Australia is characterised as a land of droughts and flooding rains. Are the floods and droughts we’ve experienced so far in the short history of European settlement the worst we will face?
Tree ring and coral records can provide part of the answer. However, they are limited in time (often much less than 500 years) and only found in very specific locations.
We have recently discovered leaves of Melaleuca quinquenervia (the broad-leaved paperbark tree) preserved over thousands of years in sediments of acid lakes on North Stradbroke and Fraser Islands, Queensland. Why might this help understand past rainfall? As it turns out, the carbon isotope ratio of plant leaves can reflect moisture stress and, by extension, rainfall. However, this relationship is not shown by all plants and varies between them.
In an amazing stroke of good fortune we discovered that Professor Margaret Greenway had collected leaves of Melaleuca quinquenervia every month for 12 years from a wetland on the mainland less than 50 km from North Stradbroke Island. This extraordinary archive of leaves allowed us to show that there is a very strong relationship between rainfall and the carbon isotope ratio of the leaves. The next step? Applying the relationship to discover how rainfall has varied over millennia by applying our relationship to the leaves we have found in the lakes.
This information can be used to inform water planning in south-east Queensland. Melaleuca quinquenervia is found next to over 200 wetlands stretching the length of the Queensland coast (and in New Caledonia and PNG) so we might have only scratched the surface of what this study can tell us.