The impact of regulation and salinisation on floodplain lakes: the lower River Murray, Australia

Floodplain lakes along the lower River Murray are subject to a wide range of human impacts including regulation, abstraction, elevated saline groundwater tables, increased nutrient and sediment fluxes and introduced biota. These perturbations are superimposed on those arising from high inter-annual rainfall variability, driven, at least in part, by variations in the southern oscillation. Sediment-based archives from two lakes within a complex of wetlands, situated near to the first site of irrigation development in the lower River Murray, reveal substantial changes over the last 800 years. While high levels of salinity are not foreign to the sites, the recent trend is towards sustained high salinity levels. As a result of European impact, freshwater diatom plankton now dominates Loch Luna, whilst Loveday Wetland is both more saline and nutrient rich than in the pre-European period. In Loveday Wetland, the post-1960 increase in Haslea spicula (Hickie) Lange-Bertalot, may be driven by increases in sulphur salt concentrations that are believed to be a cause of recent acidification episodes. A recent increase in more salt tolerant diatoms in Loch Luna suggests that this site, which has been largely buffered from substantial change, is becoming more vulnerable to perturbation.