2023 Fiscal Year Final Research Report
Effects of hillslope and in-stream processes on stream nitrogen dynamics in headwater streams
| Project/Area Number |
19K12298
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Review Section |
Basic Section 63010:Environmental dynamic analysis-related
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| Research Institution | Kyushu University |
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Principal Investigator |
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| Project Period (FY) |
2019-04-01 – 2024-03-31
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| Keywords | headwater streams / in-stream processes / nitrogen / hyporheic zone / benthic zone / riparian zone / runoff |
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| Outline of Final Research Achievements |
Headwater mountain streams account for a large part of a river network and are source of water, sediment, nutrients, etc. for the downstream environment. Thus, it is important understand the controls on water quality in mountain streams. The results of this study showed the importance of in-stream processes in nutrient, in particular inorganic nitrogen, cycle. Mountain streams tend to have a complex morphology and high saturated hydraulic conductivity, consequently high stream-groundwater exchange. More than 10 % of flow was exchanged in about 100 m reach in our study. The hyporheic zone with strong stream influence functions as an important storage and decomposition zones for terrestrial organic matter, indicating high microbial activities. As a result, the hyporheic zone is also an important uptake zone of inorganic nitrogen, and without the its presence, transport of inorganic nitrogen downstream will increase.
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| Free Research Field |
河川水文・生物地球化学
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| Academic Significance and Societal Importance of the Research Achievements |
下流河川への水、土砂、栄養塩などの物質の供給源である山地河川であるが、その水質は、流域斜面からの流入だけでなく、流路内での物質循環プロセスによって制御されていることが本研究で明らかになった。流路内プロセスには、流路から広がる飽和土砂堆積域（河川間隙水域）が重要で、落葉など山地河川に生息する生物の重要な餌資源を貯留・分解する場、そして無機態窒素などの栄養塩の循環を促進する場としても機能していることがわかった。複雑な地形と高い透水性によって維持される河川間隙水域の広がりは、山地河川の水質形成、特に平水時に、大きな影響をもつ。
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