31 Jan 2022
31 Jan 2022
Status: this preprint is currently under review for the journal HESS.

Using geochemistry to understand the sources and mean transit times of stream water in an intermittent river system: the upper Wimmera River, southeast Australia

Zibo Zhou1, Ian Cartwright1, and Uwe Morgenstern2 Zibo Zhou et al.
  • 1School of Earth, Atmosphere and Environment, Monash University, Clayton, VIC, 3800, Australia
  • 2GNS Science, Lower Hutt, 5040, New Zealand

Abstract. Determining the mean transit times (MTTs) and water sources in catchments at different flow conditions helps better understand river functioning, manage riverine system health and water resources, and discern the responses to climate change and global water stress. Despite being common in a range of environments, understanding of MTTs and variable water sources in intermittent streams remain incomplete compared to perennial streams. Major ion geochemistry, stable isotopes, 14C, 3H and were used in this study to identify water sources and MTTs of a periodically-intermittent river from southeast Australia at different flow conditions, including zero-flow periods. The disconnected pool waters during the zero-flow period in the summer months of 2019 had 3H activities of 0.64 to 3.29 TU. These and the variations in total dissolved solids and stable isotopes imply that these pools contained a mixture of groundwater and younger evaporated stream water. 3H activities during the high-flow period in July 2019 were 1.85 to 3.00 TU, yielding MTTs of up to 17 years. The 3H activities at moderate and low-flow conditions in September and November 2019 ranged from 2.26 to 2.88 TU, implying MTTs of 1.6 to 7.8 years. Regional groundwater near the Wimmera River has 3H activities of < 0.02 to 0.45 TU and 14C activities of 57 to 103 pMC and is not recharged by the river at high flows. The Wimmera River and other intermittent streams in southeast Australia are sustained by smaller volumes of younger catchment waters than comparable perennials streams, indicating that near-river stores have significant impacts on maintaining streamflow during low-flow periods than older deeper regional groundwater. These smaller reservoirs result in the intermittent streams being more susceptible to changes of climate and streamflow and necessitate protection of near-river corridors to maintain the health of the riverine systems.

Zibo Zhou et al.

Status: open (extended)

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  • RC1: 'Comment on hess-2022-18', Anonymous Referee #1, 05 Mar 2022 reply

Zibo Zhou et al.


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Short summary
Streams may receive water from different sources in their catchment. There is limited understanding of which water stores intermittent streams are connected to. Using geochemistry we show that the intermittent streams in southeast Australia are connected to younger smaller near-river water stores rather than regional groundwater. This makes these streams more vulnerable to the impacts of climate change and requires management of the riparian zone for their protection.