Abstract
Abstract. Emissions of reactive nitrogen (N) species can affect surrounding ecosystems via atmospheric deposition. However, few long-term and multi-site measurements have focused on both the wet and the dry deposition of individual N species in large areas of Northern China. Thus, the magnitude of atmospheric deposition of various N species in Northern China remains uncertain. In this study, the wet and dry atmospheric deposition of different N species was investigated during a three-year observation campaign at ten selected sites in Northern China. The results indicate that N deposition levels in Northern China were high with a ten-site, three-year average of 60.6 kg N ha−1 yr−1. The deposition levels showed spatial and temporal variation in the range of 28.5–100.4 kg N ha−1 yr−1. Of the annual total deposition, 40% was deposited via precipitation, and the remaining 60% was comprised of dry-deposited forms. Compared with gaseous N species, particulate N species were not the major contributor of dry-deposited N; they contributed approximately 10% to the total flux. On an annual basis, oxidized species accounted for 21% of total N deposition, thereby implying that other forms of gaseous N, such as NH3, comprised a dominant portion of the total flux. The contribution of NO3− to N deposition was enhanced in certain urban and industrial areas, possibly due to the fossil fuse combustion. As expected, the total N deposition in Northern China was significantly larger than the values reported by national scale monitoring networks in Europe, North America and East Asia because of high rates of wet deposition and gaseous NH3 dry deposition. Taken together, these findings show that NH3 emissions should be abated to mitigate high N deposition and associated potential impacts on ecosystems in Northern China. The present results improve our understanding of spatio-temporal variations of magnitudes, pathways and species of deposited N in the target areas, and are important not only to inform conservation and regulatory bodies but also to initiate further detailed studies. Uncertainties among current observations underscore the need to quantify the impact of vegetation on dry deposition and to refine the simulation of dry deposition velocity.
Highlights
During the 20th century, humans began to significantly affect the global cycle of nitrogen (N) by fixing N2, both deliberately for fertilizer production and inadvertently during fossil fuel combustion (Vitousek et al, 1997)
The wet deposition flux of NH+4 was, on average, 2.7-times greater than that of NO−3. This difference was more pronounced in the agricultural sites (LC and YC), thereby indicating that wNH+4 had a greater contribution to wet deposition flux of IN (wIN) in agricultural areas than in urban and industrial areas
The results from this study suggest that wet deposition cannot be used alone to determine the total deposition, because the total flux may be underestimated if the dry deposition of certain species or pathways is not considered
Summary
During the 20th century, humans began to significantly affect the global cycle of nitrogen (N) by fixing N2, both deliberately for fertilizer production and inadvertently during fossil fuel combustion (Vitousek et al, 1997). The global rate of reactive N production increased from approximately 15 Tg N yr−1 in 1860 to 187 Tg N yr−1 in 2005; more than half of this recent total was deposited onto the ground (Gruber and Galloway, 2008). Compared with biologically fixed N produced on the continents, atmospherically deposited N is becoming a proportionately larger source of N for terrestrial and aquatic ecosystems worldwide (Galloway et al, 1995). High rates of atmospheric N deposition have been widely documented in Europe (Dise and Wright, 1995), North America (Fenn et al, 1998) and East Asia (Endo et al, 2010). Pan et al.: Wet and dry deposition of atmospheric nitrogen in Northern China and increased susceptibility to secondary stresses (Liu et al, 2010)
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