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Nutrient emissions by point and diffuse sources and their loads were estimated for the
Odra catchment over the time period of the last 50 years by means of the model MONERIS. For nitrogen
a change of the total emissions from 38 kt·a–1 N in the mid of 1950s a maximum of 105 kt·a–1
N in the early 1980s and a recent value of about 84 kt·a–1 N were estimated for the total Odra Basin.
The share of the point source discharges on the total N emissions varied between 24% (1955) and
35% (1995). The emissions from groundwater and tile drained areas represent the dominant pathway
(37–56% of total N emissions) during all investigated time periods. Emissions from tile drained areas
increased from the mid of 1950s to end of 1980s by a factor of 20 and reached in this period the same
amount as emissions by groundwater. For phosphorus the emissions changed from 4 kt·a–1 P in 1955
to 14 kt·a–1 P in 1990 and a recent level of 7 kt·a–1 P. Point source discharges caused between 36 to
66% of total P emissions and represent the dominant pathway for all investigated time periods. Erosion
and discharges from paved urban areas and sewer systems was the dominant diffuse pathway of
the total P emissions into the river system. The comparison of calculated and observed nutrient loads
for the main monitoring stations along the Odra River shows that the average deviation is 12% for
total phosphorus (1980–2000) and 15% for dissolved inorganic nitrogen (1960–2000). From the
analysis it can be concluded that the present load of dissolved inorganic nitrogen (DIN) and total
nitrogen (TN) of the Odra into the Baltic Sea is about 2.3 times higher than in the mid of 1960s. The
maximum DIN load (1980s) was more than 3 times higher than in the 1960s. The change of the total
phosphorus (TP) load is characterized by an increase from the 1955s to 1980 from 2 to 7 kt·a–1 P (factor
2.6). Around 2000 the TP load was 4 kt·a–1 which is only the double of the level of the 1955s.
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