Swedish National Report on Eutrophication Status in the Kattegat and the Skagerrak OSPAR ASSESSMENT 2007

Type: Report
Series: RO 36
Author: Bertil Håkansson


The surface area of the Kattegat and the Skagerrak, located in the eastern North Sea, is about 22 000 km2 and 32 000 km2, and the mean depth is about 23 m and 210 m, respectively. The Skagerrak and the Kattegat forms the inner end of the Norwegian trench, which has the characteristics of a deep (700 m) fjord connecting the Baltic Sea with the Norwegian Sea (e.g. Rodhe, 1987). The sill depth of the fjord is about 270 m. The Kattegat offshore and inshore waters were identifi ed as problem areas, whereas the Inshore Skagerrak waters the OSPAR categories I - IV indicate a slight incoherence in the assessment, although with an overall judgement to be identifi ed as a problem area. The offshore Skagerrak was identifi ed as a non problem area, according to the OSPAR Comprehensive Procedure. (OSPAR Commission, 2005). The present assessment confi rms the general results obtained from the 2002 OSPAR Comprehensive Procedure, covering the time period 1998 to 2000. The decreasing trends of dissolved nutrients continued also during 2001 to 2005 but were still above elevated levels in Kattegat and inshore Skagerrak areas, as defi ned by the Comprehensive procedure. The Chlorophyll concentrations remain high and above background concentration, while oxygen still decreased in most areas clearly below defi ciency levels. Zoobenthos is still disturbed by low faunal diversity, abundance and biomass at many coastal sites. Phytoplankton indicator species are still present at elevated levels and algal toxins occur also during the present assessment period. In comparison with the WFD procedure, OSPAR background and elevated levels for some parameters and sub-areas are generally higher compared to WFD reference and moderate levels. In addition, summer and winter total nitrogen and phosphorus are also assessed in the WFD but not in OSPAR. Nevertheless, these two parameters support the main results obtained for winter dissolved nutrients. The Skagerrak and Kattegat area is infl uenced by transboundary fluxes to a great extent. Especially the infl ow of nitrogen and phosphorus from the Baltic Sea is a major source for both nutrients, according to the budgets presented. Lowering the inputs to the area is best achieved by reduction of nitrogen from land but also from the Baltic Sea. For phosphorus the most effective meassure should be to lower the concentration in the southern Baltic Sea, i.e. to combat eutrophication in the Baltic. Nitrogen reduction is more important than phosphorus, taking into account the OSPAR and WFD classification schemes.