LAUSR

Abstract Anthropogenic nitrogen (N) and sulfur (S) emissions triggered acid deposition and affected the environmental quality and ecosystem functions. Lichen N and S concentrations have been found increasing with N and S deposition at relatively low levels, respectively. However, it remains unclear whether lichen N and S concentrations can respond to corresponding deposition fluxes under high pollution environments and how to use lichen N isotopes (δ15N) to evaluate source contributions of N deposition quantitatively. Along an urban-to-rural transect surrounding a polluted area in northern China, we investigated lichen N and S to examine their sensitivity and applicability in estimating N and S deposition. Moreover, we established a new method to reconstruct site-based δ15N values of ammonium N (NHx) and oxidized N (NOy) deposition using lichen δ15N and then to differentiate relatively contributions of major N emission sources. Lichen N (1.0–3.9%, 2.5 ± 0.6%) and S (0.09–0.33%, 0.21 ± 0.06%) decreased linearly with distances from the polluted center area. Wet inorganic N and sulfate deposition (29.0 ± 6.1 kg-N/ha/yr and 25.8 ± 7.9 kg-S/ha/yr, respectively) estimated by integrating relationships from previous literature data were comparable with levels based on direct deposition observations in the study area. Lichen δ15N varied between −12.1 to −4.1‰ and averaged −7.1 ± 2.0‰ among our study sites, and reconstructed δ15N values of NHx and NOy deposition averaged −12.8 ± 1.0‰ and −3.2 ± 0.5‰, respectively. Source contribution analyses revealed significant contributions of volatilization ammonia (66 ± 3%) from wastes and fertilizers to NHx deposition and non-fossil fuel N oxides (62 ± 7%) from biomass burnings and microbial N cycles to NOy deposition. These results indicate that lichen N and S are sensitive to deposition fluxes under high pollution and applicable to estimating deposition levels. This work improves the methodology of atmospheric deposition biomonitoring based on lichen element and isotope records.