Abstract
The Ishikari river system witnessed increased nitrogen loading due to change in precipitation chemistry along with increased urban and agricultural land use proportion in its catchment area during last decades. The spatial variation of sedimentary denitrification rate in lower Ishikari river system and its role in removing dissolved nitrate load from river system was studied. Water and sediment samples were collected from main river channel, major tributaries. Experimental results suggest that The sedimentary denitrification rate in Ishikari river system did not showed significant increase on addition of labile carbon indicating that sediment samples had enough carbon to support denitrification process in river system. The nitrate loss rate due to denitrification within the lower Ishikari system ranged from 0.01 to 14.9% d‹SUP›-1/SUP› with an annual mean of 5% d‹SUP›-1/SUP› in main Ishikari river channel.
