Applying paleolimnological techniques in estuaries: a cautionary case study from Moreton Bay, Australia

Paleoecological techniques provide useful tools to identify restoration targets and natural variability for management programs. In the past decade development of these techniques has enabled the application of paleoecology within estuarine environments. However, despite these advances, caution needs to be exercised when employing paleoecological techniques in some estuary types. This study used a novel combination of chronological, diatom, geochemical and isotopic data to develop an understanding of the environmental changes that have occurred as a result of human activities within Moreton Bay, an open estuarine environment in sub-tropical east Australia. Results indicated mixed success of these techniques with 210Pb results indicating only background levels, 14C results indicating sediment deposition from mixed sources, no diatom preservation and inconsistent results between geochemical and isotope proxies. Sufficient evidence did exist to identify that the Moreton Bay sediments have been derived from different sources over the past 10 000 years, most likely as a result of rainfall changes to the adjacent catchment areas. However, isotope records were not able to identify the most likely sources of these sediments. Problems with diatom preservation were most probably due to the marine salinity and high temperatures associated with a sub-tropical open embayment estuary. It is recommended that these results are reflected upon for development of future estuarine paleolimnological studies. Past results have indicated successful application of paleoecological techniques in riverine estuaries. Hence, it is recommended that future studies attempting to identify environmental history of estuaries incorporate river influenced locations rather than marine dominated sites. This should ensure better diatom preservation and more definitive geochemical signals