An integrated tracer approach to determine spring aquifer attribution in Australia’s Great Artesian Basin

The Great Artesian Basin (GAB) in Australia is one of the largest aquifer systems in the world which hosts valuable groundwater resources and supports groundwater dependent ecosystems, townships and a substantial agricultural industry. While groundwater recharge and flow through the GAB and its sub-basins have been studied for decades, the regional-scale discharge mechanisms, e.g. springs, have received a lot less attention. The springs of the Great Artesian Basin hold immense ecological and cultural significance. They have sustained Australian Indigenous communities for millennia and support complex, unique ecosystems that are critical to biodiversity and global heritage protection. Greater confidence on spring source aquifer attribution is a crucially missing part of protecting these unique spring systems as water demands from the contributing aquifers for mineral extraction, agriculture and townships is steadily increasing.Here, we present an example of spring hydrogeochemistry and aquifer attribution conducted as part of a large collaborative initiative between major Australian federal and state government agencies and universities. The work involves a multi-tracer approach, including major ions, stable isotopes, Sr-isotopes, cosmogenic isotopes as well as dissolved gases concentrations and gas isotope compositions to better constrain the aquifers which contribute to spring discharge in the eastern part of the Great Artesian Basin. We have sampled multiple spring complexes, 29 springs across 6 complexes, across Queensland as well as groundwater bores in the regions around the springs to characterise spring source aquifers and provide baseline data for management decisions. The hydrogeochemistry is combined with conceptual geological models to understand the impact from water abstraction to spring discharge. Isotopes, in particular the Sr-isotopes show significant differences between aquifer units across the Great Artesian Basin.The information on spring aquifer attribution is crucial to inform decision makers in the process of developing policies to protect these unique springs. The methodology for the spring aquifer attribution can be translated to other large sedimentary basins across the world.