Studies on Nitrogen Pollution of the Tamagawa-river system.

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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 2.26*10.3mgL^<-1> and 8.73*10.7*, 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 (8.98*9.28mgL^<-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 4.50*6.48mgl^<-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