FATE OF ELEMENTAL SULFUR IN AN INTERTIDAL SEDIMENT

Sediment from a tidal flat at Wedderwarden, near the mouth of the Wese r estuary, northern Germany, was amended with elemental sulfur, and co ncentrations of metabolic end products were monitored. The production of both sulfate and sulfide was consistent with disproportionation as the most important fate of the added elemental sulfur. A population of bacteria conducting active elemental sulfur disproportionation was al so enriched from the sediment. In the enrichments, containing both ele mental sulfur and Fe oxides as a sulfide 'scrub', sulfide and sulfate were produced in a ratio of 1.5/1, somewhat lower than the predicted r atio of 2/1. The mismatch between predicted and observed production ra tios is explained by the channelling of electrons into autotrophic or mixotrophic CO2 fixation rather than sulfide formation. The production of organic carbon, in the correct amount to explain the observed sulf ide to sulfate production ratio, was verified by organic carbon analys is. Finally, rates of sulfate reduction were identical in the elementa l sulfur amended sediment, and in control sediment with no added sulfu r. Hence, the heterotrophic bacterial community was completely unaffec ted by an active metabolism conducting elemental sulfur disproportiona tion.