Temporal and spatial variation of sulfur-gas-transfer between coastal marine sediments and the atmosphere
The spatial and temporal variability of sulfur gas fluxes (H2S, COS, CH3SH, DMS, and CS2) at the sediment-air interface were studied in the intertidal Wadden Sea area of Sylt-Roemoe (Germany/Denmark) during eight measuring campaigns between June 1991 and September 1994. Measurements were performed mainly at four sites in a sheltered intertidal bay of approximately 6 km2 (Königshafen) and discontinuously in a wider range of the 400 km2 Sylt-Roemoe tidal flat area. In situ fluxes of the S-gases were determined by a dynamic chamber technique focusing on dry sediment periods. Additional experiments were conducted in order to determine changes in S-gas concentrations in the sediment between the surface and 70 cm depth. In most cases H2S was the dominant S-gas emitted from the sediment to the atmosphere, contributing up to 70% of the total S-emission at this interface. Mean H2S emission rates ranged between 0.07 and 9.95 mu g S m(exp -2) h(exp -1). Both emission rates and relative contribution of H, S were lowest from fine sand and highest from muddy sites. Diurnal variation of H2S emission was evident in summer and fall with up to 10-fold higher rates during night than during the day. Distinct seasonal variation of H2S-transfer between the sediment and the atmosphere was observed with higher emission rates in the summer than in spring or fall. The emission of H2S to the atmosphere was smaller by a factor of 1600-26 000 than the H2S produced from sulfate reduction. Apparently, the efficiency by which H2S produced in the sediment is retained and reoxidized by biogeochemical sediment processes is extremely high. Carbonyl sulfide (COS) was emitted with relatively constant rates in space and time with mean flux rates ranging between 0.24 and 2.0 mu g S m(exp -2) h(exp -1). Carbon disulfide emission rates were comparable to those of COS and varied between 0.3 and 2.23 mu g S m(exp - 2) h(exp -1). DMS played a minor role in the S-gas transfer from uncovered sediment areas contributing between 3.1 and 23% to total S-emission from the sediment to the atmosphere.