報告書番号

V05034

タイトル（和文）

わが国における渓流水のリン濃度の実態とその規定要因

タイトル（英文）

Geographical distribution of dissolved inorganic phosphate concentration of streamwaters in Japan and the factors controlling the concentration

概要 （図表や脚注は「報告書全文」に掲載しております）

全国を網羅する1,244地点における渓流水中のリン酸態リン（DIP）濃度を調べた結果，濃度はほぼ対数正規分布に従っていた。DIP濃度の中央値は6.6μg l-1であり，定量下限値（1.5μg･ L-1）以下から116μg l-1の広い範囲に分布した。表層地質の違いにより，DIP濃度に有意な差がみられ，火成岩，変成岩の分布域に比べて堆積岩で高く，堆積岩の中でも古生代堆積岩で最も高かった。火成岩では，中塩基性岩で酸性岩よりもDIP濃度が高い傾向を示した。地球化学図より得られる上流域における岩石・土壌中のリン含有量とDIP濃度との関係をみると，火成岩と変成岩では，両者の大小の傾向はほぼ一致し，また，土壌や岩石の風化により供給されるケイ酸濃度とDIP濃度との間に正の関係が認められた。以上より，土壌・岩石のリン含有量やその風化反応が，渓流水のDIPの濃度形成に影響していることが推察された。

概要 （英文）

To determine the geographical distribution of dissolved inorganic phosphate (DIP) concentration of streamwaters in Japan, 1,244 samples were collected nationwide from watersheds non-polluted by any anthropogenic sources. DIP concentrations were logarithmically normally distributed, and showed a wide range from below the minimum limit of determination (1.5 μg･l-1) to 116 μg･L-1, with the median of 6.6 μg･L-1. The sites with higher concentration (>10 μg･l-1) are predominant in the north of Ibaragi and the west of Saitama and Tokyo, Hokuriku district from Ishikawa to Tottori, Shikoku- and Kyusyu mountains, whereas the sites with lower concentration (< 4 μg･l-1) are conspicuous in Central Hokkaido, Chubu district and the west of Chugoku district. Significant difference (P< 0.001) in DIP concentrations was observed among subsurface geology by One-way ANOVA. DIP concentrations in the sites underlain by sedimentary rocks were higher than those underlain by igneous and metamorphic rocks. Sites underlain by Paleozoic sedimentary rocks had higher DIP concentrations than those by Mesozoic- and Cenozoic sedimentary rocks. In igneous rocks, sites underlain by intermediate rocks (andesite) had higher concentrations than those by acidic rocks (rhyorite and granite). The difference in DIP concentration among types of igneous and metamorphic rock coincided with the phosphorous contents obtained from Geochemical Atlas of Japan among the rock types. Also, positive correlation was observed between DIP and SiO2 in streamwaters in each site. These results indicate that DIP concentrations of streamwater are partly controlled by the phosphorous contents of soil and/or rock and the mineral weathering.

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