Abstract

Saline water was common in south-west Western Australian aquatic systems prior to land-clearing because most streams and wetlands were ephemeral and evapo-concentrated as they dried, and there were high concentrations of stored salt in groundwater and soil profiles. Nevertheless, a 1998 review of salinity trends in rivers of south-west Western Australia showed that 20-fold increases in salinity concentrations had occurred since clearing in the medium-rainfall zone (300–700 mm). More recent data confirm these trends and show that elevated salinities have already caused substantial changes to the biological communities of aquatic ecosystems. Further substantial changes will occur, despite the flora and fauna of the south-west being comparatively well adapted to the presence of salinity in the landscape. Up to one-third of wetland and river invertebrate species, large numbers of plants and a substantial proportion of the waterbird fauna will disappear from the wheatbelt, a region that has high biodiversity value and endemism. Increased salinities are not the only threat associated with salinisation: increased water volumes, longer periods of inundation and more widespread acidity are also likely to be detrimental to the biota.