Distribution of particulate trace metal in the southern part of the Patos Lagoon estuary

Abstract

The analysis of suspended particles probably provides the best basis for assessing metal contamination of aquatic environments. However, such assessments cannot be made unless suf®cient knowledge of natural contributions to observed concentrations is available. As different coastal areas are in¯uenced by different natural inputs from their watersheds, assessments of natural versus anthropogenic contributions to metal concentrations must be made on a regional or site-speci®c basis. The purpose of this research was to assess whether anthropogenic inputs of heavy metals into the surrounding waters of Rio Grande City were large enough to signi®cantly affect concentrations in the southern part of the Patos Lagoon Estuary. Particulate samples were collected during 15 monthly cruises at seven ®xed stations from May 1990 to June 1991 and analyzed under different seasonal and hydrological conditions. Results show that the local inputs from urban, industrial and harbor activities in the city of Rio Grande have produced enrichments of copper, lead and zinc (but not iron) in suspended sediments in the three areas studied. The different behavior presented by these three areas are mainly due to hydrodynamic conditions and to distance from the harbor activities. Meteorological conditions which favor resuspension of bottom sediment, resulting in high total suspended matter concentrations, mask anthropogenic inputs.