Abstract
Spatial and temporal changes in the structure of soft-bottom macrobenthic communities caused by discharges of urban wastewater were studied in the Guajara Estuary, Amazon coastal zone, Brazil. Samples were taken during the dry and rainy seasons at five sites close to wastewater sources (impacted) and two sites further away from effluent discharges (non-impacted). Samples were collected using a Petersen grab (20×20×20 cm) and passed through a 0.3 mm mesh screen. At each site, several parameters were determined in order to characterize the water (pH, QOD and NH 4 ) and sediment (mean grain size diameter, %OM and heavy metals). The benthic fauna was composed of 22 taxa dominated by polychaetes and oligochaetes. The data indicate that environmental contamination has not resulted in a highly polluted environment with a significant reduction in fauna. It would seem that the river flow and intense hydrodynamics dilute and minimize the effects of contaminants in the estuary. The main effect of the discharge effluents was a favorable organic enrichment. The fauna at the impacted sites was generally more diverse than at the non-impacted sites, dominated by Oligochaeta Tubificinae, and showed greater spatial heterogeneity.
Highlights
Benthic organisms are among the first components of aquatic communities to respond to the effects of environmental disturbance due to their relatively sedentary nature and intimate contact with sediment and pollutants, and display varying degrees of tolerance to human disturbance (Rosenberg and Resh 1993).Spatial and temporal changes in the structure of benthic communities, such as the loss of species or changes382 D
Among the wide range of anthropogenic activities that affect the environmental quality of aquatic systems and their communities, the discharge of urban effluents is certainly one of the most frequent and harmful, given the multiplicity of the pollutants that they contain (Clark 2002)
Studies addressing the effects of pollution on benthic communities have been carried out for more than a century, especially in fresh water (Rosenberg and Resh 1993), and have intensified in recent decades in marine and estuarine environments (Kennish 1997), there are still few studies in Brazil and the rest of Latin America that analyze the environmental pressure in coastal zones (e.g. Elias et al 2003, Elias et al 2005, Pagliosa and Barbosa 2006)
Summary
Benthic organisms are among the first components of aquatic communities to respond to the effects of environmental disturbance due to their relatively sedentary nature and intimate contact with sediment and pollutants, and display varying degrees of tolerance to human disturbance (Rosenberg and Resh 1993).Spatial and temporal changes in the structure of benthic communities, such as the loss of species or changes382 D. Benthic organisms are among the first components of aquatic communities to respond to the effects of environmental disturbance due to their relatively sedentary nature and intimate contact with sediment and pollutants, and display varying degrees of tolerance to human disturbance (Rosenberg and Resh 1993). Studies addressing the effects of pollution on benthic communities have been carried out for more than a century, especially in fresh water (Rosenberg and Resh 1993), and have intensified in recent decades in marine and estuarine environments (Kennish 1997), there are still few studies in Brazil and the rest of Latin America that analyze the environmental pressure in coastal zones (e.g. Elias et al 2003, Elias et al 2005, Pagliosa and Barbosa 2006). Cause-and-effect relationships have only been recorded when the impact caused by pollution is obvious (Bemvenuti et al 2003, Venturini et al 2008) or in experimental studies (Mayer-Pinto and Junqueira 2003)
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