56
R.H. Charlier and Th. Lonhienne
rocky bottom macro algae, especially red algae, numerous
invertebrates, and at least ten fish species. In the fish-raising basins
rainbow trout and salmon suffered huge losses, mussels became toxic,
and the pelagic fish biomass dropped drastically during the periods of
low oxygen concentrations.
Chronic eutrophication of several coastal areas in the North Sea led to
both an increase in primary production and the doubling of the macrobenthic biomass in the Wadden Sea. The algal biomass increases and
thereby increases the amount of organic matter that sinks to the bottom.
The thus enhanced activity of the benthos results in an increased oxygen
demand of the sediments (Lancelot et al. 1987; Smayda 1990).
Although eutrophication has occurred in the past, as shown by the
historical record, its increase is significant during the last 20 years (Billen
1991a,b). It is perhaps premature to preliminarily conclude that the
phenomenon is not man-induced. Based upon an idealized river-ecology
model, phosphate concentrations increase as coastal areas develop, the
ratio P:N climbs and nitrogen becomes the limiting factor for algal
growth. Concentration increases with urbanization but may drop as a
consequence of denitrification. Hence coastal anthropogenic eutrophication may well develop in two stages: urbanization first, secondary waste
water purification next.
During the last decade, nutrient presence has practically trebled in the
North Sea. The major part came from large rivers crossing industrial
regions, and is accumulated by the water masses moving from the Southern sector of the channels to the German Bight (Fig. 2.6). Exceptional
blooms have been due to Phaeocytis, an alga that develops each year in
ever-increasing quantity, specifically along the coasts of Belgium, The
Netherlands, and Germany (Fig. 2.7). Phaeocytis pouchetti is implicated
in DMS production (Fig. 2.8). Increased eutrophication has been held
responsible for repeated blooms in the Kiel Bight since May 1983. A new
skeletonless form of Dictyocha speculum, resulting from adaptation to
higher NISi ratios, is responsible for large fish kills.
Large blooms, followed by thanatocoenosis, have been signaled in the
Belt Sea and the German Bight. As remains of Ceratium accumulate on
the sea floor anoxia results. In addition, blooms of Ceratium trip os have
been detected in the New York area. While causes have not been elucidated, there is a strong suspicion that eutrophication is the culprit.
Weather has an important influence. 1988 was named "Red Seas"
because blooms were exceptional, obviouly favored by a mild winter with
abundant precipitation. Rain and higher temperatures favored Phaeocytis
blooms. This alga changes from a unicell to form large flagellum-less
colonies (5 to 10% of individuals) enrobed in a self-secreted polysacchar-
R.H. Charlier and Th. Lonhienne
rocky bottom macro algae, especially red algae, numerous
invertebrates, and at least ten fish species. In the fish-raising basins
rainbow trout and salmon suffered huge losses, mussels became toxic,
and the pelagic fish biomass dropped drastically during the periods of
low oxygen concentrations.
Chronic eutrophication of several coastal areas in the North Sea led to
both an increase in primary production and the doubling of the macrobenthic biomass in the Wadden Sea. The algal biomass increases and
thereby increases the amount of organic matter that sinks to the bottom.
The thus enhanced activity of the benthos results in an increased oxygen
demand of the sediments (Lancelot et al. 1987; Smayda 1990).
Although eutrophication has occurred in the past, as shown by the
historical record, its increase is significant during the last 20 years (Billen
1991a,b). It is perhaps premature to preliminarily conclude that the
phenomenon is not man-induced. Based upon an idealized river-ecology
model, phosphate concentrations increase as coastal areas develop, the
ratio P:N climbs and nitrogen becomes the limiting factor for algal
growth. Concentration increases with urbanization but may drop as a
consequence of denitrification. Hence coastal anthropogenic eutrophication may well develop in two stages: urbanization first, secondary waste
water purification next.
During the last decade, nutrient presence has practically trebled in the
North Sea. The major part came from large rivers crossing industrial
regions, and is accumulated by the water masses moving from the Southern sector of the channels to the German Bight (Fig. 2.6). Exceptional
blooms have been due to Phaeocytis, an alga that develops each year in
ever-increasing quantity, specifically along the coasts of Belgium, The
Netherlands, and Germany (Fig. 2.7). Phaeocytis pouchetti is implicated
in DMS production (Fig. 2.8). Increased eutrophication has been held
responsible for repeated blooms in the Kiel Bight since May 1983. A new
skeletonless form of Dictyocha speculum, resulting from adaptation to
higher NISi ratios, is responsible for large fish kills.
Large blooms, followed by thanatocoenosis, have been signaled in the
Belt Sea and the German Bight. As remains of Ceratium accumulate on
the sea floor anoxia results. In addition, blooms of Ceratium trip os have
been detected in the New York area. While causes have not been elucidated, there is a strong suspicion that eutrophication is the culprit.
Weather has an important influence. 1988 was named "Red Seas"
because blooms were exceptional, obviouly favored by a mild winter with
abundant precipitation. Rain and higher temperatures favored Phaeocytis
blooms. This alga changes from a unicell to form large flagellum-less
colonies (5 to 10% of individuals) enrobed in a self-secreted polysacchar-