From rainforest to wasteland in 100 years: The limnological legacy of the Queenstown mines, Western Tasmania

Areas within the rainforests of south-west Tasmania, home to Aboriginal tri bes for more than 36,000 years, were dramatically changed in the late 1800s with the arrival of European prospectors. Subsequent large-scale mining an d smelting operations resulted in acid rain, local deforestation and extens ive soil erosion. Much of the area is now bare rock. The aims of this study were to examine the terrestrial and lacustrine responses to industrial aci dification and deforestation as revealed by a sediment core from 'Owen Tarn ', a small cirque lake down-wind of the mining town of Queenstown, and adja cent to a World Heritage Area. Terrestrial responses were investigated usin g pollen analysis to document both the state of the rainforest before and a fter the arrival of the Europeans. Limnological responses were documented b y examining changes in diatom communities in the core. Results show both th e terrestrial vegetation and the aquatic microscopic vegetation have been c onsiderably modified by mining activities in the last 100 years. Pollen ana lysis provides a chronology of industrial deforestation and diatom analysis shows changes in species composition and a decline in species richness. In direct ordination (PCA) of sediment diatom assemblages in the core with aut ecological data from 76 Tasmanian highland lakes (TASDIAT) reveals that dia tom assemblages in the bottom parts of the core are analogous to those of T asmanian oligotrophic 'corridor lakes' while recent species assemblages are similar to those of acidic Tasmanian 'western lakes'. Although a number of 'cosmopolitan' species indicative of lake acidification in the northern he misphere are present in Owen Tarn, acidification has resulted in a differen t species response. In the most recent sediments the assemblage is dominate d by Eunotia species in which valve deformation is manifest. These are a po ssible response to chemical stress. Lower abundances of deformed diatoms oc cur in the surface sediments and there is an increase in pollen from herbac eous taxa which reflects the revegetation of the catchment. Both responses are consistent first signs of recovery of the lake and revegetation of the catchment following the cessation of smelting activities in 1969. The most recent diatom assemblages in Owen Tarn (top 1.5 cm) resemble those of L. Sp icer and L. Dora in the nearby Tyndall range. It cannot be excluded that th ese, and other lakes in the World Heritage Area, may have experienced some degree of ecological change as a result of long-range pollution from histor ic smelting activities.