Reduction of ferric iron in anaerobic, marine sediment and interaction with reduction of nitrate and sulfate.

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