| Short description
of the environmental status
The year 2005 will probably be most associated with the storm/hurricane "Gudrun" that hit the southern part of Sweden on January 8 th to 9 th . This storm brought down more trees than any other on record. Otherwise, the winter was one of many mild ones since 1988. In the northern and western Sweden , precipitation was heavy in January and light during February. In eastern parts it was light in January and heavy in February. March was cold, and spring came suddenly with warmth that lasted for the whole of April, which was also extremely sunny. May was generally cold and rainy, though spring as a whole was rather dry. Summer began with a cold and rainy June, especially in eastern parts. The first half of July and the second half of August was sunny and dry, while the period in between was very wet. Almost the whole country had a dry and warm autumn. In some eastern parts it was the driest autumn for 105 years. December was warmer than usual with normal precipitation.
No major inflows to the Baltic took place during 2005, and only the Arkona- and Bornholm Basins were influenced by inflowing saltwater.
During the storm "Gudrun" in January there was an inflow through the Sound of approximately 25 km 3 with salinities between 20 and 25 psu. Later during spring and summer, some other minor inflows occurred with volumes around 10 to 15 km 3 . From the end of October to mid November another 40 km 3 flowed into the Baltic, this time with salinities between 10 and 25 psu. In the middle of December the last inflow of 20 km 3 took place, this time salinity was about 20 psu. These figures refer to flows through the Sound only.
Hydrography and hydrochemistry
The Skagerrak, Kattegat and the Sound
Nutrient concentrations in most areas followed the mean annual cycle. In the Sound however, phosphate and silicate levels were elevated during the main part of the year because of outflowing water from the Baltic.
Lack of oxygen in the deep waters of the open Skagerrak is very uncommon, while it often appears in the inner fjords along the coast of Bohuslän . Low oxygen concentrations can also be found in the archipelago along the cost but during 2005 the situation never became poor. The lowest concentration, 4 ml/l, was measured during August/September. Oxygen conditions were also good throughout the year in the Kattegat . Here, the lowest deepwater oxygen concentrations were 2.5 ml/l, found during autumn both in the open Kattegat at Anholt E and in the deep trench at W Landskrona in the Sound. In Skälderviken and Laholm Bay , where lack of oxygen was very common during the 1980-ies, concentrations never fell below 2.7 ml/l.
The first signs of spring bloom were detected in the Kattegat and in the coastal waters of Skagerrak , in the beginning of February. At the end of the month the bloom was at its peak in the Kattegat, while this occurred a few weeks later in the Skagerrak . No exceptional blooms occurred during the year, and the situations as a whole can be considered as typical.
The Baltic Proper
During 2004, elevated concentrations of phosphate were found in the northern and central Baltic Proper. During 2005, phosphate concentrations were higher than normal throughout the year, though this time the effect was especially pronounced in the southern Baltic. Winter concentrations in these areas were almost double normal winter values, and summer concentrations were comparable to normal winter concentrations. These extreme levels, together with sunny and calm weather, were advantageous for blooms of blue-green algae (cyanobacteria).
Oxygen conditions in the deep water were relatively bad at the beginning of the year throughout the whole of the Baltic Proper. Conditions were good in the Arkona Basin alone. In general, oxygen concentrations below 2 ml/l were found at depths greater than 70 to 100 metres . Hydrogen sulphide was present in the bottom water of the Eastern, Western and Northern Gotland Basins . In the Arkona Basin , conditions in the bottom water worsened towards late summer, when the lowest oxygen concentration, 0.10 ml/l, was measured. After that, oxygen concentrations increased again and by December were around 4 ml/l. In the Bornholm Basin , concentrations in January were just above 0 ml/l and then fell down to -3.5 ml/l (hydrogen sulphide expressed as negative oxygen). In late November/early December, oxygen concentrations quickly improved, probably as a result of inflows in October/November. In the Eastern, Western and Northern Gotland Basins concentrations of hydrogen sulphide increased slowly during the whole year.
The spring bloom started in the southern Baltic during March and peaked in most areas during April. The first signs of bluegreen algae were detected in May, and by June clear blooms were seen north of Gotland . The blooms maximum extent (ca. 130 000 km 3 ) was observed in mid July and was concentrated in the northern parts of the Baltic Proper and the areas around Öland and Gotland . The blooms decreased from early August and by the middle of the month all visual surface accumulations had disappeared, and only dead or dying bacteria were found in water samples. The 2005 Baltic Proper cyanobacteria bloom had the longest recorded duration since regular monitoring started in 1997. However, the bloom remained concentrated in the northern parts so the spatial extent was below average. During late summer and autumn the algae situation was normal and no more exceptional blooms occurred
Gulf of Bothnia
2005 can be considered as a typical year. Nutrient concentrations were normal, except for silicate that in the Bay of Bothnia showed very high levels during the main part of the year, but in December concentrations were back to normal. Also, in the deepwater of the Bothnian Sea there is still high levels of phosphate, but not as high as during the last winter.
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