Atlas of near-surface Total Suspended Matter concentrations in the Dutch coastal zone of the North Sea

Abstract

Suspended matter in the water column governs the under water light climate and is thus an important factor for life in the sea. Next to nutrients, light is essential for the growth of phytoplankton and in this way for the food chain in the sea. Suspended matter concentrations are highly variable in time and space. Thus it is very hard to assess the influence on these concentration levels of any anthropogenic acting. Furthermore, the relations between suspended matter and the food chain are very complicated. These two facts hamper a fair estimate of the effects on the ecosystem of foreseeable anthropogenic measures that may infer changes in suspended matter transports. As a prerequisite for managing a sustainable use of the North Sea, basic information on the highly variable suspended matter concentrations in the marine environment is therefore needed. Through charts and graphs, this atlas gives an insight in the nearsurface suspended matter concentrations and their variability in the Dutch coastal zone (ca. 70 km wide). The charts of the near-surface suspended matter concentrations are based on the DONAR data of the monitoring WAKWON programme carried out between 1975 and 1983. The variability in space and time is further elucidated by dedicated graphs and charts. As a result of research (Suijlen and Duin, 2001) the suspended matter concentrations appear to be mainly determined by the wave heights. This results in high concentrations during the stormy winter periods and low concentrations during calm summer periods. Besides a seasonal variability, a long-term variability exists with periods of 4-8 years. Taking into account the variability in the concentration levels, it is estimated that the net northward transport of suspended matter in the coastal zone (ca. 70 km wide) ranges between about 6 and 60 Mton per year. This transport depends on the waves during that year, as well as on the flux of sediments from the English Channel and the Flemish banks. Although based on data measured between 1975 and 1983, the charts and graphs presented in this atlas are representative for the present suspended matter concentrations.