title: Assessment of denitrification process in lower Ishikari river system, Japan.
abstract: Sediment denitrification rate and its role in removal of dissolved nitrate load in lower Ishikari river system were examined. Denitrification rate were measured using acetylene inhibition technique on the sediment samples collected during August 2009-July 2010. The denitrification rate varied from 0.001 to 1.9 μg Ng(-1) DM h(-1) with an average value of 0.21 μg Ng(-1) DM h(-1) in lower Ishikari river system. Denitrification rate showed positive correlation with dissolved nitrate concentration in the river basin, indicating overlying water column supplied nitrate for the sediment denitrification processes. Nutrient enrichment experiments result showed that denitrification rate increased significantly with addition of nitrate in case of samples collected from Barato Lake however no such increase was observed in the samples collected from Ishikari river main channel and its major tributaries indicating that factors other than substrate concentration such as population of denitrifier and hydrological properties of stream channel including channel depth and flow velocity may affects the denitrification rate in lower Ishikari river system. Denitrification rate showed no significant increase with the addition of labile carbon (glucose), indicating that sediment samples had sufficient organic matter to sustain denitrification activity. The result of nutrient spiraling model indicates that in- stream denitrification process removes on an average 5%d(-1) of dissolve nitrate load in Ishikari river. This study was carried out to fill the gap present in the availability of riverine denitrification rate measurement and its role in nitrogen budget from Japanese rivers characterize by small river length and high flow rate.
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido 060 0810, Japan; Amity Institutes of Environmental Sciences, Amity University, Noida, Uttar Pradesh 201 303, India. Electronic address: pkjha@amity.edu.
authors.forename: Pawan Kumar
authors.initials: PK
authors.lastname: Jha
authors.forename: Masao
authors.initials: M
authors.lastname: Minagawa
mesh_terms: D058440:Denitrification; D004784:Environmental Monitoring; D007564:Japan; D009566:Nitrates; D009584:Nitrogen / Q000032:analysis*; D045483:Rivers / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D009566:Nitrates; D014874:Water Pollutants, Chemical; D009584:Nitrogen
keywords: Acetylene inhibition technique; Denitrification rate; Ishikari river; Nutrient spiraling metrics