Natural fluorescence in the North Sea and its major estuaries

Abstract

An updating is given on the concentration and behaviour of dissolved fluorescent matter in the North Sea, particularly in its major estuaries and the German Bight. The values of dissolved fluorescence in the coastal zone of the North Sea and in its major estuaries are relatively high (3–200 mFl) compared with the fluorescence in the Atlantic water entering the North Sea (0.5–1 mFl). It is concluded that the rivers are the main source of dissolved fluorescent matter in the North Sea. In all estuaries studied, in the German Bight and in the North Sea a conservative behaviour of dissolved fluorescence is found. In contrast to the nutrients, the dissolved fluorescence in the German Bight has not changed over the last 30 years. With a transport model for the North Sea the annual riverine flux of dissolved fluorescence to the North Sea is calculated: 585·10 6 mFl·dm 3. A minor part of the dissolved fluorescent matter in the North Sea originates from decomposition processes in the Wadden Sea: 0.6·10 6 mFl·dm 3 per year. It remains unclear whether dissolved fluorescent matter in the sediments in the Wadden Sea results from particulate fluorescent matter or if it is produced in situ from non-fluorescent compounds. Also, further research is needed to establish the importance of the flux of fluorescent matter from the sediment to the water column and its relation with the mobilization of micro-pollutants.