Groundwater/surface water exchange and its influence on stable water isotopic signatures along the Darling River, NSW, Australia

Abstract

Stable water isotopes (SWIs) have been analysed in surface waters collected from the Darling River over the past five years (2002 to 2007). Run-of-River sampling results were compared with temporal SWI 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 waters and depleted groundwaters allowed for the identification of groundwater/surface water exchange. Preliminary 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 but also create the desired environmental conditions for cyanobacteria blooms in the Darling River.