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Accueil du site → Doctorat → Australie → Groundwater chemistry and hydrogeochemical processes in fractured bedrock aquifers beneath dryland salinity occurrences in SE Australia

University of New South Wales (1999)

Groundwater chemistry and hydrogeochemical processes in fractured bedrock aquifers beneath dryland salinity occurrences in SE Australia

Shekarforoush, Seyed Shahrokh

Titre : Groundwater chemistry and hydrogeochemical processes in fractured bedrock aquifers beneath dryland salinity occurrences in SE Australia

Auteur : Shekarforoush, Seyed Shahrokh.

Université de soutenance : University of New South Wales

Grade : Doctor of Philosophy (Ph. D.) 1999

Résumé
Saline seepage and land degradation are the cause of major agricultural problems in Australia. Three catchments in Murray Darling Basin New South Wales, were chosen for investigation in dryland salinisation. The major water-rock reactions in the Begalia site are reverse ion-exchange in deep groundwaters and ion-exchange processes in shallow groundwaters. Oxidation of pyrite in recharge waters and removal of sulfate in shallow groundwaters by sulfate reduction are the major redox reactions. Hydrogeochemical modelling reveals that carbon isotopic composition of the deep groundwaters can be explained by dissolution of calcite driven by carbon dioxide from degradation of organic matter in a close system environment. Precipitation of siderite is possible in these reducing waters due to the high concentration of bicarbonate and dissolved iron. Plot of δ34S versus δ18 O reveals that sulfate reduction is mainly taking place in deep discharging groundwaters. However, re-oxidation of precipitated sulfide due to mixing with oxidising waters in the presence of dissolved nitrate has to be considered to explain the ·34S of the sulfate and sulfide of the groundwater system. The hydrogeochemical model considers the isotopic exchange of 1.1 mmol FeS/kg(H2O) which, refers to dissolution and subsequent precipitation of the equal amount of iron sulfide. Extensive oxidation of pyrite particularly in the Williams Creek catchment results in groundwaters with extremely high sulfate concentration. The results of the stable isotope analyses of oxygen and hydrogen from the three study catchments suggest that evaporation from open surface in discharging areas is not an important factor in the development of the dryland salinisation. However, slight enrichment of oxygen and hydrogen has occurred, in some saline shallow groundwaters from the Spring Creek catchment. Shallow groundwaters of the Kyeamba Valley catchment show slight enrichment of D and 18 O and plot along a line with slope, around 4 which indicates the effect of evaporation enrichment most likely prior to the infiltration in the recharge areas. Shallow groundwaters can be classified into shallow fresh groundwaters which show simple evaporation for the samples high in Na+Cl and saline shallow groundwaters which are evolved from deep groundwaters with lower concentration of Na compared to the first group due to ion-exchange processes in the confining clay layer. Ion-exchange processes increase the sodium concentration in the clay layer and cause clay dispersion.

Mots clés : Aquifers Australia, Southeastern • Salinization Control Australia, Southeastern • Geochemistry • Groundwater Australia, Southeastern • Hydrogeology

Annonce (National Library of Australia)

Page publiée le 20 juin 2008, mise à jour le 6 juillet 2017