Biological availability and turnover rate of acetate in marine and estuarine sediments in relation to dissimilatory sulphate reduction

Abstract Acetate turnover rates were determined using ¹⁴C acetate in sediment slurries from two Scottish sea lochs and an estuary which had different rates of oxygen uptake and sulphate reduction. Turnover rates in Loch Etive and Loch Eil were 0.504 and 0.651 μMh⁻¹ respectively, but in the River Tay Estuary there was substantially higher acetate turnover (12.22 μMh⁻¹). The addition of 20 mM sodium molybdate, a specific metabolic inhibitor of sulphate-reducing bacteria (SRB), resulted in a complete inhibition of acetate turnover. These data suggest that SRB were solely responsible for acetate oxidation in these sediments. A comparison of acetate turnover rates in the absence of molybdate and accumulation rate in the presence of the inhibitor demonstrated that at least two pools of acetate with different biological availabilities existed. In Loch Etive only 19% of chemically measured acetate was available with corresponding values of 48% and 65% for Loch Eil and the Tay Estuary respectively.