The Itamaraca Estuarine Ecosystem, Brazil
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hot and humid (Koppen classification type Aws). The mean annual air temperature is 26 oc (mean range 2.8 °C) with a maximum of 34 oc and a minimum of 18 oc (Ratisbona 1976). The advance of maritime air masses over
the continent causes rainfall, which gradually decreases towards the inland.
Annual precipitation in the Itamaraca drainage area is 1,500-1,700 mm
(Medeiros 1991). During the rainy season (February to August), with mean
monthly rainfall of 180-212 mm, about 50% of the annual precipitation occurs between April and June (400mm month-'; Passavante 1981) and the
hydrological balance is strongly positive. Low mean monthly rainfall
(40-51 mm), evaporation exceeding precipitation, and a negative hydrologic balance characterize the dry season (September to January).
5.3 Hydrodynamics
Most of the freshwater is added to the northern branch of the Santa Cruz
Channel (94% during the dry season and 70% during the rainy season)
through the Catuama, Carrapicho, do Congo, Arataca, Botafogo, and Igarassu rivers, the last three being the major freshwater sources (Fig. 5.1).
Seasonal differences in precipitation (4.5x) and freshwater runoff (SOx)
are significant, with total average river discharge varying between
55.9 m 3 s- 1 at the peak of the rainy season and 0.8 m 3 s-1 at the peak of
the dry season. The overall freshwater balance (river discharge and direct
rainfall) in the Itamaraca system yields a freshwater input of 0.28 m 3 s- 1
during peak summer and 57.7 m 3 s- 1 during winter conditions, representing a 206-fold freshwater input to the system (Medeiros and Kjerfve
1993).
Tides in the Santa Cruz Channel are strongly semidiurnal (F=0.08-0.12).
The mean tidal range along the channel varies between 1.0 and 1.8 m (spring
1.4-2.2 m, neap 0.5-1.1 m) with lower ranges near the nodal point about
1.7 km north of Itapissuma Bridge (Medeiros 1991). Water elevation responds largely to tidal forcing with main diurnal and semidiurnal tidal constituents and shallow water overtides explaining 78 to 95 % of the total
variability. The remaining variability of water elevation is due to meteorological forcing and runoff (Medeiros and Kjerfve 1993). The amplitude and
phase of semidiurnal tides are identical at both entrances, with an amplitude of 88% and a phase lag of 15 min at Itapissuma Bridge (Fig. 5.1). Tides
propagating through the northern Catuama channel (1.5 km wide and 15m
deep) are subject to funneling and shoaling, and tidal amplitude attenuation
is more pronounced. Tides propagating through the southern Orange channel are only affected by shoaling, and phase shifts are more prominent. The
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hot and humid (Koppen classification type Aws). The mean annual air temperature is 26 oc (mean range 2.8 °C) with a maximum of 34 oc and a minimum of 18 oc (Ratisbona 1976). The advance of maritime air masses over
the continent causes rainfall, which gradually decreases towards the inland.
Annual precipitation in the Itamaraca drainage area is 1,500-1,700 mm
(Medeiros 1991). During the rainy season (February to August), with mean
monthly rainfall of 180-212 mm, about 50% of the annual precipitation occurs between April and June (400mm month-'; Passavante 1981) and the
hydrological balance is strongly positive. Low mean monthly rainfall
(40-51 mm), evaporation exceeding precipitation, and a negative hydrologic balance characterize the dry season (September to January).
5.3 Hydrodynamics
Most of the freshwater is added to the northern branch of the Santa Cruz
Channel (94% during the dry season and 70% during the rainy season)
through the Catuama, Carrapicho, do Congo, Arataca, Botafogo, and Igarassu rivers, the last three being the major freshwater sources (Fig. 5.1).
Seasonal differences in precipitation (4.5x) and freshwater runoff (SOx)
are significant, with total average river discharge varying between
55.9 m 3 s- 1 at the peak of the rainy season and 0.8 m 3 s-1 at the peak of
the dry season. The overall freshwater balance (river discharge and direct
rainfall) in the Itamaraca system yields a freshwater input of 0.28 m 3 s- 1
during peak summer and 57.7 m 3 s- 1 during winter conditions, representing a 206-fold freshwater input to the system (Medeiros and Kjerfve
1993).
Tides in the Santa Cruz Channel are strongly semidiurnal (F=0.08-0.12).
The mean tidal range along the channel varies between 1.0 and 1.8 m (spring
1.4-2.2 m, neap 0.5-1.1 m) with lower ranges near the nodal point about
1.7 km north of Itapissuma Bridge (Medeiros 1991). Water elevation responds largely to tidal forcing with main diurnal and semidiurnal tidal constituents and shallow water overtides explaining 78 to 95 % of the total
variability. The remaining variability of water elevation is due to meteorological forcing and runoff (Medeiros and Kjerfve 1993). The amplitude and
phase of semidiurnal tides are identical at both entrances, with an amplitude of 88% and a phase lag of 15 min at Itapissuma Bridge (Fig. 5.1). Tides
propagating through the northern Catuama channel (1.5 km wide and 15m
deep) are subject to funneling and shoaling, and tidal amplitude attenuation
is more pronounced. Tides propagating through the southern Orange channel are only affected by shoaling, and phase shifts are more prominent. The