258
R.R. Twilley et a!.
associated with mangroves, P. californiensis, P. vannamei, and P. stylirostris are abundant, though it is uncertain whether the habitats enhance their
survival or their growth (Zimmerman and Minello 1986). After approximately 3 months, predominantly benthic adults (80-100mm length)
return to the coastal ocean to re-supply the estuary with a new generation
of post -larvae (Garcia 1985).
17.7 Human Impacts
Changes in environmental quality of the Gulf of Guayaquil and the Guayas
River estuary are associated with land use in upland and intertidal watersheds. Deforestation of natural vegetation, replacement by agro-ecosystems, and urban and industrial activities have changed the quality,
quantity, and seasonality of river discharge, thus influencing distribution
and turnover rates in the estuary and Gulf. The diversion of water for irrigation and industrial use after the construction of a dam at the Daule River
resulted in a loss of freshwater to the Guayas River ( 15%) and the Guayas
River estuary (13 %; Arriaga 1989). Urban areas and industry are associated with point-source chemical inputs. About 86% of 54.83 x 10 6 m 3 of
waste generated annually by 3.14 million people in the Guayas River basin
is discharged into the aquatic ecosystems. Domestic and industrial wastes
also introduce bacterial contamination and cause nutrient enrichment and
eutrophication (Solorzano 1989; Pin et al. 1998). Despite BOD values of
0.65-2.88 mg 1- 1 , anoxic waters are rare and only occur near sewage outfalls
of Guayaquil ( <2.7 mg 1- 1 ; Solorzano and Viteri 1981; Arriaga 1989; Solorzano 1989), because strong tides with large amplitude (3-5m) effectively
mix the water column in the Guayas River estuary. Irrigated agriculture
(approx. 175,000ha) in the Guayas River watershed is likely to introduce
agrotoxins; however, only traces of pesticides have been detected at the
beginning of the rainy season in the Daule River (Solorzano 1989). In contrast, mining activities in Guayas River basin add iron, copper
(36.92-94.52j.tgl- 1 ),and cadmium (0.1-14.5j.tg 1- 1 ) to the water column and
sediments of Babahoyo, Daule, and Guayas rivers. Copper (> 10 jlg 1- 1 ) and
cadmium concentrations in the water and mercury concentrations in sediments of the Guayas River estuary are reason for concern (Solorzano
1989).
Shrimp pond construction has caused loss in area and function of mangrove habitats (Fig. 17 .4; Twilley et al. 1997) and shrimp pond operation
(pumping, fertilization, dredging, harvest of post-larvae) has impacted the
environmental quality of the Gulf and Guayas River estuary (Csavas 1994).
R.R. Twilley et a!.
associated with mangroves, P. californiensis, P. vannamei, and P. stylirostris are abundant, though it is uncertain whether the habitats enhance their
survival or their growth (Zimmerman and Minello 1986). After approximately 3 months, predominantly benthic adults (80-100mm length)
return to the coastal ocean to re-supply the estuary with a new generation
of post -larvae (Garcia 1985).
17.7 Human Impacts
Changes in environmental quality of the Gulf of Guayaquil and the Guayas
River estuary are associated with land use in upland and intertidal watersheds. Deforestation of natural vegetation, replacement by agro-ecosystems, and urban and industrial activities have changed the quality,
quantity, and seasonality of river discharge, thus influencing distribution
and turnover rates in the estuary and Gulf. The diversion of water for irrigation and industrial use after the construction of a dam at the Daule River
resulted in a loss of freshwater to the Guayas River ( 15%) and the Guayas
River estuary (13 %; Arriaga 1989). Urban areas and industry are associated with point-source chemical inputs. About 86% of 54.83 x 10 6 m 3 of
waste generated annually by 3.14 million people in the Guayas River basin
is discharged into the aquatic ecosystems. Domestic and industrial wastes
also introduce bacterial contamination and cause nutrient enrichment and
eutrophication (Solorzano 1989; Pin et al. 1998). Despite BOD values of
0.65-2.88 mg 1- 1 , anoxic waters are rare and only occur near sewage outfalls
of Guayaquil ( <2.7 mg 1- 1 ; Solorzano and Viteri 1981; Arriaga 1989; Solorzano 1989), because strong tides with large amplitude (3-5m) effectively
mix the water column in the Guayas River estuary. Irrigated agriculture
(approx. 175,000ha) in the Guayas River watershed is likely to introduce
agrotoxins; however, only traces of pesticides have been detected at the
beginning of the rainy season in the Daule River (Solorzano 1989). In contrast, mining activities in Guayas River basin add iron, copper
(36.92-94.52j.tgl- 1 ),and cadmium (0.1-14.5j.tg 1- 1 ) to the water column and
sediments of Babahoyo, Daule, and Guayas rivers. Copper (> 10 jlg 1- 1 ) and
cadmium concentrations in the water and mercury concentrations in sediments of the Guayas River estuary are reason for concern (Solorzano
1989).
Shrimp pond construction has caused loss in area and function of mangrove habitats (Fig. 17 .4; Twilley et al. 1997) and shrimp pond operation
(pumping, fertilization, dredging, harvest of post-larvae) has impacted the
environmental quality of the Gulf and Guayas River estuary (Csavas 1994).