Iron isotope fractionation during biogeochemical cycle: Information from suspended particulate matter (SPM) in Aha Lake and its tributaries,Guizhou, China |
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| Authors: | Liuting Song Cong-Qiang Liu Zhong-Liang Wang Xiangkun Zhu Yanguo Teng Lili Liang Suohan Tang Jin Li |
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| Institution: | 1. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences. Guiyang 550002, China;2. College of Water Sciences, Beijing Normal University, Beijing 100875, China;3. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;1. Department of Geoscience, University of Wisconsin-Madison, Madison, WI 53706, USA;2. Department of Civil and Environmental Engineering, The University of Iowa, Iowa City, IA 52242, USA;1. Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand;2. Centre for Trace Element Analysis, University of Otago, P.O. Box 56, Dunedin, New Zealand;3. Antarctic Climate and Ecosystems CRC, University of Tasmania, Private Bag 80, Hobart, TAS 7001, Australia;4. Royal Netherlands Institute for Sea Research, Department of Ocean Systems (OCS), and Utrecht University, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands;1. Instituto de Geociências, Universidade de Brasília, 70910-900, Brasília, Brazil;2. Laboratoire Géosciences Environnement Toulouse, Institut de Recherche pour le Développement – Centre National de la Recherche Scientifique – Université de Toulouse III, 14-16, Avenue Edouard Belin, 31400 Toulouse, France;3. Agência Nacional das Águas – ANA, Brasília, DF, Brazil;1. Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, Paris, France;2. University of California, Riverside, Department of Earth Sciences, Riverside, CA, USA;3. Yale University, Department of Geology and Geophysics, New Haven CT, USA;4. University of British Columbia, Department of Microbiology & Immunology, Vancouver, BC, Canada;5. University of British Columbia, Department of Earth, Ocean & Atmospheric Sciences, Vancouver, BC, Canada |
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| Abstract: | Iron isotope compositions of suspended particulate matters (SPM) collected from the Aha Lake, an artificial lake in the karst area of Yun-Gui Plateau, and its tributaries in summer and winter were investigated for our understanding of the behavior of Fe isotopes during iron biogeochemical cycling in lake. δ56Fe values of SPM display statistically negative shift relative to IRMM-014. Samples from the lake display a range from ?1.36‰ to ?0.10‰ in summer and from ?0.30‰ to ?0.07‰ in winter, while river samples vary from ?0.88‰ to 0.07‰ in summer and from ?0.35‰ to ?0.03‰ in winter. The average iron isotope composition of aerosol samples is + 0.10‰, which is very similar to that of igneous rocks (0.09‰). The SPM in most rivers and water column showed seasonal variation in δ56Fe value: the δ56Fe values of SPM in summer were lower than in winter. The seasonal variation in δ56Fe value of the riverine SPM should be ascribed to the change in source of particulate Fe and geochemical process in the watershed: More particulate Fe was leached from soil and produced by weathering of pyrite widely distributed in coal-containing strata. It is suggested that both allochthonous inputs and the redox iron cycling control the variations of δ56Fe values for SPM in lake.During summer stratification, an Fe cycle named “ferrous wheel” is established near the redox boundary where the upwardly diffusing Fe(II) is oxidized and the reactive Fe oxides formed will continuously sink back into the reduction zone to complete the cycle. The δ56Fe values for SPM reach the minima, ?0.88‰ for DB station and ?1.36‰ for LJK station, just near the redox boundary as a result of the Fe cycling, where a rough 45% to 76% of Fe in these particles was produced by the repetitive cycle. Due to random transportation and diffusion, δ56Fe values of the particles near the redox zone distributed into approximately a Gaussian shape. The good negative correlation existed between δ56Fe values and Fe/Al ratios for DB station, suggesting that they together can be used as good indicators of the redox-driven Fe transformations. |
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