32
Gilberto Rodriguez
Table 2.2. Nitrogen balance in
the lake
Amount of nitrogen (x 10 6 kg d- 1 )
Import from rivers
0.21
Import through the Strait
0.1
Outflow to the sea
0.07 - 0.4
Storage
0.09 - 0.16
duction occurs. In this sector Battelle Memorial Institute (1974) found at one station a
mean of 4.38 g C m- 2 d-', but occasionally values over 10 g C m- 2 d-' were found in two
localities within this area. The high productivity is the result of the large algal blooms,
with peak values of 18 mg 1-' in chlorophyll content (Escam 1991). These algal blooms
have also been document through the analysis of remote sensing data using Landsat
satellite imagery (Fundacion Instituto de Ingenieria 1991).
From the data on productivity and chlorophyll content, Delft Hydraulics and
Haskoning (1991) has calculated the total nitrogen requirement for primary production to be 5 x 10 6 kg N d-', and the mineralization 1.1 x 10 6 kg N d-'. According to these
values the import of nitrogen given above is largely insufficient for the nitrogen metabolism in the lake, and a self supporting mechanism is postulated as the origin of a
nitrogen pool in the lake.
2.8
Conclusions
The Maracaibo system consists of three interactive bodies of water: an oligohaline lake,
a deep strait and a shallow semienclosed bay. The final discharge to the adjacent
sea occurs through a narrow mouth, at present dredged to 14 m. Since this discharge
influences the pattern of currents in the Gulf, the brackish water in the whole system extends for more than 220 km. The hydrography of this system is constrained
by its geomorphology: An extensive intermontane north-facing valley, open to the
trade winds. This setting causes the moisture to be displaced southward over the
slopes of the sierras, producing a heavy rainfall which drains on one corner of the
lake. The force and position of the streams set in movement a counter-clockwise
current, allowing only a fraction of the circulating water to escape as a thin upper
layer through the sharply stratified Strait, while the salinity in the hypolimnium is
increased by the saline wedge that enters the lake through the action of the semidiurnal
tides and the seasonal changes in the hydraulic balance. The oligohaline water from
the lake spreads into the shallow semi-enclosed Tablazo Bay where its salinity is increased by the mixing processes caused by the tides. The final discharge into the water through a narrow mouth establish a two-cell estuarine circulation in the Gulf of
Venezuela.
The circular current in the lake creates a cone-shaped hypolimnium that acts as a
trap for the nutrients. This nutrient pool account for the large productivity of the lake
which is considered as one of the most productive areas in the world. Management
and pollution control has to take into account the peculiar dynamics of this large water
reservoir.
Gilberto Rodriguez
Table 2.2. Nitrogen balance in
the lake
Amount of nitrogen (x 10 6 kg d- 1 )
Import from rivers
0.21
Import through the Strait
0.1
Outflow to the sea
0.07 - 0.4
Storage
0.09 - 0.16
duction occurs. In this sector Battelle Memorial Institute (1974) found at one station a
mean of 4.38 g C m- 2 d-', but occasionally values over 10 g C m- 2 d-' were found in two
localities within this area. The high productivity is the result of the large algal blooms,
with peak values of 18 mg 1-' in chlorophyll content (Escam 1991). These algal blooms
have also been document through the analysis of remote sensing data using Landsat
satellite imagery (Fundacion Instituto de Ingenieria 1991).
From the data on productivity and chlorophyll content, Delft Hydraulics and
Haskoning (1991) has calculated the total nitrogen requirement for primary production to be 5 x 10 6 kg N d-', and the mineralization 1.1 x 10 6 kg N d-'. According to these
values the import of nitrogen given above is largely insufficient for the nitrogen metabolism in the lake, and a self supporting mechanism is postulated as the origin of a
nitrogen pool in the lake.
2.8
Conclusions
The Maracaibo system consists of three interactive bodies of water: an oligohaline lake,
a deep strait and a shallow semienclosed bay. The final discharge to the adjacent
sea occurs through a narrow mouth, at present dredged to 14 m. Since this discharge
influences the pattern of currents in the Gulf, the brackish water in the whole system extends for more than 220 km. The hydrography of this system is constrained
by its geomorphology: An extensive intermontane north-facing valley, open to the
trade winds. This setting causes the moisture to be displaced southward over the
slopes of the sierras, producing a heavy rainfall which drains on one corner of the
lake. The force and position of the streams set in movement a counter-clockwise
current, allowing only a fraction of the circulating water to escape as a thin upper
layer through the sharply stratified Strait, while the salinity in the hypolimnium is
increased by the saline wedge that enters the lake through the action of the semidiurnal
tides and the seasonal changes in the hydraulic balance. The oligohaline water from
the lake spreads into the shallow semi-enclosed Tablazo Bay where its salinity is increased by the mixing processes caused by the tides. The final discharge into the water through a narrow mouth establish a two-cell estuarine circulation in the Gulf of
Venezuela.
The circular current in the lake creates a cone-shaped hypolimnium that acts as a
trap for the nutrients. This nutrient pool account for the large productivity of the lake
which is considered as one of the most productive areas in the world. Management
and pollution control has to take into account the peculiar dynamics of this large water
reservoir.