Abstract
Porewater dynamics and the formation of iron sulfides were studied in the Brazilian mangrove. Porewater samples were collected during tidal cycles using in situ equipment and physical–chemical and chemical data were obtained. The advective transport of porewater by tidal currents was found to be more effective between 0 and 5 cm depth than below 15 cm. The diffusive input of atmospheric oxygen during low tides resulted in oxidation of porewater dissolved sulfides. Thermodynamic considerations identified pyrite as the main iron sulfide forming at this depth, and the amorphous iron hydroxides are probably the main iron source. Below 15 cm depth, irregular root distribution underground and benthic faunal bioturbation caused considerable spatial variation in a small scale (20 cm). The correlation between alkalinity and total dissolved sulfide suggests that the main pathway for organic matter decomposition is sulfate reduction. Formed in the highly sulfidic diagenetic zone, the dissolved iron went through iron sulfide formation process. Crystalline iron oxides like hematite and magnetite may constitute an important iron source below 15 cm, whereas pyrite is still the most probably occurring iron sulfide, according to thermodynamic considerations.
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Aragon, G.T., Ovalle, A.R.C. & Carmouze, J. Porewater dynamics and the formation of iron sulfides in a mangrove ecosystem, Sepetiba Bay, Brazil. Mangroves and Salt Marshes 3, 85–93 (1999). https://doi.org/10.1023/A:1009960218748
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DOI: https://doi.org/10.1023/A:1009960218748