rights reserved.