Isotopic Fingerprints of Anthropogenic Molybdenum in Lake Sediments

详细信息    查看全文

• 作者：Anthony Chappaz ; Timothy W. Lyons ; Gwyneth W. Gordon ; Ariel D. Anbar
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2012
• 出版时间：October 16, 2012
• 年：2012
• 卷：46
• 期：20
• 页码：10934-10940
• 全文大小：303K
• 年卷期：v.46,no.20(October 16, 2012)
• ISSN：1520-5851

文摘

We measured the molybdenum isotope compositions (未⁹⁸Mo) of well-dated sediment cores from two lakes in eastern Canada in an effort to distinguish between natural and anthropogenic contributions to these freshwater aquatic systems. Previously, Chappaz et al.(1) ascribed pronounced 20th-century Mo concentration enrichments in these lakes to anthropogenic inputs. 未⁹⁸Mo values in the deeper sediments (reflecting predominantly natural Mo sources) differ dramatically between the two lakes: 鈭?.32 卤 0.17鈥?for oxic Lake Tantare and +0.64 卤 0.09鈥?for anoxic Lake Vose. Sediment layers previously identified as enriched in anthropogenic Mo, however, reveal significant 未⁹⁸Mo shifts of 卤0.3鈥? resulting in isotopically heavier values of +0.05 卤 0.18鈥?in Lake Tantare and lighter values of +0.31 卤 0.03鈥?in Lake Vose. We argue that anthropogenic Mo modifies the isotopic composition of the recent sediments, and we determine 未⁹⁸Mo_{anthropogenic} values of 0.1 卤 0.1鈥?(Lake Vose) and 0.2 卤 0.2鈥?(Lake Tantare). These calculated inputs are consistent with the 未⁹⁸Mo of molybdenite (MoS₂) likely delivered to the lakes via smelting of porphyry copper deposits (Lake Vose) or through combustion of coal and oil also containing Mo (Lake Tantare). Our results confirm the utility of Mo isotopes as a promising fingerprint of human impacts and perhaps the specific sources of contamination. Importantly, the magnitudes of the anthropogenic inputs are large enough, relative to the natural Mo cycles in each lake, to have an impact on the microbiological communities.