Nitrogen Generation in the Middle Basin of Tone River and Its Effects

Abstract

There is a great concern about the increase in nitrogen pollution at the middle stream of Tone River. In the basin of Tone River (Gunma Prefecture), contributions of nitrogen generated from different sources such as livestock (cattle, swine and poultry), agricultural land (paddy field and upland field), forest and anthropogenic activities (human and urban area) were evaluated by using a pollutant load factor. The result showed that livestock waste was the major source of nitrogen in this basin. Due to the remarkable increase in livestock waste, a high nitrogen load zones appeared in the basin. After several years of nitrogen load peak in the basin, nitrogen load into Tone River was increased up to about 120 ton-N/day, which indicated the possibility of accumulation of nitrogen in the basin. The fluctuation of run-off ratio calculated from nitrogen load generated in the basin and nitrogen load into the Tone River was large. It was considered that recycling of the livestock waste could be the best way to reduce the nitrogen load. In addition, due to the decreasing tendency of agricultural land in the basin, measures such as supplying livestock waste to other prefectures, dispersal of stock raising activities into many rural areas and utilization of livestock waste as energy source are recommended.