lation of matter in nature functions only when these nutrient salts are continually
released. Without them, no plant growth could take place (Fig. 1). However, it is too
much of a good thing when more nutrients are introduced into bodies of water than
are used for good plant growth. As a result, these bodies of water are genuinely overfertilized, not eutrophized but hypertrophized, with the result that too lush a plant
growth results. If a farmer fertilized without farming, nothing but weeds would
be the result. In the sea, weeds cannot be pulled up. As a result of over-fertilization,
a flora results which is not always desirable because it displaces the normal algae
flora.
The North Sea receives nutrient imports from three sources: from the atmosphere,
from the Atlantic Ocean, and from rivers and coastal towns. By far the most important source are the currents which bring water from the Atlantic Ocean into the
North Sea: about 85% of all phosphorus input comes from the Atlantic. Rivers bring
about 15%, 800,000 t of nitrogen and 70,000 t of phosphorus per year. Nutrient
input from rivers has increased very much over the past decades.
The River Rhine, in 1932, brought approximately 3000 t of phosphorus to the estuarine region of the Netherlands. In 1955, the figure was 7000 t, in 1970,30,000 t
(Postma 1978). Most of this amount is from human activities. Evaluations for the
Federal Republic of Germany show that 40% of the phosphorus in rivers is from
detergents in washing ingredients, 27% from feces, 17% from agriculture (specially
from liquified feces and urine produced by modern cattle-raising operations), and 13%
from industrial sources. Evaluations from the W. German State Schleswig-Holstein
support the view that agricultural land use contributes only little compared with
domestic sewage: only 5% of the phosphorus and 32% of the nitrogen that go to the
Western Baltic are from agriculture plus natural groundwater, that is 100 g P/ha agricultural area. All the rest comes with domestic sewage or from small industry, with
a rate of 3 g P and 10 g N, for example, from each inhabitant of Kiel city per day
(Hoffmann 1979).
The purification of effluents by waste water treatment plants has only a limited effect
on this transportation of nutrients. Biological treatment plants hold back only around
a third of the phosphorus, because waste water bacteria set phosphorus compounds
free in dissolved form. Only by special chemical methods of waste water purification,
by precipitatio)1 with ferrous or aluminum sulfate, can nutrients effectively be
removed from effluents, and such measures are not applied with effluents to the
North Sea.
In the coastal areas of the southwestern North Sea and the German Bight, the concentrations of nutrients are high for this reason (Figs. 10 and 11). The question then
is, whether the increasing input of nutrients into the North Sea has an effect on
phytoplankton productivity, herbivore production, and fisheries yield. Unfortunately,
there are but few extensive long-term studies of nutrient concentrations and plankton, so that the effects of eutrophication can only be studied by a few examples.
There are calculations that primary production in the Southern Bight of the North
Sea and in the Dutch Wadden-Sea did increase (Postma 1978).
In the area around Helgoland, which is affected by the Elbe and Weser Rivers, the
amounts of phosphorus in the seawater have apparently increased (Fig. 12). If one
compares characteristic hydrographic situations during summer 1954 and summer
17
released. Without them, no plant growth could take place (Fig. 1). However, it is too
much of a good thing when more nutrients are introduced into bodies of water than
are used for good plant growth. As a result, these bodies of water are genuinely overfertilized, not eutrophized but hypertrophized, with the result that too lush a plant
growth results. If a farmer fertilized without farming, nothing but weeds would
be the result. In the sea, weeds cannot be pulled up. As a result of over-fertilization,
a flora results which is not always desirable because it displaces the normal algae
flora.
The North Sea receives nutrient imports from three sources: from the atmosphere,
from the Atlantic Ocean, and from rivers and coastal towns. By far the most important source are the currents which bring water from the Atlantic Ocean into the
North Sea: about 85% of all phosphorus input comes from the Atlantic. Rivers bring
about 15%, 800,000 t of nitrogen and 70,000 t of phosphorus per year. Nutrient
input from rivers has increased very much over the past decades.
The River Rhine, in 1932, brought approximately 3000 t of phosphorus to the estuarine region of the Netherlands. In 1955, the figure was 7000 t, in 1970,30,000 t
(Postma 1978). Most of this amount is from human activities. Evaluations for the
Federal Republic of Germany show that 40% of the phosphorus in rivers is from
detergents in washing ingredients, 27% from feces, 17% from agriculture (specially
from liquified feces and urine produced by modern cattle-raising operations), and 13%
from industrial sources. Evaluations from the W. German State Schleswig-Holstein
support the view that agricultural land use contributes only little compared with
domestic sewage: only 5% of the phosphorus and 32% of the nitrogen that go to the
Western Baltic are from agriculture plus natural groundwater, that is 100 g P/ha agricultural area. All the rest comes with domestic sewage or from small industry, with
a rate of 3 g P and 10 g N, for example, from each inhabitant of Kiel city per day
(Hoffmann 1979).
The purification of effluents by waste water treatment plants has only a limited effect
on this transportation of nutrients. Biological treatment plants hold back only around
a third of the phosphorus, because waste water bacteria set phosphorus compounds
free in dissolved form. Only by special chemical methods of waste water purification,
by precipitatio)1 with ferrous or aluminum sulfate, can nutrients effectively be
removed from effluents, and such measures are not applied with effluents to the
North Sea.
In the coastal areas of the southwestern North Sea and the German Bight, the concentrations of nutrients are high for this reason (Figs. 10 and 11). The question then
is, whether the increasing input of nutrients into the North Sea has an effect on
phytoplankton productivity, herbivore production, and fisheries yield. Unfortunately,
there are but few extensive long-term studies of nutrient concentrations and plankton, so that the effects of eutrophication can only be studied by a few examples.
There are calculations that primary production in the Southern Bight of the North
Sea and in the Dutch Wadden-Sea did increase (Postma 1978).
In the area around Helgoland, which is affected by the Elbe and Weser Rivers, the
amounts of phosphorus in the seawater have apparently increased (Fig. 12). If one
compares characteristic hydrographic situations during summer 1954 and summer
17