Is the Sr isotope ratio of mosses a good indicator for Asian dust (Kosa)?

The need for monitoring Asian dust is increasing owing to concerns about its harmful effects on ecosystems and human health. Strontium isotope ratios of mosses can be used to monitor Asian dust because of the traceability of these ratios and nutrient uptake by mosses from atmospheric deposition. Hence, the present study examined the suitability of strontium isotope ratios of mosses for monitoring Asian dust. Given the higher strontium isotope ratios of Asian dust than those of domestic origins, these ratios of mosses would be higher in areas with Asian dust. Moss samples were collected from 13 sites across Japan. The strontium isotope ratios of mosses in all study sites were lower than those of Asian dust. Although western Japan is more strongly influenced by Asian dust than eastern Japan, there were no significant differences in the strontium isotope ratios between these regions. Notably, the strontium isotope ratios of mosses significantly and positively correlated with those of the local soil across the study sites. These results indicate that strontium in mosses was derived from the local soil, and this uptake pattern may be attributed to a considerable supply of soil-derived strontium. In conclusion, the strontium isotope ratio of mosses is not a suitable indicator for the influence of Asian dust in Japan. Future studies should investigate whether these results could be applied to epiphytic mosses as potential indicators for Asian dust because epiphytes are less influenced by soil-derived minerals than terrestrial mosses.