Developments in nutrient inputs

​Inputs in 2010

In 2010, the total water- and airborne input of nitrogen and phosphorus to the Baltic Sea was 977,000 tonnes of nitrogen and 38,300 tonnes of phosphorus, respectively. Atmospheric nitrogen deposition amounted to 218,600 tonnes - 22% of the total nitrogen input. Atmospheric phosphorus deposition, which is assumed to be the same every year, constituted 5% of the total phosphorus input to the Baltic Sea.

N_P input per subbasin in 2010.jpg 

Figure: Total water- and airborne inputs of nitrogen and phosphorus to the Baltic Sea by sub-basin in 2010. (BB: Bothnian Bay, BS: Bothnian Sea, BP: Baltic Proper, GF: Gulf of Finland, GR: Gulf of Riga, DS: Danish Straits, KT: Kattegat)

The Baltic Proper received 53% of total nitrogen and 54% of total phosphorus input, followed by the Gulf of Finland (13% of total nitrogen and 17% of total phosphorus inputs) in 2010. The main countries contributing to nitrogen inputs were Poland (30%), Sweden (12%), and Russia (11%). The largest inputs of phosphorus originated from Poland (37%), Russia (16%) and Sweden (9%).

During 2010, high precipitation occurred over southern and some eastern parts of the Baltic Sea catchment area, leading to greater atmopsheric deposition than normal and very high run-off and nutrient inputs from especially Poland. The HELCOM PLC-5.5 report presents normalized nutrient input data which smoothens the effect of annual variations in meteorological condition and allows for better evaluation of trends in inputs (HELCOM, in prep).

Atmospheric inputs

Atmospheric deposition of total nitrogen is affected by climatic conditions and inter-annual variation of meteorological conditions, such as dominating wind direction, precipitation (intensity, frequency, distribution and type) and temperature. Hence, deposition does not directly reflect reductions in air emissions.

Emissions of nitrogen from all HELCOM Contracting Parties, except Russia, reduced during the period 1995 – 2011, ranging from 42% in Denmark to 11% in Estonia. Normalized data indicate that nitrogen deposition to the Baltic Sea has decreased by about 47,000 tonnes during 1995-2010. In 2010, however, the actual atmospheric nitrogen deposition was rather high (approximately 218,000 tonnes or 12% higher than in 2009) mainly due to rather high precipitation over some parts of the Baltic Sea catchment area.

atmospheric N deposition 1995-2010.jpg  

Figure: Annual actual atmospheric total nitrogen deposition from HELCOM Contracting Parties, Baltic Sea shipping (Ships) and other countries and sources (Other contr.) on the Baltic Seas during 1995-2010 (tonnes nitrogen). The line shows the annual normalized total nitrogen atmospheric deposition to the Baltic Sea.

Waterborne inputs

Actual annual waterborne inputs (riverine and direct inputs) to the Baltic Sea of total nitrogen and total phosphorus (see figures below) show rather high annual variation, making it difficult to compare inputs between years. A trend analysis carried out by the HELCOM PLC-5.5 project indicates that at least for phosphorus there has been a significant reduction in inputs to the Baltic Sea as a whole. Trends in inputs from different countries to different sub-basins vary, however.

The latest HELCOM PLC report​ shows that, in general, measures taken before and after 1994 to improve wastewater treatment, reduce emissions to air from combustion processes and curb losses from diffuse sources (agriculture and forestry) has reduced the inputs to the Baltic Sea by more than 200,000 tonnes of nitrogen and about 7,000 tonnes of phosphorus.

 Actual waterborne nutrient inputs 1994-2010.jpg

Figure: Actual annual waterborne inputs of nitrogen (N) and phosphorus (P) to Baltic Sea. The trend line for the flow normalized waterborne total phosphorus input is inserted as a line to indicate possible trend (solid line = a statistically significant trend; dotted line = no statistically significant trend).

 

References

HELCOM, 2013. Review of Fifth Baltic Sea Pollution Load Compilation for 2013 HELCOM Ministerial Meeting. Baltic Sea Environment Proceedings No. 141