7 The North Sea Coasts of Denmark, Germany
and The Netherlands
P. H. NIENHUIS
7.1 Introduction
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 ScheIdt
(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 ScheIdt
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-Ioading
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).
An important hydrographic characteristic of the southern North Sea is
the northerly directed residual current along the coast of the
Netherlands, Germany and Denmark. Water from the river Rhine for
example is transported along the coast in a 50- to 70 km- wide zone and
Netherlands Institute of Ecology, Centre for Limnology, Rijksstraatweg 6, 3631 AC
Nieuwersluis, The Netherlands
Ecological Studies, Vol. 123
Schramm/Nienhuis (eds) Marine Benthic Vegetation
© Springer-Verlag Berlin Heidelberg 1996
and The Netherlands
P. H. NIENHUIS
7.1 Introduction
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 ScheIdt
(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 ScheIdt
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-Ioading
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).
An important hydrographic characteristic of the southern North Sea is
the northerly directed residual current along the coast of the
Netherlands, Germany and Denmark. Water from the river Rhine for
example is transported along the coast in a 50- to 70 km- wide zone and
Netherlands Institute of Ecology, Centre for Limnology, Rijksstraatweg 6, 3631 AC
Nieuwersluis, The Netherlands
Ecological Studies, Vol. 123
Schramm/Nienhuis (eds) Marine Benthic Vegetation
© Springer-Verlag Berlin Heidelberg 1996