Spatial and temporal changes in macrobenthic communities in the Amazon coastal zone (Guajará Estuary, Brazil) caused by discharge of urban effluents

Abstract

Spatial and temporal changes in the structure of soft-bottom macrobenthic communities caused by discharges of urban wastewater were studied in the Guajará 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 NH4) 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.