Temporal and spatial trends in Hg deposition monitored by moss analysis

Results for Hg from a nation-wide survey of atmospheric deposition of heavy metals in Norway in 2000 are presented and compared to similar results from 1985, 1990 and 1995. The study is based on sampling of the naturally growing feather moss Hylocomium splendens at approximately 500 sites all over the country. Cold vapor AAS (1985, 1990) or atomic fluorescence spectrometry (1995, 2000) was used for Hg determinations after HNO3 digestion of the moss samples. As different from the wet deposition of Hg and several other heavy metals in Norway the Hg concentration in moss shows no significant north–south gradient. This is explained by a considerable supply of Hg to the moss from dry deposition of Hg0 in addition to the retention of Hg2+ from wet deposition. Presumably the cool summer climate particularly in the middle and northern parts of the country explains that some of the Hg0 retained in the moss is not lost by re-volatilisation. Whereas the level and geographic distribution of Hg in moss showed only small differences during 1985–1995 the 2000 data are approximately 30% lower. A satisfactory explanation of this difference remains to be found.