Historical alteration in the nitrogen concentration and 15N natural abundance of mosses in Germany: Indication for regionally varying changes in atmospheric nitrogen deposition within the last 140 years

Historical alterations of nitrogen deposition in the western part of Germany were investigated by comparing nitrogen concentrations and 15N natural abundance of historical and recent samples of the two pleurocarpous mosses Pleurozium schreberi and Scleropodium purum. Pooling of the data revealed only slight tissue N increases over the past 140 years which were significant nevertheless. At closer examination on the single site level historical increases of N concentrations were found particularly for some sites in regions where agricultural activities were considerably intensified during the second half of the 20th century. The comparison of δ15N values showed a strong depletion of 15N natural abundance in areas currently heavily influenced by livestock management. This indicates an increased impact of NHy compounds. However, the almost unchanged δ15N values in some low mountain range areas with only moderate intensification of agriculture point to a more or less constant ratio of NHy/NOx input over time. Significant correlations of both tissue N concentrations and 15N natural abundance between the two species justify the assumption that they use the same nitrogen source, probably atmospheric deposition.