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This chapter revisits the major problems relating to manmade disturbances in the global nitrogen (N) cycle, and links the local findings from the project to the large-scale effects. The human transformationof atmospheric N2 to chemically and biologically more reactive species causes a number of environmental effects. The focus of this project has been budget estimates of N for two large watersheds with a set of subcatchments in southern Norway, accompanied by process studies to explain patterns of retention and runoff of N. Atmospheric inputs were close to 2.5 mg N m- 2 yr-1 and by far the dominant source of N for the sparsely populated, heathlanddominated watershed. Low retention and apparent N saturation could be accredited to high atmospheric inputs of N, but also hydrology, poorly developed soils and terrestrial P limitation. In this acidified watershed, nitrate contributed nearly 50% to surface water acidification, underlining the importance for strong cuts in NOx and NHx emissions. P concentrations were low, frequently < 1 mu g L- 1, causing high N:P ratios in runoff, and promotingP limitation both in freshwater and the nearshore marine recipient. For the agriculturally and forested watershed, atmospheric N deposition was < 1.5 mg N m-2 yr-1, and agricultural activities were the totally dominant source of N, yielding generally high but fluctuating concentrations of N and P in runoff water. Forestry and agricultural practices were major determinants of N runoff. Thehigh concentrations of both N and P in the major outlet of this watershed would be a major source of eutrophication for the recipient fjord. For both watersheds, climatic fluctuations strongly affected annual runoff patterns of N. The fate of ammonium relative to nitrate andlong-term climatic changes with a possible mineralization of soil stores of organic N are unpredictable determinants to future effects ofN. [ABSTRACT FROM AUTHOR]

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]