河川の水質形成と集水域の土地利用形慴との関俿

摘要

窒素濃度の上昇が確認されている霞ケ浦流入河川において水質・流量調査およびGISを用いた集水域情報の整理・ 見積を実施し，各河川の水質と集水域内土地利用形態との関係を検討した。流入河川中のNO_3-N濃度は特に北浦流 入河川で高濃度であり，低水温期に向けて上昇する傾向が観測された。またこのNO_3-N濃度は降雨後の増水時には 希釈され低下していた。主成分分析により河川の水質と集水域の土地利用状況との関係を検討した結果，河川水中の NO_3-N濃度は平水時においては河川集水域内の養豚数，畜年数，畑地面積および森林地面積と相関性が高く，リン， 有機物，粒子状物質濃度は市街地面積や水田面積と相関性を有していることが明らかとなった。また増水時において は，小規模河川水中のNO_3-N濃度は養豚数のみと高い相関性を示した。%The relationship between the formation of river water quality and the land use of river watershed at Lake Kasumigaura (Ls. Nishiura and Kitaura) was investigated in this study using measured in situ data and data calculated using a geographic information system (GIS). NO_3-N concentrations in river water were high, particularly in L. Kitaura watershed. The NO_3-N concentrations increased at a low-water-temperature period and decreased with dilution after rainfall. The relationship between river water quality and land use characteristics in river watershed was examined by principal component analysis. The nitrogen concentrations in river water were correlated with the number of livestock, upland field and forest area in their watershed at ordinary flow. A high correlation was confirmed particularly between the number of pigs and NO_3-N concentration. Paddy field and urban area were correlated with phosphorus, organic matter and particulate matter concentrations. During flood due to rainfall, the nitrogen concentrations in small-scale rivers showed a high correlation with only the number of pigs.