Thermodynamics and organic matter: constraints on neutralization processes in sediments of highly acidic waters |
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| Institution: | 1. Laboratori de Càlcul Numèric (LaCàN), Universitat Politècnica de Catalunya-BarcelonaTech., Spain;2. Barcelona Graduate School of Mathematics–BGSMath, Barcelona, Spain;3. Department of Biomedical Engineering, Case Western University, Cleveland, OH 44106, United States;4. Department of Civil and Environmental Engineering, University of Houston, Houston, TX 77204, United States;5. Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta”, Politecnico di Milano, Milan, Italy;1. Faculty of Chemistry and Pharmacy, University of Sofia “St. Kliment Ohridski”, 1 J. Bourchier Blvd., Sofia 1164, Bulgaria;2. Institute of Soil Science, Agrotechnologies and Plant Protection “N. Pushkarov”, 7 Shosse Bankya Str., Sofia 1331, Bulgaria;3. Institute of Biology and Environmental Protection, Faculty of Mathematics and Natural Sciences, Pomeranian University in S?upsk, 22b Arciszewskiego Str., 76-200 S?upsk, Poland;4. Faculty of Geology and Geography, University of Sofia “St. Kliment Ohridski”, 15 Tsar Osvoboditel Blvd., Sofia 1504, Bulgaria |
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| Abstract: | The controls on the internal neutralization of low productivity, highly acidified waters by sulfide accumulation in sediments are yet poorly understood. It is demonstrated that the neutralization process is constrained by organic matter quality and thermodynamic effects which control the relative rates of SO4 and Fe reduction, and the fate of the reduced Fe and S in the sediments. The investigated sediments were rich in dissolved Fe(II) (0.005–12 mmol l?1) and SO4 (1.3–22 mmol l?1). The pH ranged from 3.0 to 6.8. Contents of reduced inorganic S (0.1–9.5%), molar C/N ratios of the organic matter (12–80) and metabolic turnover rates (1–110 μeq cm?3 a?1) varied strongly. Substantial amounts of Fe sulfides were only found at a simultaneous partial thermodynamic and solubility equilibrium of the involved biogeochemical processes. Sulfide oxidation was apparently inhibited, and SO4 and Fe reduction coexisted. In this type of sediment increases in C availability cause enhanced neutralization rates. In the absence of a partial equilibrium, the sediments were in a sulfide oxidizing and Fe reducing state, and did not accumulate Fe sulfides. The latter type of sediment will increase neutralization rates in response to decreasing deposition of reactive Fe oxides but not necessarily in response to increases in lake productivity by e.g. fertilization measures. |
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