Evolution of water quality in a large eutrophic European estuary under changing pressures: past, present and future of the Scheldt Estuary

The freshwater Scheldt Estuary (Belgium), located in one of the most densely populated areas of Europe (over 500 inh./km²), is a highly eutrophic system currently recovering from hyper-eutrophication thanks to improved waste water treatment efforts. As a result, the ecosystem shifted from a respiration dominated system towards a more autotrophic system, causing a spectacular and rapid improvement of the water quality, especially documented by increased oxygen levels. However, focusing at the biogenic parameters in the water column, the freshwater Scheldt does not meet good water quality standards yet, and for the past 10 years, no important further improvement is recorded. On the contrary, there are indications of a declining quality again. This time, water quality from the catchment is no longer the major problem. Important hydrodynamic and geomorphologic changes caused by dredging, deepening, … what else? Activities in favor of navigation ( ) within the estuary itself seem to influence water quality. Altered residence times and a changing light climate can indeed strongly reduce pelagic primary production.