Sulfur speciation monitored in situ with solid state gold amalgam voltammetric microelectrodes: polysulfides as a special case in sediments, microbial mats and hydrothermal vent waters

Sulfur speciation was determined in real time in salt marsh microbial mats, subtidal sediments and hydrothermal vent diffuse now waters using solid st are gold-amalgam voltammetric microelectrodes. Chemical species were measur ed in situ without any sample manipulation or processing. The partially oxi dized sulfur species detected were polysulfides, thiosulfate, elemental sul fur and tetrathionate. Fe(III) oxidation of hydrogen sulfide does not occur within the mats where microbially mediated processes are responsible for o xidation of H2S. In sediments and diffuse flow vent waters, Fe(ill) phases are the direct oxidant of H2S. Sulfur speciation determined in this work is due to in situ biogeochemical processes and is not due to artefacts of sam ple manipulation. The voltammetric data show that polysulfides are the firs t detectable intermediate during sulfide oxidation which is consistent with previous laboratory studies.