A geochemical approach to determining the hydrological regime of wetlands in a volcanic plain, South-Eastern Australia

The Corangamite region in south-eastern Australia contains a large number of lakes and wetlands within an extensive, basaltic plain. To assess the impact of land-use change and groundwater pumping on wetland ecosystems, there is a need to develop a better understanding of their hydrology. This paper describes an approach using groundwater and surface water chemistry and stable isotopes to determine the extent that they are surface or groundwater dominant, and whether they are through-flow or terminal in nature. The ionic ratio HCO^- ₃/Cl^- is higher in surface waters than groundwater, and lakes plot on a continuum between these two water types. Deuterium “excess’' (δ_xs, where δ_xs =δ²H - 8*δ¹⁸O) reflects the deviation of a given sample from the global meteoric water line, with lower values indicating the increasing influence of evaporation, which in turn reflects longer water residence time (terminal lakes) compared with high δ_xs lakes that represent through-flow lakes.