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Australian National University (2009)

Dust and terrestrial salt (NaCl) in SE Australia : implications for Aeolian co-transportation and co-deposition

Shiga, Yuki

Titre : Dust and terrestrial salt (NaCl) in SE Australia : implications for Aeolian co-transportation and co-deposition

Auteur : Shiga, Yuki

Université de soutenance : Australian National University

Grade : Master of Geographical Sciences 2009

Description
Aeolian dust exerts major effects across the Australian continent in terms of soil-landscape processes and impacts on human society. It not only has serious health implications, but is also thought to be an insidious carrier of terrestrial salts, which when deposited cause salinisation and/or sodification of the soil. However, this argument is still controversial and especially lacks information regarding co-transportation and co-deposition of terrestrial soil and terrestrial salt (NaCl) from their presumed source - enclosed inland drainage systems in South Australia. Therefore, the purpose of this research is to overcome this lack of information, with a special focus on the potential role of aeolian dust to co-transport and co-deposit with terrestrial salt. One hundred and fifteen dust samples, each representing one month’s deposition, were acquired from samplers located in 16 different sites across Australia, mainly covering the southeastern region. These samples were subjected to several analyses to reveal their properties. The analyses included ion beam analysis (IBA) to determine their chemical characteristics. Subsequently, sets of equations were applied to the IBA analyses to reveal the contributions from soil, salt (both terrestrial and oceanic) and smoke to the dust samples. Principal Component Analysis (PCA) was also applied to the IBA results to detect the important components of the dust samples. Scanning electron microscope (SEM) and back trajectory analyses, plus rainfall records, were then applied to selected samples to determine differences in their morphology and aeolian dust dispersion routes, respectively. Careful study of the results has revealed the following findings : (i) Despite limitations due to errors arising in some of the calculations, the use of a combination of equations to determine the contribution of terrestrial NaCl to aeolian dust (i.e., terrestrial salt ratio), was able to discriminate between samples with extreme or no terrestrial salt influence ; (ii) The use of principal component analysis (PCA) gave similar results to terrestrial salt ratios and validated the use of these ratios ; (iii) Back trajectory plots, along with rainfall records (at the site and along the trajectory), appeared overall to be consistent with high and zero values of the terrestrial salt ratios calculated from IBA results ; (iv) The SEM images appeared to indicate that dust samples which had high terrestrial salt ratios have smaller particle size. Two samples out of five which had a high terrestrial salt ratio had a conspicuously smaller particle size. This implied that these samples were influenced to a greater extent by the distant source(s) compared to other samples. However, overall, morphological traits were unclear ; (v) The above features suggest that there is evidence for the existence of terrestrial salt dispersion associated with aeolian dust from the presumed source - the inland salt lake regions of South Australia ; and (vi) An influence of terrestrial salt appeared to be dependent on only one or two events, of no more than six hours duration within a monthly collection period.

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