Lead isotope ratios in moss for the assessment of transboundary pollutants in the Yatsugatake Mountains, central Japan

Transboundary atmospheric pollutants emitted from mainland Asia are transported to Japan and pose a serious threat to mountain ecosystems. Pb isotope ratios (Pb-207/Pb-206 and Pb-208/Pb-206) of the transboundary pollutants are generally higher than those that characterize domestic pollutants in Japan. Hence, this study examined the influence of transboundary pollutants on the Yatsugatake Mountains by detecting the higher Pb isotope ratios in moss. Based on this examination, we discussed the usefulness of Pb isotope ratios in moss for monitoring transboundary pollutants. As northwesterly-westerly winds transport these pollutants to Japan, we hypothesized that the Pb isotope ratios in moss would be higher on the western slopes of the mountains than on the eastern slopes. Furthermore, this difference would be more apparent at higher elevations because of the smaller influence of domestic Pb pollutants. Contrary to these hypotheses, all the Pb isotope ratios in moss were within the ranges of domestic Pb pollutants across the study area, indicating that the influence of transboundary Pb pollutants on moss was small. Notably, these responses of moss to transboundary Pb pollutants differ from those to transboundary nitrogen pollutants. These results imply that the sensitivity of moss to transboundary pollutants largely depends on pollutant types.

Automated summary

The study examined the impact of transboundary pollutants from mainland Asia on the Yatsugatake Mountains, finding that the Pb isotope ratios in moss were not significantly affected by transboundary lead pollutants. The sensitivity of moss to transboundary pollutants varies depending on the type of pollutant.