Abstract
By using the Diagnosis Model of Organic Resources Circulation, this research aimed at identifying the major sources of nitrogen loading in the Yamato River Basin in Nara City and examining the effectiveness of measures to reduce nitrogen loading to the river water bodies. The study area has been developed as a suburb of the Osaka metropolitan area, and 40% of the land is covered by forest and agricultural land. The simulation result showed that the expected nitrogen loading was overestimated by 16% and had a correlation of R2=0.62 with measured loading. The simulation also showed that approximately 78% of the loading to the major rives in the area was caused by municipal wastewater, which is both treated and untreated. The three scenarios simulated were: (1) replacing conventional septic tanks in the houses with combined household wastewater treatment facilities;(2) applying river water to paddy fields during the non-irrigation season; and (3) composting organic waste produced in the area The estimations indicated that a maximum of 40% to 45% of nitrogen loading could be reduced by adopting scenarios (1) and (2) above, and that the nitrogen demand for agriculture could be met with composting 8% of annual organic solid waste or 60% of household raw garbage in the area with the scenario (3) above.
