Salt mobilisation processes from a salinised catchment featuring a perennial stream

Stream salinity is a major concern in the Murray-Darling Basin (MDB) for its impact upon irrigation, urban water supplies and biota. This study investigated the source of salt to a perennial stream in a small salt affected catchment in the eastern MDB. Using a Bayesian mixing model on an event basis, it was found that between one third and two thirds of the salt came from the near surface zone (0–0.2 m) and the remainder came from groundwater. For the year 2006, 38% of the salt exported from the catchment was sourced from the near surface zone. The source of water for the near surface zone comprises less than 1% of the catchment area and is associated with a saline seep/scald. This area becomes saturated during the winter months when saturated overland flow is generated. This mechanism for salt delivery to a stream is not explicitly included in most models used to generate management scenarios for the mitigation of stream salinity. There is a growing body of evidence to suggest that the near surface zone is very important for salt delivery to streams, therefore models should explicitly incorporate this mechanism.