Changes in salinity can affect biota in freshwater directly or indirectly. Toxic effects as a consequence of increasing salinity cause physiological changes, resulting in a loss (or gain) of species. Indirect changes can occur where increasing salinity modifies community structure and function by removing (or adding) taxa that provide refuge, food or modify predation pressure. Other factors such as water-logging or loss of habitat may interact with salinity or have a more immediate impact on species richness (Savage 1979; Froend et al . 1987; Bailey and James 2000; Clunie et al. 2002).
Over the past 12 years several reviews on the effects of salinity in freshwater ecosystems have highlighted the paucity of suitable information for making informed predictions on what future aquatic communities will look like as salinity increases (Hart et al . 1991; Metzeling et al . 1995; Gutteridge, Haskins and Davey Pty Ltd 1999; Bailey and James 2000; Nielsen and Hillman 2000; Clunie et al . 2002). In this review, increases in salinity from less that 500 mg L–1 up to above 10 000 mg L–1 are considered . This is the most likely range of salinities that Australian freshwater rivers and wetlands may experience in the next 50 years. Pulses of higher salinity are also likely to be encountered in some rivers and for some wetlands higher levels of salinity may be experienced as they evaporate and dry out. Ecological effects of salinity ar e likely to be observed within these ranges (Hart et al . 1991).