Rime – a non-negligible pathway of sulphur and nitrogen atmospheric deposition in middle-elevated Central European mountains

Abstract

Rime is an under-researched pathway of the atmospheric deposition of ecological and environmental relevance, in particular in mountain regions. Rime alongside with snow were sampled and assessed for S-SO42- and N-NO3- at ten border mountaintop sites across the Czech Republic (CR) in the three consecutive winters of 2009–2011. Our observations indicated significantly higher sulphur (S) and nitrogen (N) contents in rime as compared to snow at all sites.  Whereas the highest S contamination was found in the industrial North, the highest N contamination was found unexpectedly in the relatively unpolluted South. The measurements were put in context with data driven geo-spatial modeling results (Hůnová et al., 2016) of annual wet vertical (rain and snow) and horizontal (fog and rime) deposition. Despite relatively low hydrological input of rime, it contributed significantly to annual atmospheric deposition. At nine out of ten sites, the winter-time deposition of S via rime corresponded to 5–13% of annual wet-only S deposition, while it reached full 25% at the most S-polluted TET site in the Orlicke hory Mts., a region bordering Poland (Hůnová et al., 2022). Modelled results showed that mean winter rime deposition corresponded to about 6–25%, and mean winter snow deposition made up 25–72.5% of mean annual N-NO3- wet-only deposition (Hůnová et al., submitted). Model N-NO3-occult deposition estimated from throughfall and total (wet and dry) deposition is highly uncertain, however: N throughfall is not a relevant proxy for estimation of realistic total N deposition due to N exchange between the tree canopy and atmosphere.  Considering the fact that wet-only deposition is a year-long phenomenon, whereas rime forms under the climatological conditions of the Czech middle elevated mountains during only a few (2–3) months a year, we can conclude that the rime deposition pathway should not be neglected in quantifying the real atmospheric deposition flux in mountain regions as it might contribute to the real deposition flux substantially even in mountains of medium elevation, as was observed in the CR.