Measurement of Bacterial Sulfate Reduction in Sediments: Evaluation of a Single-Step Chromium Reduction Method

A procedure which includes the Total Reduced Inorganic Sulfur (TRIS) in a single distillation step is described for the radiotracer measurement of sulfate reduction in sediments. The TRIS includes both Acid Volatile Sulfide (AVS: H2S+FeS) and the remaining Chromium Reducible Sulfur (CRS: S0, FeS2). The single-step distillation was simpler and faster than the consecutive distillations of AVS and CRS. It also resulted in higher (4-50%) sulfate reduction rates than those obtained from the sum of 35S in AVS and CRS. The difference was largest when the sediment had been dried after AVS but before CRS distillation. Relative to the 35S-AVS distillation alone, the 35S-TRIS single-step distallation yielded 8-87% higher reduction rates. The separation and recovery of FeS, S0 and FeS2 was studied under three distillation conditions: 1) cold acid, 2) cold acid with Cr2+, and 3) hot acid with Cr2+. The FeS was recovered by cold acid alone while pyrite was recovered by cold acid with Cr2+. A smaller S0 fraction, presumably of the finer crystal sizes, was recovered also in the cold acid with Cr2+ while most of the S0 required hot acid with Cr2+ for reduction to H2S.