Atmospheric dry and bulk nitrogen deposition to forest environment in the North China Plain

Atmospheric nitrogen (N) deposition fluxes has dramatically increased in past few decades and has aroused great concerns of its impacts on forest ecosystems. However, complete quantitative information on dry and wet deposition of various reactive nitrogen (Nr) species is very limited for forest environments. Therefore, two-year (2014-2015) measurements of gaseous NH3, NO2, and HNO3 and particulate NH4+ and NO3- (pNH(4)(+) and pNO3) in air and/or precipitation were conducted in Jigong Mountain National Nature Reserve in the North China Plain (NCP). Our results showed that ambient concentrations of all Nr species were highest in winter and lowest in summer except for NH3; conversely, bulk deposition fluxes of each Nr species generally peaked in summer and were lowest in winter. Annual mean bulk Nr deposition fluxes was 15.5 kg N ha(-1)yr(-1) (7.9 kg N ha(-1)yr(-1) for NH4+ and 7.6 kg N ha(-1)yr(-1) for NO3-), with higher monthly fluxes occurring in spring and summer. Average annual dry Nr deposition fluxes was 44.3 kg N ha(-1) yr(-1) (30.1 kg N ha(-1)yr(-1) for reduced N (NH3 plus pNH(4)(+)) and 14.2 kg N ha(-1)yr(-1) for oxidized N (the sum of HNO3, NO2 and pNO(3)(-)). Total Nr deposition fluxes (dry plus bulk) reached 59.8 kg N ha(-1)yr(-1) with more contributions from reduced N than from oxidized N (64% vs 36%). When consider the N critical load (10-20 kg N ha(-1)yr(-1)) in forest ecosystem, potential negative effects may cause by N deposition in the NCP which should be paid more attention.