Reduction of Ferric Iron in Anaerobic, Marine Sediment and Interaction with Reduction of Nitrate and Sulfate

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Abstract
Studies were carried out to elucidate the nature and importance of Fe 3+ reduction in anaerobic slurries of marine surface sediment. A constant accumulation of Fe 2+ took place immediately after the endogenous NO 3 − was depleted. Pasteurized controls showed no activity of Fe 3+ reduction. Additions of 0.2 mM NO 3 − and NO 2 − to the active slurries arrested the Fe 3+ reduction, and the process was resumed only after a depletion of the added compounds. Extended, initial aeration of the sediment did not affect the capacity for reduction of NO 3 − and Fe 3+ , but the treatments with NO 3 − increased the capacity for Fe 3+ reduction. Addition of 20 mM MoO 4 2− completely inhibited the SO 4 2− reduction, but did not affect the reduction of Fe 3+ . The process of Fe 3+ reduction was most likely associated with the activity of facultative anaerobic, NO 3 − -reducing bacteria. In surface sediment, the bulk of the Fe 3+ reduction may be microbial, and the process may be important for mineralization in situ if the availability of NO 3 − is low.