Decoupling of solutes and water in regional groundwater systems: The Murray Basin, Australia

Cartwright, I, Hofmann, H, Currell, M and Fifield, K 2017, 'Decoupling of solutes and water in regional groundwater systems: The Murray Basin, Australia', Chemical Geology, vol. 466, no. 5, pp. 466-478.

Document type: Journal Article
Collection: Journal Articles

Title Decoupling of solutes and water in regional groundwater systems: The Murray Basin, Australia
Author(s) Cartwright, I
Hofmann, H
Currell, M
Fifield, K
Year 2017
Journal name Chemical Geology
Volume number 466
Issue number 5
Start page 466
End page 478
Total pages 13
Publisher Elsevier
Abstract Documenting the origins, residence times, and movement of groundwater and the solutes that it contains is critical to understanding hydrogeological systems. This study uses Cl mass balance to determine the Cl accession time (i.e. the time required for Cl to accumulate) and 36 Cl to estimate the residence times of Cl in the Victorian portion of the Murray Basin, southeast Australia. Much of the Murray Basin contains saline groundwater with total dissolved solids (TDS) concentrations commonly > 14,000mg/L and locally up to 300,000mg/L. The total mass of Cl stored in the Victorian portion of the basin is estimated as between 12,400 and 47,100MT. Using present day rainfall totals and Cl concentrations in rainfall, the Cl accession time is 170 to 650ka. Aquifer thicknesses and groundwater salinity both increase westwards in this part of the Murray Basin. Consequently, the Cl accession times increase westward from 0.1-0.6ka to 286-1080ka. By contrast, 14 C activities of the majority of the groundwater are > 2pMC, and commonly much higher. Notwithstanding the difficulty in correcting 14 C residence times, the widespread occurrence of groundwater with above background 14 C activities implies that groundwater residence times are generally < 30ka, which is substantially shorter than the Cl accession times. R 36 Cl (the ratio of 36 Cl to total Cl×10 15 ) values of the groundwater are between 20 and 230, and are uncorrelated with Cl concentrations. While it is difficult to determine precise Cl residence times, the observation that the R 36 Cl values are significantly higher than those that represent secular equilibrium with the aquifer matrix (R 36 Cl of 5 to 10) indicates that they are up to a few hundred thousand years and similar to the Cl accession times.
Subject Hydrogeology
Isotope Geochemistry
Keyword(s) 36 Cl
Accession times
Residence times
DOI - identifier 10.1016/j.chemgeo.2017.06.035
Copyright notice © 2017 Elsevier B.V. All rights reserved
ISSN 0009-2541
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