2014 Volume 37 Issue 5 Pages 205-210
The nitrogen load in the basin of Shinano River was calculated by a pollutant load method using administrative data from 1970 to 2005 and compared with the concentrations of total nitrogen in the river. Livestock, farmland and forest primarily generated nitrogen load in the upper basin, whereas livestock, farmland and sewage were the main nitrogen sources in the middle basin. Industrial waste occupied half the total amount of nitrogen load in the lower basin. The total amount of nitrogen load generated in the basin decreased by 20% from 1985 to 2005, and it was 35,000 tonN•yr-1 in 2005. The decrease in nitrogen load from livestock and farmland, and the construction of sewage systems with improved treatment efficiency caused a decrease in the nitrogen load in the basin. This decrease in the nitrogen load was reflected in the decrease in total nitrogen concentration in the middle and lower basins of the river from 1990 onward. In order to further improve water quality, new measures may be required for industrial waste treatment in the middle and lower basins of the river.
