抄録
To determine the geographical distribution of dissolved inorganic phosphate (DIP) concentrations in stream water in Japan, 1,244 water samples were collected nationwide from watersheds unpolluted by any anthropogenic sources. DIP concentrations were logarithmically normally distributed, and showed a wide range from below the minimum limit of detection (1.5 μg · l-1) to 116 μg · l-1, with a median of 6.6 μg · l-1. The streams with higher concentrations (> 10 μg · l-1) were predominantly in the northern part of Ibaraki, the western parts of Saitama and Tokyo, the region from Ishikawa to Kyoto, and around the Shikoku and Kyusyu mountains. Those with lower concentrations (< 4 μg · l-1) were predominantly in central Hokkaido, Yamagata, the northern part of Gunma and the western part of the Chugoku district. A significant difference (P < 0.001) in DIP concentration was found among subsurface geologies. Watersheds with underlying sedimentary rocks had higher DIP concentrations in their stream water than those with underlying igneous and metamorphic rocks. Among sedimentary rocks, higher DIP concentrations were found in Paleozoic rocks than in Mesozoic and Cenozoic rocks. In igneous rocks, intermediate rocks (andesite) had higher DIP concentrations than acidic rocks (rhyorite and granite). The differences in DIP concentration among various types of igneous and metamorphic rocks coincided with the differences in phosphorus content obtained from the Geochemical Atlas of Japan. In other substances, DIP concentration positively correlated with SiO2 concentration except in Paleozoic and Mesozoic sedimentary rocks. These results indicate that DIP concentrations in stream water are partly controlled by phosphorus content and the mineral weathering of rock or soil.
