Résumé
The Sado estuary is located on the western coast of Portugal, 40 km south of Lisbon. The present study was undertaken in areas where major dredging activities are planned in relation to harbour development. Investigations of benthic macrofauna assemblages and ecotoxicological effects from sediments collected at the Entrance Channel and the Northern Channel were undertaken as part of a sediment quality assessment prior to a dredging programme.
The macrofaunal study was based on the analysis of species richness and abundance. Benthic assemblages were identified through cluster and ordination analysis and compared to baseline data. Species richness and abundance showed spatial gradients very similar to those identified previously. The present data showed a richer amphipod fauna associated with cleaner sediments, marine species typical from coarse clean sediments and fewer species associated with organic enrichment.
The ecotoxicology study was based on acute and chronic whole sediment tests with the amphipod Corophium multisetosum and sub-lethal sediment elutriate tests with the sea urchin Paracentrotus lividus. The results showed that the sediments do not present potential toxicity to the organisms tested. These conclusions agree with the results from the macrofauna survey, which illustrated rich, diverse and well-defined gradients. Concerning sediment quality, none of these components impose constraints to dredging. A biodiversity loss resulting from species substitutions may be expected in this area of the estuary.