Assessment of estuarine macrobenthic assemblages and ecological quality status at a dredging site in a southern Europe estuary

Abstract

The Water Framework Directive (WFD) strengthened the need for the protection and enhancement of Ecological Quality Status (EQS) in water bodies of EU Member States. However, in terms of the EQS assessment, there is a lack of detailed studies that assess the consequences of dredging, especially concerning macrobenthic communities. Therefore, the main objective of this study was to evaluate the EQS assessment, as important need to WFD, based on diversity and ecological quality indices after dredging activity.Data was collected in Mondego estuary, Portugal, between October 2007 and November 2008, within and around the area to be dredged (3 ha): one dredging occasion and ten sampling dates along one year. Physical–chemical changes were examined. The relative performance of Margalef, Shannon–Wienner, AMBI–AZTI Marine Biotic Index and the multimetric BAT –Benthic Assessment Tool (BAT) were analyzed before and after dredging.In the first days, dredging increased the share of fine and coarse sand sediment and had changed TSS, POM and SOM, affecting the macrofauna assemblages. Two months after the dredging, the number of taxa, density, diversity and ecological indices showed similar values to pre-dredging conditions and one year later the number of species and density values almost duplicated. However, the macrofauna composition and structure were still significantly different in relation to pre-dredging and the biomass values did not return to the original values. Nevertheless, BAT was sensitive to the changes that occurred in the area, showing that the system recovered to pre-dredging values after one year, in terms of EQS. The present work reinforced the robustness of BAT as an accurate ecological quality assessment tool.