Summary
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 Environment Protection Agency and the project is part of the national programme for environmental monitoring (PMK). The greater part of the results from the project described here are also reported as a national Swedish contribution to the Baltic Monitoring Programme (BMP) of the Helsinki Commission.
The monitoring is carried out through a number of regular cruises in the Kattegat,the Sound (Öresund), the Baltic Proper and the Gulf of Bothnia. 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 programmes is made available also for the national monitoring. Consequently, this report contains more information than is really financed by the monitoring budget.
The autumn of 1988 was mild almost all over Sweden. The winter was very mild in the southern part of the country with moderate amounts of precipitation. Only in the northern part the precipitation was as snow to any significant extent. During spring and summer the weather was more warm and dry than normal. The autumn of 1989 was as mild as during the previous two years and the amount of precipitation was modest. The sea ice covered very small areas; in fact the extent was the smallest since regular observations were organised.
The temperature of the sea surface layer was higher than normal the whole year and most noticeable during winter and autumn. In the entire sea area the temperatures were 1- 2 °C above the long term mean value for the period 1968 - 1985.
The oxygen conditions in the south eastern Kattegat once again turned into an unfavorable situation in late summer and early autumn. However, in comparison with the situation in 1988, a smaller area was affected and in general the lowest concentrations were not as low as in that year. Also in the Baltic Proper the bad oxygen situation in the deep water prevailed the whole year. No major infiow of oxygen rich water occurred to uentilate the deep basins. In the Bornholm Basin hydrogen sulphide was present under the halocline (with an extension into the Hanö Bight) almost the whole year; in the Eastern Gotland Basin hydrogen sulphide has been present in the bottom water for more than 12 years continuously and in the eastern part of the Northern Central Basin hydrogen sulphide was present the whole 1989. In the Landsort Deep hydrogen sulphide was detected only during a short period in the late summer.
Nutrient conditions did not show any remarkable changes during 1989. During the winter period phosphate and nitrate are present in about usual concentrations, which decrease to near detection limit during the production period in the spring and early summer. In general there is an increasing trend of nitrate and phosphate in the surface waters of the Kattegat and the Baltic Proper, while the silicate in the Baltic shows a decreasing trend.
The analyses of petroleum hydrocarbons showed roughly the same concentrations as during the previous last years. This indicates that the load of oil pollution of the Baltic and the Kattegat has not changed significantly.