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

Abstract

Quantitative field methods were used to refine eco-hydrogeological conceptual models of terrestrial groundwater dependent ecosystems (GDEs) in the Great Artesian Basin (GAB), Queensland, Australia. There are few studies which report on the effectiveness of published methods to ground truth the occurrence of assumed GDEs, particularly in areas subject to coal seam gas development. Using a combination of methods, a field investigation was completed at four sites in vegetation communities dominated by river red gum (Eucalyptus camaldulensis) in areas overlying the GAB. Multiple lines of evidence determined the predominant source of water utilised by large trees at each locality to assess if the terrestrial ecosystems were dependent on the presence 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 oxygen found in tree xylem, soil moisture and groundwater. Results indicate that despite study locations being conceptually mapped as GDEs, trees located within at least three of the four assessed sites were predominantly utilising shallow sources of soil moisture located 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 importance of ground-truthing to refine the eco-hydrogeological conceptual models of GDEs using a combination of methods to create a holistic understanding of water sources for terrestrial vegetation communities in areas vulnerable to groundwater abstraction.