Macroalgae and phytoplankton as indicators of ... - Naturstyrelsen

dicted TN concentrations from the model are, on average, 27.8 µmol l -1
(±8.3) lower than measured concentration in the river, indicating a TN
sink in the German Bight.
Figure 2.3 Mean annual TN concentrations in River Elbe compared to estimated TN
concentrations based on the salinity-TN regression model. Data from 1996 were not included
in the regression.
Assuming that the land use, and presumably nitrogen loss also, in the
catchment areas of River Elbe and other contributing rivers is similar to
the land use in Denmark, equivalent TN concentrations calculated from
TN inputs to the Danish straits in an average freshwater discharge year
(Table 2.1) minus an average TN sink of 27.8 µmol l -1 were employed as
end-point members. Reference conditions and boundaries between ecological
status classes are therefore found as salinity-dependent lines
starting at 13.18 µmol l -1 for salinity 35 and intersecting 0 salinity at 80,
189, 403, 650, and 805 µmol l -1 (Table 2.2) for reference conditions, H-G
boundary, G-M boundary, M-P boundary, and P-B boundary, respectively.
Such reference conditions and boundaries were found for 4 sites
along the west-coast of Jutland using average salinities characteristic for
each site (Table 2.2). The uncertainty associated with these estimates derives
from the estimated TN level at salinity 35 and the TN sink, since the
TN concentrations at salinity 0 are fixed values. The values in Table 2.2
will be used for deriving reference condition and boundary values for
Nissum Fjord, Ringkøbing Fjord and the inner Wadden Sea.
Table 2.2 Suggested reference conditions and boundary values for TN concentration (µmol l -1 ) normalised to standard salinity
of 33 for Hirtshals, 31.7 for the coastal area off Nissum Fjord, 31.4 for the coastal area off Ringkøbing Fjord, and 30.4 for outer
Wadden Sea.
Intercalibration site Ref. cond. H-G G-M M-P P-B
Hirtshals 17.0 (±0.7) 23.2 (±0.7) 35.5 (±0.7) 49.6 (±0.7) 58.4 (±0.7)
Coast off Nissum Fjord 19.5 (±0.9) 29.8 (±0.9) 49.9 (±0.9) 73.2 (±0.9) 87.8 (±0.9)
Coast off Ringkøbing Fjord 20.1 (±1.0) 31.3 (±1.0) 53.3 (±1.0) 78.7 (±1.0) 94.6 (±1.0)
Outer Wadden Sea 22.0 (±1.2) 36.3 (±1.2) 64.4 (±1.2) 96.9 (±1.2) 117.3 (±1.2)
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