Seasonal variations in sediment sulfur cycling in the Ballastplaat mudflat, Belgium

Panutrakul, S.; Monteny, F.; Baeyens, W.F.J.

Seasonal variations in sediment sulfur cycling in the Ballastplaat mudflat, Belgium

2002

Panutrakul, S. | Monteny, F. | Baeyens, W.F.J.

Sulfate reduction rate (SRR) and pools of reduced inorganic sulfur, acid volatile sulfide (AVS), chromium reducible sulfur (CRS), and elemental sulfur (S degrees), were studied from June 1990 till March 1992 at two locations on the Ballastplaat mudflat in the Scheldt estuary. The sediment composition at station A was mainly sand with low organic content whereas sediments at station B were dominated by silt and clay with high organic content. SRR was positively related to temperature; more pronounced at station B (Ea = 190 kJ mol(-1)) than at station A (Ea = 110 kJ mol(-1)). The maximum SRR values observed equalled 14 mu mol cm(-3) d(-1) at station B and 1 mu mol cm(-3) d(-1) at station A. AVS was the dominant radiolabelled end product of the sulfate reduction reaction, except in surface sediments where pyrite and S degrees were more dominant. However, CRS was the predominant reduced inorganic sulfur pool in the sediments. Both AVS and CRS pools showed temporal variations out of phase with SRR. SRR peaked in summer, while the concentrations of AVS and CRS were highest in fall. The accumulation of AVS and CRS started late summer after depletion of oxidants, which had accumulated during winter and spring. The estimated annual SRR and thus sulfide production in the upper 15 cm of station B was of the order of 100 mol m(-2) yr(-1), and at station A of the order of 12 mol m(-2) yr(-1). The sulfur mass balance shows that only a very small fraction, if any, of the produced sulfide is retained as reduced inorganic sulfur in the sediment.

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