ABSTRACT
Stable isotopes have been analysed in river waters collected from the Barwon-Darling River over the years (2002 to 2007). Run-of-river sampling results were compared with temporal data from three gauging stations located along the river. Darling River surface water samples are generally enriched in heavy isotopes due to evaporation. Partitioning of distinctly labelled isotopic waters such as enriched surface water and depleted groundwater allowed for the identification of groundwater/surface water exchange. Results showed that large flood events recharge the shallow aquifer with fresh-enriched waters and during low flow conditions, saline-depleted groundwaters rebound towards the river. Consequently, during drought periods saline groundwaters discharge into the river system. The flux of saline groundwaters into the surface water system was found to not only increase the salinity of scarce fresh water supplies in the region but also create environmental conditions ideal for cyanobacteria blooms to develop.
