This chapter revisits the major problems relating to manmade disturban
ces in the global nitrogen (N) cycle, and links the local findings fro
m the project to the large-scale effects. The human transformation of
atmospheric N-2 to chemically and biologically more reactive species c
auses a number of environmental effects. The focus of this project has
been budget estimates of N for two large watersheds with a set of sub
catchments in southern Norway, accompanied by process studies to expla
in patterns of retention and runoff of N. Atmospheric inputs were clos
e to 2.5 mg N m(-2) yr(-1) and by far the dominant source of N for the
sparsely populated, heathland dominated watershed. Low retention and
apparent N saturation could be accredited to high atmospheric inputs o
f N, but also hydrology, poorly developed soils and terrestrial P limi
tation. In this acidified watershed, nitrate contributed nearly 50% to
surface water acidification, underlining the importance for strong cu
ts in NOx and NHx emissions. P concentrations were low, frequently < 1
mu g L-1, causing high N:P ratios in runoff, and promoting P limitati
on both in freshwater and the nearshore marine recipient. For the agri
culturally and forested watershed, atmospheric N deposition was < 1.5
mg N m(-2) yr(-1), and agricultural activities were the totally domina
nt 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. The high concentrations of both N and
P in the major outlet of this watershed would be a major source of eut
rophication for the recipient fjord. For both watersheds, climatic flu
ctuations strongly affected annual runoff patterns of N. The fate of a
mmonium relative to nitrate and long-term climatic changes with a poss
ible mineralization of soil stores of organic N are unpredictable dete
rminants to future effects of N.