Groundwater dependent pools in seasonal and permanent streams in the Clare Valley of South Australia.

1. Study region The Clare Valley region of South Australia. 2. Study focus Continuing extraction of groundwater threatens pools in seasonal and permanent streams. In order to determine this groundwater dependence, the pools and groundwater from corresponding fractured rock aquifers were investigated using environmental tracers (δD, δ¹⁸O, ⁸⁷Sr/⁸⁶Sr, and major and minor elements). For the 11 paired pool-groundwater sites in the four different catchments, groundwater dependence was evaluated over a four season sampling period. 3. New hydrological insights In this Mediterranean climate with cool wet winters and dry hot summers strong salinity changes (up to 2.5 times) due to seasonal cycles of wetting and drying were observed in surface water. Oxygen and hydrogen isotope values from pool sites showed strong evaporative enrichment during the dry season with up to 50% net evaporation calculated. Water isotopes from groundwater, however, cluster at the depleted end of the local meteoric water line and most do not show change despite significant seasonal salinity changes. Strontium isotope values and concentrations from the pools over the one year period do not define a mixing relationship. Instead, most pool sites have unchanging strontium isotope values despite the large seasonal change in salinity indicating strong evaporation of groundwater fed pools during this drought year.