Identifying the key sources of metal (loid) deposition to remote Tasmanian lakes: is legacy mining a problem?

Abstract

Reports have shown that even remote lakes have been negatively affected by anthropogenic activities. This study used metal concentrations and enrichment factors to comprehensively determine key metal sources and identify potential impacts of recent anthropogenic activity in remote Central Highland Tasmanian (Australia) lakes. Metal concentrations (Al, As, Cd, Cu, Fe, Pb, and Zn) in these lakes remain below Australian interim sediment quality guidelines but have been slowly increasing since the start of the twentieth century. This increase is likely related to increasing organic matter content, rather than any direct, increased input of metals. The largest anthropogenic impact to these systems was damming, which typically led to an increase in organic matter content either directly, by the trapping of particles and nutrients, or indirectly, by stimulating primary production in the lake. This increased organic matter content, in turn, increased the retention of metals, manifesting as an increase to measured metal concentrations. Minor impacts are the historical use of lead shot, leaded petrol, and industrial processes, which may have contributed to the higher Pb enrichment, compared to the other studied metals, in these lakes. Despite recent concerns of metal contamination in the Tasmanian Wilderness World Heritage Area from distant mining activities, there is no strong evidence in this study indicating that lakes in the Central Highlands (a similar distance away) have been impacted by long-distance atmospheric deposition. This is likely related to the decreased rainfall, and thus decreased rates of wet deposition of aerosols in the east of Tasmania, compared to that of the west and in the Tasmanian Wilderness World Heritage Area.