Elevation, landuse and water-rock interaction effects on groundwater quality

Determining processes controlling groundwater chemistry is essential for effective water resource management and protection. The Yarra Catchment is an important water resource in SE Victoria, Australia. This catchment is characterised by fractured rock aquifers; a high baseflow component to rivers; high, localised recharge; and diverse land use, Here, we identify processes controlling groundwater chemistry through stable isotope (O and H) and major ion geochemistry, Landsat imagery, and geochemical modelling of groundwater in the Dandenong Ranges sub-catchment. Various stages of groundwater flow are identified. At high elevations, Na-Cl molar ratios (1.0) and low TDS values (similar to 50-100 mg/L) indicate direct recharge of precipitation into sedimentary or granitic aquifers. Where precipitation directly recharges younger basalt aquifers TDS values increase (similar to 100-150 mg/L). At lower elevations, Na-Cl ratios decreases, reflecting an increase in Cl and a decrease in Na. In these areas, higher major ion concentrations (TDS similar to 350-450 mg/L) and pH values reflect cumulative effects of water-rock interaction and agricultural land use lower in the catchment.