The Maracaibo System, Venezuela
51
and Doe 1964). In the strait, variations in oxygen content are rarely more
than 1.5 mll- 1 (Parra Pardi 1977) and surface water is frequently supersaturated due to algae blooms. Although the oxygen content in the water
column drops to 40% saturation at 10 m and 30% at 14m, anoxic conditions have not been reported.
3.2.3 Nutrients
The resuspension of bottom sediments is the principal source of nutrients in the gulf (0.2-0.4 mg atom per 1 P at surface; 1.0 mg atom per 1 P
at bottom), Tablazo Bay, and the strait. Elevated phosphorus levels in the
lake are largely due to terrestrial runoff. The saline wedge in the strait is
an important source of nitrogen compounds, which are added through
sewage discharge from Maracaibo City. Owing to sedimentation of organisms and slow outward circulation of the cone-shaped hypolimnion,
phosphorus concentrations tend to increase from surface ( 1.0- 10.32 mg
atom 1- 1 ) to depth (15.0-158mg atom 1- 1 ; Battelle 1974; Parra Pardi 1979;
Escam 1991). Phosphorus levels in the water column are likely to the control by bottom sediments and adsorption processes to them (LopezHernandez et al. 1980). The concentrations of nitrogen compounds follow
similar distribution patterns, with ammonia concentrations reaching
6 mg atom 1- 1 at 10m depth and exceeding 180 mg atom per 1 at the base
of the cone (Parra Pardi 1979). Based on the nitrogen balance in the lake
and on NIP ratios (Parra Pardi 1979), nitrogen is a limiting factor under
most conditions in the lake.
3.3 Biological Components
3.3.1 Benthic Communities
The species composition of littoral communities in the Maracaibo System
largely depends on salinity and on substrate characteristics (Rodriguez
1973). Dunes with a sparse cover of Hypomoea pes-caprae fringe the extensive sandy shores of the Gulf of Venezuela. The drift lines are characterized
by the presence of talictrid amphipods. Intertidal beaches are dominated
by the clam Donax striatus which in the mid-shore zone occurs together
with some nereid, capitellid, and spionid polychaetes, and on the lower
51
and Doe 1964). In the strait, variations in oxygen content are rarely more
than 1.5 mll- 1 (Parra Pardi 1977) and surface water is frequently supersaturated due to algae blooms. Although the oxygen content in the water
column drops to 40% saturation at 10 m and 30% at 14m, anoxic conditions have not been reported.
3.2.3 Nutrients
The resuspension of bottom sediments is the principal source of nutrients in the gulf (0.2-0.4 mg atom per 1 P at surface; 1.0 mg atom per 1 P
at bottom), Tablazo Bay, and the strait. Elevated phosphorus levels in the
lake are largely due to terrestrial runoff. The saline wedge in the strait is
an important source of nitrogen compounds, which are added through
sewage discharge from Maracaibo City. Owing to sedimentation of organisms and slow outward circulation of the cone-shaped hypolimnion,
phosphorus concentrations tend to increase from surface ( 1.0- 10.32 mg
atom 1- 1 ) to depth (15.0-158mg atom 1- 1 ; Battelle 1974; Parra Pardi 1979;
Escam 1991). Phosphorus levels in the water column are likely to the control by bottom sediments and adsorption processes to them (LopezHernandez et al. 1980). The concentrations of nitrogen compounds follow
similar distribution patterns, with ammonia concentrations reaching
6 mg atom 1- 1 at 10m depth and exceeding 180 mg atom per 1 at the base
of the cone (Parra Pardi 1979). Based on the nitrogen balance in the lake
and on NIP ratios (Parra Pardi 1979), nitrogen is a limiting factor under
most conditions in the lake.
3.3 Biological Components
3.3.1 Benthic Communities
The species composition of littoral communities in the Maracaibo System
largely depends on salinity and on substrate characteristics (Rodriguez
1973). Dunes with a sparse cover of Hypomoea pes-caprae fringe the extensive sandy shores of the Gulf of Venezuela. The drift lines are characterized
by the presence of talictrid amphipods. Intertidal beaches are dominated
by the clam Donax striatus which in the mid-shore zone occurs together
with some nereid, capitellid, and spionid polychaetes, and on the lower