Constraining groundwater flow, residence times, inter-aquifer mixing, and aquifer properties using environmental isotopes in the southeast Murray Basin, Australia

Ian Cartwright, Tamie Weaver, Dioni Cendon, L Fifield, Sarah Tweed, Ben Petrides, Ian Swane

    Research output: Contribution to journalArticle

    55 Citations (Scopus)

    Abstract

    Environmental isotopes (particularly δ 18O, δ 2H, and δ 13C values, 87Sr/ 86Sr ratios, and a 14C) constrain geochemical processes, recharge distribution and rates, and inter-aquifer mixing in the Riverine Province of the southern Murray Basin. Due to methanogenesis and the variable δ 13C values of matrix calcite, δ 13C values are highly variable and it is difficult to correct 14C ages using δ 13C values alone. In catchments where δ 13C values, 87Sr/ 86Sr ratios, and major ion geochemistry yield similar a 14C corrections, ~15% of the C is derived from the aquifer matrix in the silicate-dominated aquifers, and this value may be used to correct ages in other catchments. Most groundwater has a 14C above background (~2pMC) implying that residence times are <30ka. Catchments containing saline groundwater generally record older 14C ages compared to catchments that contain lower salinity groundwater, which is consistent with evapotranspiration being the major hydrogeochemical process. However, some low salinity groundwater in the west of the Riverine Province has residence times of >30ka probably resulting from episodic recharge during infrequent high rainfall episodes. Mixing between shallower and deeper groundwater results in 14C ages being poorly correlated with distance from the basin margins in many catchments; however, groundwater flow in palaeovalleys where the deeper Calivil-Renmark Formation is coarser grained and has high hydraulic conductivities is considerably more simple with little inter-aquifer mixing. Despite the range of ages, δ 18O and δ 2H values of groundwater in the Riverine Province do not preserve a record of changing climate; this is probably due to the absence of extreme climatic variations, such as glaciations, and the fact that the area is not significantly impacted by monsoonal systems.

    Original languageEnglish
    Pages (from-to)1698-1709
    Number of pages12
    JournalApplied Geochemistry
    Volume27
    Issue number9
    DOIs
    Publication statusPublished - 2012

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