2019 Volume 32 Issue 4 Pages 125-140
The prevailing westerlies that blow from China across the Japanese archipelago carry acidic wet depositions to higher mountains and solitary islands in Japan face the East China Sea and the Sea of Japan. These mountains and islands receive much of the long-range air pollutant load. The water quality of mountain streams can be considered an indicator of an “output” from the surface zone of a mountain watershed that receives an “input” of acidic depositions and sea salts. The wet deposition of NO3− on Oki Island and Rishiri Island increased annually in the period from 1991 to 2016. On yakushima, the annual wet deposition of NO3−+NH4+-N and the average concentration of NO3− in mountain streams increased annually in the period from 1996 to 2013.
For three areas the NO3−-N concentrations in mountain streams are highest in the west, becoming lower towards the east. For Myokou-san, Ihide-san, Asahi-dake, Gassann and Chokai-san, the NO3−-N concentrations become lower from south to north. For Tsushima, Fukuejima, Amakusa-shimojima and Yakushima, those concentrations become lower from north to south. Mountain ridges on the Noto Peninsula, in the Ryohaku Mountains and in the Ibuki Mountains of central Honshu Island are oriented north-south, and the concentrations of SO42− and NO3− are higher in streams in the west of each of these regions than in streams in the east of each of these regions.
