The Management of Eutrophicated Waters
51
Algal blooms are currently common in Europe along coasts in the
Mediterranean, Atlantic, The Channel, North Sea and Baltic. The Venice
lagoon has a 15kgm- 2 biomass (dry matter) and mixed-bag annual algal
production of 1 million metric tonnes dry matter. On the French Atlantic
coasts densities may reach 240 kg m -2 and a thickness of 1 m
(Figs. 2.3,2.4). On some parts of the Mediterranean densities of 5 kg m- 2
are not unusual; densities may reach 10 kg m -2 and algal decay may
destroy an important part of the fauna. Biomass densities off the coast of
south-east England are 2 kg m -2, and off Ireland are 45 kg m -2. In Germany, the Isle of Sylt is particularly affected, and the literature is replete
with examples from Norway, Scotland, The Netherlands, Spain and Portugal (Reise 1983; Chassany de Casabianca 1984; Lowthion et al. 1985;
Montgomery et al. 1985).
In Italy, severe problems have been reported for example in Orbetello, north of Rome, and in the Venice lagoon. In Orbetello, algal
proliferation competes with fisheries and is detrimental to the tourist
trade of the area. Algae, in particular Chaetomorpha or Cladophora, are
a mere nuisance, there being no economic utilization of their biomass.
Cut, picked up, transferred to trucks, they are dumped inland, making
heaps infested by insects and left to rot. Near the city of the doges,
Gracilaria is manually harvested and used for agar-agar extraction.
Besides the types mentioned, blooms of Ulva and Valonia species are
not uncommon.
Eutrophication in European waters is generally believed to be mainly
man-caused by increase in wastes. Nutrients taken on by the seas have
two major and one less important origin: (1) nutrients carried by streams
and rivers and coming from domestic and industrial "used" water, as well
as the leaching by rainwater of fertilized soil; (2) nutrients contributed by
the atmosphere contained in rainwater, and by nitrogen fixation by bluegreen algae or cyanobacteria; and (3) nutrients contributed by artificial
fish ponds, namely, fish excreta and food surplus.
Surrounded by industrialized countries, with a restricted communication with the ocean, the Baltic Sea is rich in nutrients brought by rivers
and by the atmosphere (NHt, NOn. Nitrogen fixation by blue-green
algae is not negligible. It is estimated that since 1900, inorganic phosphorus has increased eightfold and inorganic nitrogen fourfold. Phosphate increases have been stemmed through a concerted effort to treat
used waters. Fertilizers used on farms remain the culprits for a continued
increase in nitrogen.
Blooms are recurrent during the entire vegatative period, i.e. spring
and summer. They were already reported at the end of the nineteenth
century, and were similar to those of the 1980s.
51
Algal blooms are currently common in Europe along coasts in the
Mediterranean, Atlantic, The Channel, North Sea and Baltic. The Venice
lagoon has a 15kgm- 2 biomass (dry matter) and mixed-bag annual algal
production of 1 million metric tonnes dry matter. On the French Atlantic
coasts densities may reach 240 kg m -2 and a thickness of 1 m
(Figs. 2.3,2.4). On some parts of the Mediterranean densities of 5 kg m- 2
are not unusual; densities may reach 10 kg m -2 and algal decay may
destroy an important part of the fauna. Biomass densities off the coast of
south-east England are 2 kg m -2, and off Ireland are 45 kg m -2. In Germany, the Isle of Sylt is particularly affected, and the literature is replete
with examples from Norway, Scotland, The Netherlands, Spain and Portugal (Reise 1983; Chassany de Casabianca 1984; Lowthion et al. 1985;
Montgomery et al. 1985).
In Italy, severe problems have been reported for example in Orbetello, north of Rome, and in the Venice lagoon. In Orbetello, algal
proliferation competes with fisheries and is detrimental to the tourist
trade of the area. Algae, in particular Chaetomorpha or Cladophora, are
a mere nuisance, there being no economic utilization of their biomass.
Cut, picked up, transferred to trucks, they are dumped inland, making
heaps infested by insects and left to rot. Near the city of the doges,
Gracilaria is manually harvested and used for agar-agar extraction.
Besides the types mentioned, blooms of Ulva and Valonia species are
not uncommon.
Eutrophication in European waters is generally believed to be mainly
man-caused by increase in wastes. Nutrients taken on by the seas have
two major and one less important origin: (1) nutrients carried by streams
and rivers and coming from domestic and industrial "used" water, as well
as the leaching by rainwater of fertilized soil; (2) nutrients contributed by
the atmosphere contained in rainwater, and by nitrogen fixation by bluegreen algae or cyanobacteria; and (3) nutrients contributed by artificial
fish ponds, namely, fish excreta and food surplus.
Surrounded by industrialized countries, with a restricted communication with the ocean, the Baltic Sea is rich in nutrients brought by rivers
and by the atmosphere (NHt, NOn. Nitrogen fixation by blue-green
algae is not negligible. It is estimated that since 1900, inorganic phosphorus has increased eightfold and inorganic nitrogen fourfold. Phosphate increases have been stemmed through a concerted effort to treat
used waters. Fertilizers used on farms remain the culprits for a continued
increase in nitrogen.
Blooms are recurrent during the entire vegatative period, i.e. spring
and summer. They were already reported at the end of the nineteenth
century, and were similar to those of the 1980s.