Trends in Sulphur and Nitrogen Deposition Fluxes in the GEOMON Network, Czech Republic, between 1994 and 2000

Deposition fluxes of sulphur and nitrogen in bulk and throughfall precipitation were monitored for the 1994–2000 period for seven small forest catchments in the GEOMON network, Czech Republic (CR). Four catchments are situated at similar elevations (roughly between 800 and 1000 m) and represent three areas: the Black Triangle near the Kru?né hory Mts. coalfield (catchments JEZ and LYS), the Orlické hory Mts., close to the Polish industrial regions (UDL), and the ?umava Mts., a relatively unpolluted area (LIZ). Three catments (GEM, POM, LES) lie at lower elevations (400–600 m) in Central Bohemia. A substantial decrease in the bulk and throughfall deposition of pollutants occurred as a result of the desulphurisation programme implemented in the Czech Republic between 1996 and 1998. A reduction has been described mainly in the Kru?né hory Mts. (JEZ), in Slavkovský les (LYS) and also in Central Bohemia (GEM). The decrease in the throughfall to less than one half within a single year in POM (Central Bohemia) was an example of a direct response to the local emission reduction in the nearby Chvaletice power plant. However, in some areas, the throughfall deposition of sulphur, which includes wet and dry deposition, is still significant, especially at higher elevations. Recent forest degradation was observed in the Orlické hory Mts., where, particularly in 1998, as much as 91.1 kg S was found in coniferous throughfall. The fraction of dry deposition in the coniferous forests of CR represents 30–70% of the total deposition. The difference between coniferous (higher) and deciduous (lower) throughfall fluxes is significant because of the larger surface area of conifers and year-round exposure to air-borne sulphur. At several of the GEOMON sites, the flux of nitrogen via throughfall increased during the observation period and, at the end of the studied period (2000), nitrogen became the main source of acidification, replacing sulphur compounds. The highest fluxes (81.7 kg N ha^-1 yr^-1)were measured in 2000 in the Orlické hory Mts., which provide an example of multiple causes of forest decline – the direct impact of air pollution, abundance of nitrogen, acidification and secondary stressors (weather changes, insect pests, fungal infections). A comparison is given with data from other countries.