Sulfate reduction in fine-grained sediments in the Eastern Scheldt, southwest Netherlands

Abstract

Sulfate reduction and sulfide accumulation were examined in fine-grained sediments from rapidly accreting abandoned channels and mussel culture areas in the Eastern Scheldt, which covered 4 and 5% of the total surface area, respectively.

Reduction rates were measured in batch experiments in which the SO₄ ²⁻ depletion was measured during anoxic incubation. The reduction rates in summer varied between 14–68 mmol SO₄ ²⁻ m⁻² day⁻¹ and were related to the sedimentation rate. In the most rapidly accreting channels, SO₄ ²⁻ was exhausted below 15–50 cm and methanogenesis became the terminal process of organic carbon oxidation

One-dimensional modelling of sulfate profiles in mussel banks indicated that the subsurface influx of SO₄ ²⁻ was almost of the same order as the diffusive flux at the sediment-seawater interface, during the initial stages of the mussel bank accretion. The energy dissipation of waves and tidal currents on the mussel bank surface increased the apparent sediment diffusivity up to 3-fold, especially in the winter

The results indicate that acid volatile sulfide (AVS) was the major, in-situ reduced, sulfur compound in the sediment. The sulfidation of easily extractable iron was nearly complete. Pyrite concentrations (40–80 μM S cm⁻³) were as high as the AVS concentrations, but there was apparently no in-situ transformation of AVS into pyrite. The detrital pyrite originated from eroding marine sediments elsewhere