Total N content and δ15N signatures in moss tissue for indicating varying atmospheric nitrogen deposition in Guizhou Province, China

Unsurprisingly, the amount of reactive nitrogen circulating annually on land has been doubled because of increasing anthropogenic activities. Exceedingly large amounts of reactive nitrogen (Nr) are likely to disrupt N dynamics and negatively impact the environment and human health. Guizhou Province, a major energy-producing province in southwest China, is suffering from serious long-term acid deposition. However, little work has been done to quantify the levels of atmospheric N deposition in this province, in which some ecologically vulnerable areas have resulted from rocky desertification. In this study, tissue N contents and δ15N signatures in 109 epilithic mosses were analyzed by the ordinary kriging (OK) interpolation technique to determine atmospheric N deposition. Moss N content (1.36-2.65%) showed a significant decrease from west to east, indicating that the spatial variance of TN deposition was the same as that of moss N content, with an average of 27.74 kg N ha−1 yr−1. Moss δ15N ranged from −5.89‰ to −0.72‰ and showed an opposite spatial variance compared with moss N contents. Negative δ15N indicated that the main sources for N deposition were urban sewage and agricultural NH3. According to Moss δ15N values, it could be concluded that NH4+-N and NO3−-N were the main components of wet deposition, accounting for 52% and 44% of TN, respectively. The deposition fluxes were 14.49 kg N ha−1 yr−1 and 12.16 kg N ha−1 yr−1, respectively. Although the emission flux of NO3−-N far exceeded that of NH4+-N, the amount of NH4+-N deposited on land was larger than that of NO3−-N. N deposition in 99.6% of the province exceeded the critical load for terrestrial ecosystems. High N deposition is the main environmental problem facing Guizhou Province, and recommendations regarding regulatory strategies for mitigating atmospheric N pollution are urgently needed.