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Atmospheric nitrogen depositions
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Key message
The annual load varies across different parts of the Baltic Sea: from 200 mg/m2 N in the northern Gulf of Bothnia up to 1500 mg/m2 N in the Belt Sea.
No significant temporal pattern in nitrogen depositions to the Baltic Sea and its sub-basins can be detected. Annual total depositions of nitrogen to the Baltic Sea are oscillating around the 1996 value within 25 % range.
Assessment
Atmospheric deposition of oxidized and reduced nitrogen was computed with the latest version of the new unified model developed at MSC-W of EMEP. The latest available emission data for the HELCOM countries have been used in the model calculations. For the emissions from the international ship traffic, annual values for 1990 have been used in the model calculation because of the lack of updated data.
Calculated annual total (oxidized plus reduced) nitrogen depositions to the entire Baltic Sea basin in the period 1996 – 2001 are shown in Figure 1.
Calculated annual total nitrogen depositions to the six sub-basins of the Baltic Sea in the period 1996 – 2001 are presented in Figure 2.
No significant trends could be determined for nitrogen loads entering the Baltic Sea or its various sub-basins.
Annual atmospheric nitrogen deposition into the Baltic Sea fluctuated at around 300 kt over the period 1996 – 2001. This total deposition consisted of almost equal proportions of reduced nitrogen and oxidized nitrogen.
Figure 1. Atmospheric deposition of total (oxidized and reduced) nitrogen to six sub-basins of the Baltic Sea for the period 1996-2000. Units: ktonnes N/year.
Click the image to enlarge.
Figure 2. Atmospheric deposition of oxidized, reduced and total nitrogen to six sub-basins of the Baltic Sea for the period 1996 - 2000. Units: ktonnes N/year.
Note: the scales for the sea regions are different!
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Last update 20 November 2003