Abstract
Atmospheric reactive nitrogen (N) deposition has been proven to be an important nutrient input from external environments to forest ecosystems. However, the magnitude of atmospheric N deposition in the Tibetan region of China is not well known. In this study, multi-year (between 2005 and 2016) measurements of dry and wet N deposition were carried out in Nyingchi (NC) city, southeastern Tibet. Bulk deposition was collected by the rain gauge method; dry deposition was calculated by the inferential method, namely, multiplying ambient N concentrations by dry deposition velocity (Vd) of the N species. During the entire period, annual bulk and dry N deposition fluxes averaged 2.19 and 1.85 kg N ha−1 yr−1, respectively. Total N deposition fluxes (the sum of reduced and oxidized N species in dry and bulk deposition) showed an obvious increasing trend, especially for oxidized N species. Both bulk and dry N deposition showed a consistent seasonal pattern, with the highest fluxes in summer and the lowest in winter. Our findings suggest that N deposition to the urban environment in southeast Tibet has recently shifted from ammonium-dominated to nitrate-dominated conditions.
Highlights
The Qinghai-Tibet Plateau has N nutrition restricted ecosystems which are sensitive to enhanced nitrogen deposition[9,10,11]
Bulk deposition fluxes of NH4+ and NO3− were in the ranges of 0.01–0.26 kg N ha−1 and 0.01–0.16 kg N ha−1, respectively (Fig. 1b)
Lots of studies have revealed that the lowest concentrations of N species in bulk precipitation are associated with the highest precipitation rates in summer[18,19], atmospheric N bulk deposition fluxes are positively correlated with local precipitation[20]
Summary
The Qinghai-Tibet Plateau has N nutrition restricted ecosystems which are sensitive to enhanced nitrogen deposition[9,10,11]. At the single site scale, wet N deposition fluxes were from 0.44 to 1.55 kg N ha−1 yr−1 at five remote sites in Tibet[17], whilst in the population concentrated areas, such as Lhasa, N deposition fluxes have reached up to 20 kg N ha−1 yr−1 16. These results indicate that the spatial distribution of N deposition in Tibetan Plateau varies largely and could be enhanced by anthropogenic disturbance. The objectives of the present study were to (1) quantify the magnitudes of dry and bulk N deposition fluxes, and (2) investigate the monthly and annual patterns of wet and dry deposition fluxes of various N species
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