Combining geophysics, near surface chemistry and environmental tracers to define a critical ecohydrological management zone for the Walyarta (Mandora Marsh) mound springs, Australia
The current conceptual hydrological model suggests that the springs are sustained by groundwater discharge along deep-seated geological faults as well as groundwater throughflow and discharge from shallow aquifers. In the absence of surface water and groundwater infrastructure, research focuses on non-invasive methods to evaluate the hydrology, including chemistry and environmental tracers to fingerprint aquifers, soil chemistry and microbes to assess near surface hydrogeochemical processes and remote sensing and airborne EM to map the hydrogeology. Groundwater chemistry and environmental tracers (δ18O, δ2H and δ14C) indicate groundwater discharge from the deeper confined Wallal Aquifer sustains end of dry season flowing springs. Geochemical modelling (PHREEQC), environmental tracers (δ18O, δ2H and δ87/86Sr) and REE data help map aquifer gradients, explain the hydrogeochemical evolution of groundwater and assist in quantifying shallow aquifer throughflow. DEMs and airborne EM data resolve deep-seated re-activated basement structures that propagate through to the surface and coincide with spring locations. The near-surface electrical conductivity structure delineates vadose zone thickness and shallow aquifer throughflow zones. This new conceptualisation was tested within an existing numerical flow model, with results showing mound springs with a higher reliance on fault derived groundwater discharge are more resilient to changes in climate, but more sensitive to long term groundwater abstraction from the deeper confined Wallal Aquifer.