A research project that has examined sediment cores from several Victorian lakes has gained new insights into how the climate has changed over the past 2,000 years, revealing that the most severe impact on the water systems have occurred in the last four decades.

The research found that the sediment cores have seen several severe, protracted droughts over the last 2,000 years that have led to considerable changes in the ecology of the lakes. However, the research concluded that the present stake of the lakes is highly unusual, if not unprecedented.

The study, conducted by a joint team of researchers from the University of Ballarat and Monash University, examined sediment cores from six lakes - Lakes Colac, Purrumbete, Modewarre, Burn, Rosine and Tower Hill Main Lake - in the region between Melbourne and the South Australian border.

The sediment cores were taken from six different sites at each of the six lakes and were used to measure their aquatic plant, salinity and nutrient history. By analysing algae and fossil remains - such as seeds, leaves and pollen - in the sediment cores the researchers were able to assess the response of aquatic plants to climate, lake levels and water quality at different times during the last 2,000 years. The sediment cores used in the study were taken during the last severe drought when several of the lakes were dry.

The project’s chief researcher, Prof Peter Gell from the University of Ballarat said the use of lake sediment cores provided an effective ‘measuring stick’ to compare the impact of past droughts with the recent severe drought experienced in Victoria and the rest of south east Australia.

“The results from our study indicate that the level of effective rainfall in the western Victoria region over the last 40 years, and particularly since 1997, is possibly unprecedented relative to the last 5,000 years,” Prof Gell said.

“The evidence from the large lakes in particular shows that the drying of the regional climate has its origins over 100 years ago. The sediment cores show that since European settlement there has been a significant, additional driver of climate that has taken the water balance deficit in these lakes to extreme levels that are unprecedented in the last 5,000 years.”

“It must also be noted that the impact on the ecology and quality of the lakes is not limited to climate change. Human land use has clearly had an impact on the condition of the wetlands, something the sediment cores also gave evidence to.”
The Rural Industries R&D Corporation’s Managing Director, Craig Burns said the study is an important addition to Australia’s growing knowledge of the history and impacts of climate change.

“This study has looked at the impacts of a changing climate over thousands of years and has provided further evidence that the last few decades have been drier, and in that regard have been without precedent,” Mr Burns said.