3:36 PM - 3:39 PM
[HTT31-P08] The origin of nitrate in river water in Tohoku region based on the nitrogen and oxygen stable isotope ratios
3-min talk in an oral session
Recently, nitrogen pollution assessment using the stable isotope technique has been recognized, as the nitrogen stable isotope ratios of anthropogenic nitrate originating from sewage and fertilizers have a unique range of δ15N values, and a nitrogen removal process such as denitrification increases nitrate nitrogen δ15N. In this study, we determined nitrogen and oxygen isotope ratios of nitrate for 372 river water samples in Iwate and Miyagi prefectures to examine the origin of nitrogen and environment of rivers.
Nitrogen isotope ratios tended to be high in urban and agricultural areas and low in mountain areas. These trends are consistent with the empirical knowledge that the nitrogen isotope ratio increases as the anthropogenic impact increases. A few high isotope values were observed in mountainous areas, however, there were some livestock farms up the river of the sampling points. It suggested the waste water from these farms has a significant influence on river water.
Oxygen isotope ratios tended to be high in mountain areas, such as Hayachine and Kurikoma, suggesting that atmospheric deposition (snow) was major source of nitrogen at that areas. High isotope ratios of both nitrogen and oxygen in some agricultural areas suggested the possibility of denitrification.