Changing Patterns of Water Quality Associated with Hyporheic Flow of a Gravel Bar in the Kamo River

Abstract

本研究は，平水時の砂州間隙水域の水質環境のうち，とくに間隙生物にとって重要な溶存酸素の分布様式や時系列変化に着目し，それらに影響を及ぼす要因について，間隙水の動態と関連付けて検討した．その結果，平水時における砂州間隙水域の溶存酸素濃度分布には，間隙水流動性そのものよりもむしろ，間隙水温の上昇に伴う酸素溶解度の低下，生物による有機物の分解の影響が強く働いていることが示唆された．また，間隙水の溶存酸素濃度の高い場所は，水際近傍に限られており，砂州内の大半で低かった．さらに，晴天時，上空が開けた裸地下では，地温の上昇に伴い間隙水温も上昇しやすいことから，平水時の砂州間隙水域は，生物にとって変動の激しい過酷な生息環境であると考えられた．

Aquatic environmental conditions of the hyporheic zone in a gravel bar were investigatedunder normal low-flow conditions in the Kamo River, in Kyoto city, Japan.Horizontal distribution and chronological changes in DO concentration, water temperatureand electric conductivity in the hyporheic zone were examined in relation to thehyporheic flow as a factor for the changes in water quality. Distribution patterns of thewater quality parameters showed that the reduction in DO concentration was stronglyrelated to the hyporheic water temperature, indicating that it was influenced by decompositionprocess of organic matters as well as the liquidity of the hyporheic flow. Hyporheicwater temperature at the area without vegetation cover tended to rise followingthe increase in the ground surface temperature in the daytime.