Excessive amounts of nutrients entering the Baltic are disturbing the ecological balance of the sea. This process - known as eutrophication - makes a visible difference to the water, which becomes murky and in warm summers is more often clogged up with dense algal blooms - some of them poisonous. Eutrophication can seriously affect the entire marine food web, including valuable fish stocks.

	Between 1930 and 1980 the transparency of the sea water in the Northern Baltic decreased by as much as 3-4 metres.

What is Eutrophication?

Eutrophic means nutrient-rich, and eutrophication literally means enrichment with nutrients, although nowadays the term is more often used in a negative sense to mean over-enrichment. Nutrients - especially nitrogen and phosphorus - are vital for marine life. But the presence of excessive nutrients can seriously disturb the functioning of marine ecosystems.

Excessive nutrient inputs into a water body induce biological, chemical and physical changes in aquatic plant and animal communities, often leading to oxygen depletion, especially in deeper waters. Greenish, murky water is typically the first sign of eutrophication as microscopic plants and algae grow profusely, consuming the surplus nutrients. But algae are short-lived, and when they die they sink to the bottom of the sea, where their decomposition uses up oxygen. The worst affected areas can become completely anoxic. In the absence of oxygen, decomposition can release toxic hydrogen sulphide, poisoning organisms and making the sea-bed lifeless. 

Weather conditions can alleviate or accelerate eutrophication. Mild, wet winters are usually bad news for shallow, coastal waters, as nutrients are washed from farmland into rivers, lakes and ultimately the sea. This creates suitable conditions for intense algal blooms in the spring, which can lead to serious oxygen depletion, especially if the summer is then warm and calm.

Figure 1. Conceptual model for assessing eutrophication in the European seas linking nutrient enrichments and its direct and indirect effects in the ecosystem. The biological components are shadowed in green; the elements common with WFD are framed in red.

	Trends in the Baltic Sea The inflows of oxygen-rich saltwater from the North Sea have temporarily improved the oxygen depletion in the deep basins of the Baltic Proper and the western waters of the Gulf of Finland. In 2003, the intrusion of over 200 km3 of well oxygenated water increased in the Mecklenburg Bay near bottom salinity values to the highest values ever recorded and the deep areas of Southern Baltic and the Gotland Deep showed remarkable amounts of oxygen. However, e,g, the Fåro Deep was still completely anoxic. Several coastal areas have suffered oxygen depletion related to eutrophication. In coastal waters of Belt Sea, Sound and Kattegat, wide spread and long lasting severe oxygen depletion was observed in 2002 killing bottom fauna including fish. In the inner Gulf of Gdansk and in the Szczecin Lagoon, incidents of severe oxygen deficiency occurred in August 2003 in the near bottom waters. Bad oxygen situation was also observed in near bottom water in the Lübeck Bay and in the Pomeranian Bay (the German part). Large quantities of phosphorus have been released from anoxic bottom sediments. Algal blooms, many of them toxic or otherwise undesirable, have occurred in all parts of the Baltic. The surface accumulations of blue-green algae in the warm summer of 1997 were the most extensive ever recorded and they have been repeatedly extensive during summers.

Actions

Progress in cutting nutrient loads

A major study (link to BSEP 89) has been conducted to assess progress towards the strategic goals of the 1988 Ministerial Declaration regarding nutrient load reductions. This review shows that the progress in reducing nutrient loads from point sources such as municipal and industrial wastewater treatment plants has been good, with the 50% reduction target for phosphorus achieved by almost all the Contracting Parties. The results also show that measures to reduce nutrients from agriculture have fallen short of their aims.

Further reductions in nutrient loads from point sources are likely, since the continued implementation of nitrogen and phosphorus removal measures will further curb loads from municipal plants, especially in the EU accession countries. Further implementation of Best Available Techniques will also cut industrial nutrient pollution loads.

Comprehensive official plans to reduce inputs of nutrients to the Baltic Sea have so far been adopted by national governments in Finland, Latvia and Sweden. Plans to reduce nutrient loads in the other Contracting Parties which are or will be EU members mainly focus on the implementation of the related EU Directives, which also contribute to the reduction of nutrient inputs into the Baltic Sea.

The struggle to curb agricultural pollution

Agriculture is a major source of nutrients and the agricultural production is expected to increase after the EU enlargement, which will probably lead to increased discharges from this sector. Reducing nutrient loads from agriculture is more complicated than cutting loads from point sources. The implementation of agri-environmental measures is expected to promote reductions in nutrient loads from agriculture, but there is evidently a considerable time lag between the implementation of agricultural water protection measures and any visible effects in water bodies.

More work needed to limit nutrient loads

• More efforts must be made to reduce nutrient loads, especially from agriculture.

• There is an urgent need to reduce airborne inputs of nitrogen from both land-based and sea-based sources.

• Inputs of nutrients from urban areas, smaller municipalities and scattered settlements must also be addressed.

Work on scenarios

In order to ensure that adequate measures are taken to combat eutrophication, HELCOM has specifically pointed to the use of tools to assess the implications of different policy scenarios on nutrient inputs, and the resulting eutrophication status of the Baltic Sea and specific sub-regions. HELCOM has initiated an activity where current modelling tools may be used to simulate the impact of the implementation of the EU Common Agriculture Policy and other policies in the Baltic Sea area. Based on the existing regulations, and the extent to which they have been implemented, HELCOM may consider the need for additional measures, and examine where these measures could be implemented most cost-effectively.

	Get a grip on eutrophication and learn about state, impact, driving forces, pressures and responses (BOING) The MARE research programme (Marine Research on Eutrophication) aims to help decision-makers develop cost-effective measures to alleviate eutrophication in the Baltic Sea. For more information contact Mr. Sif Johansson, Tel: +46 8 698 1536 The Baltic Eutrophication Regional Network BERNET involves co-operation between 7 regions around the Baltic Sea.

Contacts

Chairman of HELCOM MONAS

Ms. Heike Herata
Federal Environmental Agency
P.O.Box 33 00 22
D-14191 Berlin
Tel: +49-30-8903 0
Fax: +49-30-8903 2965

HELCOM Secretariat

Professional Secretary
Mr. Juha-Markku Leppänen
Tel: +358-9-6220 2227