Potential for atmospheric sulfur from microbiological sulfate reduction

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A discussion is presented of recent calculations and measurements relating to biogenic sulfur (S) emissions. These emissions are associated with reduced sulfur gases such as hydrogen sulfide and organosulfides. Combined observations of gaseous and particulate sulfur concentrations in the air have helped to elucidate S-budgeting. However, they do not readily lend themselves to consistent interpretation of the importance of natural S emissions, or atmospheric oxidation and removal rates on a regional scale. Direct biogenic flux measurements are becoming available, and are beginning to clarify the significance of the biogenic contributions to atmospheric sulfur. A wide range of variation in sulfur emissions from anaerobic bacterial reduction in freshwater and marine sediments can be expected depending on location, the organic carbon and sulfur content of sediments, and time of year. An empirical relationship is used to estimate sulfate reduction rates in saline and freshwater environments. These calculations suggest “hypothetical” regional atmospheric release rates values of biogenic sulfur of 7.2 kg(S) ha −1 y −1 and 660 kg(S) ha −1 y −1, respectively, for freshwater and marine sediments. However, recent observations of Adams et al. (1980) indicate regional release rates in the order of 1 kg(S) ha −1 y −1 or lower. The calculated range is larger than values estimated previously assuming a mechanism of proteolysis (Rice et al., 1979). Comparison of results from the calculations and experimental observations imply that the fraction of total biogenic sulfur released to the atmosphere may be as low as 10 −3−10 −4 on a regional scale (~10 4 km 2) rather than 0.1 as hypothesized previously. The intensity and areal extent of biogenic sulfur emissions remain uncertain. However, the evidence available and this analysis suggests that such emissions are of minor significance in industrialized regions such as the northeastern United States which cover thousands of square kilometers. This does not preclude localized biogenic contributions to the atmospheric sulfur burden which could be very large over the order of a few square meters, as reported recently by some investigators.