HELCOM Baltic Sea Environment Fact Sheet 2015, Published: 14 December 2015
Authors: Valiyaveetil Shamsudheen Semeena and Jerzy Bartnicki , EMEP MSC-W
The total deposition of nitrogen to the Baltic Sea in 2013 was 226 kt N, 6% lower than in 1995. But the total deposition of nitrogen to Baltic Sea in 2012 was only 2% lower than in 1995.
This indicator shows the levels and trends in oxidized reduced and total atmospheric nitrogen depositions to the Baltic Sea. The deposition of nitrogen compounds represents the pressure of emission sources on the Baltic Sea basin and catchment.
The HELCOM Ministerial Declaration of 1988 called for a 50 % reduction in discharges of nutrients to air and water by 1995 with 1987 as a base year. The 1992 Helsinki Convention and the 1998 Ministerial Declaration reaffirmed the need to further reduce discharges; leading to the adoption of several relevant Recommendations concerning measures to reduce emissions from point sources and diffuse sources. In 1990 HELCOM adopted its first Recommendation on Monitoring of Airborne Pollution Load (HELCOM Recommendation 11/1) which was later superseded by the Recommendations 14/1 and 24/1.
Atmospheric deposition of oxidized and reduced nitrogen was computed with the latest version of the EMEP/MSC-W model. The latest available emission data for the HELCOM countries and all other EMEP sources have been used in the model calculations presented here.
Calculated annual oxidized, reduced and total nitrogen depositions to the entire Baltic Sea basin in the period 1995 – 2013 are shown in Figure 1.
Atmospheric deposition of oxidized, reduced, and total nitrogen to the
entire Baltic Sea basin for the period 1995-2014, in per cent of 1995
In annual nitrogen deposition no significant trends could be determined in the considered period, where the annual deposition of oxidized nitrogen and total nitrogen are 12% and 6% lower in 2013 than in 1995 respectively, wile the reduced nitrogen deposition is 2% higher in 2013. The annual depositions of oxidized, reduced and total nitrogen decreased by 5%, 3% and 4% in 2013 than in 2012 while this was by 7% , 11% and 9% higher in 2012 than in 2011.
Mainly because of inter-annual changes in meteorological conditions, annual nitrogen deposition to the Baltic Sea and its sub-basins varies significantly from one year to another in the entire period 1995 – 2013. Maximum annual deposition of oxidized nitrogen (145 kt N) and reduced nitrogen (112 kt N) to the Baltic Sea takes place in the years 1998 and 2000, respectively. Minimum of annual deposition can be noticed in the years 2007 and 2002 for oxidized nitrogen (103 kt N) and reduced nitrogen (85 kt N), respectively.
Average annual atmospheric nitrogen deposition into the Baltic Sea is 220 kt over the period 1995 – 2013 with approximately 10% standard deviation.
To avoid a strong influence of inter-annual meteorological variability on annual nitrogen deposition, the so called "normalized" nitrogen deposition was calculated in the way described in Appendix D of the EMEP report for HELCOM. The calculated normalized annual deposition of total nitrogen in the period 1995-2013 is shown in Figure 2.
Figure 2. Normalised deposition of total nitrogen for the period 1995-2013.
Minimum, maximum and actual annual values of the deposition are also shown. The
minimum and maximum annual values are determined by the meteorological
conditions for each particular year.
A quick inspection of Figure 2 indicates slightly decreasing trend in normalized annual total deposition of nitrogen which roughly corresponds to decreasing trend in nitrogen emissions from the HELCOM area of interest. Compared to 1995, normalized depositions of oxidized and reduced nitrogen in 2013 are lower: 36% and 23%, respectively.
Calculated annual total nitrogen depositions to new nine sub-basins of the Baltic Sea in the period 1995 – 2013 are presented in Figure 3.
Figure 3. Atmospheric deposition of oxidised, reduced and total nitrogen to nine
sub-basins of the Baltic Sea for the period 1995 - 2013. Units: ktonnes N/year.
Note: the scales for the sea regions are different! Sub-basins:
ARC=Archipelago Sea; BAP=Baltic Proper; BES=Belt Sea; BOB=Bothnian Bay;
BOS=Bothnian Sea; GUB=Gulf of Bothnia; GUF=Gulf of Finland; GUR=Gulf of Riga;
KAT=Kattegat; SOU=The Sound; WEB=Western Baltic.
No significant trends can be recognized in nitrogen depositions to sub-basins of the Baltic Sea in the Period 1995 – 2013, however annual depositions of oxidized nitrogen are lower in 2013 than in 1995 in all sub-basins. On the other hand, depositions of reduced nitrogen are higher in 2013 than in 1995 in four sub-basins, with 7.5% increase in The Sound, 6.6% in Baltic Proper, 5.8% in Gulf of Finland and 0.7% in Gulf of Riga. On the other hand in 2012, the reduced nitrogen depositions were higher than that of 1995 in seven out of nine sub basins.
Compared to 2012, deposition of oxidized and reduced nitrogen in 2013 is lower in all sub basins except Western Baltic (8.6% higher for oxidized nitrogen and 12.9% in the case of reduced nitrogen) which is caused by the increased ammonia emissions from Germany in 2013. Thus the total nitrogen depositions are higher in 2013 compared to 2012 only in the Western Baltic by 11.2%. All other sub basins received considerably lower nitrogen depositions in 2013 compared to both 1995 and 2012.
Table 1. Annual depositions of oxidised nitrogen to the sub-basins and the entire basin of the Baltic Sea in the period 1995-2013. Units: kt N per year and basin.
Table 2. Annual depositions of reduced nitrogen to the sub-basins and the entire
basin of the Baltic Sea in the period 1995-2013. Units: kt N per year and
Table 3. Annual depositions of total nitrogen to the sub-basins and the entire
basin of the Baltic Sea in the period 1995-2013. Units: kt N per year and
Table 4. Normalized depositions of oxidized, reduced and total nitrogen to the
Baltic Sea basin in the period 1995-2013. Units: kt N per year.
1. Source: EMEP/MSC-W.
2. Description of data: The atmospheric depositions of oxidized and reduced nitrogen were calculated with the latest version of EMEP/MSC-W model in Oslo. The latest available official emission data for the HELCOM countries have been used in the model computations. Emissions of two nitrogen compounds for each year of this period were officially reported to the UN ECE Secretariat by the HELCOM Contracting Parties. Missing information was estimated by experts. Both official data and expert estimates were used for modeling atmospheric transport and deposition of nitrogen compounds to the Baltic Sea - http://www.ceip.at/ .
3. Geographical coverage: Atmospheric depositions of oxidized and reduced nitrogen were computed for the entire EMEP domain, which includes Baltic Sea basin and catchment.
4. Temporal coverage: Time series of annual atmospheric depositions are available for the period 1995 – 2013.
5. Methodology and frequency of data collection:
Atmospheric input and source allocation budgets of nitrogen (oxidised, reduced and total) to the Baltic Sea basins and catchments were computed using the latest version of EMEP/MSC-W model. EMEP/MSC-W model is a multi pollutant, three-dimensional Eulerian model which takes into account processes of emission, advection, turbulent diffusion, chemical transformations, wet and dry depositions and inflow of pollutants into the model domain. Complete description of the model and its applications is available on the web http://www.emep.int.
Calculations of atmospheric transport and depositions of nitrogen compounds are performed annually two years in arrears on the basis of emission data officially submitted by Parties to CLRTAP Convention and expert estimates.
6. Strength and weakness:
Strength: annually updated information on atmospheric input of oxidized and reduced nitrogen to the Baltic Sea and its sub-basins.
Weakness: gaps and uncertainties in officially submitted by countries time series of nitrogen emissions to air
The results of the EMEP Unified model are routinely compared with available measurements at EMEP and HELCOM stations. The comparison of calculated versus measured data indicates that the model predicts the observed air concentrations of lead and cadmium within the accuracy of approximately 30%. Comparison of annual wet deposition based on observations at selected HELCOM stations and calculated by the EMEP model for the period 1995-2006 are shown in Figure 4.
Figure 4. Comparison of annual wet deposition based on observations (obs) at selected HELCOM stations and calculated by the EMEP model (mod) for the grid squares including these stations, for each year of the period 1995-2006. Units: mg N m-2.
8. Further work required:
Further work is required on reducing uncertainties in emission data and better parameterization of physical processes in the EMEP Unified model.
For reference purposes, please cite this Baltic Sea environment fact sheet as follows:
[Author's name(s)], [Year]. [Baltic Sea Environment Fact Sheets title]. HELCOM Baltic Sea Environment Fact Sheet(s) 2015. Online. [Date Viewed], http://www.helcom.fi/environment2/ifs/en_GB/cover/.