Climate is ever changing and we must acknowledge this fact. Hence, we need to better understand the range of climate variability as well extremes, and in order to better comprehend changes, we can look at the past. The Holocene, which spans the last 12,000 years, is a good reference point as this period witnessed significant and broad changes, going from very wet years to prolonged drought all occurring when humans were present in Australia. The arrival of Europeans also dramatically changes the environments and we must identify these changes so as to better understand how aquatic systems, including groundwater, responded to such modifications.
We have now been able to unravel the differences between human-related changes from natural ones on aquatic systems, and have been able to document the timing and rates of changes during the Holocene. These findings enable us to comprehend the scale of possible changes and these can be of great value to environmental managers. Nevertheless, there are new 'unknowns' which we are already facing, and these are related to significant landscape alterations, the increase of atmospheric CO2 which can modify water chemistry and introduction of exotic biota and chemicals in our aquatic systems.
I will document our current knowledge of selected lake records using geochemical signatures of biogenic carbonates (principally ostracods) that show the scope of past changes in eastern Australia. I will also use the geochemical records of riverine clays obtained from a core taken offshore the Murray mouth to document past river regimes in the Murray Darling Basin spanning also the Holocene. Finally, I will remind the audience that SE Australia has entered into a progressively arid phase that commenced some 6,000 years, with serious implications for aquatic systems and their biota.