Atmospheric deposition of nitrogen, sulfur and chloride in two watersheds located in southern Norway

The deposition of atmospheric pollutants in southern Norway is relatively high, and exceeds the critical load for acid deposition in sensitive ecosystems. While the effects of the sulfur deposition are relatively well known and documented, the fate and effects of oxidized and reduced nitrogen compounds are much less well known. In order to study the cycling of nitrogen in southern Norway, the inter-institutional research program, Nitrogen from Mountains to Fjords, was launched in 1991. The program aims to describe the nitrogen mass balance and the effects of nitrogen deposition in two different watersheds in southern Norway. In this respect, quantification of the atmospheric inputfor comparison with runoff and other transfer data has been an important task. The atmospheric input has been estimated on the basis of available data from the national monitoring of air and precipitation chemistry, and additional measurement activities within the study areas, for the period 1993--1995. In the Bjerkreim watershed topographical effects result in large variation in precipitation amounts within the study area, and between the individual 44 hydrological subcatchments. Annual nitrogen deposition varied between 1400 and 2300 mg N m-2 yr-1, with the highest figures obtained for themountainous areas receiving most precipitation. Similar observationswere made for the atmospheric deposition of sulfur and chloride, which were determined in order to compare input and runoff data as well as a basis for calculation of exceedances of the critical loads. Annual deposition of sulfur and chloride were 900--1500 mg S m- 2 yr-1 and 12 000--21 000 mg Cl- m-2 yr-1. The Auli watershed shows much less variation in the amount of precipitation and, consequently, in the deposition of nitrogen, sulfur and chloride to the 12 subcatchments for which input data were estimated. Annual average deposition of nitrogen was estimated [ABSTRACT FROM AUTHOR]