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Accueil du site → Doctorat → Australie → 2007 → Cyclic deposition of salt-laden dusts as an explanation of salinisation in a groundwater recharge zone Coleambally irrigation area Riverine plain NSW

University of New South Wales (UNSW) 2007

Cyclic deposition of salt-laden dusts as an explanation of salinisation in a groundwater recharge zone Coleambally irrigation area Riverine plain NSW

Bell, Justin Robert William

Titre : Cyclic deposition of salt-laden dusts as an explanation of salinisation in a groundwater recharge zone Coleambally irrigation area Riverine plain NSW

Auteur : Bell, Justin Robert William

Université de soutenance : University of New South Wales (UNSW)

Grade : Doctor of Philosophy (PhD) 2007

Résumé
Salinisation of the shallow groundwater system has occurred coincident with the development of irrigation in the Coleambally Irrigation Area. Salinisation in irrigation areas has previously been attributed to the evaporative concentration of the water table ; however, there are other sources of salt such as the accumulation of rainfall by vegetation and the dry deposition of salt-laden dusts.A significant store of crystalline gypsum, together with high concentrations of Na, Mg and Confidence limit, was found within the previously unsaturated zone of the Upper Shepparton Formation. The salt store was identified both within and outside of the groundwater mound ; therefore evaporative concentration of the water table cannot be the source of salt. The transition from regional groundwater quality, as applied as irrigation to the ground surface, to shallow groundwater quality is simply explained by solubilisation of this salt store in the presence of soil CO2.Dating of basal palaeochannel sands indicates that the identified salt store, a profile of only 20 m, was accumulated during the last glacial cycle. Radiocarbon dating indicates that the peak in eluate salinity, at approximately 2 m below ground surface, is between 15,000 and 25,000 years old, coincident with the Last Glacial Maximum. The Last Glacial Maximum was a period of significantly enhanced aridity on the Australian continent. It was also found that the peak in eluate salinity coincided with a bi-modal particle size distribution. The bi-modal signature implies that these sediments were subject to the aeolian accession of dusts.It was found that the contribution of salt from dry deposition of dusts exceeded the contribution from rainfall by at least 1.9 to 11 times during the last glacial cycle. The results of this study imply that salt-laden dusts have, and continue to play an important role in the salinity and sodicity of soils in the Coleambally Irrigation Area and beyond.

Mots clés : Soil salinization — New South Wales — Coleambally. ; Groundwater — New South Wales — Coleambally. ; Geochemistry — New South Wales — Coleambally. ; Irrigation — Environmental aspects — New South Wales — Coleambally.

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