Molecular fossils, environmental genomics and the natural history of an Australian salt lake
This project is collaborative with Jochen Brocks (ANU) and Jill Banfield and her students (University of California, Berkeley). A PhD student (P. Sarge Bray) has started work on a project in this area.
The central theme of this study is salinity, its history in Australian lakes and its influence on microbial ecosystems. Our major aim is the development of new technologies based on molecular fossils detected in sediments and sedimentary rocks. Lake Tyrrell was chosen as our study site as it is the hydrologically best understood salt lake in Australia and contains a well preserved sedimentary record of the past ~120,000 years. With a surface area of ~160 km2, it is the largest saline groundwater discharge lake in the Murray Basin located in semi-arid Mallee landscape 380 km east of Adelaide.
Australians inhabit the saltiest continent on Earth. Eighty percent of Australian lakes by area are naturally saline. Unfortunately, salt lakes as well as non-saline freshwater systems, are threatened by secondary, human-induced salinization. To preserve or remediate wetlands, we have to understand how their microbial ecosystems respond to changing salt levels in the present and how they responded to climatic changes in the past. A chronicle of past ecosystems and their geochemical cycles is recorded in lake sediments tens of thousands to millions of years old. A very powerful approach for reading these subtle signatures is the study of molecular fossils or biomarkers.
Organic matter from decaying organisms in lakes is predominantly recycled back into carbon dioxide and water. However, a small fraction of recalcitrant biomass usually escapes remineralization and accumulates in bottom sediments. Many lipids and pigments are stable for tens of thousands of years with little alteration. As many lipids are also specific for groups of organisms, their structures as well as their carbon and hydrogen isotopic compositions, often retain useful taxonomic and ecological information. For instance, halophilic archaea contain a large variety of glycolipids, many of which are diagnostic for individual genera and are used for easy classification of hypersaline communities. The group also contains a diagnostic carotenoid that gives saltern ponds a characteristic red colour. Its fossil remains are tell-tale signs for halophilic archaea in ancient lake bed sediments. Biomarkers also record past environmental conditions such as anoxia, paleotemperatures and perturbation of geochemical cycles. We propose to study the biomarker record of Lake Tyrrell.
Jill Banfield and Simon George at Lake Tyrell, March 2006