To what extent are floods and droughts a natural part of Australia’s climate cycle? What was it really like in Australia before the Europeans came, and how can Australians get back to nature if we cannot be sure about our country's natural state?
These are some of the questions scientists from the Australian Nuclear Science and Technology Organisation (ANSTO) and universities around Australia are working together to answer in a major project that aims to set benchmarks for what human activity has done to change the environmental face of Australia.
The Human Activity and Climate Variability Project is being led by ANSTO’s Environment Division, and involves scientists from around Australia and overseas. The project uses ANSTO’s unique nuclear facilities for analysing minute quantities of natural radioactivity in the lake sediments.This natural radioactivity provides the scientist with a "clock" to date the sediment samples and the history contained within the sediments.
ANSTO environmental scientists Dr Henk Heijnis and Dr Kate Harle are starting to piece together some of the answers through their studies into the deposition of sediments in Australian lakes. Their work already shows some very definite correlations between human activities, such as forestry and increased burning, mining and water pollution, and the types of lake sedimentation to be found.
"By taking cores of the sedimentary material at the bottom of lakes in six different climatic zones, we are beginning to get an idea of how the same human activity can produce very different impacts under different climate regimes," Dr Heijnis said.
"For example, deforestation in a more arid region will probably lead to a salinity problem, whereas deforestation in Tasmania, where rainfall is heavy, can destabilise hill slopes and lead to their being washed away. By taking core samples in different climate zones we can see what changes can be put down to natural shifts in climate such as El Nino and La Nina events, and what can be attributed to changes caused by human occupation, such as the felling of trees," he said.
"Whenever there are major weather events, such as the floods at Wollongong a few years ago, a debate crops up about how much the floods can be attributed to nature and how much to human-initiated changes to the environment. We are hoping to be able to answer some of these questions."
One study, in Lake Burragorang, south west of Sydney, found a very significant human fingerprint in the form of increased trace metal concentrations in sedimentary deposits from mines at Yerranderie, which were abandoned in the 1930s. The influx of metals correlates with heavy rainfall events.
Dr Kate Harle has also been analysing fossilised pollen in the sediments.
"Although we have limited historical records from people such as Sir Joseph Banks, a common problem for people wanting to bring land back to its natural state in Australia is not knowing what the natural environment was like before European habitation.
We would also like to know what fire events occurred in Australia before colonial occupation, to give us a better idea as to how we should manage the land."
The three-year project of Dr Heijnis and Dr Harle, which involves collaborative studies with scientists from universities, is currently in its second year.
Their investigations into the natural archives of climate variability are a major component of an overall project being headed by ANSTO in which other scientists are studying the present global atmosphere by measuring radon and fine particles in the air, and the effects of land-surface descriptions in climate modelling.