This report describes a project for environmental monitoring in the sea areas around Sweden, from the Kattegat to the northern part of the Bothnian Sea. SMHI carries out this project based on a contractual arrangement with the National Swedish Environment Protection Agency (SEPA) and the project is part of the national programme for environmental monitoring (PMK). The greater part of the results from the project described here is also reported as a national Swedish contribution to the Baltic Monitoring Programme (BMP) of the Helsinki Commission (HELCOM).
The monitoring is carried out through a number of regular cruises in the Kattegat, the Sound (Öresund), the Baltic Proper and the Gulf ofBothnia. Physical, chemical and biological parameters are studied in water samples, zoobenthos is studied in sediment grab samples and samples of fish and mussels are collected for the determination of harmful substances.
The work is entirely integrated with the regular oceanographical programme of SMHI. By this arrangement the result of the SMHI programme is made available also for the national monitoring. Consequently, this report contains a lot more information than is really financed by the SEPA monitoring budget.
The winter of 1989 - 90 was very mild; it was in fact the fourth mild winter in sequence! The sea ice cover was small; By and large, it was only the Bothnian Bay that was covered and this ice broke up about two weeks earlier than usual. The first part of 1990 was warm and windy and yielded at lot of precipitation, particularly in the southern part of Sweden. The spring was early and warmer than normal. In May and later the weather was more unstable and the summer had changing weather and somewhat low temperatures. The autumn started as calm and rainy, but ended in December as mild and windy.
The temperature of the sea surface layer was higher than normal most part of the year, just as it was in 1989. lnfact, the temperatures were 1- 3 °C above the long term mean value for the period 1979- 1989 in the entire area.
The oxygen conditions in the south eastern Kattegat once again turned into an unfavorable situation in late summer and early autumn. However, despite the unusually calm autumn with only weak mixing of the water masses the oxygen concentrations increased again and the situation never was serious. Also in the Baltic Proper the bad oxygen situation in the deep water prevailed in several basins the whole year. No major infiow of oxygen rich water occurred to ventilate the deep basins. In the Bornholm Basin hydrogen sulphide was present under the halocline (with an extension into the Hanö Bight) the whole year with the exception of the August cruise. In the Gdansk Basin there is no longer any stratification and oxygen is mixed into hte water from the surface
layer. This has improved the conditions int he bottom water. However, in the Eastern Gotland Basin hydrogen sulphide has been present in the bottom water for more than 13 years continuously. The Northern Central Basin, including the Landsort Deep, and the Western Central Basin were free from hydrogen sulphide the whole year.
Nutrient conditions did not show any remarkable or unexpected changes during 1990. During the winter period phosphate and nitrate were present in about normal concentrations, which decreased to near detection limit during the production period in the spring and early summer and then increased again during autumn.
The analyses of petroleum hydrocarbons showed slightly lower concentrations for the spring as compared to the results from the 1980-ties. This indicates that the load of oil pollution of the Baltic and the Kattegat had not changed significantly. However, the results from the autumn sampling were strikingly different. Although the surface samples showed normal concentrations the results from 10 m (and 30 m) were higher. The reason for this could not be identified but it is unlikely to be a contamination of the samples.