Determination of sulfur isotope ratio of sulfate in mountainous streams on Yakushima Island after in-situ collection/concentration of sulfate

The sulfur isotope ratio (δ34S) has been used as an indicator to determine the origin of sulfur compounds that are air pollutants acidifying freshwater and damaging ecosystems. In this study, the simple in-situ collection/concentration method of sulfate in freshwater was developed for δ34S determination. The quantity of sulfate required for that determination can be readily collected by dipping a mesh bag in water containing a small amount of anion exchange resin. This sampling method is appropriate for research into mountains and remote islands where the long-term research and the transport of large amounts of water samples and bulky samplers are difficult. This method was used in our study of stream water on Yakushima Island. The sulfur isotope ratios of non-seasalt sulfate (nssδ34S) were higher in the western and mountain regions of the island (+1.1∼+7.5‰) than in the northeastern region (-3.9∼+0.3‰). This suggested that the air mass containing sulfate-sulfur with a high δ34S value emitted by coal combustion in the Asian continent, flowed into the island from the west and northwest and deposited sulfur in the western and mountain regions when the air mass reached high mountains such as Miyanoura-dake (1936 m).