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 delta N-15 signatures of nitrate (NO3-), ammonium (Nflt) 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 NOT, 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 NO3-, 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 8.15N values in cooler months (13.1 parts per thousand) than in warmer months (-7.0 parts per thousand), 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. (C) 2017 Elsevier Ltd. All rights reserved.