Agricultural acid sulfate soils: a potential source of volatile sulfur compounds?

Environmental context. Acid sulfate soils are important contributors to global environmental problems. Agricultural acid sulfate soils have recently been shown to emit sulfur dioxide, an important gas in global issues of acid rain, cloud formation and climate change. This emission is surprising because these soils tend to be wet and the gas is extremely water-soluble. The potential origins of this gas are not yet understood within the context of acid sulfate soils. Our new study reports the measurement of two potential precursors of sulfur dioxide, dimethylsulfide and ethanethiol, from both a natural and an agricultural acid sulfate soil in eastern Australia. Abstract. Most agricultural soils are generally considered to be a sink for sulfur gases rather than a source; however, recent studies have shown significant emissions of sulfur dioxide and hydrogen sulfide from acid sulfate soils. In the current study, acid sulfate soil samples were taken in northern New South Wales from under sugarcane cropping, as well as from an undisturbed nature reserve. Using gas chromatography/flame photometric detection in conjunction with headspace solid-phase microextraction, we have now determined that these soils are a potential source of the low molecular weight volatile sulfur compounds, dimethylsulfide and ethanethiol. Although the mechanism for their production remains unclear, both compounds are important in the transfer and interconversions of atmospheric and terrestrial sulfur. Therefore, these novel findings have important implications for refining local and regional atmospheric sulfur budgets, as well as for expanding our understanding of sulfur cycling within acid sulfate soils and other sediments.