Level of water transparency stabilized in parts of the Baltic Sea

Helsinki, 17 January (HELCOM) – Water transparency has ceased to decrease and appears to have stabilized in some sub-basins of the Baltic marine area, according to a new assessment by the Helsinki Commission.

In the Kattegat, Southern and Eastern Baltic Proper, the Bothnian Sea and the Bothnian Bay the decreasing trend has ceased during the recent 10 to 15 years, and since then water transparency has remained in about the same level and in some cases even has slightly improved. Today, the decline in underwater visibility continues only in the Gulf of Finland and the Northern Baltic Proper.

According to assessments, the overall water transparency has decreased considerably in all sub-basins of the Baltic Sea over the last one hundred years. The trend has been of a steady linear decline ever since the measurements were started in 1903.

The decrease has been most pronounced in the Northern Baltic Proper (from almost 9 m to 4 m), and in the Gulf of Finland (from 8 m to 4 m). The most dramatic decline in underwater visibility has been recorded during the last 25 years in the western and northern parts of the Baltic Proper, as well as in the Gulf of Finland.

The primary cause for the decreased summer time (June-September) water transparency is most likely the increase in phytoplankton biomass, and especially in the Baltic Proper and the Gulf of Finland the increasing intensity of cyanobacterial blooms. Intensified cyanobacteria blooms are an indication of increased nutrient concentrations, diminished ratios of phosphorus to nitrogen and an obvious symptom of the ongoing eutrophication of the Baltic Sea.

Reductions in water transparency over the past century were less dramatic in the Bothian Bay. The visibility there has declined from 8 m to 6 m. In the Southern Baltic Proper and the Kattegat the changes have not been as dramatic as in the northern regions. Kattegat is a transitional region between the highly saline North Sea and the brackish water Baltic Sea, which may explain such variation.

Follow up:

http://www.helcom.fi/environment2/ifs/ifs2005/en_GB/transparency/

Contacts

HELCOM Secretariat

Mr Juha-Markku Leppänen
Professional Secretary
Tel: +358 9 62202227
Fax: +358 9 6220 2239

E-mail: juha-markku.leppanen@helcom.fi

Mr Nikolay Vlasov
Information Secretary
Tel: +358 9 6220 2235
Fax: +358 9 6220 2239

E-mail: nikolay.vlasov@helcom.fi