Key message
Almost 35% of the total nitrogen load entering the whole Baltic Sea originates from airborne inputs.
The annual load varies across different parts of the Baltic Sea: from 200 mg/m2 N in the northern Gulf of Bothnia up to 1,500 mg/m2 N in the Belt Sea.
Taking into account uncertainty in emission data, model uncertainty and natural variability in meteorological conditions from one year to another, 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 15 % range. For sub-basins of the Baltic Sea differences between annual depositions for different years are slightly higher.
Assessment
Airborne load of nutrients
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 – 2000 are shown in Figure 1.
No significant trends could be determined for nitrogen loads entering the Baltic Sea or its various sub-basins.
Calculated annual total nitrogen depositions to the six sub-basins of the Baltic Sea in the period 1996 – 2000 are presented in Figure 2.
Annual atmospheric nitrogen deposition into the Baltic Sea fluctuated at around 300 kt over the period 1996-2000. This total nitrogen deposition consisted of almost equal proportions of reduced nitrogen and oxidised nitrogen (Figure 16).
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.
To enlarge, click on image.
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
Further information
Atmospheric Supply of Nitrogen, Lead, Cadmium, Mercury and Lindane to the Baltic Sea in the period 1996 - 2000
Helsinki Commission