Tracing source and evolution of suspended particles in the Rio Negro Basin (Brazil) using chemical species of iron |
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| Authors: | T Allard T Weber C Bellot C Damblans M Bardy G Bueno NR Nascimento E Fritsch MF Benedetti |
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| Institution: | 1. Institut de Minéralogie et de Physique des Milieux Condensés, UMR CNRS 7590, Universités Pierre & Marie Curie et Denis Diderot, IPGP, IRD, 4 Place Jussieu, F-75252 Paris Cedex 05, France;2. Ecole et Observatoire des Sciences de la Terre, Laboratoire d''Hydrologie et de Géochimie de Strasbourg, UMR 7517, Université de Strasbourg et CNRS 1, rue Blessig, F-67084 Strasbourg Cedex, France;3. DEPLAN/IGCE/UNESP, Instituto de Geociencias e Ciencias Exatas, Rua 10, n 2527, 13500-230 Rio Claro, SP, Brazil;4. Laboratoire de Géochimie des Eaux, Université Paris Diderot, IPGP UMR CNRS 7047, Bât. Lamarck case courrier 7052, 35 rue Hélène Brion, 75205 Paris Cedex 13, France;1. Department of Earth Sciences, Institute of Geochemistry and Petrology, ETH-Zürich, Zürich, Switzerland;2. Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan;3. CNRS, Univ Brest, IRD, Ifremer, LEMAR, F-29280 Plouzane, France;1. Tomsk Department of the Trofimuk Institute of Petroleum-Gas Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Academichesky ave. 4, Tomsk 634055, Russia;2. National Research Tomsk Polytechnic University, Lenin ave. 30, Tomsk 634050, Russia;1. National Research Tomsk Polytechnic University, 30 Lenin av., Tomsk, 634050, Russia;2. Tomsk State Pedagogical University, 75 Komsomolskiy av., Tomsk, 634041, Russia;1. Universidade de São Paulo, Instituto de Geociências, Rua do Lago 562, Cidade Universitária, São Paulo, Brazil;2. Laboratoire de Biogéochimie des Contaminants Métalliques, IFREMER, Centre Atlantique, F44311, Nantes Cedex 3, France;3. Laboratoire Mixte International-Observatoire des changements Environnementaux –LMI-OCE, Institut de Recherche pour le Développement (IRD) / Universidade de Brasilia, Campus Darcy Ribeiro, Brasilia, Brazil;4. Universidade Federal Fluminense, Departamento de Geoquímica, Campus do Valonguinho, Niterói, Rio de Janeiro, Brazil;5. Imperial College London, Earth Science and Engineering, London, United Kingdom;6. Universidade Federal do Tocantins, Departamento de Química Ambiental, Rua Badejós, Lote 7, Chácaras 69/72, Zona Rural, Gurupi, Tocantins, Brazil |
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| Abstract: | Suspended solids found in porewaters obtained in waterlogged soil sequences that included representative laterite–podzol transitions, associated brooks and major rivers of the Rio Negro watershed (Brazil) were studied using electron paramagnetic resonance (EPR) and Fourier-transform infrared spectroscopies. The main goal was to ascertain sources and track the evolution of suspended matter using a ubiquitous chemical species, FeIII complexed to organic matter (FeOM). Three size fractions were separated by tangential-flow (ultra)filtration: particulate (> 0.2 μm), dense (P) and light (Ps), and colloidal (5 kD < Col. < 0.2 μm) fractions. Quantitative results were acquired for Col. and Ps fractions which are predominantly organic in nature.FeOM concentration (in ‰ dry weight) was determined to be relatively low in suspended solids found in black waters from podzol porewaters and brooks whereas in the main rivers it was several times higher. FeOM concentrations were also correlated with Fe(II)/Fe(III) ratios in solution; these ratios were high in podzol porewaters and low in the rivers. Considering that organic complexation of Fe(II) is minor when compared to that of Fe(III), two interpretations were proposed to account for the above observation. First, FeOM] was assumed to be distributed along a mixing line, with the clear waters from laterites and the black waters from podzols being its end-members. Consequently, FeOM] can be used to trace the source of suspended material. Second, dissolved Fe(II) from podzol areas was considered to be progressively oxidized as pore waters move towards the mainstream. According to this mechanism, iron is complexed by organic matter or precipitated as oxides, thus producing an evolution of colloidal matter. As a result of these mechanisms' action, both the high production of Fe(II) and organic matter at the waterlogged podzol–laterite transition areas are major factors affecting iron export in the Rio Negro watershed. |
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