Pioneering research has confirmed that the current level of rainfall recharging groundwater in southwest WA is at its lowest for at least the last 800 years

Published on the 23rd June 2023 by ANSTO Staff

Key Points

The current level of rainfall recharging groundwater in southwest WA is at its lowest for at least the last 800 years
Using cave stalagmites as a record of groundwater replenishment over time, the evidence indicated that there has been a decline in rainfall recharge to groundwater in southwest Australia over the last 20 years due to reduced rainfall
Oxygen isotopic composition (δ¹⁸O) at ANSTO was used for the analyses

In a world-first study, Australian environmental scientists have used cave stalagmites as a record of groundwater replenishment over time, that showed the current level of rainfall recharging groundwater in southwest WA is at its lowest for at least the last 800 years.

The evidence indicated that there has been a decline in rainfall recharge to groundwater in southwest Australia over the last 20 years due to reduced rainfall.

This scientific development was achieved by using stalagmites and ceiling dripwater from caves that are located between the land surface and the groundwater table.

The research has been published in Communications, Earth and Environment.

Cave record — Recent uptick in δ18O values indicates a disconnection in rainfall recharge to groundwater Reprinted under Creative Commons CC BY license http://creativecommons.org/licenses/by/4.0/ Priestley, S.C., Treble, P.C., Griffiths, A.D. et al. Commun Earth Environ 4, 206 (2023)

Water that filters through the cave from the surface towards the groundwater can form cave stalagmites. These stalagmites can be used to obtain records of past groundwater replenishment (technically known as recharge) using the oxygen isotopic composition (δ¹⁸O). The stalagmites collected in this study indicated that rainfall recharge to groundwater has declined in response to the rainfall reduction.

Prof Andy Baker, School of Biological Earth and Environmental Sciences (UNSW)and co-author, said the most compelling aspect of the study was watching this groundwater record evolve over the last few years as more and more stalagmite data was compiled.

“Our work confirmed that records from the most recent decades were unprecedented.
This approach opens a new ‘toolbox’ for using stalagmites to provide records of groundwater recharge in the past. The capability will allow us to better understand how to sustainably manage our groundwater resource in the future .”

The research was devised and led by Dr Stacey Priestley, (formerly of ANSTO and University of Adelaide, who is now at CSIRO) and Dr Pauline Treble (senior research scientist at ANSTO).

“By analysing (δ¹⁸O) in stalagmites, we can assess how rainfall recharge rates have changed over even longer time periods”, said Dr Priestley.

Uptick in cave — The uptick in cave δ18O data is too large to be driven by changes in mean annual rainfall δ18O and is interpreted to be a reduction in preferential flow reaching the cave Reprinted under Creative Commons CC BY license http://creativecommons.org/licenses/by/4.0/ Priestley, S.C., Treble, P.C., Griffiths, A.D. et al. Commun Earth Environ 4, 206 (2023)

Dr Pauline Treble explained that the Southwest Australia region is dependent on groundwater to meet approximately 75% of its water demand.
“The research highlights the vulnerability of this resource,” Dr Treble said.

As the current record only goes back 800 years, work will continue to extend it back further in time.

“We are now working towards extending the record to 10,000 years ago, to understand when groundwater was recharged and under what past climate scenarios this occurred. This means we can better understand the limits and sustainability of this valuable resource for communities that rely heavily on groundwater, “said Dr Priestley.

The investigators used the X‐ray fluorescence microscopy (XFM) beamline at the ANSTO’s Australian Synchrotron to map the strontium for the CRY-S1 chronology.

Other contributors to the research include Dr Allan Griffiths and Dr Karina Meredith of ANSTO and Prof Nerilie Abram of ANU.

This research is supported by funding from the Australian Research Council, Australian Synchrotron beamtime, and with the assistance of resources and services from the National Computational Infrastructure (NCI), which is supported by the Australian Government.
The authors respectfully acknowledge the Wadandi Noongar peoples as the traditional and spiritual custodians of the study region.

DOI: https://doi.org/10.1038/s43247-023-00858-7