The condition of coastal waters in the Gulf of Finland has clearly deteriorated from last year.

   

Scientists on the Muikku, a research vessel of the Finnish Environment Institute (SYKE), have been taking samples in coastal waters during five summers, and most results from this year's two-week voyage are considerably more alarming than last year.

   

Thousands of square kilometres of sea bed in the Gulf of Finland are believed to be completely without oxygen. In addition to the bottom layers, there is a shortage of oxygen in the upper layers of the sea, which also kills life on the sea bed.

   

The amount of nutrients on the bottom has increased many times over in places.

   

At worst the bed of the Gulf of Finland can release an amount of phosphorous equivalent to that contained in the untreated sewage of 16 million people.

   

On Friday, after the end of the Muikku voyage, SYKE limnologist Seppo Knuuttila explained the phenomenon:

   

"The lack of oxygen increases the internal burden of the sea. By this we mean the return into circulation of phosphorous that had already settled on the bottom as sediment."

This internal pollution

of the Gulf of Finland is overtaking the impact of emissions from land.

   

According to studies by special researcher Jouni Lehtoranta, an area of oxygen-free sea bed one square kilometre in area can release an amount of phosphorous equivalent to the untreated sewage of 4,000 people. "There are about four thousand of these square kilometres in the Gulf of Finland", Knuuttila says.

   

The city of St. Petersburg, which dumps about one third of its sewage into the Gulf of Finland completely untreated, is one of the main sources of pollution in the Gulf of Finland. However, the bottom of the Gulf of Finland can release an amount of phosphorous in a day that is many times greater than that which is caused by the emissions from St. Petersburg.

The oxygen shortage

on the bottom is the result of decades of nutrient emissions from household and industrial waste and agricultural runoff, all of which have brought organic material to the sea, which further depletes oxygen in the depths.

   

Another factor in the equation is the exceptionally strong layering of water in the Gulf of Finland.

   

The heavy water on the bottom with a higher salt content does not mix with the oxygen-rich surface water. The oxygen depletion in the lower layers of the sea releases more phosphorous from the sediments on the bottom.

   

However, the nutrients will not rise to the surface before the layering eases and the sea water is mixed up more. Not all of the phosphorous reaches the upper layers to feed surface algae - much of it sinks back to the bottom.

   

Nevertheless, there are so many nutrients in the lower layers that summers of heavy algae growth are likely whenever the layers get mixed and the weather is favourable.

The lack of oxygen

in the shallow areas along the coast is exclusively the result of external pollution. There is no layering in shallow areas, and the water gets mixed at regular intervals.

   

"External pollution is still too high. It has decreased, but not enough", says biologist Mikaela Ahlman of the Uusimaa Environment Centre.