Benthic habitat characterisation in the upper Scheldt Estuary: a hydromorphological approach

Van Braeckel Alexander; Speybroeck Jeroen; Vanoverbeke Joost, Van Ryckegem Gunther & Van den Bergh Erika Benthic habitat characterisation in the upper Scheldt Estuary: a hydromorphological approachThe Scheldt Estuary faces future challenges with the expected increase of hydrological pressure caused by sea level rise. Morphological river modifications can reduce or amplify the expected ecological effects. This, together with a need for a more cost-effective monitoring tool, allowing inclusion of hydrodynamics in the evaluation is the basic rationale of this study. In order to develop such an improved tool a sampling campaign and an ecological modelling approach were set up to characterise the habitat of the benthic species and communities in inter- and subtidal habitats of the fresh and brackish parts of the Scheldt.Each macrobenthic sample has been related to flow velocities, soil morphology type, water depth, sediment characteristics and organic matter content. Multiple regression analyses reveal an ecologically unique subtidal benthic community typical for areas with low maximum flood velocity in shallower water. Additionally, at low tide, flood-dominated areas with low dynamics during ebb tide have been identified as preferred habitat of hyperbenthic species in the meandering single-channel part of the Scheldt.Based on the explanatory variables identified as statistically significant by the regression analysis, a new habitat typology is derived by threshold analysis of the most relevant variables in relation to macrobenthic density. The robustness of the typology is tested based on independent macrobenthic monitoring data (the Belgian-Dutch framework of MONEOS).Additionally, the flow velocities output of two different numerical models is used and compared. Based on the evaluation, the best typology and numerical model is chosen for future monitoring purposes. Compared to the present ecological typology, a hydrodynamic variable will be included to monitor the evolution of the habitats in the upper Scheldt Estuary. This will result in an improved, ecologically validated instrument for impact assessment of management measures and infrastructure works, such as dumping or channel widening. As such, abiotic data can allow defining mitigation measures to minimise the ecological impact of these measures.