BS2 Nitrogen

>> Background information

Development

Nitrogen enters the Baltic Sea mainly in river water. Almost 95% of the total nitrogen load from Finnish territory originated from rivers in the 2000s. On average, 78 000 tonnes of nitrogen was discharged annually from all sources from Finland into the Baltic Sea. This accounts for 11% of the total nitrogen load from all countries in the catchment area.

Like phosphorus, nitrogen loads carried by rivers are correlated with water discharge. Discharge is in turn affected by wheather conditions. Thus there is a lot of annual variation, which may hide any possible general trend.

The nitrogen load from land to the Baltic Sea originates mainly from agricultural sources and municipalities. Depending on area, other sources include deposit on lakes, forestry, industry and fish farming. Scattered dwellings and peat production have a smaller scale effect. In addition, deposition directly from the atmosphere is a major source of nitrogen in the Baltic Sea.

Impact on biodiversity

Increased nutrient loads from external sources together with internal loads from sediments and the fixation of atmospheric nitrogen by cyanobacteria cause eutrophication in the Baltic Sea. This means that primary production (the production of organic matter) increases. Phosphorus is usually considered the most significant factor limiting primary production, but nitrogen may be equally important especially in the northern Baltic Sea. The nutrient limitation patterns also change somewhat seasonally.