Eutrophication Status Report of the North Sea, Skagerrak, Kattegat and the Baltic Sea: A model study. Present and future climate

Type: Report
Series: Oceanography 115
Author: 1) K. Eilola, 4)J.L.S. Hansen, 1)H.E.M. Meier, 3)M.S. Molchanov, 3)V.A. Ryabchenko and 2)M.D.Skogen 1)Swedish Meteorological and Hydrological Institute, Sweden, 2) Institute of Marine Research, Norway 3) St. Petersburg Branch, P.P. Shirshov Institute of Oceanology, Russia 4)Department of Bioscience, Aarhus University, Denmark


An ensemble of models has been used to assess eutrophication in the North Sea and Baltic Sea in the present and the future climate, using a method suggested in Almroth and Skogen (2010). In the control run, the assessment of eutrophication status according to the integration of the categorized assessment parameters indicates that the Kattegat, the Danish Straits, the Gulf of Finland, the Gotland Basin as well as main parts of the Arkona Basin, the Bornholm Basin, and the Baltic proper may be classified as problem areas. The main part of the North Sea and also the Skagerrak are nonproblem areas while the main parts of the Gulf of Bothnia, Gulf of Riga and the entire southeastern continental coast of the North Sea may be classified as potential problem areas (Fig. 16). The temperature increase by itself will worsen the oxygen condition throughout the area and on top of this; elevated nutrient levels in the whole Baltic will amplify this effect due to elevated primary production. Therefore declining oxygen condition and increasing phytoplankton biomasses will be the main problem causing the areas to be classified as problem areas. In the Western Gotland Basin low oxygen seems to be the sole reason for this classification. In the North Sea, the classification as potential problem areas are due to high nitrate and N:P ratio. In the future climate scenarios most of the previous potential problem areas in the Baltic Sea have become problem areas, except for the Bothnian Bay where the situation remain fairly unchanged. Also in the North Sea there seems to be no obvious changes in the projected future climate. Comparing the ECHAM5 driven changes to simulations using the HadCM3 forcing show that; all changes except the surface layer winter DIN in the future climate have the same sign and that; the overall eutrophication status assessment is robust and insensitive to the choice of future scenario.