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News The Baltic Sea in 2002 a bumper year for algal blooms

Concerned URL
Source Helcom
Release date 31/10/2002
Contributor janhei

Concluding the findings presented during the fourth meeting of the HELCOM Monitoring and Assessment Group, held in Warnemünde, Germany, 21 – 25 October, the year 2002 has been exceptional in many ways. Algal blooms were enhanced by high nutrient inputs from spring onwards, which were even increased by an abnormally high precipitation in the western Baltic drainage area – in February precipitation was more than 273% of the average, for instance. The weather conditions in the following summer - which was the second warmest since 1890 – added to the formation of algal blooms, especially of blue-green algae, or cyanobacteria. Followed by exceptionally calm, sunny and hot weather, the algae could successfully grow and accumulate at the surface. In 2002, in the Gulf of Finland and the northern Baltic Proper, cyanobacterial blooms were clearly more intense than during the summer 1999 and 2001, and almost as intense as in 1997. The blue-green algal blooms had been successfully forecasted about 5 months in advance. The same weather conditions that had favoured the growth of planktonic algae also caused the oxygen content in the near bottom waters of the western Baltic Sea to decrease rapidly in late summer. The result was a wide-range depletion of bottom-dwelling animals in Danish and German waters and of fish kills over wide areas. The affected areas were larger than ever observed since the early 1980s, covering the area between Kattegat and Mecklenburg bight. The anoxic conditions in wide areas of the Baltic are typical for a "stagnation period", which has lasted since 1995, and has only been shortly interrupted by an inflow of oxygen-rich water in October/November 2001, but which did not have any long-lasting effect. According to the present information, the mass death among harbour seals in the Skagerrak-Kattegat seems to be over for this year. Since the outbreak of the phocine distemper virus on the Danish isle of Anholt in April-May, approximately 7000 harbour seals have been reported dead in the Kattegat-Skagerrak, but probably totally 10,000 seals have died.

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