260
P. Dion and S. Le Bozec
Salomon 1988; Menesguen 1990; Piriou and Menesguen 1992). With the
help of this model it was possible to quantify the limiting role of N for
growth, and to predict relationships between Nand P flows and green
tide development in the Bay of St. Brieuc.
Reducing the nitrogen input at the river basin level is undoubtedly the
most suitable way (if not the only one available) to prevent green tides in
the long term. This solution, however, introduces serious short-term
economical problems, in particular when intensive agriculture is the
main source of nutrients, as is the case in Brittany. The effects of phosphate removal in wastewater treatment plants have been monitored as an
alternative solution in the Bay of St. Brieuc over a period of 5 years.
Despite a 50% reduction in the total phosphorus load and a considerable
reduction (60%) in tissue phosphorus levels in Ulva sp., mass development of green algae continued to occur (CEVA, unpubl.).
9.3 Other Cases of Eutrophication
Along the French Coast
9.3.1 The Bay of Arcachon
The Bay of Arcachon in southwestern France is an example of a relatively
closed marine bay, where mass proliferation of green macro algae occurs.
The area of the bay (150 km 2 ) is divided at low tide into three NE-SW
oriented main channels, which are connected with the Atlantic Ocean
through a strait (Fig. 9.6). The total low tide area of the main and
secondary channels is about one-third of the total Bay area (cf. Auby
et al. 1994).
The Bay of Arcachon is well known for its attractive landscape, favouring an important seasonal touristic economy. The bay is urbanized,
and crowded in summer. The other basis of the local economy is
mariculture, in particular oyster cultivation, producing 15 000 to 20 000 t
of oysters per year.
The general topographic conditions in the bay and the tidal regime
allow oyster production in the intertidal zone and the presence of 7000 ha
of seagrass meadows (Zostera noltii) whies colonize mobile sand and the
mud substratum.
Macroalgal mass blooms have been occurring in the Bay of Arcachon
for many years, but they have become conspicuous only recently, because of increased production of green algae in the water body, and the
P. Dion and S. Le Bozec
Salomon 1988; Menesguen 1990; Piriou and Menesguen 1992). With the
help of this model it was possible to quantify the limiting role of N for
growth, and to predict relationships between Nand P flows and green
tide development in the Bay of St. Brieuc.
Reducing the nitrogen input at the river basin level is undoubtedly the
most suitable way (if not the only one available) to prevent green tides in
the long term. This solution, however, introduces serious short-term
economical problems, in particular when intensive agriculture is the
main source of nutrients, as is the case in Brittany. The effects of phosphate removal in wastewater treatment plants have been monitored as an
alternative solution in the Bay of St. Brieuc over a period of 5 years.
Despite a 50% reduction in the total phosphorus load and a considerable
reduction (60%) in tissue phosphorus levels in Ulva sp., mass development of green algae continued to occur (CEVA, unpubl.).
9.3 Other Cases of Eutrophication
Along the French Coast
9.3.1 The Bay of Arcachon
The Bay of Arcachon in southwestern France is an example of a relatively
closed marine bay, where mass proliferation of green macro algae occurs.
The area of the bay (150 km 2 ) is divided at low tide into three NE-SW
oriented main channels, which are connected with the Atlantic Ocean
through a strait (Fig. 9.6). The total low tide area of the main and
secondary channels is about one-third of the total Bay area (cf. Auby
et al. 1994).
The Bay of Arcachon is well known for its attractive landscape, favouring an important seasonal touristic economy. The bay is urbanized,
and crowded in summer. The other basis of the local economy is
mariculture, in particular oyster cultivation, producing 15 000 to 20 000 t
of oysters per year.
The general topographic conditions in the bay and the tidal regime
allow oyster production in the intertidal zone and the presence of 7000 ha
of seagrass meadows (Zostera noltii) whies colonize mobile sand and the
mud substratum.
Macroalgal mass blooms have been occurring in the Bay of Arcachon
for many years, but they have become conspicuous only recently, because of increased production of green algae in the water body, and the