How water isotopes (18O, 2H, 3H) within an island freshwater lens respond to changes in rainfall

Eliza Bryan; Karina T Meredith; Andy Baker; Martin S Andersen; Vincent E A Post; Pauline C Treble

doi:10.1016/j.watres.2019.115301

How water isotopes (¹⁸O, ²H, ³H) within an island freshwater lens respond to changes in rainfall

Water Res. 2020 Mar 1:170:115301. doi: 10.1016/j.watres.2019.115301. Epub 2019 Nov 11.

Authors

Eliza Bryan¹, Karina T Meredith², Andy Baker³, Martin S Andersen⁴, Vincent E A Post⁵, Pauline C Treble⁶

Affiliations

¹ Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia; Connected Waters Initiative Research Centre, UNSW Sydney, NSW, 2052, Australia; School of Biological Earth and Environmental Sciences, UNSW Sydney, NSW, 2052, Australia.
² Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia; Connected Waters Initiative Research Centre, UNSW Sydney, NSW, 2052, Australia. Electronic address: karina.meredith@ansto.gov.au.
³ Connected Waters Initiative Research Centre, UNSW Sydney, NSW, 2052, Australia; School of Biological Earth and Environmental Sciences, UNSW Sydney, NSW, 2052, Australia.
⁴ Connected Waters Initiative Research Centre, UNSW Sydney, NSW, 2052, Australia; School of Civil and Environmental Engineering, UNSW Sydney, NSW, 2052, Australia.
⁵ College of Science and Engineering and National Centre for Groundwater Research and Training, Flinders University, Adelaide, Australia.
⁶ Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia; Connected Waters Initiative Research Centre, UNSW Sydney, NSW, 2052, Australia.

PMID: 31765825
DOI: 10.1016/j.watres.2019.115301

Abstract

Coastal aquifers provide an important source of water globally. Understanding how groundwater responds to changes in rainfall recharge is important for sustainable development. To this end, we investigate how water isotopes (¹⁸O, ²H, ³H) and chloride (Cl) concentrations within an island freshwater lens respond under varying rainfall conditions in a region experiencing climate change. Uniquely, this study presents a three year dataset of groundwater collected seasonally between May 2013 and August 2016 from ten wells. Variation in all tracers was observed. The Cl and tritium (³H) show opposing seasonal variation in some sections of the lens, with higher Cl observed in the austral summer when less rainfall occurs and evapotranspiration is highest. The opposite occurs in the austral winter months when ³H increases from atmospheric input via rainfall recharge, and Cl is diluted. An overall decline in ³H values and enrichment in stable water isotopes over the study period was also observed. This study shows that understanding groundwater of freshwater lenses should not rely on a single sampling campaign because seasonal variability is large. The identification of a dual recharge regime, with contributions from both winter rainfall and episodic events, has important implications for understanding the future fate of the freshwater lens on Rottnest Island. The finding that episodic rainfall is a major contributor to groundwater recharge is important and can only be assessed with a multi-year isotope dataset for groundwater and rainfall.

Keywords: Island freshwater lens; Mean groundwater residence time; Seawater intrusion; Water isotopes.

MeSH terms

Environmental Monitoring
Fresh Water
Groundwater*
Isotopes
Water Wells
Water*

Substances

Isotopes
Water