Project 2.7 - Ecohydrology and sensitivity of riparian flora

Pit closure at the Ranger uranium mine is predicted to result in exfiltrating groundwater with high levels of MgSO4 derived from waste rock. Solute modelling predicts that within 10 years of closure, groundwater may have a MgSO4 concentration >3 mg L-1, in excess of desired exposure limits for surface waters (Sigda et al. 2013, cited in Tomlinson and Metherall, 2017). This presents a potential threat to the ecology of Magela Creek for any organisms utilising groundwater sources. This project will focus on risks posed to groundwater dependant ecosystems (GDEs), in particular, riparian vegetation of Magela Creek. Project activity will centre around two aims: Aim 1 - Use stable isotopes and tritium to age and quantify water sources (soil water, creek water and/or surface and deep groundwaters) used by riparian vegetation within the Magela Creek catchment, Aim 2 - Undertake a pot trial to examine the sensitivity of dominant riparian woody species to MgSO4. Planning will be undertaken with SSB, ERA staff plus other NESP researchers to discuss a range of project detail; 1) Site selection for vegetation surveys – discussions with SSB staff (Humphries, Bartolo, van Dam), NESP P2.6 (Setterfield), NESP P2.9 (Crook), KNP Staff. Consultation will also be undertaken with the Mirrar Traditional Owners. 2) Vegetation, soil pore water, plus surface and groundwater sampling strategy within and outside the mine area – discussions with SSB staff (Humphries), ERA (Lu et al.) and external expert knowledge (UWA, Dr Pauline Grierson) 3) Riparian woody species selection for toxicity trials, and number of species to test – SSB staff and Mirrar Traditional Owners. For a properly replicated and multi-level MgSO4 concentration treatments (e.g. 3 to 5), the number of species tested will need to be carefully selected given resource constraints. Current suggestion is 3 common species. A 4th species could include a species that may have some tolerance.