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-Romo (Germany/Denmark) during eight measuring camp aigns between June 1991 and September 1994. Measurements were performed mai nly at four sites in a sheltered intertidal bay of approximately 6 km(2) (K onigshafen) and discontinuously in a wider range of the 400 km(2) Sylt-Romo tidal flat area. In situ fluxes of the S-gases were determined by a dynami c chamber technique focusing on dry sediment periods. Additional experiment s were conducted in order to determine changes in S-gas concentrations in t he sediment between the surface and 70 cm depth. In most cases H2S was the dominant S-gas emitted from the sediment to the a tmosphere, contributing up to 70% of the total S-emission at this interface . Mean H2S emission rates ranged between 0.07 and 9.95 mu gSm(-2)h(-1). Bot h emission rates and relative contribution of H2S were lowest from fine san d and highest from muddy sites. Diurnal variation of H2S emission was evide nt in summer and fall with up to 10-fold higher rates during night than dur ing the day. Distinct seasonal variation of H2S-transfer between the sedime nt 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 1600-26000 than the H2S produced from sulfate reduction. App arently, the efficiency by which H2S produced in the sediment is retained a nd reoxidized by biogeochemical sediment processes is extremely high. Carbo nyl sulfide (COS) was emitted with relatively constant rates in space and t ime with mean Aux rates ranging between 0.24 and 2.0 mu g S m(-2) h(-1). Ca rbon disulfide emission rates were comparable to those of COS and Varied be tween 0.3 and 2.23 mu gSm-(2)h(-1). DMS played a minor role in the S-gas tr ansfer from uncovered sediment areas contributing between 3.1 and 23% to to tal S-emission from the sediment to the atmosphere. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.