Browsing by Author "Johnston, SG"

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    The impact of de-icing salts on alpine bogs in Kosciuszko National Park
    (International Union of Geodesy and Geophysics, 2011-07-04) Hocking, RK; Greene, RSB; Hughes, CE; Johnston, SG; Grover, S
    Several roads in Kosciuszko National Park (KNP), NSW, are kept open each winter with the use of snow ploughs and the de-icing salts; sodium chloride and calcium chloride. Alpine Bogs and Fens, which are endangered Sphagnum cristatum bog communities of high conservation significance, receive saline run–off from de-iced roads in KNP. Chloride de-icing salts raise the osmotic potential of soil water, degrade soil physical properties and both sodium and chloride ions are toxic to alpine flora. However, The impact of de-icing salts on alpine environments has not been previously studied in Australia. To establish salt loads and residence times in Alpine Bogs bog ground water electrical conductivity (EC) was measured weekly using a network of piezometers in sixteen roadside bogs during winter and spring 2010. A treatment of 7.5kg of NaCl and 1Gbq of tritium (3H) was diluted into 100l of water and applied to two bogs to establish if de-icing salts moved slower through the bogs than ground water. Monitoring revealed a significant flux of salt through roadside bogs. ECs were raised significantly in salted bogs with levels highest closest to the road 3520uS/cm and dropping to 100uS/cm at a distance of 120m from the road. The 3H injection suggests NaCl moves slower than ground water and salts have a shorter residence time in wetter bogs. The results indicate that Alpine Bog hydrology is significantly altered by current snow clearing practices. Peak ECs are significantly higher than the 30uS/cm of undisturbed bogs and may potentially retard bog flora vigour.
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    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
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    Reconstructing extreme climatic and geochemical conditions during the largest natural mangrove dieback on record
    (European Geosciences Union (EGU), 2020-02-28) Sippo, JZ; Santos, IR; Sanders, CJ; Gadd, PS; Hua, Q; Lovelock, CE; Santini, NS; Johnston, SG; Harada, Y; Reithmeir, G; Maher, DT
    A massive mangrove dieback event occurred in 2015–2016 along ∼ 1000 km of pristine coastline in the Gulf of Carpentaria, Australia. Here, we use sediment and wood chronologies to gain insights into geochemical and climatic changes related to this dieback. The unique combination of low rainfall and low sea level observed during the dieback event had been unprecedented in the preceding 3 decades. A combination of iron (Fe) chronologies in wood and sediment, wood density and estimates of mangrove water use efficiency all imply lower water availability within the dead mangrove forest. Wood and sediment chronologies suggest a rapid, large mobilization of sedimentary Fe, which is consistent with redox transitions promoted by changes in soil moisture content. Elemental analysis of wood cross sections revealed a 30- to 90-fold increase in Fe concentrations in dead mangroves just prior to their mortality. Mangrove wood uptake of Fe during the dieback is consistent with large apparent losses of Fe from sediments, which potentially caused an outwelling of Fe to the ocean. Although Fe toxicity may also have played a role in the dieback, this possibility requires further study. We suggest that differences in wood and sedimentary Fe between living and dead forest areas reflect sediment redox transitions that are, in turn, associated with regional variability in groundwater flows. Overall, our observations provide multiple lines of evidence that the forest dieback was driven by low water availability coinciding with a strong El Niño–Southern Oscillation (ENSO) event and was associated with climate change. © Author(s) 2020.