Mud, mines and rainforest: a short history of human impact in western Tasmania, using pollen, trace metals and lead-210

Abstract

Lead-210, pollen and trace-element analyses of a finely sampled 7.5-cm sediment core from a subalpine tarn in western Tasmania have provided a detailed record of post-colonial human impact in the region. Lead-210 analysis indicated that the record extends back to about 1811 AD, with several changes in sediment rates evident. These have been tentatively related to disturbance in the catchment associated with ore prospecting. The regional vegetation has been reconstructed for this period using pollen abundances. Prior to 1860 AD, there appears to have been little disturbance in the regional vegetation, with relatively high taxon diversity and pollen concentrations. Important communities included rainforest dominated by Nothofagus cunninghamii and subdominated by Phyllocladus and Eucryphia, eucalypt-dominated mixed and wet sclerophyll forest and subalpine and/or alpine complexes. From the 1860s, the evidence suggests an overall reduction in the extent of regional forests, particularly rainforest and subalpine woodland. Initially, this appears to have been associated with both elevated charcoal levels and minor increases in concentrations of trace metals, particularly lead, tin, arsenic and copper. By the 1950s, however, significant reductions in taxon diversity and pollen abundance (particularly for rainforest and subalpine woodland) were strongly associated with rapidly increasing concentrations of trace metals. This evidence corresponds with historic records of mineral prospecting and mining in the region, especially around Queenstown where significant deforestation occurred due to logging and pollution from smelters. Interestingly, the evidence for the most significant impacts coincided with the escalation of open-cut mining from the 1950s to the 1970s, rather than earlier phases of smelter-produced pollution.