环境地球化学国家重点实验室知识库

Dual isotopes of nitrate (N-15 and O-18) and carbon isotopes of dissolved inorganic carbon (C-13) together with water chemistry were used to identify the sources and fate of nitrate in the upper stream of Chaobai River, north China. The results show that NO3- concentrations ranges from 0.03 mmol L-1 to 0.80 mmol L-1. Sampling sites from watershed with dominant forest land had higher NO3- concentrations and lower delta N-15-NO3- (<10%) in the wet season than in the dry season, while those from watershed with more anthropogenic activities had lower NO3- concentrations and higher delta N-15-NO3- (>10%) in the wet season. Compositions of isotopes and chemistry indicated that NO3- originated mainly from soil N, sewage and livestock wastes and atmospheric nitrogen. Furthermore, the mixing model suggested that soil N was the major NO3- source in the wet season, while the sewage and livestock wastes contributed the most in the dry season. Compared to rivers, the Miytin Reservoir had a higher contribution of atmospheric N and the N input from the upper rivers exerted significant influence over the reservoir. Mineralization and nitrification played an important role in N biogeochemistry based on the isotopes (N-15 and O-18 and C-13) and chemical data. There appeared to be no significant denitrification in the watershed according to the three isotopes and chemical ions. The combined use of N-15, O-18 and C-13 proved to be useful for further identification of the sources and fate of nitrate in watersheds with dominant forest land in the wet season.