The fate of atmospheric metal pollutants in the landscape, Snowy Mountains, south-eastern Australia

Abstract

Industrial metals, emitted to the atmosphere by human activity, have been transported and deposited to almost every location on Earth, including Antarctica and Greenland. This is demonstrated by an increasing body of literature in which many atmospheric industrial metals (e.g. Pb, Hg, Cd and Cu) have been shown to be significantly enriched in environmental archives. Studies have largely focussed on peat mires and ice cores, which receive high rates of atmospheric deposition relative to terrestrial inputs. By contrast, few studies have examined the extent of atmospherically derived metals across the wider landscape, where processes such as pedogenesis, erosion and sedimentation affect the spatial extent and magnitude of metal enrichment. In the Snowy Mountains, Australia, atmospheric pollutant metals have previously been identified in alpine peat mires, although their impact on the wider environment has not been assessed. Interest in the fate of atmospheric pollutants in the Snowy Mountains has increased due to the operation of a cloud seeding program in which, silver iodide, AgI, is released to the atmosphere, leading to concerns that silver, Ag, contamination may be accumulating in this ecologically important region. This thesis examines the spatial extent and magnitude of atmospherically derived metals in the SnowyMountains by investigating patterns of enrichment in a range of geomorphic settings and catchment positions, including in soils, peat mires, lakes and reservoirs. The potential movement of metals through the landscape was also assessed by examining rates of geomorphic processes, including rates of pedogenesis and erosion, determined via radionuclides. The thesis was undertaken in three parts which are summarised below. by atmospheric deposition (ombrotrophic peat mires in the upper parts of catchments), the order and magnitude of metal enrichment most closely resembled that of collected aerosols, however, on average enrichment was 5-7 fold lower than in the aerosols. Metals most sensitive to enrichment, i.e., those with low natural abundance in local sediments (Cd, Ag, Sb, Mo), were enriched in all environments including the most geomorphically active settings (tarn lake sediments). In reservoirs, located lower in catchments, patterns of metal enrichment largely reflected concentrations in catchment soils but metals were additionally enriched or depleted depending on their relative particle reactivity. For those metals which are most sensitive to enrichment (Ag, Cd, Sb), the increase in excess flux required to reach trigger value concentrations is lowest in the reservoir sediments (Ag: 13-18, Cd: 7-10 and Sb: 17-61 times the current flux) and highest in the tarn lake (Ag: 60, Cd: 15, Sb: 27 times the current flux) and the peat mire (Ag: 74, Cd: 15, Sb: 18 times the current flux).In part three of this thesis, rates of soil production and soil erosion were quantified using radiocarbon dating, fallout radionuclides and sediment yields in lakes and reservoirs in order to assess the stability of l...