Stable sulphur and nitrogen isotopes of the moss Haplocladium microphyllum at urban, rural and forested sites

Elemental (S and N) and isotopic (δ34S and δ15N) contents in the moss Haplocladium microphyllum at urban, rural and forested sites in acid rain area of South China have been analyzed for comparisons to show whether they are different and can be effectively used to identify S and N sources of atmospheric deposition. Average moss S content at rural sites (0.29 ± 0.06%) was found to be in between those at urban (0.35 ± 0.05%) and forested (0.25 ± 0.04%) sites, which are significantly different. Average N contents of urban (2.60 ± 0.56%) and rural mosses (2.84 ± 0.77%) are not significantly different, while both are significantly different to that of forested mosses at most areas, indicating that the atmosphere over rural sites has been polluted by N as seriously as that over urban sites. Nitrogen supply, relative to S supply, was in excess of the requirement for protein synthesis, especially at rural and forested sites. Moss stable isotope signatures have been proven to be effective tools for deciphering atmospheric S and N sources at these sites. Through moss δ34S signatures, we found that atmospheric S at urban and forested sites was mainly from local coal combustion and domestic biomass burning, respectively, whereas northerly air masses contributed more S to forested sites. The relatively negative moss δ15N values (−7.5 ± 3.0, −3.4 ± 2.1 and −0.8 ± 2.1‰) demonstrated that the main form in the N deposition was NHx in these sites. More negative δ15N signatures in urban mosses (−7.5 ± 3.0‰) indicated the contribution of NH3 released from untreated city sewage and wastes, while relatively less negative δ15N for rural and forested mosses (3.4 ± 2.1 and −0.8 ± 2.1‰) was largely derived from agricultural NH3.