ABSTRACT

Increased emission of acidic pollutants on the Asian continent and long-distance transport of such pollutants have caused soil acidification in eastern Asia. In Japan, Hokuriku district experiences high deposition of acidic pollutants, and soil acidification and acidic fog have been observed at Mt. Tateyama in central Japan. To preserve the Mt. Tateyama ecosystem, it is necessary to understand when soil acidification began, the extent of soil acidification, and its influence on forest soil environments. The historical evolution of soil acidification in this area is not yet fully understood. In this study, we analyzed Ca, Mg, Mn, Sr, Ba, and Pb concentrations in tree-rings of a Tateyama cedar (Cryptomeria japonica) at Bijodaira, covering a record from 1915 to 1993. The radial distributions of each element in the Tateyama cedar were classified into four groups: (I) increasing concentrations toward the outermost ring (Ca²⁺ and Mn²⁺); (II) sharp decrease across the heartwood/sapwood boundary (Mg²⁺); (III) higher values in the late 1950s and around 1990 superimposed on the slightly increasing trend from the 1920s (Sr²⁺ and Ba²⁺); and (VI) higher values around the late 1960s to early 1980s (Pb²⁺). Among these elements, Ca and Pb were interpreted to have a low radial mobility in Japanese cedar. It is worthy of note that Ca concentrations in the tree rings began to increase gradually in the 1950s–1960s, and increased significantly around 1970, and reached yet higher values in the 1980s–1990s. We interpreted that these signals, suggesting higher uptake of Ca²⁺ from the 1950s–1960s, may be related to increased nutrient availability in the rooting zone during the early stages of acidic deposition. Potential sources of acidic deposition may be H₂SO₄ and HNO₃ from local road building activities of the Tateyama-Kurobe Alpine route during the 1950s–1971s, regional industrial activities during the rapid economic growth in Japan during the 1960s–1970s and in Asian nations from the 1980s. Accelerated soil acidification in the 1990s is documented by a significant loss of base cations and an increase in Al³⁺ concentrations in the soil water in 1993 and 1996. Given that soil acidification (pH < 4.0) is still observed at Bijodaira, a deficiency of nutrient cations and Al stress at Bijodaira may have continued for at least ~20 years.