Dredged material disposal: Does it substantially affect the ecosystem?

To counter the degradation of marine ecosystems, a variety of legislative measurements are being developed, mainly under the umbrella of the Marine Strategy Framework Directive (MSFD). The policy behind this is to ensure that human activities are performed in a sustainable way, which means that the impact of all human activities on the marine system has to be scrutinized. Which human activities have a substantial, not sustainable effect on our marine ecosystem? To avoid a subjective debate, the sustainability of those activities has to be scientifically evaluated from an ecological and socio-economic point of view.
In this study, we illustrate a sustainability assessment of one human activity, namely ‘dredge disposal’ on the Belgian Part of the North Sea (BPNS). Substantial dredging activities take place in the navigation channels and harbors throughout the year. This dredged material is disposed at 5 designated areas (16 km²). The disposal of dredged material may have effects on the water surface, in the water column and on the seabed. These effects are followed up in a joint monitoring program and a two-yearly integrated assessment is made, which is a good basis for confident sustainability evaluation.
The research at the dredge disposal sites indicates some local (biodiversity changes due to habitat modification) and neighboring (increase of turbidity, a wider settling of the sediment plume) effects on the ecosystem. However, from a socio-economical point of view, it is clear that the dredging and disposal activity on the BPNS cannot be halted. By combining both views and all available information we can judge the sustainability of dredge disposal and determine its operational limits. If this approach is applied to all human activities on the BPNS, we will have made a great step towards sustainable management of our marine ecosystem.