The Estuary Ecosystem of Buenaventura Bay, Colombia
277
18.5.1 Pollution
The sewage contamination by Buenaventura City (Q=820 1 s- 1 ,
BOD 5 =14 tons day- 1 ) has introduced localized but pronounced structural
changes of the benthic soft-bottom community. In contrast to the impact
of sewage on the soft-bottom community structure elsewhere, chronic
contamination near most of the sewage outfalls in Buenaventura Bay has
led to an intertidal benthic soft-bottom community with few (1-10) species, low total density ( 0.48-14.56 in d. m- 2 ), and high evenness ( 0.44-0.99;
CAE 1995). Together, polychaetes (i.e., Capitella sp.), the fiddler crab Uca
spp., the snapper shrimp Alpheus columbiensis, and the jackknife clam
Tagelus sp. represent 82% of the total density with polychaetes accounting
for 59%. However, the benthic soft-bottom community is dominated by
Capitella sp. (90%) and nematodes around the main sewage outfall and
near the petroleum dock, respectively (Cantera et al.1992). In general, total
community biomass of impacted areas (2-4.5 g m- 2 ) exceeds that of nonimpacted areas ( 1.2-2 g m- 2 ).
Elevated heavy metal concentrations in waters and sediments at the
mouth of the Anchicaya and Dagua Rivers and around Buenaventura City
are largely a result of river discharge, land-runoff, and local sewage input
(T. Fernandez and A. Pion, unpubl. data). Additionally, dredging activities
and natural resuspension influence the relationship between metal concentrations in the water column and sediments (Univalle 1997; Cortez
1998). Heavy metal surveys of biological tissue in mangrove cockles (Anadara), catfish (Arius), and swimming crabs ( Callinectes) indicate concentrations close to permitted levels (Benitez 1995; Cortez 1998). Elevated
mercury (5-10 Jlg 1- 1 ) and lead (5-20 11g 1- 1 ) concentrations in the blood of
human populations living around Buenaventura Bay have been associated
with seafood preference and frequent consumption (Benitez 1995).
18.5.2 Exploitation
For more than 400 years mangrove timber has been an important economic resource for the region (Prahl et al. 1990). Cutting of mangroves
increased drastically during the 1960s, owing to demands by the leather
industry for tanning dyes contained in the bark of the red mangrove, which
led to intense exploitation of well-developed red mangrove forests
(10-15 em dbh). During the last 20 years, extensive mangrove areas were
cleared for shrimp aquaculture and agricultural activities (i.e. banana,
coconut, casaba). Today, the illegal cutting of mangrove trees represents up
to 30% of their total density in Buenaventura Bay (Blanco and Cantera
277
18.5.1 Pollution
The sewage contamination by Buenaventura City (Q=820 1 s- 1 ,
BOD 5 =14 tons day- 1 ) has introduced localized but pronounced structural
changes of the benthic soft-bottom community. In contrast to the impact
of sewage on the soft-bottom community structure elsewhere, chronic
contamination near most of the sewage outfalls in Buenaventura Bay has
led to an intertidal benthic soft-bottom community with few (1-10) species, low total density ( 0.48-14.56 in d. m- 2 ), and high evenness ( 0.44-0.99;
CAE 1995). Together, polychaetes (i.e., Capitella sp.), the fiddler crab Uca
spp., the snapper shrimp Alpheus columbiensis, and the jackknife clam
Tagelus sp. represent 82% of the total density with polychaetes accounting
for 59%. However, the benthic soft-bottom community is dominated by
Capitella sp. (90%) and nematodes around the main sewage outfall and
near the petroleum dock, respectively (Cantera et al.1992). In general, total
community biomass of impacted areas (2-4.5 g m- 2 ) exceeds that of nonimpacted areas ( 1.2-2 g m- 2 ).
Elevated heavy metal concentrations in waters and sediments at the
mouth of the Anchicaya and Dagua Rivers and around Buenaventura City
are largely a result of river discharge, land-runoff, and local sewage input
(T. Fernandez and A. Pion, unpubl. data). Additionally, dredging activities
and natural resuspension influence the relationship between metal concentrations in the water column and sediments (Univalle 1997; Cortez
1998). Heavy metal surveys of biological tissue in mangrove cockles (Anadara), catfish (Arius), and swimming crabs ( Callinectes) indicate concentrations close to permitted levels (Benitez 1995; Cortez 1998). Elevated
mercury (5-10 Jlg 1- 1 ) and lead (5-20 11g 1- 1 ) concentrations in the blood of
human populations living around Buenaventura Bay have been associated
with seafood preference and frequent consumption (Benitez 1995).
18.5.2 Exploitation
For more than 400 years mangrove timber has been an important economic resource for the region (Prahl et al. 1990). Cutting of mangroves
increased drastically during the 1960s, owing to demands by the leather
industry for tanning dyes contained in the bark of the red mangrove, which
led to intense exploitation of well-developed red mangrove forests
(10-15 em dbh). During the last 20 years, extensive mangrove areas were
cleared for shrimp aquaculture and agricultural activities (i.e. banana,
coconut, casaba). Today, the illegal cutting of mangrove trees represents up
to 30% of their total density in Buenaventura Bay (Blanco and Cantera