Sulphur gas emissions in the Boreal Forest: The West Whitecourt case study V. Stable sulphur isotopes

Abstract

Sulphur (S) gas emissions from the West Whitecourt Gas Plant were shown to have δ34S value near +22%. while the δ34S value for pre-industrial soil and ground water was found to be near 0‰ This isotopic ‘leverage’ provided a means of assessing the fate of S-gas emissions and the movement of S-compounds among the four main compartments of the forest ecosystem: air, vegetation, soil, and water. Several high volume sampling techniques were used to relate the δ34S values of atmospheric S-compounds to wind direction at the intensive experimental site 1.5 km cast of the gas plant. These techniques included field testing of a wind directionally controlled high volume sampling array. Winds from the direction of the gas plant carried particulates and SO2 which were considerably more enriched in δ34S than for other wind directions. The stable S isotopic compositions of lodgepole × jack pine needles at sampling locations around the S-gas emission source were consistent with the wind rose summary for the area. Height dependences were found for the δ34S values of atmospheric particulates and for pine foliage. Needles in the upper canopy frequently had δ34S values 5 to 10‰ higher than S-gas emission from the gas plant, thereby suggesting an isotopically selective metabolic process. δ34S values of total S-compounds in surface waters increased with increasing organic S content, approaching a limit near +22‰, suggesting that both parameters were mutually influenced by the input of S-gas emissions to the forest ecosystem. Limited soil profile δ34S data indicated that S of industrial origin penetrated the soil to at least 1 m depth in exposed, dry areas lacking biological cover while in a light forest cover, penetration to 60 cm had not yet occurred. Stable S isotopes were found to be a practical environmental tracer of industrial S in the forest ecosystem in Alberta.