Studies on Nitrogen Pollution of the Tamagawa-river system.

Research Project

Project/Area Number	08456041
Research Category	Grant-in-Aid for Scientific Research (B)
Allocation Type	Single-year Grants
Section	一般
Research Field	Plant nutrition/Soil science
Research Institution	Tokyo University of Agriculuture
Principal Investigator	KUMAZAWA Kikuo NODAI Research Institute, Tokyo University of Agriculuture, Professor, 農学部, 教授 (00011825)
Project Period (FY)	1996 – 1998
Project Status	Completed (Fiscal Year 1998)
Budget Amount *help	¥5,700,000 (Direct Cost: ¥5,700,000) Fiscal Year 1998: ¥1,500,000 (Direct Cost: ¥1,500,000) Fiscal Year 1997: ¥1,400,000 (Direct Cost: ¥1,400,000) Fiscal Year 1996: ¥2,800,000 (Direct Cost: ¥2,800,000)
Keywords	delta^<15>N / Denitrification / Nitrate / Nitrogen Pollution / Spring Water / Tamagawa-river / 浅川 / 南浅川 / 野川 / 仙川 / 秋川 / 窒素安定同位体 / 浄化作用
Research Abstract	The sources of nitrogen pollution of the Tamagawa-river system were studied with the Nitrogen Isotope ratio (delta ^<15>N) method. The results are follows : 1) NO_3-N concentrations anti delta^<15>N values of Hiraigawa-river were high 2.2610.3mgL^<-1> and 8.7310.7, respectively. NO_3-N concentration (0.61mgL^<-1>) and delta^<15>N value (-0.20) in the upstream water of Akikawa-river were the same as those of rainfall. Those of downstream water were 1.38mgL^<-1> and +5.44, respectively, by the inflow of the nitrate polluted stream from the cultivated land. NO_3-N concentrations and delta^<15>N values of spring waters beneath the cliff of Akitome plateau were high (8.989.28mgL^<-1> and +7.95+8.75), reflecting the farming activities, particularly livestock rasing. 2) The concentrations of NO_3-N of waters collected from the upstream of Asakawa-river up to point beyond the confluence of Asakawa and Minami Asakawa-river showed a gradual increase from 1.16 to 4.42mgL^<-1>. NH_4-N and NO … More _2-N were also detected in waters from the junction of Asakawa and Minami Asakawa-river and beyond it. This is due to the increasing the human waste within the vicinity of Minami Asakawa-river. 3) NO_3-N concentrations and delta^<15>N values of the springs water from the human activity which are the sources of Nogawa-river, were 4.506.48mgl^<-1> and +4.67+5.34, respectively. However, proceeding downstream, there was a decrease in the NO_3-N concentration and an increase in the delta^<15>N value, suggesting a natural purification and denitrification during the flow within this river. At the confluence of Nogawa-river and Senkawa-river, the NO_3-N concentration and delta^<15>N value markedly increased to 6.40mgL^<-1> and +11.7, respectively. 4) It is considered that the sources of nitrate of spring waters in the right side of the upper and central part of Tamagawa-river are coming from soil and human activities. The decrease of NO_3-N concentration and increase of delta^<15>N value in spring waters on the left side of the central part of the Tamagawa-river are due to the presence of reed plants. Less