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Reactive nitrogen (Nr) plays a key role in the atmospheric environment and its deposition has induced large negative impacts on ecosystem health and services. Five-year continuous in-situ monitoring of N deposition, including wet (total nitrogen ( W TN), total dissolved nitrogen ( W TDN), dissolved organic nitrogen ( W DON), ammonium nitrogen ( W AN) and nitrate nitrogen ( W NN)) and dry ( D NH 3 , D HNO 3 , D pNH 4 + , D pNO 3 − and D NO 2 ) deposition, had been conducted since August 2008 to December 2013 (wet) and May 2011 to December 2013 (dry) in Yan-ting, China, a typical agricultural area in the central Sichuan Basin. Mean annual total N deposition from 2011 to 2013 was 30.8 kg N ha −1 yr −1 , and speculated that of 2009 and 2010 was averaged 28.2 kg N ha −1 yr −1 , respectively. Wet and dry N deposition accounted for 76.3% and 23.7% of annual N deposition, respectively. Reduced N ( W AN, D NH 3 and D pNH 4 + ) was 1.7 times of oxidized N ( W NN, D HNO 3 , D NO 2 and D pNO 3 − ) which accounted for 50.9% and 30.3% of TN, respectively. Maximum loadings of all N forms of wet deposition, gaseous NH 3 , HNO 3 and particulate NH 4 + in dry deposition occurred in summer and minimum loadings in winter. Whether monthly, seasonal or annual averaged, dissolved N accounted for more than 70% of the total. N deposition in the central Sichuan Basin increased during the sampling period, especially that of ammonium compounds, and has become a serious threat to local aquatic ecosystems, the surrounding forest and other natural or semi-natural ecosystems in the upper reaches of the Yangtze River. [ABSTRACT FROM AUTHOR]

Abstract While the ongoing increases in the deposition of atmospheric nitrogen (N) in China have attracted ever more attention, to date there has been little research in N deposition in inland aquatic ecosystems. In this study, we quantified the bulk and dry atmospheric N deposition around the Dongting Lake, which is connected to the Yangtze River and is the second largest freshwater lake in China. Bulk N deposition averaged 48.0 kg N ha−1 yr−1, of which ammonium (NH 4 N), nitrate (NO 3 N), and dissolved organic nitrogen (DON) accounted for 41.6%, 35.1%, and 23.3%, respectively. Dry N deposition averaged 27.0 kg N ha−1 yr−1, and was dominated by NH 3. Bulk N deposition was higher in spring and summer than in autumn and winter at the sites around the lake because of the high precipitation. NH 3 deposition was the highest in spring and summer due to fertilization, and NO x deposition was the highest in winter because of the combustion of coal for domestic heating. The concentrations of NH 3 significantly decreased with the concentration of NH 4 N, indicating below-cloud scavenging and local sources. The concentrations of NO x and NO 3 N were not correlated, indicating long-distance transfer of NO x. Bulk N deposition in our study was generally twice that reported in other studies, even when only inorganic N species in bulk deposition were considered. Total N deposition averaged 75.0 kg N ha−1 yr−1, which was much higher than that reported in other studies. Both N deposited directly into the lake and N deposited across the lake basin that was subsequently transported to the lake in runoff could enrich the N concentration of the lake water and increase the gross primary productivity (GPP). Our results highlighted the importance of integrated management that includes both aquatic and atmospheric systems at either the lake basin scale or regional scale, rather than at the individual lake-scale. Graphical abstract Image 1 Highlights • Total N deposition was much higher than that reported in other studies around the Dongting Lake. • DON deposition, which usually be ignored, is a significant contributor. • Potential eutrophication effects of N loading to the Dongting Lake from atmospheric N deposition should be re-evaluated. [ABSTRACT FROM AUTHOR]

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 NH 3 and NO 2) 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 concentrations of NH 3 (3.66 μg N m−3) and NO 2 (1.52 μg N m−3) than the grassland (2.73 μg NH 3 –N m−3 and 0.72 μg NO 2 –N m−3). The amount of reduced N deposition (NH 4 + and NH 3) was around 3 times of that of oxidized N deposition (NO 3 − and NO 2) 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. [Display omitted] • The boundary of Tarim Basin and Tibet Plateau has relatively low N deposition. • Bulk and dry deposition dominated in grassland and desert, respectively. • The reduced/oxidized N ratio in N deposition was close to 3 in both ecosystems. • N deposition exceeded the minimum critical load value for sensitive ecosystems. [ABSTRACT FROM AUTHOR]

Abstract Very few comparative studies on atmospheric dry and wet nitrogen (N) deposition have been conducted in agro-pastoral catchment areas. In an effort to fill this knowledge gap, three interconnected land use types (cropland, mountain pasture, and plain pasture) with six sampling sites (Chinese cropland (CC), Chinese mountain pasture (CM), Chinese plain pasture (CP) Mongolia cropland (MC), Mongolia mountain pasture (MM) and Mongolia plain pasture (MP)) were selected in the transboundary regions of northwest China and western Mongolia. During 16 months from May 2014 to September 2015 atmospheric and precipitation samples were collected to assess levels of nitrogen deposition. Cropland had the highest NO 3 −N (1.0 mg N L−1 in China and 1.2 mg N L−1 in Mongolia) and NH 4 +-N concentrations (1.6 mg N L−1 in China and 2.0 mg N L−1 in Mongolia) in our six sampling sites. The CC experienced the highest wet deposition (5.2 kg N ha−1 yr−1), followed by MM pasture (3.2 kg N ha−1 yr−1) while wet deposition in other sites ranged from 2.1 to 2.8 kg N ha−1 yr−1. The ambient concentrations of NH 3 , NO 2 and dry N deposition were significant higher in cropland than being other land use with 3.0, 3.8 and 1.2 μg N m−3 respectively in China and 2.2, 2.8 and 0.6 μg N m−3 respectively in Mongolia. The highest total N deposition was at CC (14.5 kg N ha−1 yr−1) and MC (9.4 kg N ha−1 yr−1), followed by the mountain pasture (5.8–6.8 kg N ha−1 yr−1), and the plains pasture (5.6–5.7 kg N ha−1 yr−1). Overall, agro-pastoral catchments areas had relatively low total N deposition compared to other studies, and cropland had the highest wet and dry N deposition than mountain and plain pastures, and dry N deposition absolutely dominated the percentage (64–70% in cropland and 53–64% in pasture areas) of total atmospheric N deposition. Comparing the total N deposition in China and Mongolia, we found the CC had 54% higher value than in MC while the reverse was true for mountain pastures Mongolia received 17% more N. Graphical abstract Image 1 Highlights • Passive samplers, PM 10 samplers and rain gauges equipments were used to quantify the nitrogen deposition in six typical land use types. • The cropland sites had significant higher NH 3 and NO 2 concentration and total N deposition than pasture areas in our research area. • Dry deposition absolutely dominated the percentage of total atmospheric N deposition in agro-pastoral catchment areas of China and Mongolia. • Nitrogen deposition in CC had 54% higher value than in MC while the reverse was true for mountain pastures Mongolia received 17% more N. [ABSTRACT FROM AUTHOR]