Stable isotope analyses of precipitation nitrogen sources in Guiyang, southwestern China

To constrain sources of anthropogenic nitrogen (N) deposition is critical for effective reduction of reactive N emissions and better evaluation of N deposition effects. This study measured δ15N signatures of nitrate (NO3−), ammonium (NH4+) and total dissolved N (TDN) in precipitation at Guiyang, southwestern China and estimated contributions of dominant N sources using a Bayesian isotope mixing model. For NO3−, the contribution of non-fossil N oxides (NOx, mainly from biomass burning (24 ± 12%) and microbial N cycle (26 ± 5%)) equals that of fossil NOx, to which vehicle exhausts (31 ± 19%) contributed more than coal combustion (19 ± 9%). For NH4+, ammonia (NH3) from volatilization sources (mainly animal wastes (22 ± 12%) and fertilizers (22 ± 10%)) contributed less than NH3 from combustion sources (mainly biomass burning (17 ± 8%), vehicle exhausts (19 ± 11%) and coal combustions (19 ± 12%)). Dissolved organic N (DON) accounted for 41% in precipitation TDN deposition during the study period. Precipitation DON had higher δ15N values in cooler months (13.1‰) than in warmer months (−7.0‰), indicating the dominance of primary and secondary ON sources, respectively. These results newly underscored the importance of non-fossil NOx, fossil NH3 and organic N in precipitation N inputs of urban environments. Non-fossil-derived NOx and fossil-derived NH3 are important contributors to precipitation N in urban environments. [Display omitted] •Concentrations and δ15N signatures of NO3−, NH4+ and DON in urban precipitation were measured at Guiyang, SW China.•Major sources of precipitation NH4+ and NO3− were estimated by a Bayesian isotope mixing model (SIAR).•Non-fossil-derived NOx and fossil-derived NH3 are important contributors of inorganic N in urban precipitation. Precipitation nitrogen sources based on the SIAR model.