Lakes and Watercourses

show the availability of nitrogen in relation to phosphorus in lakes.
In class 1 the availability of phosphorus alone governs production; in
class 2 there is a tendency for accumulation of cyanobacteria (”bluegreen
algae”) in general; in class 3 the occurrence of nitrogen fixation and
specific nitrogen-fixing cyanobacteria is likely; in class 4 nitrogen fixation
is highly likely but cannot fully compensate for the nitrogen deficit, and
in class 5 the nitrogen deficit is extreme and fixation is unable to
compensate.
TABLE 5.
CURRENT CONDITIONS: area-specific loss of total nitrogen,
watercourses (kg N/ha, year)
Class Description Area-specific loss
1 Very low losses ≤ 1.0
2 Low losses 1.0 – 2.0
3 Moderately high losses 2.0 – 4.0
4 High losses 4.0 – 16.0
5 Very high losses > 16
Area-specific losses refer to the monitoring of concentrations 12 times
a year over three years and recorded or modelled water flow per 24-hour
period. It may be necessary to monitor concentrations more frequently in
small watercourses. 24-hour water flow figures are multiplied by the
corresponding concentrations obtained using linear interpolation between
readings. The 24-hour transport figures thus obtained are accumulated
to give annual figures and show area-specific losses after division by
the area of the catchment.
Nitrogen loss includes input from all sources upstream of the monitoring
point, which classifies the total area-specific input from the catchment
to lakes and seas, for example. The scale is also intended to be used
to assess losses from all types of soil in comparison with normal losses
from different types of land use. Known input from point sources can be
deducted to gain a better picture of diffuse nitrogen losses.
Class 1 represents normal leaching from mountain heaths and the
poorest forest soils. Class 2 shows normal leaching from non-nitrogensaturated
forest soils in northern and central Sweden. Class 3 contains
losses from unaffected bog/peat land and affected forest soils (eg,
leaching from certain clear-cut areas), as well as leaching from arable
soils (unfertilised seeded grassland). Class 4 shows common leaching
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