Comparison of nitrogen deposition between two ecosystems in the southern edge of Tarim Basin

Quantifying the similarities and differences in atmospheric nitrogen (N) deposition between different ecosystems is important to develop effective measures to reduce air pollution and maintain biodiversity. Here we show that the constitution of N deposition differed significantly between a grassland and a desert ecosystem in Northwestern China. Flux of bulk (wet plus part of dry deposition) and dry (gaseous NH3 and NO2) deposition were continuously monitored from 2018 to 2020. The grassland and desert sites had similar amount of total N deposition, being 7.29 and 6.33 kg N ha-1 yr-1, respectively. However, N deposition at the grassland was dominated by the bulk deposition (4.44 kg N ha-1 yr-1, 61% of the total N deposition), whereas that at the desert was dominated by dry deposition (4.20 kg N ha-1 yr-1, 66% of total deposition). The desert had greater ambient con-centrations of NH3 (3.66 mu g N m-3) and NO2 (1.52 mu g N m-3) than the grassland (2.73 mu g NH3-N m-3 and 0.72 mu g NO2-N m- 3). The amount of reduced N deposition (NH4+ and NH3) was around 3 times of that of oxidized N deposition (NO3- and NO2) in both ecosystems. The N deposition rates in both ecosystems have exceeded the critical load for the fragile ecosystems (5-10 kg N ha-1 yr-1), highlighting the importance of reducing N emission sources that are related with anthropogenic disturbance.

Automated summary

The composition of atmospheric nitrogen deposition differed significantly between a grassland and a desert ecosystem in Northwestern China. The grassland had a higher proportion of bulk deposition, while the desert had a higher proportion of dry deposition. Both ecosystems had exceeded the critical load for fragile ecosystems, underscoring the need to reduce anthropogenic N emission sources.