The use of trace elements and stable isotopes as indicators of recharge regimes and groundwater mixing in an alluvial aquifer

摘要

Trace element and isotopic data was utilised to explain the chemical heterogeneity, recharge regimes and hydraulic connectivity between aquifers in a regional scale alluvial aquifer system in Australia. Changes in Sr~(2+), Li~(2+), Rb~+ and B concentrations along the flow path in the three alluvial aquifers of the Lower Namoi River catchment were examined and combined with stable isotopic data of δ~(18)O, δ~2H and δ~(13)C. In the southeastern portion of the catchment, high concentrations of Li~(2+), B, and Rb~+ and heavy δ~(13)C values in all three alluvial aquifers indicates that these groundwaters are mixing with groundwaters from the underlying Great Artesian Basin (GAB) that also have the same trace element and isotopic signature. In the northwest of the catchment, saline groundwaters in the upper and middle aquifers have high concentrations of Na~+, Cl~-, B, Li~(2+) and Sr~(2+) and a good correlation exists between Sr~(2+), B and Li~(2+) versus Cl~- and B and Li~(2+) versus Sr~(2+), suggesting a marine origin of groundwater salinity. The geology in this part of the catchment supports this hypothesis, as Cretaceous units of the GAB in this area have a marine origin.