Introduction
Salt is a natural component of the Australia landscape and
has been deposited from a variety of sources over millions of
years. Salt enters aquatic systems from groundwater,
terrestrial material via the weathering of rocks or from the
atmosphere, transported by wind and rain (Baldwin 1996a;
Williams 1987). The relative contributions of these sources
depend on factors such as distance inland, climate and
geology (Williams 1987).
Under natural flow conditions in many wetlands and
rivers, periods of low flow resulted in the concentration of
salts in wetlands and riverine pools. Evaporation, combined
with intrusions of groundwater often caused natural salinity
levels to be high for periods of time (Close 1990; Williams
1999; Kay et al. 2001) (Fig. 1A). During these periods of low
flow/high salinity, biota that could not readily disperse
managed to survive either with little or no reproduction and
recruitment (Mills and Geddes 1980; Williams and Williams
1991) or as dormant propagules (Williams 1985; Brock et al.
2003). Biota that are unable to tolerate these periods either
perish or disperse to recolonise when more favourable
conditions occur (Williams 1985).
In many river system such as the River Murray, alteration
of flows, through modification of temporal and spatial