Nitrogen and Oxygen Isotope Composition of Nitrate in Stream Water of Fuji River Basin

Abstract

To identify the nitrate source and spatial distribution of nitrogen isotope values originated from forest and agricultural lands, fifty-seven stream water samples from Fuji River Basin were analyzed for nitrate concentration and nitrate-nitrogen (δ15N-NO3-) and oxygen (δ18O-NO3-) isotope values. The δ18O-NO3- showed that the nitrate originated through nitrification. These values were plotted against fraction of each land use category in the study catchments. The δ15N-NO3- was positively correlated with the fractions of agricultural and residential areas in the catchments. The increasing of δ15N-NO3- with fraction of agricultural area converged to 5.4‰ which was similar to a reported nitrate isotope value of groundwater at orchard area in Kofu-Basin. The increasing δ15N-NO3- with more than 1% residential area suggested that potential source of nitrate contamination was domestic aste water. An increase of δ15N-NO3- in the catchments with less than 98% forest area suggested the sources of nitrate contamination were thropogenic. The estimated value of δ15N-NO3- in forest catchment was 0.9±1.2‰.