Quantification of nitrogen dry and wet deposition in Fujian tobacco planting area

Abstract In this study, the wet/bulk and dry atmospheric deposition of different inorganic nitrogen (N) species was investigated in the Fujian tobacco planting area from 2010 to 2014. Wet/bulk N deposition flux of inorganic N was monitored at five sites (Fuzhou, Shanghang, Changting, Taining, and Wuyishan) of Fujian by using precipitation gauges. While dry deposition fluxes of gaseous NH 3 , NO 2 , and HNO 3 ( g NH 3 , g NO 2 , and g HNO 3 ), and particulate NH 4 + and NO 3 − ( p NH 4 + and p NO 3 − ) were estimated only at the Fuzhou site through multiplying monthly mean N r concentrations obtained from DELTA (DEnuder for Long-Term Atmospheric sampling) system ( g NH 3 , g HNO 3 , p NH 4 + , p NO 3 − ) and passive samplers ( g NO 2 ) and the modeled monthly mean dry deposition velocities provided by the GEOS-Chem global chemical transport model. Annual mean NH 4 + -N, NO 3 − -N, and total inorganic N (TIN) concentrations in precipitation (rainwater and snow) were 0.21–1.05, 0.33–0.74, and 0.59–1.68 mg N L −1 , respectively, and the averages over the monitoring period were 0.55, 0.49, and 1.04 mg N L − 1 , respectively. Across the five monitoring sites, the average annual wet/bulk N deposition was 17.6 kg N ha −1  a −1 , while that of NH 4 + -N and NO 3 − -N amounted to 9.2 and 8.4 kg N ha − 1  a − 1 , respectively. Wet/bulk deposition was lowest at Changting, but no significant differences were found between the other four sites. Annual mean atmospheric concentrations of g NH 3 , g NO 2 , g HNO 3 , p NH 4 + , and p NO 3 − were 1.87, 2.95, 0.45, 2.36, and 1.23 μg N m −3 , respectively. Gaseous NH 3 concentrations were highest in summer and lowest in winter. In contrast, seasonal fluctuations in other measured N r species (e.g., g NO 2 ) were not as large as those of g NH 3 . The annual mean total dry deposition was estimated to be 9.6 kg N ha −1  a −1 , and those of the individual species, g NH 3 , g NO 2 , g HNO 3 , p NH 4 + , and p NO 3 − were estimated to be 4.1, 2.2, 2.0, 0.8, and 0.4 kg N ha −1  a −1 , respectively. Based on the similarities in wet deposition, if we assume a similar level of dry deposition at all the sites, the total (dry and wet) N deposition was 27.2 kg N ha −1  a −1 on average, which twice the critical load (10–15 kg N ha −1  a −1 ) for forest ecosystems, suggesting a risk of “N saturation” in the local natural environment.