GAB | Field investigation of potential terrestrial groundwater-dependent ecosystems within Australia’s Great Artesian Basin

• Chris Jones  
• David Stanton
• Ned Hamer
• Stephen Denner
• Kavita Singh
• Steven Flook
• Madeleine Dyring

Quantitative field methods were used to refine eco-hydrogeological conceptual models of terrestrial groundwater dependentecosystems (GDEs) in the Great Artesian Basin (GAB), Queensland, Australia. There are few studies which report on theeffectiveness of published methods to ground truth the occurrence of assumed GDEs, particularly in areas subject to coal seamgas development. Using a combination of methods, a field investigation was completed at four sites in vegetation communitiesdominated by river red gum (Eucalyptus camaldulensis) in areas overlying the GAB. Multiple lines of evidence determined thepredominant source of water utilised by large trees at each locality to assess if the terrestrial ecosystems were dependent on thepresence of groundwater. Methods included soil coring to observe tree rooting depth and underlying hydrogeological conditions,matching of soil moisture with leaf water potential, and analysis of naturally occurring stable isotopes of hydrogen and oxygenfound in tree xylem, soil moisture and groundwater. Results indicate that despite study locations being conceptually mapped asGDEs, trees located within at least three of the four assessed sites were predominantly utilising shallow sources of soil moisturelocated above the regional water-table aquifer. Also, rooting depths of targeted tree species were consistently much shallower(maximum depth 7.6 mbgl) than what is commonly reported in literature (12–22.6 mbgl). The findings highlight the importanceof ground-truthing to refine the eco-hydrogeological conceptual models of GDEs using a combination of methods to create aholistic understanding of water sources for terrestrial vegetation communities in areas vulnerable to groundwater abstraction.