Östersjöns interna fosforbelastning – från ord till handling för återställande av den ekologiska balansen

En historisk tillbakablick visar att betydande resultat uppnåtts inkluderande en halvering av de landbaserade fosforutsläppen. I det senaste gemensamma HELCOM programmet BSAP överenskoms om landsvisa utsläppsnivåer som skulle uppnås tom 2020. I detta sammanhang var ännu inte termen ”Intern belastning” i allmänt bruk. Under de senaste 3-4 åren har man emellertid börjat fästa allt större uppmärksamhet avseende följderna av internbelastningen på Östersjöns tillstånd. Skälen till detta är bl a att förväntade positiva effekter av den betydande sänkningen av fosforutsläppen som ägt rum inte har realiserats. De ständigt återkommande blomningarna av cyanobakterier såväl i kustområden som i det öppna havet har om möjligt blivit kraftigare trots att de förväntats minska. Ett av huvudskälen till de ökade blomningarna har visat sig vara den lösta fosforn som finns i det syrefria bottenvattnet i Östersjöns djuphålor, den s.k. interna fosforbelastningen.

Läs mer om bakgrunden på projektsidan Östersjöns interna fosforbelastning

Välj föreläsare enligt tidtabell:

Introduktion Mikael Sjövall 7:17

Karl-Johan Lehtinen 9:52

Mats Svensson 16:02

David Austin 54:34

Alex Horne 1.28:00

Dennis Hamro-Drotz 2.14:00

Henrik Ringbom 2.42:00

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English

Scope of event:

Eutrophication of the Baltic Sea reached its peak in the 1970s and 1980s. The continuous deterioration of the situation ended with the establishment of the Helsinki Commission (HELCOM) as the body for international co-operation between all Baltic states.

A historical retrospect shows that significant results were achieved, including a 50% reduction in land-based phosphorus emissions. Target levels for land-based emissions to be accomplished by 2020 were set in the latest common HELCOM programme, the Baltic Sea Action Plan (BSAP). In this context, the term “internal load” was not yet commonly used. However, in the last 3–4 years, increasing attention has been given to the impact of the internal load on the condition of the Baltic Sea. Among others, one reason for this is that the expected positive effects of the significant decrease in land-based phosphorus emissions have not materialised. The annually occurring cyanobacterial blooms along coastal areas as well as in the open sea have, if anything, increased, instead of showing the expected signs of decreasing. The increased levels of soluble phosphorus in oxygen-free deep water have been shown to be one of the main reasons for the increased blooms. The extent of the dead bottom areas is now aprox. 100 000 km2, and new research suggests that the water containing hydrogen sulphide has now reached a depth of 50 m from the surface in areas west of Gotland. The amount of soluble biologically available phosphorus is estimated at aprox 100 000 tonnes/year, compared with a land-based load of about 10 000 tonnes/year.

As phosphorus-rich bottom water reaches our coasts through upwelling, large amounts of phosphorus are transported to archipelagos and other coastal areas according to wind directions.

Results from new research on the high volumes of water containing hydrogen sulphide strongly indicate that not even a large intrusion of saltwater through the Danish straits would suffice to both oxidize the hydrogen sulphide and bind the soluble phosphorus to the sediments.
In other words, it can be assumed that the situation in terms of the self-restoration capacity of the Baltic Sea has gone too far.