Total N content and δ15N signatures in moss tissue for indicating varying atmospheric nitrogen deposition in Guizhou Province, China. (October 2016) - Qu, Linglu
Abstract: 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 δ 15 N 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 δ 15 N ranged from −5.89‰ to −0.72‰ and showed an opposite spatial variance compared with moss N contents. Negative δ 15 N indicated that the main sources for N deposition were urban sewage and agricultural NH3 . According to Moss δ 15 N 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. Highlights: Atmospheric N deposition in Guizhou province was first reported. TN deposition was 27.74 kg N ha −1 yr −1 with significant spatial variation. NH4 + -N and NO3 − -N contributed 52% and 44% of wet N deposition. Urban sewage and agricultural NH3 were the main N sources. Opposite trends between N deposition and N emission were observed in this study.