310
M.-L. De Casabianca
U sing this, approach, it was expected that species indicative of the
degree of eutrophication could be identified. Brackish zones show higher
degrees of eutrophication than marine zones, in which the occurrence of
indicator species can be used to analyze progressive eutrophication.
From a practical point of view, the ability to control the development of
these species prior to offshore eftluent discharge can be useful in the
fight against pollution.
13.2.1 Characteristics of the Lagoons and Study Methods
A lagoon may be characterized by its annual salinity variations which are
basically controlled by freshwater inputs and seawater intrusion for a
given topography.
From a topographical point of view, two types of lagoons can be
distinguished on the east coast of Corsica (De Casabianca-Chassany
1988; Fig. 13.2): (1) Deep and rounded basins of tectonic origin (Diana
and Urbino Lagoon, about 10 m deep and 550 and 750 ha surface area,
respectively); (2) basins isolated from shallow zones by a spit ofland, e.g.
the lagoons of Biguglia and Palo (1 m deep, 1600 and 250 ha, respectively). They are shallow, elongated and parallel to the coast line.
Other smaller lagoons can be included in one or the other of these
categories. As far as the freshwater input is concerned, the rainy period
lasts from October to April (700 to 1100 mm annual rainfall), the dry
season from May to October. Rainwater input into the deep basins is
low, whereas it is high but intermittent in the two shallow lagoons.
Sea water penetrates into the basins between rainy periods, and especially during the dry period before the lagoons become isolated from
the sea. This isolation may occur as the result of a lowering of the water
level in the lagoon and the silting up of the connecting canals between
the lagoon and the sea.
Due to these factor combinations, the first two lagoons are marinetype brackish lagoons, with little pluriannual variations (salinity
variations over a 5-year period for the Diana Lagoon 25-28 PSU, and for
the Urbino Lagoon, having the lowest freshwater input, 31-38 PSU which
is close to marine conditions).
The second type comprises brackish lagoons with large pluriannual
salinity variations (from 2 to 39 PSU at Biguglia, and 1 to 42 PSU at
Palo). Palo, the smaller lagoon, reacts with more pronounced extremes
compared to Biguglia Lagoon. An increasing gradient of variation (in
temperature and salinity) occurs from the centre towards the edges of
the lagoon, with an accumulation of detritus around the shores.
M.-L. De Casabianca
U sing this, approach, it was expected that species indicative of the
degree of eutrophication could be identified. Brackish zones show higher
degrees of eutrophication than marine zones, in which the occurrence of
indicator species can be used to analyze progressive eutrophication.
From a practical point of view, the ability to control the development of
these species prior to offshore eftluent discharge can be useful in the
fight against pollution.
13.2.1 Characteristics of the Lagoons and Study Methods
A lagoon may be characterized by its annual salinity variations which are
basically controlled by freshwater inputs and seawater intrusion for a
given topography.
From a topographical point of view, two types of lagoons can be
distinguished on the east coast of Corsica (De Casabianca-Chassany
1988; Fig. 13.2): (1) Deep and rounded basins of tectonic origin (Diana
and Urbino Lagoon, about 10 m deep and 550 and 750 ha surface area,
respectively); (2) basins isolated from shallow zones by a spit ofland, e.g.
the lagoons of Biguglia and Palo (1 m deep, 1600 and 250 ha, respectively). They are shallow, elongated and parallel to the coast line.
Other smaller lagoons can be included in one or the other of these
categories. As far as the freshwater input is concerned, the rainy period
lasts from October to April (700 to 1100 mm annual rainfall), the dry
season from May to October. Rainwater input into the deep basins is
low, whereas it is high but intermittent in the two shallow lagoons.
Sea water penetrates into the basins between rainy periods, and especially during the dry period before the lagoons become isolated from
the sea. This isolation may occur as the result of a lowering of the water
level in the lagoon and the silting up of the connecting canals between
the lagoon and the sea.
Due to these factor combinations, the first two lagoons are marinetype brackish lagoons, with little pluriannual variations (salinity
variations over a 5-year period for the Diana Lagoon 25-28 PSU, and for
the Urbino Lagoon, having the lowest freshwater input, 31-38 PSU which
is close to marine conditions).
The second type comprises brackish lagoons with large pluriannual
salinity variations (from 2 to 39 PSU at Biguglia, and 1 to 42 PSU at
Palo). Palo, the smaller lagoon, reacts with more pronounced extremes
compared to Biguglia Lagoon. An increasing gradient of variation (in
temperature and salinity) occurs from the centre towards the edges of
the lagoon, with an accumulation of detritus around the shores.