Acid atmospheric deposition in a forested mountain catchment

Acid atmospheric deposition is harmful to both forest and aquatic ecosystems. In mountain catchments, acidification also leads to difficulties in water resource management. In 2010-2012, acid atmospheric deposition was analysed in a small forest catchment located in the upper plain of the Jizera Mountains (Czech Republic). Patch observations included monitoring of the canopy interception in two mature stands of Norway spruce (Picea abies) at elevations of 745 and 975 metres a.s.l., and twelve passive fog collectors situated along an elevation gradient between 862 and 994 metres a.s.l. In the studied area, fog (and low cloud) precipitation starts to affect the interception loss of the spruce canopy at elevations above 700 metres. However, fog drip was found to also rise with the canopy area. At the catchment scale, methods of spatial interpolation (ArcGIS 10.2) were used to approximate the aerial atmospheric deposition of water and acidic substances (sulphate, nitrate and ammonia). In the watersheds of two adjacent drinking water reservoirs, Josefuv Dul and Souš, the mean annual fog drip from the canopy was between 88 and 106 mm (i.e., 7-8% of the mean annual gross precipitation, or 10-12% of the mean annual runoff). Simultaneously, this load also deposited 658 kg km-2 of sulphur and 216 kg km-2 of nitrogen (i.e., 55% and 48% of the “open field” bulk amounts). Therefore, in headwater catchments stressed by acidification, the additional precipitation (measured under the canopy) can increase the water yield, but can also contribute to a decline in water quality, particularly in environments of low buffering capacity