so
G. Rodriguez
3.2.2 Physico-chemical Characteristics
Water temperatures follow a seasonal pattern, with an extreme minimum
mean temperature of 29.0 °C at 1 meter depth in the lake in February and a
maximum temperature of 32.5 °C in September. Highest water temperatures occur in the strait, occasionally exceeding air temperature by 20 °C. The
water column in the Gulf of Venezuela is only slightly stratified, with a
maximum temperature difference of 1.4 °C at 20m in March.
The lowest salinity (0.02) in the Maracaibo System occurs at the mouth
of the Catatumbo River in the lake. About 7 km off the coast, surface water
(<1m) salinity is 1.3 but values increase to 2-3 at deeper layers (Hyne et al.
1979). The brackish water, which enters the lake through the strait, moves
close to the bottom towards the deeper portions and contributes to the
saline cone-shaped hypolimnion in the center of the lake. The cone is a
permanent feature of the lake (Parra Pardi 1983; Escam 1991) though its
volume, which may represent up to 25 o/o of the total lake volume, changes
seasonally with input of brackish water from the strait or freshwater
discharge from the rivers. The counterclockwise circulation of the cone
moves brackish water towards the epilimnion where it becomes completely mixed. Salinity distributions in the strait, Tablazo Bay, and the southern
part of the gulf are typical of partially mixed estuaries. The tidal movements produce cyclic oscillations and periodic mixing, which result invertical and longitudinal gradients. Seasonal maximum and minimum salinities occur from February to May and from June to August, respectively.
Salinities in the Limon River estuary at the northwest corner of Tablazo
Bay may vary between 0.1 and 8 in the wet and dry season, respectively
(Rodriguez 1973). Salinity stratification in the navigation channel of Tablazo Bay and the strait is related to the intrusion of a saline wedge from
the gulf. The discharge of water from the estuarine region (i.e., strait and
Tablazo Bay) principally effects the southern part of the gulf, where an isohaline (30) usually forms in a SW-NE direction at 6-7 m depth. Pronounced stratification, with a salinity of 2 at 12m depth, occurs at the SW corner of the gulf. In the outer gulf (approximately 120° N) salinity differences
between surface and 60 m depth are less than 0.1.
Anoxic conditions may occur in a large area (up to 50 km across) in the
hypolimnion of the lake when the water column becomes completely stratified (Gessner 1953; Parra Pardi 1979). The oxygen content in the epilimnion varies little (Escam 1991). Lowest concentrations under limited inflow
of saline water are common in December, when the base of the cone is
reduced and the apex approaches the surface. Under these conditions, the
volume of the hypolimnion is reduced and the water is mixed (Redfield
G. Rodriguez
3.2.2 Physico-chemical Characteristics
Water temperatures follow a seasonal pattern, with an extreme minimum
mean temperature of 29.0 °C at 1 meter depth in the lake in February and a
maximum temperature of 32.5 °C in September. Highest water temperatures occur in the strait, occasionally exceeding air temperature by 20 °C. The
water column in the Gulf of Venezuela is only slightly stratified, with a
maximum temperature difference of 1.4 °C at 20m in March.
The lowest salinity (0.02) in the Maracaibo System occurs at the mouth
of the Catatumbo River in the lake. About 7 km off the coast, surface water
(<1m) salinity is 1.3 but values increase to 2-3 at deeper layers (Hyne et al.
1979). The brackish water, which enters the lake through the strait, moves
close to the bottom towards the deeper portions and contributes to the
saline cone-shaped hypolimnion in the center of the lake. The cone is a
permanent feature of the lake (Parra Pardi 1983; Escam 1991) though its
volume, which may represent up to 25 o/o of the total lake volume, changes
seasonally with input of brackish water from the strait or freshwater
discharge from the rivers. The counterclockwise circulation of the cone
moves brackish water towards the epilimnion where it becomes completely mixed. Salinity distributions in the strait, Tablazo Bay, and the southern
part of the gulf are typical of partially mixed estuaries. The tidal movements produce cyclic oscillations and periodic mixing, which result invertical and longitudinal gradients. Seasonal maximum and minimum salinities occur from February to May and from June to August, respectively.
Salinities in the Limon River estuary at the northwest corner of Tablazo
Bay may vary between 0.1 and 8 in the wet and dry season, respectively
(Rodriguez 1973). Salinity stratification in the navigation channel of Tablazo Bay and the strait is related to the intrusion of a saline wedge from
the gulf. The discharge of water from the estuarine region (i.e., strait and
Tablazo Bay) principally effects the southern part of the gulf, where an isohaline (30) usually forms in a SW-NE direction at 6-7 m depth. Pronounced stratification, with a salinity of 2 at 12m depth, occurs at the SW corner of the gulf. In the outer gulf (approximately 120° N) salinity differences
between surface and 60 m depth are less than 0.1.
Anoxic conditions may occur in a large area (up to 50 km across) in the
hypolimnion of the lake when the water column becomes completely stratified (Gessner 1953; Parra Pardi 1979). The oxygen content in the epilimnion varies little (Escam 1991). Lowest concentrations under limited inflow
of saline water are common in December, when the base of the cone is
reduced and the apex approaches the surface. Under these conditions, the
volume of the hypolimnion is reduced and the water is mixed (Redfield