Biogeochemistry of iron in an acidic lake |
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| Authors: | Barbara Sulzberger Jerald L Schnoor Rudolf Giovanoli Janet G Hering Jürg Zobrist |
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| Institution: | (1) Institute for Water Resources and Water Pollution Control (EAWAG/ETH, CH-8600 Dübendorf, Switzerland;(2) Department of Civil and Environmental Engineering, University of Iowa, Iowa City, USA;(3) Laboratory of Electron Microscopy, Institute of Inorganic Chemistry, University Bern, Switzerland |
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| Abstract: | In this paper, the fate of iron in Lake Cristallina, an acidic lake in the Alps of Switzerland, is discussed. A simple conceptual model is developed in order to explain the observed diel variation in dissolved iron(II) concentration. Biotite weathering provides reduced iron that is oxidized and subsequently precipitated in the lake. The amorphous Fe(III)hydroxide (FeOOH  xH2O), found in the sediments of Lake Cristallina, is an Fe(II) oxidation product. This oxygenation reaction is most probably catalyzed by bacteria surfaces, as indicated by the relatively high estimated oxidation rate compared to the oxidation rate of the homogeneous oxidation of inorganic Fe(II) species at the ambient pH of Lake Cristallina (pH 5.4 at 4 °C) and by the scanning electron micrograph pictures. Under the influence of light, these amorphous iron(III)hydroxide phases are reductively dissolved. The net concentration of Fe(II) reflects the balance of the reductive dissolution and the oxidation/precipitation reactions and tends to parallel the light intensity, leading to a diurnal variation in the Fe(II) concentration. The rate of the photochemical reductive dissolution of Lake Cristallina iron(III)hydroxides is greatly enhanced in situ and in the laboratory by addition of oxalate to the lake water. |
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| Keywords: | Acidic lake biogeochemistry of iron diurnal variation iron(II) oxidation iron(III) reduction light induced dissolution weathering |
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