Gulf of Finland recovering slowly
Nearly all St. Petersburg sewage is now treated
The calm Gulf of Finland bathes in the spring sun in Sandöfjärden off Raseborg in the southwest of Finland.
The water looks clear at the surface, but the bottom area is almost dead: the only living creatures there are bacteria.
Ari Honkonen and Asko Mustonen of Vesi-Eko as well as farmer Aarre Arrajoki are attaching cables to an oxygenator, which is to pump oxygen-rich surface water to the oxygen-free lower levels. The aim of the project is to see if it is feasible to revive the depths by artificially introducing oxygen to the sea bottom.
Dead areas at the bottom of sea are seen as a big problem in the Gulf of Finland, where thousands of square kilometres of sea bottom suffer from a lack of oxygen.
It is because of these areas that the sea has not benefitted as much as had been hoped from the 50 per cent reduction in phosphorous emissions from land in the past 30 years.
The lack of oxygen maintains has led to a self-perpetuating cycle in which nutrients that sink to the bottom with dead algae are released again into the water to cause further eutrophication. This slows the recovery of the sea.
“When the sea receives emissions for long enough, the internal load starts to build. That is why recovery does not proceed at the same pace as the reduction of the external load”, says special researcher Seppo Knuuttila of the Finnish Environment Institute (SYKE).
The sea is affected by emissions from several decades, and it reacts with a delay to reductions in emissions. The recovery of areas such as Sandöfjärden, which are in the worst shape, could take decades.
The biggest source of emissions in the Gulf of Finland, the Russian city of St. Petersburg, has been cleaning up its act. Phosphorous emissions from St. Petersburg have been cut by 80 per cent and nitrogen emissions by 60 per cent from what they were in the 1970s, when the first moves at sewage treatment were made. Now nearly all of the city’s waste water is channelled to the new and efficient treatment plants.
When the massive sewage treatment project is completed in 2012, the city will account for only 15 per cent of phosphorous emissions into the Gulf of Finland, down from 40 per cent in 2004.
“Thanks to measures taken in St. Petersburg the total phosphorous load affecting the Gulf of Finland is declining by 30 per cent in ten years, which is a dazzling amount”, Knuuttila says.
This should also be reflected in the growth of algae. It is expected to take about five years for the improvement to show.
“In about 2017 a marked improvement is expected in the condition of the Gulf of Finland. After that, the summer growth of algae should decline considerably, thanks to the lower phosphorous level”, Knuuttila says.
Emissions should be reduced further if the Gulf of Finland is to get into really good shape.
Agriculture is a key factor in Finland. Emissions from agricultural runoff should be reduced by one third. City sewage treatment has already reached an optimum level.
Artificial oxygenation has brought good results in the Stockholm archipelago. In Sandöfjärden, however, the artificial respiration was not sufficient for the whole summer.
“We were not able to raise the oxygen level in the water near the bottom so much that there would have been enough oxygen for the whole summer”, says SYKE researcher Jouni Lehtoranta.
An oxygen shortage hit the depths in late August, when phosphorous started being released from the bottom, immediately increasing the internal load. Lehtoranta says that this summer pumping will be ramped up to see if it will help.
Three new oxygenation devices have been placed at the depths. Ari Hakkonen and Vesi-Eko project chief Petteri Kontila turn on the switch to make sure that the devices are in working order and pump water from the surface into the depths.
The pumps will be put into use as soon as the researchers install measuring devices in the coming week. Divers will also look for a pump that sank to the bottom after the cables holding them in place had corroded. Sea water can be unpredictable.
Lehtoranta emphasises that even if it works, the oxygenation project alone is of limited help in reviving the area that is in poor shape.
“Even if there were good results from oxygenation, it must not be allowed to affect the reduction of external emissions.”
Previously in HS International Edition:
Poor oxygen situation threatens Gulf of Finland - once again (26.3.2009)
Significant reduction in phosphorous emissions from St. Petersburg (1.9.2010)
Oxygen situation in Gulf of Finland improved (26.8.2009)