The North Sea Coasts of Denmark, Germany and The Netherlands

Eutrophication is defined here as the process of increasing concentration and load of inorganic nutrients, inducing changes in the aquatic communities. In general terms the large European rivers provide the main source for nutrient enrichments in coastal waters. The main rivers loading the surface waters along the eastern North Sea coasts are, from north to south, the Elbe, Weser, Ems, Rhine, Meuse and Scheldt (Fig. 7.1). Roughly 50% of the total N load comes from the rivers Rhine and Meuse together, strongly connected to the total discharge of fresh water, which is larger in wet years (1981, 1987,1988) and smaller in dry years (1985, 1989, 1990). The river Elbe gives the second most important fresh-water flow into the North Sea (30%) and the river Ems and Weser together are responsible for 20% of the N load. The river Scheldt adds only an insignificant amount (less than 5%) to the overall loading. Although there is a recent trend of decreasing loads of N on the North Sea, a significant decrease over the period 1980–1990 cannot be calculated (Fig. 7.2), De Vries et al. 1993). A comparable explanation accounts for the total P load (Fig. 7.2), where the Rhine-Meuse discharge is responsible for roughly 60%. A decreasing trend in P-loading over the period 1980–1990 can be observed, but after corrections for discharges and connected salinities, the decline is not significant (De Vries et al. 1993).