Elucidating sources to aridland Dalhousie Springs in the Great Artesian Basin (Australia) to inform conservation

Dalhousie Springs is the largest spring complex in the western Great Artesian Basin (GAB), Australia. Aridland springs like Dalhousie provide the only aquatic habitats in regions lacking surface water and are globally threatened by unsustainable groundwater development. Groundwater use in the more densely populated eastern GAB historically was higher than that in the western GAB, where groundwater is primarily used for ranching; however, economically important mineral and energy industries have increased groundwater use. Throughout the western GAB, groundwater development has reduced spring discharge and artesian head. Of concern are potential impacts on spring discharge from future pumping; thus, an understanding of groundwater sources to springs is needed to develop effective groundwater management strategies that maintain spring flow. The generally accepted hydrogeologic model suggests Dalhousie Springs discharge is entirely composed of Jurassic-Cretaceous aquifer contributions; however, this study improves understanding of Dalhousie Springs by integrating new hydrogeologic and hydrochemical data with historic, previously unpublished petroleum exploration well-test data. A thermal model is used to estimate potential aquifer source depths of 270–802 m. ⁸⁷Sr/⁸⁶Sr > 0.715 suggests water–rock interaction with radiogenic basement and the importance of faults for vertical fluid transfer across multiple aquifers. Results show that Dalhousie Springs discharge is sourced by the previously unreported Permian Crown Point Formation and the Jurassic-Cretaceous aquifer. Mitigating effects of future groundwater development on Dalhousie Springs requires managing groundwater from Jurassic-Cretaceous and Permian aquifers to preserve near-spring potentiometric surfaces. Expanded multiple-environmental-tracer monitoring could be used to further refine groundwater sources to Dalhousie Springs.