Langzeitveränderungen essentieller Nährstoffe in der zentralen Ostsee

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Abstract
The continuing phosphate accumulation with 0.04… 0.075 μmol · 1−1 · a−1 in the deep water and 0.024… 0.026 μmol · 1−1 · a−1 in the winter‐time surface layer of central Baltic Sea stations is confirmed by the continued previous investigations. After an increase the nitrate concentrations in the deep water decreased significantly between 1979 and 1982, which is obviously due to denitrification processes caused by unfavourable oxygen conditions in the boltom water. In the Fårö Deep and in the Landsort Deep a significant correlation between nitrate and oxygen concentrations was found. In the winter‐time surface layer, for the nitrate a positive trend prevailed with 0.148… 0.225 μmol · 1−1 · a−1, which was in close correlation with an increase in salinity. This eutrophication is caused by the prevailing anthropogenic influences and also by oceanological changes as the decrease in the stability of stratification in the Gotland Deep with an intensification of the vertical exchange of matter. Consequences of eutrophication consist in the increase of the biomass of zooplankton and zoobenthos and in the yields of the Baltic Sea fisheries, but also in the increased loading of the oxygen balance causing longer anoxie periods in the deep water.