Emissions of biogenic sulfur gases from a danish estuary

Abstract

The diurnal variations in sulfur emission were studied at seven sites in a Danish estuary, Norsminde Fjord. The sites comprised grass vegetation, intertidal mud flats, accretions of green algae, an exposed shore and a river outlet. Direct measurements of emission rates from soil and water were done by a dynamic flux chamber technique in connection with gas Chromatographie detection and separation of the cryogenically trapped sulfur gases. Sulfur gas concentrations in air and sea water were measured together with emission rates at 0.5–1 h intervals over 25–40 h periods. DMS was the most important sulfur gas released from grass and algae, while mostly H 2S was released from intertidal mud flats. OCS, CH 3SH and CS 2 were released from most sites at lower rates. Emission of DMS followed the daylight variations, often with a delay towards maximum emission rates in the evening. H 2S was mostly emitted at night or in short outbursts during low tides. Total sulfur emission rates were 1–10μmol Sm −2 d −1. Extreme rates of 335μmol DMSm −2 d −1 were measured over decomposing green algae ( Ulva lactuca). H 2S emission fractions were < 10 −6 to 2.10 −4. H 2S was detected, along with DMS, CH 3SH, OCS and CS 2, in the oxic seawater of the estuary at diurnal mean concentrations of 0.1–6.5nmol S/ol −1 . This may indicate a more widespread occurrence of H 2S in shallow, near-shore waters at nanomolar levels.