LAUSR

Globally, mining activities have been responsible for the contamination of soils, surface water and groundwater. Following mine closure, a key issue is the management of leachate from waste rock accumulated during the lifetime of the mine. At Ranger Uranium Mine in northern Australia, magnesium sulfate (MgSO 4 ) leaching from waste rock has been identified as a potentially significant surface and groundwater contaminant which may have adverse affects on catchment biota. The primary objective of this study was to determine the effect of elevated levels of MgSO 4 on two riparian trees; Melaleuca viridiflora and Alphitonia excelsa . We found that tolerance to MgSO 4 was species-specific. M. viridiflora was tolerant to high concentrations of MgSO 4 (15,300 mg l -1 ), with foliar concentrations of ions suggesting plants regulate uptake. In contrast, A. excelsa was sensitive to elevated concentrations of MgSO 4 (960 mg l -1 ), exhibiting reduced plant vigour and growth. This information improves our understanding of the toxicity of MgSO 4 as a mine contaminant and highlights the need for rehabililitation planning to mitigate impacts on some tree species of this region.