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 of³⁵S in AVS and CRS. The difference was largest when the sediment had been dried after AVS but before CRS distillation. Relative to the³⁵S-AVS distillation alone, the³⁵S-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.     

Seasonality of sulfate reduction and pore water solutes in a marine fish farm sediment: the importance of temperature and sedimentary organic matter

Sulfate reduction and pore water solutes related to sulfur cycling and anaerobic processes (short chain fatty acids (SCFA), SO₄ ^2–, TCO₂, NH₄ ⁺, dissolved sulfides (H₂S) and CH₄) were examined during one year at a marine fish farm. Mineralization of fish farm waste products was rapid in this non-bioturbated, organic rich sediment. Stimulation of sulfate reduction rates (SRR) occurred primarily in the surface layers where the organic matter was deposited. Acetate was the most important (<99%) of the measured SCFA attaining high concentrations during summer months (up to 4.7 mM). The acetate profiles exhibited distinct seasonal cycles, where periods with high concentrations in the pore waters were found coincident with a high pool of particulate organic matter in the surface sediments and a low activity of the sulfate reducing bacteria (early spring and late summer). Periods with low acetate pools occurred when sulfate reduction rates were high in early summer and in winter were pools of particulate organic matter were decreasing. Methane production was observed concurrent with sulfate reduction in the microbial active surface layers in late summer. Subsurface peaks of SO₄ ^2–, TCO₂, NH₄ ⁺ and H₂S were evident in July and August due to rapid mineralization in these surface layers. With decreasing autumn water temperatures mineralization rates declined and subsurface peaks of these solutes disappeared. A strong relationship was found between pore water TCO₂, and NH₄ ⁺. Ratios between TCO₂, and NH₄ ⁺ were low compared to a control site, attaining minimum values in mid-summer. This indicated rapid nitrogen mineralization of nitrogen rich labile substrates in the fish farm sediment during the entire season.