48
R.H. Charlier and Th. Lonhienne
These compounds are, in part responsible for acid rain; (3) heavy beach
pollution resulting from algal strandings.
With increased eutrophication, "specialists" in resource competition
will be replaced by phytoplankton "generalists", then by poorly edible
primary producers. The positive aspect of nutrient increase leading to
more algae, more zooplankton, and hence more fishes certainly does not
hold true in highly eutrophicated areas (Riegman 1991).
There is no absolute evidence whether changes recorded in recent
years in the shelf system are the consequences of excess nutrient input,
the results of climatic cycles, or simply an effect of the improvement in
observation coverage. What is generally agreed upon are the considerable
detrimental effects of eutrophication. They outweigh by far the beneficial
effects such as an increased productivity or the removal of atmospheric
carbon dioxide by way of burial of organic matter. Increased fish yields have
been considered a positive effect, but realistic limits should notwithstanding
be set to allowable chemical pollution (Tatara 1981; Clark 1989).
Examining the causes of eutrophication, we note that nitrogen rather
than phosphorus is probably the limiting plant nutrient in the sea. Agriculture, the development of river beds and, in catchment basins, soil
erosion are major sources of eutrophication materials. Among other
factors involved are acceleration of river flow and drainage of wetlands,
with accumulation of sediments in estuaries as a result. Remedies needed
so that navigation is not impeded include dredging, and the deeper water
allows leaching of nutrients. Car emissions and energy conversion cause
"inadvertent" fixing of nitrogen, while pollution by toxins results in a
reduction of freshwater plants, and eventually the harmful, substances
are picked up by the marine phytoplankton. Additionally, touristic activities and the development of sandy areas generate quantities of untreated
wastes and lead, in the long term, to severe consequences.
2.2.1 Eutrophication, Dystrophication and Mediators
Two concepts should be introduced here. Dystrophication is the modification of the bacterial flora with the concurrent development of an
anoxic environment and hydrogen sulfide production, the final stages in
the eutrophication process. Toxic "red tides" result which may kill marine biota and even produce problems for humans. Plant- or animalproduced chemical "mediators" dispersed in the marine milieu influence
the behavior and physiology of these, or other species. Some are called
telemediators because they act from a considerable distance.
While it is widely held that the excessive contribution of nutrients to
sea waters are at the basis of marine eutrophication, some researcher!),
R.H. Charlier and Th. Lonhienne
These compounds are, in part responsible for acid rain; (3) heavy beach
pollution resulting from algal strandings.
With increased eutrophication, "specialists" in resource competition
will be replaced by phytoplankton "generalists", then by poorly edible
primary producers. The positive aspect of nutrient increase leading to
more algae, more zooplankton, and hence more fishes certainly does not
hold true in highly eutrophicated areas (Riegman 1991).
There is no absolute evidence whether changes recorded in recent
years in the shelf system are the consequences of excess nutrient input,
the results of climatic cycles, or simply an effect of the improvement in
observation coverage. What is generally agreed upon are the considerable
detrimental effects of eutrophication. They outweigh by far the beneficial
effects such as an increased productivity or the removal of atmospheric
carbon dioxide by way of burial of organic matter. Increased fish yields have
been considered a positive effect, but realistic limits should notwithstanding
be set to allowable chemical pollution (Tatara 1981; Clark 1989).
Examining the causes of eutrophication, we note that nitrogen rather
than phosphorus is probably the limiting plant nutrient in the sea. Agriculture, the development of river beds and, in catchment basins, soil
erosion are major sources of eutrophication materials. Among other
factors involved are acceleration of river flow and drainage of wetlands,
with accumulation of sediments in estuaries as a result. Remedies needed
so that navigation is not impeded include dredging, and the deeper water
allows leaching of nutrients. Car emissions and energy conversion cause
"inadvertent" fixing of nitrogen, while pollution by toxins results in a
reduction of freshwater plants, and eventually the harmful, substances
are picked up by the marine phytoplankton. Additionally, touristic activities and the development of sandy areas generate quantities of untreated
wastes and lead, in the long term, to severe consequences.
2.2.1 Eutrophication, Dystrophication and Mediators
Two concepts should be introduced here. Dystrophication is the modification of the bacterial flora with the concurrent development of an
anoxic environment and hydrogen sulfide production, the final stages in
the eutrophication process. Toxic "red tides" result which may kill marine biota and even produce problems for humans. Plant- or animalproduced chemical "mediators" dispersed in the marine milieu influence
the behavior and physiology of these, or other species. Some are called
telemediators because they act from a considerable distance.
While it is widely held that the excessive contribution of nutrients to
sea waters are at the basis of marine eutrophication, some researcher!),