On the Use of Epigaeic Mosses to Biomonitor Atmospheric Deposition of Nitrogen

In this study, we investigated whether the terrestrial moss Pseudoscleropodium purum can be used to biomonitor atmospheric deposition of nitrogen (N). For this purpose, we first determined whether there are any interspecific differences in the concentrations of total N and delta N-15 between the two species of terrestrial moss most commonly used in biomonitoring studies, P. purum and Hypnum cupressiforme. Second, we determined the spatial distribution of N and delta N-15 at small and large scales: (1) by analysis of 165 samples from the surroundings of an aluminium smelter and (2) by analysis of 149 samples from sites forming part of a regular 15 x 15-km sampling network in Galicia (northwest Spain). We did not find any interspecific differences in either total N or delta N-15. Analysis of delta N-15 enabled us to identify large-scale spatial patterns of distribution that were congruent with the location of the main N emission sources (unlike the analysis of total N). However, we did not identify any such patterns for the small-scale source of N emission studied. The results show that analysis of delta N-15 has an advantage compared with the analysis of total N in that it provides information about the source of N rather than about the amount of N received. Furthermore, isotope discrimination appears to occur, with the bryophytes preferentially accumulating the N-14 isotope. Although this amplifies the signal of reduced forms, it is not problematical for determining spatial-distribution patterns.