The role of nitrogen (N) in acidification of soil and water has become relatively more important as the deposition of sulphur has decreased. Starting in 1991, we have conducted a whole-catchment experiment with N addition at Gårdsjön, Sweden, to investigate the risk of N saturation. We have added 41 kg N ha(-1) yr(-1) as NH(4)NO(3) to the ambient 9 kg N ha(-1) yr(-1) in fortnightly doses by means of sprinkling system. The fraction of input N lost to runoff has increased from 0% to 10%. Increased concentrations of NO(3) in runoff partially offset the decreasing concentrations of SO(4) and slowed ecosystem recovery from acid deposition. From 1990-2002, about 5% of the total N input went to runoff, 44% to biomass, and the remaining 51% to soil. The soil N pool increased by 5%. N deposition enhanced carbon (C) sequestration at a mean C/N ratio of 42-59 g g(-1).
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