Nitrate pollution in water bodies is a worldwide environmental problem, and identifying the sources of nitrate is of great significance to guarantee the sustainable use of water resources. A variety of water chemistry indicators and nitrate nitrogen and oxygen isotopes （δ15N-NO3- and δ18O-NO3-） were used to analyze the water chemistry characteristics of water bodies in Shiyan to identify the sources of nitrate in the water bodies and to calculate the contribution rate of nitrate from different pollution sources of the water bodies using the SIMMR model. The results showed that the hydrochemical types of surface water and groundwater in the study area were dominated by the HCO3-Ca·Mg type, and the formation of nitrate in the water body was mainly affected by nitrification, with non-obvious denitrification. The main sources of nitrate in water bodies were atmospheric deposition, chemical fertilizers, soil nitrogen, feces, and sewage. SIMMR model outputs showed that feces and sewage, atmospheric deposition, chemical fertilizer, and soil nitrogen contributed 43.1%, 2.2%, 43.3%, and 11.4% to nitrate in surface water and 37.2%, 9.4%, 28.3%, and 25.1%, respectively, to nitrate in groundwater in the study area. The main sources of surface water nitrate were fertilizer, feces and sewage, whereas the main sources of groundwater nitrate were manure and sewage.
Keywords: hydrochemical characteristics; nitrate; nitrogen and oxygen isotopes; source resolution; stable isotope mixing model in R（SIMMR）.