2005 Fiscal Year Final Research Report Summary
Nitrogen migration analysis in the Yamato river using nitrogen stable isotope
| Project/Area Number |
16560480
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Civil and environmental engineering
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| Research Institution | Wakayama University |
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Principal Investigator |
II Hiroyuki Wakayama University, Faculty of Systems engineering, Professor, システム工学部, 教授 (60283959)
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| Co-Investigator(Kenkyū-buntansha) |
HIRATA Tatemasa Wakayama University, Faculty of Systems engineering, Professor, システム工学部, 教授 (30093454)
ISHIZUKA Masahide Kagawa University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (50324992)
NISIKAWA Masataka National Institute for Environmental Studies, Chief, 化学環境研究領域, 主任 (80228171)
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| Project Period (FY) |
2004 – 2005
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| Keywords | Yamato River / nitrogen _isotope / nitrogen migration / BOD / River purification / photosynthesis / purification facility / water duality control |
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| Research Abstract |
The BOD value of the Yamato River is the highest of all the Japanese first class rivers. Water chemistries along the Yamato River were investigated intensively to improve water quality. As a result, seasonal concentrations of BOD and NH_4^+-N derived from domestic sewage were high in winter and low in summer. The concentrations decreased with an increase in water temperature.
The general finding was that river water contains organic compounds and Cl^- derived from domestic sewage, and Cl^- was quite stable in rivers. As the ratios of BOD/Cl^- decreased down the river and changed seasonally, organic compounds were thought to be decomposed during flow. NO_3^- which organic compounds were finally decomposed into, also decreased further down the river, and were high in winter and low in summer. NO_3^--N is thought to be used for photosynthesis because pH, DO, δ^<15>N values and chlorophyll concentration of the Yamato River increased with temperature and decrease of NO_3^--N concentration. Therefore, organic compounds are decomposed into NO_3^- intensively in summer and plants along the Yamato River absorb NO_3^- and then the BOD value in summer becomes low. Hence, natural remediation for the Yamato River reduces BOD value in summer. Organic compounds in sewage are decomposed in private sewage systems and naturally in rivers in the Yamato River catchment.
As both decomposition systems depend on temperature, the BOD value in winter is thought to be high. As sewage disposal plants are large scale, the system can keep high temperature and the quality of the final effluent can be controlled. Therefore, the BOD value of Yamato River decreases annually as some new sewage disposal plants are built in the branches of the Yamato River, although the BOD value of Yamato River is the highest of any Japanese first class river. It is important to change private sewage systems into large scale disposal plants, to improving water quality.
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Research Products
(12 results)
