A Mentum In Time: Chironomids as Palaeotemperature Indicators at Thirlmere Lakes, NSW, Australia

The Thirlmere lakes, within the Blue Mountains Heritage Area, offer excellent potential to provide records of past climate/environmental change for the southeast Australian region where currently few records exist. Palaeo-records provide a longer-term perspective on lake conditions, which is important given the recent lake drying observed in the system. The primary aim of this study was to use chironomids (non-biting midges) to reconstruct temperature through the Holocene at Thirlmere Lakes National Park. Temperature reconstructions over the Holocene are scarce for the southeast Australian region and chironomids can be ideal proxies to enhance our understanding of climatic variation over this period. The unique characteristics of chironomids, including their ability to respond rapidly to climatic fluctuations, makes them ideal tools for reconstructing palaeotemperature. 31 Chironomid taxa were identified from a master core from Thirlmere Lakes and assessed against an existing training set for the region to infer the likely environmental variables effecting the down-core assemblages. However, temperature was identified as having no significant impact on the changing down-core assemblages, disallowing the creation of a temperature reconstruction. Depth, conductivity and productivity explained the most significant variance in the assemblages. The training set contained insufficient modern analogues, limiting the reliability of inferring environmental conditions at Thirlmere through the Holocene. However, the ecology of the chironomid assemblages implied warm shallow eutrophic conditions prevailed, while modern chironomid assemblages indicate that there is a degree of variability between the lakes within the National Park. They also potentially indicate the lakes are characterised by high variability in environmental conditions, as would result from water level fluctuations and drying. Even though the chironomid record failed to supply reliable interpretations of environmental conditions at Thirlmere Lakes through the Holocene, a better understanding of in-lake process has resulted, enabling identification of future research objectives