Nitrogen inputs and isotopes in precipitation in the North China Plain: Fid-Bau Portal

Nitrogen inputs and isotopes in precipitation in the North China Plain

Zhang, Y. / Liu, X.J. / Fangmeier, A. / Goulding, K.T.W. / Zhang, F.S.

AbstractNitrogen (N) deposition in the North China Plain (NCP), an intensive agricultural region undergoing rapid economic development in China, has not been well documented until now. In a 4-year study, using a deposition network (11 sites), we analyzed bulk and wet-only deposition, and the isotopic composition (δ¹⁵N) of ammonium and nitrate in precipitation in the NCP. Annual bulk deposition of inorganic N averaged 27kgNha⁻¹ (ranging from 15 to 50kgNha⁻¹) across sites and years, but with very large variation in both space and time. Bulk and wet deposition of inorganic N were significantly higher at sites in the Beijing area compared with that at rural sites in the NCP, implying more air N pollution around Beijing. Although there was a wide seasonal variation of δ¹⁵N for NH4-N (−12.7‰ to +12.9‰) and NO3-N (−10.0‰ to +20.7‰) in precipitation across the sites in the NCP, a significant difference in the mean isotopic composition of NH4-N and NO3-N was measured in precipitation samples from two suburban sites (Dongbeiwang, DBW; Campus experimental farm, CEF) in Beijing (+0.45±4.39‰ for NH4-N and +4.23±4.34‰ for NO3-N on average) compared to two rural sites (Quzhou, QZ; Wuqiao, WQ) in Hebei (−2.8±4.06‰ for NH4-N and −1.19±3.74‰ for NO3-N on average). Both deposition flux and isotopic composition of inorganic N in precipitation suggest that N deposition is most probably influenced by multiple pollution sources in the urban area around Beijing area, while it is mainly derived from local agricultural sources of reactive N species at rural areas of the NCP.