Determination of substrates oxidized by sulfate reduction in intact cores of marine sediments1

Abstract

A method is presented for quantifying the in situ rates of substrate oxidation by sulfate‐reducing bacteria in sediment. Molybdate (100 µ l of 2 M Na 2 MoO 4 ) injected into intact sediment cores inhibited sulfate reduction efficiently. The subsequent accumulation of acetate was linear. The accumulation rate in molybdate‐inhibited cores was determined from linear regressions of the acetate concentrations as a function of incubation time. The acetate contributed about 65% of the electron donor for sulfate reduction. In the surface layers the acetate accumulation rate leveled off with time, indicating that acetate was transported by diffusion to the surface where it could be oxidized by O 2 and NO 3 ‒ respiration. On the basis of linear regressions of the accumulation of propionate, butyrate, and isobutyrate, it was calculated that these substrates contributed 14, 5, and 8% of the electron donors for sulfate reduction.