Stable isotopic signatures of water resources of metropolitan Adelaide region

Author: Thi Le Trang Ngo

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Ngo, Thi Le Trang, 2017 Stable isotopic signatures of water resources of metropolitan Adelaide region, Flinders University, School of the Environment

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Abstract

The Adelaide metropolitan region has a semi-arid climate that has strong influences on water isotope variation. Isotopic signatures of waters are useful tracers to identify the source and evolution of water in the environment. Information from water isotopes may help to investigate problems and challenges in water resource management in urban areas. This thesis reports a preliminary characterization of stable water isotopes of water, including tap water and surface water resources in the Adelaide metropolitan area. Water samples were collected and analysed for δ2H and δ18O and deuterium excess (d = δ2H – 8 x δ18O). Different types of water were characterised by referring to Global Meteoric Water Line (GMWL) and Local Meteoric Water Line (LMWL). It is found that the δ18O of surface water and tap water in the Adelaide metropolitan area are quite similar (-3.16‰ vs. -3.12‰ for δ18O, respectively) but they are different for δ2H (-13.33‰ vs.-17.28‰) and d-excess (11.94‰ vs. 7.64‰). Stable isotopes of both tap water and surface water show evaporative influences; however, more depleted isotopes of tap water show stronger evaporative influences. The research found that mixing with desalinated water and longer residence time in the reservoirs, combining with evaporation play important roles in the enrichment of tap water isotopes. In term of spatial pattern, tap water isotope data do not follow hydrological, climatic or natural isotope gradients but shows clustering distribution for each water supply zones. The variation of tap water isotopes through various water supply zones reflects the environmental pressure on water resources and dynamics of water supply systems. Water from the River Murray as one of main water resources for the Adelaide metropolitan area has a meteoric signature; however, tap water supplied by it is more isotopically enriched in various water supply zones. The spatial distribution of surface water isotopes does not show a clear pattern across the Adelaide metropolitan area but water isotopes vary significantly across small areas of the catchment. The surface water from the Smith Catchment has more depleted isotopes, which are closer to meteoric water than surface water from the Onkaparinga catchment. This highlights the complex influences resulting from the combinations of evaporation, precipitation and landscape characteristics relating to residence time.

Keywords: Adelaide metropolitan, stable water isotopes, tap water, surface water, precipitation, evaporation, Picarro CSRD, spatial pattern

Subject: Environmental management thesis

Thesis type: Masters
Completed: 2017
School: School of the Environment
Supervisor: Huade Guan