A H2S MICROSENSOR FOR PROFILING BIOFILMS AND SEDIMENTS - APPLICATION IN AN ACIDIC LAKE SEDIMENT

We developed a microsensor for the amperometric detection of dissolved hydrogen sulfide, H2S, in sediments and biofilms. The microsensor exh ibits a fast (t(90) <0.2 to 0.5 s) and linear response to H2S over a c oncentration range of 1 to >1000 pmol H2S l(-1), and has a low stirrin g dependency of the microsensor signal (<1 to 2%). We used the new mic rosensor to obtain the first microprofiles of H2S in an acidic lake se diment with a several cm thick flocculant surface layer. Despite the l ow pH of 4.6, a relative low SO42- level in the lake water, and a broa d O-2 respiration zone of ca 6 mm, we were able to measure H2S depth p rofiles in the sediment at a good resolution, that allowed for calcula tion of specific sulfate reduction and H2S oxidation activities. Such calculations showed highest sulfate reduction activity in the anoxic s ediment down to ca 20 mm depth. A comparison of calculated areal rates of O-2 consumption and sulfate reduction indicated that sulfate reduc tion accounted for up to 13% of total organic carbon mineralization in the acidic sediment. All produced H2S was reoxidized aerobically with O-2 at the oxic-anoxic interface. In addition to its good performance in acidic environments, the new H2S microsensor has proven useful for sulfide measurements in neutral and moderate alkaline (pH < 9) biofil ms and sediments, and thus is a true alternative to the traditionally used potentiometric Ag/Ag2S microelectrode for most applications in aq uatic ecology and biogeochemistry.