Two ombrotrophic peat bogs (NC2 and BL2) from North Stradbroke Island, Australia, were precisely dated using 210Pb and analyzed by scanning electron microscopy. Sub-samples were total digested and sequentially leached for trace and major elements concentrations using ICP-MS and ICP-OES. Total Pb concentrations in both profiles increased with the time. PAAS normalized REE patterns were characterized by relatively flat patterns, with slight enrichment in LREE, and a significant negative Eu anomaly. The temporal changes in metal concentrations, 206Pb/207Pb ratios, REEs, and ash content observed in the two profiles suggest three different periods with distinct conditions in terms of dust provenance and atmospheric pollution: (1) Pre-anthropogenic (pre-1842); (2) Early industrial (from 1840s to 1920s); (3) Industrial (post-1930s). Ombrotrophic peat bogs may be reliable archives of environmental pollution, but also shows that adjacent sites may provide contrasting evidence. Despite their close proximity, the two sites show different trends in metal deposition. Metals in NC appear to be largely bound to minerals and inorganic materials, while in BL they are mainly organic-related. Indeed the peculiar behaviour of Pb in the BL profile suggests that biological process may cause Pb isotopic fractionation. Ash contents, texture, Pb isotopic compositions, Sb/Pb values, patterns of selected trace elements (Pb, Cu, Zn, Cd, Cr, Co, Sb, Ni, Se, As, Be and Mo), and their leaching behaviours suggests that NC and BL are chemically different types of peat bogs. NC peat bog is an open sink for elements, and can be used to define regional anthropogenic impacts. In contrast, the BL site appears to be influenced by local natural and anthropogenic processes and activities, such as changes in land use. Furthermore, it demonstrated that only some of the environmental-related trace elements preserve their original depositional record. Arsenic, Be, Co, and Zn are highly mobile under weak acid conditions, and are therefore not suitable for assessing temporal trends of pollution. Cadmium, Ni, and V may also be highly mobile under certain conditions. In contrast, Pb, Cu, Cr, Mo, and Sb are not subject to vertical migration, and are useful for establishing the pollution record of ombrotrophic peat bogs.
| Identifer | oai:union.ndltd.org:ADTP/286828 |
| Creators | Jiajia Zheng |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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