The Estuary Ecosystem of Buenaventura Bay, Colombia
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channel (1-2m s- 1 ) and lower velocities in the inner bay and creeks
(0.2-l.Om s- 1 ).
At high slack water, salinity ranges from 18-27 at the mouth of Buenaventura Bay (Punta Soldado) to 4.8 at the Dagua River inlet in the inner
bay. During low slack water, the freshwater discharge of Anchicaya River
produces a low salinity zone (5) at the southern coast of the bay and traps
seawater (19.8-21) near the northern shore. Salinities are predominantly
stratified at the mouth of the rivers and also along the southern coast,
especially at high tide (surface salinity 9.4 and at 13m depth 20.5). Stratification is weak and occasionally homogeneous in the navigation channel
and at the mouth of the bay, thus Buenaventura Bay can be considered a
partially mixed estuary (circulation 3.08; stratification 0.62; Kjerfve 1990).
Surface water temperatures experience annual variations between April
(28 oc) and October (30.2 oc), with higher temperatures occurring during
flood tides ( +4 °C) though vertical temperature fluctuation ( <2 °C) is
not significant (CAE 1995). Anomalous temperatures ( + 3.5 oc) in the inner
bay (October 1997) appear to be related to the occurrence of El Nino
events (Univalle 1997). Water turbidity increases between the mouth
(27-30 mg l- 1 ) and the inner bay (40 mg l- 1 ), owing to high total suspended
sediment (TSS) input by rivers (i.e., Dagua 116mg l- 1 ) and trapping of
freshwater during ebb flow. The high suspension load accounts for mean
water transparencies of 91.75±20.11 em. Phytoplankton biomass peaks
may further decrease transparency (50 em) and cause high attenuation (up
to 60 %) of light.
The dissolved oxygen concentrations in the bay (5.5-10mg l- 1 ) tend to
increase towards the mouth and during high tide and rainy seasons. The
pH of the waters is alkaline (pH 7.2-8.5) but decomposition processes near
mangrove habitats (Cantera 1993; Univalle 1997) and sewage discharge
of Buenaventura City into the inner bay may lower the pH to 5.0-6.2
(CAE 1995). Nutrient concentrations in Buenaventura Bay (peak N0 3
0.539mg I- 1 ; mean N0 2 0.03mg I- 1 ; mean NH 4 0.221 mg l- 1 ; peak P0 4
0.160mg l- 1 ; Si0 4 0.75-1.64mg l- 1 ) increase with land-runoff. In trapping
zones at the mouth of creeks (N0 3 1.5-8.9mg I- 1 , P0 4 0.1-0.Smg l- 1 , Si0 4
0.9-1.8 mg l- 1 ) and falls of rivers (N0 3 0.5-3 mg I- 1 , P0 4 0.1-0.5 mg l- 1 , Si0 4
0.7-6.4mg l- 1 ) concentrations are five to ten times higher than in the outer
bay, with a clear tendency to augment upstream (Cantera 1993).
267
channel (1-2m s- 1 ) and lower velocities in the inner bay and creeks
(0.2-l.Om s- 1 ).
At high slack water, salinity ranges from 18-27 at the mouth of Buenaventura Bay (Punta Soldado) to 4.8 at the Dagua River inlet in the inner
bay. During low slack water, the freshwater discharge of Anchicaya River
produces a low salinity zone (5) at the southern coast of the bay and traps
seawater (19.8-21) near the northern shore. Salinities are predominantly
stratified at the mouth of the rivers and also along the southern coast,
especially at high tide (surface salinity 9.4 and at 13m depth 20.5). Stratification is weak and occasionally homogeneous in the navigation channel
and at the mouth of the bay, thus Buenaventura Bay can be considered a
partially mixed estuary (circulation 3.08; stratification 0.62; Kjerfve 1990).
Surface water temperatures experience annual variations between April
(28 oc) and October (30.2 oc), with higher temperatures occurring during
flood tides ( +4 °C) though vertical temperature fluctuation ( <2 °C) is
not significant (CAE 1995). Anomalous temperatures ( + 3.5 oc) in the inner
bay (October 1997) appear to be related to the occurrence of El Nino
events (Univalle 1997). Water turbidity increases between the mouth
(27-30 mg l- 1 ) and the inner bay (40 mg l- 1 ), owing to high total suspended
sediment (TSS) input by rivers (i.e., Dagua 116mg l- 1 ) and trapping of
freshwater during ebb flow. The high suspension load accounts for mean
water transparencies of 91.75±20.11 em. Phytoplankton biomass peaks
may further decrease transparency (50 em) and cause high attenuation (up
to 60 %) of light.
The dissolved oxygen concentrations in the bay (5.5-10mg l- 1 ) tend to
increase towards the mouth and during high tide and rainy seasons. The
pH of the waters is alkaline (pH 7.2-8.5) but decomposition processes near
mangrove habitats (Cantera 1993; Univalle 1997) and sewage discharge
of Buenaventura City into the inner bay may lower the pH to 5.0-6.2
(CAE 1995). Nutrient concentrations in Buenaventura Bay (peak N0 3
0.539mg I- 1 ; mean N0 2 0.03mg I- 1 ; mean NH 4 0.221 mg l- 1 ; peak P0 4
0.160mg l- 1 ; Si0 4 0.75-1.64mg l- 1 ) increase with land-runoff. In trapping
zones at the mouth of creeks (N0 3 1.5-8.9mg I- 1 , P0 4 0.1-0.Smg l- 1 , Si0 4
0.9-1.8 mg l- 1 ) and falls of rivers (N0 3 0.5-3 mg I- 1 , P0 4 0.1-0.5 mg l- 1 , Si0 4
0.7-6.4mg l- 1 ) concentrations are five to ten times higher than in the outer
bay, with a clear tendency to augment upstream (Cantera 1993).