Reliance on 210Pb Chronology Can Compromise the Inference of Preindustrial Hg Flux to Lake Sediments

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• 作者：Colin A. Cooke ; William O. Hobbs ; Neal Michelutti ; Alexander P. Wolfe
• 刊名：Environmental Science & Technology
• 出版年：2010
• 出版时间：March 15, 2010
• 年：2010
• 卷：44
• 期：6
• 页码：1998-2003
• 全文大小：280K
• 年卷期：v.44,no.6(March 15, 2010)
• ISSN：1520-5851

文摘

Lake sediments are frequently used to reconstruct the rate and magnitude of human impacts on the biogeochemical cycle of mercury (Hg). The vast majority of these studies rely on excess ²¹⁰Pb inventories in short cores to temporally constrain recent trends in Hg deposition, revealing an approximately 3-fold increase in Hg deposition since preindustrial times. However, the exhaustion of unsupported ²¹⁰Pb and the onset of widespread global Hg pollution converge temporally in the late 19th century, raising the possibility that preindustrial Hg fluxes are poorly constrained. Here, we combine ²¹⁰Pb and accelerator mass spectrometry (AMS) ¹⁴C dated lake sediment records from arctic and Andean lakes to assess the reliability of ²¹⁰Pb-derived chronologies in the estimation of preindustrial Hg fluxes. For all four studied lakes, relying on ²¹⁰Pb chronologies results in an overestimate of preindustrial Hg fluxes, because extrapolated basal ²¹⁰Pb sedimentation rates are systematically overestimated in comparison to accumulation models that include ¹⁴C dates. In the Andes, the use of ¹⁴C dates is critical toward assessing the full history of Hg pollution, which extends beyond the industrial era. In the Arctic, ¹⁴C dating suggests that Hg deposition may have increased >10-fold since the Industrial Revolution, rather than the commonly quoted 3-fold increase. The incorporation of ¹⁴C dates may therefore be necessary if accurate Hg flux histories are sought from oligotrophic lake sediments.