sea except in unusual circumstances and then in those immediate areas where domestic effluents are introduced into seawater.
The city of Marseilles pours around 4 t of detergents into the Mediterranean daily. In
the vicinity of the point of introduction, the concentration of detergents is 0.5 mg/l;
at a distance of 6 km the concentration drops to 0.01 mg/l.
In those areas where the concentrations are over 0.1 mg/l, the brown alga Cystoseira
ceases to be present in the shore areas. Farther away, at concentrations of 0.020.05 mg/l, the first signs of a change in the flora become noticeable (Bellan 1976).
In the areas of the mouths of the Elbe and Weser River in Germany, concentrations
are approximately 0.3 mg/l, so that here too effects should be noticed. However, it is
difficult to distinguish the effects of detergents in nature from the influences of
other effluents (see Chap. 2.9).
2.8 Residual Heat
Marine life is found in temperatures that range from - 2°C in the Antarctic and in
deep sea regions, to 40°-50°C in tropical shallow areas with strong exposure to the
sun's rays. However, temperatures between 32° and 34°C have a fatal effect on most
tropical marine life. Basically, it cannot be said that marine life flourishes better at
low temperatures than say, at 28°C; on the contrary, metabolism, growth, and reproduction are more intensive at higher temperatures. Why then is the warming of bodies
of water by the residual heat from power plants and other industrial plants a problem
that is so passionately argued?
As is the case with the introduction of domestic effluents, the overall order is essential. When large amounts of warm water heat up a small body of water, the maximum
temperature which water organisms can stand is quickly surpassed. Naturally, this
depends on the particular adaptability of the organisms. In deep ocean water, even at
scarcely 100 m, many animals are subject to a narrow range of cold temperatures
similar to those in a freshwater wellstream. Year in and year out, the temperature
varies but little, and animals and plants are damaged and die if the surrounding temperature should vary even minimally. Fortunately, the organism community in river
mouth areas and placid sea coasts is adaptable to a wider range of temperatures.
There, the water temperature varies with the season even more than the 1 ° to 18°C
range found for example in the open North Sea. In intertidal areas it falls to temperatures below the freezing point in icy winters and rises to temperatures of 30°C and
more under the summer sun. Those organisms which live close to the shore are capable
of tolerating the vascillations of temperature, as long as they do not occur suddenly,
and if they permit a period of adaptation.
When a new power plant is to be built in a coastal Central Europe area and seawater
is to be used for cooling, the stipulation is generally made that the temperature difference that results after mixing is not to exceed 2°C and that in the peak heat season
the water temperature is not to rise above 26°C. Both of these extremes are around
1°C lower than the recommended temperatures for freshwater. Based on experience
to date, they seem to be reasonable rules of thumb for temperate regions; at least
until research into the effects of existing power plants furnishes a better basis of
measurement. In the tropics, however, an increase of l.SoC may be lethal.
29
The city of Marseilles pours around 4 t of detergents into the Mediterranean daily. In
the vicinity of the point of introduction, the concentration of detergents is 0.5 mg/l;
at a distance of 6 km the concentration drops to 0.01 mg/l.
In those areas where the concentrations are over 0.1 mg/l, the brown alga Cystoseira
ceases to be present in the shore areas. Farther away, at concentrations of 0.020.05 mg/l, the first signs of a change in the flora become noticeable (Bellan 1976).
In the areas of the mouths of the Elbe and Weser River in Germany, concentrations
are approximately 0.3 mg/l, so that here too effects should be noticed. However, it is
difficult to distinguish the effects of detergents in nature from the influences of
other effluents (see Chap. 2.9).
2.8 Residual Heat
Marine life is found in temperatures that range from - 2°C in the Antarctic and in
deep sea regions, to 40°-50°C in tropical shallow areas with strong exposure to the
sun's rays. However, temperatures between 32° and 34°C have a fatal effect on most
tropical marine life. Basically, it cannot be said that marine life flourishes better at
low temperatures than say, at 28°C; on the contrary, metabolism, growth, and reproduction are more intensive at higher temperatures. Why then is the warming of bodies
of water by the residual heat from power plants and other industrial plants a problem
that is so passionately argued?
As is the case with the introduction of domestic effluents, the overall order is essential. When large amounts of warm water heat up a small body of water, the maximum
temperature which water organisms can stand is quickly surpassed. Naturally, this
depends on the particular adaptability of the organisms. In deep ocean water, even at
scarcely 100 m, many animals are subject to a narrow range of cold temperatures
similar to those in a freshwater wellstream. Year in and year out, the temperature
varies but little, and animals and plants are damaged and die if the surrounding temperature should vary even minimally. Fortunately, the organism community in river
mouth areas and placid sea coasts is adaptable to a wider range of temperatures.
There, the water temperature varies with the season even more than the 1 ° to 18°C
range found for example in the open North Sea. In intertidal areas it falls to temperatures below the freezing point in icy winters and rises to temperatures of 30°C and
more under the summer sun. Those organisms which live close to the shore are capable
of tolerating the vascillations of temperature, as long as they do not occur suddenly,
and if they permit a period of adaptation.
When a new power plant is to be built in a coastal Central Europe area and seawater
is to be used for cooling, the stipulation is generally made that the temperature difference that results after mixing is not to exceed 2°C and that in the peak heat season
the water temperature is not to rise above 26°C. Both of these extremes are around
1°C lower than the recommended temperatures for freshwater. Based on experience
to date, they seem to be reasonable rules of thumb for temperate regions; at least
until research into the effects of existing power plants furnishes a better basis of
measurement. In the tropics, however, an increase of l.SoC may be lethal.
29