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J.G. Tundisi and T. Matsumura-Tundisi
Ribeira de Iguape River and the Cananeia Sea to facilitate navigation and
transportation in the northern part of the estuary system. Freshwater
from the Ribeira de Iguape River drainage basin (23,350 km 2 ) began to discharge through the Valo Grande channel into the lagoon region. The action
of the river gradually widened the channel (250m), which has become the
principal tributary (mean annual input 435m 3 s- 1 ) to the lagoon region.
After the closure of the Valo Grande channel (1978-1995), the salinity in
the lagoon system changed from a minimum of 0-22 and a maximum of
14-33 to 16-30 and 26-34, respectively (de Camargo 1987). As a consequence, during the last 150 years the input of freshwater and the introduction of sediments into the system have modified physiographic and hydrologic characteristics, which influence biological structure and ecological
functions of the lagoon region.
The general pattern of water circulation in the main channels and small
rivers (Fig. 9.1; Tessler and Souza 1998) depends on tides that enter the
Barra de Cananeia and Icaparra (Myiao et al. 1986). Tides are semidiurnal
(with a diurnal inequality; Mesquita 1983). The mean tidal amplitude is
0.8m and surface current velocities ranged from 0.7 to 0.8m s- 1 , though
during low tide surface velocities may reach 1.2 m s- 1 in the Cananeia Sea
channel near the entrance. Residual flux, probably freshwater from rivers
and creeks, is dammed by inflowing coastal water (Myiao 1977). Tidal propagation is a coupling of progressive and stationary waves, thus Cananeia
is a partially stratified estuary. The vertical structure is more stratified
near the open channels (Trapande Bay, Cubatao Sea) and less stratified
upstream, with almost all upstream salt flux due to turbulent diffusion
(Myiao et al. 1986; da Miranda et al. 1995; Fig. 9.3).
Dissolved oxygen concentrations are highest ( 80-90 o/o) in the large
channels, such as Trapande Bay or the Cananeia Sea, while concentrations
decrease to 20-30 o/o in small rivers and channels, due to large amounts
of mangrove-originated organic matter and decomposition processes
(Teixeira et al. 1965; Kato 1966; Myiao et al. 1986). Diurnal dissolved oxygen at the surface may fluctuate between 120 and 10-20 o/o at day and night,
respectively. Dissolved inorganic nutrients tend to be low. Higher values
of dissolved inorganic phosphate during high tide might be a result of
nutrient addition by coastal waters or re-suspension and transport of
bottom sediments by tidal action (Myiao et al. 1986). Low correlation
between dissolved inorganic phosphate, nitrate, and nitrite concentrations
and salinity suggests different sources of nutrients, regeneration, and distribution. The large contribution of decomposing mangrove litter (Gerlach
1958; Kato 1966) plays a fundamental role for the nutrient cycles.
J.G. Tundisi and T. Matsumura-Tundisi
Ribeira de Iguape River and the Cananeia Sea to facilitate navigation and
transportation in the northern part of the estuary system. Freshwater
from the Ribeira de Iguape River drainage basin (23,350 km 2 ) began to discharge through the Valo Grande channel into the lagoon region. The action
of the river gradually widened the channel (250m), which has become the
principal tributary (mean annual input 435m 3 s- 1 ) to the lagoon region.
After the closure of the Valo Grande channel (1978-1995), the salinity in
the lagoon system changed from a minimum of 0-22 and a maximum of
14-33 to 16-30 and 26-34, respectively (de Camargo 1987). As a consequence, during the last 150 years the input of freshwater and the introduction of sediments into the system have modified physiographic and hydrologic characteristics, which influence biological structure and ecological
functions of the lagoon region.
The general pattern of water circulation in the main channels and small
rivers (Fig. 9.1; Tessler and Souza 1998) depends on tides that enter the
Barra de Cananeia and Icaparra (Myiao et al. 1986). Tides are semidiurnal
(with a diurnal inequality; Mesquita 1983). The mean tidal amplitude is
0.8m and surface current velocities ranged from 0.7 to 0.8m s- 1 , though
during low tide surface velocities may reach 1.2 m s- 1 in the Cananeia Sea
channel near the entrance. Residual flux, probably freshwater from rivers
and creeks, is dammed by inflowing coastal water (Myiao 1977). Tidal propagation is a coupling of progressive and stationary waves, thus Cananeia
is a partially stratified estuary. The vertical structure is more stratified
near the open channels (Trapande Bay, Cubatao Sea) and less stratified
upstream, with almost all upstream salt flux due to turbulent diffusion
(Myiao et al. 1986; da Miranda et al. 1995; Fig. 9.3).
Dissolved oxygen concentrations are highest ( 80-90 o/o) in the large
channels, such as Trapande Bay or the Cananeia Sea, while concentrations
decrease to 20-30 o/o in small rivers and channels, due to large amounts
of mangrove-originated organic matter and decomposition processes
(Teixeira et al. 1965; Kato 1966; Myiao et al. 1986). Diurnal dissolved oxygen at the surface may fluctuate between 120 and 10-20 o/o at day and night,
respectively. Dissolved inorganic nutrients tend to be low. Higher values
of dissolved inorganic phosphate during high tide might be a result of
nutrient addition by coastal waters or re-suspension and transport of
bottom sediments by tidal action (Myiao et al. 1986). Low correlation
between dissolved inorganic phosphate, nitrate, and nitrite concentrations
and salinity suggests different sources of nutrients, regeneration, and distribution. The large contribution of decomposing mangrove litter (Gerlach
1958; Kato 1966) plays a fundamental role for the nutrient cycles.