Browsing by Author "Fakra, SC"

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    Past fires and post-fire impacts reconstructed from a southwest Australian stalagmite
    (Australasian Quaternary Association (AQUA), 2021-07-09) McDonough, LK; Treble, PC; Baker, AA; Borsato, A; Frisia, S; Nagra, G; Coleborn, K; Gagan, MK; Fakra, SC; Paterson, DJ
    Stalagmites provide records of past changes in climate, vegetation, and surface events, with cave dripwaters shown to respond to fires. It is, therefore, most likely that these cave mineral deposits capture the environmental effects of palaeo-wildfires in their chemical and physical properties, as well as the climate conditions antecedent to palaeo-fire events. We analysed multiple proxies in stalagmite (YD-S2) from a shallow cave in south-west Western Australia. Principal Component Analysis revealed that short term peaks in combinations of phosphorus, copper, aluminium, lead and zinc in the stalagmite correspond to the timing of documented fire events occurring in the modern portion of the record. One particularly significant fire event is identified at 1897 ± 5 CE and shows a clear peak in P interpreted to be derived from ash, and a peak in 𝛿18O interpreted to indicate evaporation of sub-surface water during the heat of the fire. A post-fire threshold rise in organic matter content and a shift in calcite fabric associated with higher and more variable drip rates are consistent with a post-fire changes in surface-cave hydrology resulting from heat-induced deformation of the shallow karst bedrock brought about by the intensity of this fire. The combination of climate and fire sensitive proxies in YD-S2 indicates that the 1897 ± 5 CE wildfire was preceded by a multi-decadal dry period. We also identify lower and less variable peak phosphorus concentrations in the pre-European period that are consistent with low-intensity cultural burning by Indigenous Australians. The YD-S2 record shows the potential of stalagmites in capturing the climate-fire relationship and the effects of land-management practices on wildfire frequency and intensity.
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    X-ray absorption spectroscopy at the Ni-K edge in stackhousia tryonii bailey hyperaccumulator
    (Wiley-Blackwell, 2008-11) Lonescu, M; Bhatia, NP; Cohen, DD; Kachenko, AG; Siegele, R; Marcus, MA; Fakra, SC; Foran, GJ
    Young plants of Stackhousia tryonii Bailey were exposed to 34 mM Ni kg(-1) in the form of NiSO4 center dot 6H(2)O solution and grown under controlled glasshouse conditions fora period of 20 days. Fresh leaf, stem and root samples were analysed in vivo by micro x-ray absorption spectroscopy (XAS) at the Ni-K edge. Both x-ray absorption near edge structure and extended x-ray absorption fine structure spectra were analysed, and the resulting spectra were compared with spectra obtained from nine biologically important Ni-containing model compounds. The results revealed that the majority of leaf, stem and root Ni in the hyperaccumulator was chelated by citrate. Our results also suggest that in leaves Ni is complexed by phosphate and histidine, and in stems and roots, phytate and histidine. The XAS results provide an important physiological insight into transport, detoxification and storage of Ni in S. tryonii plants. © 2008, Wiley-Blackwell.