Derweduwen, J.

Devriese, L.

Dewitte, B.

Fettweis, M.

Hostens, K.

Martens, C.

Robbens, J.

Van Hoey, G.

Van Lancker, V.

Open Marine Archive

Dredged material disposal: does it substantially affect the 
ecosystem? 
Van Hoey Gert1, Jozefien Derweduwen1, Lisa Devriese1, Bavo Dewitte1, Michael Fettweis2,  
Kris Hostens1, Chantal Martens3, Johan Robbens2 and Vera Van Lancker2 
1 Institute for Agricultural and Fisheries Research (ILVO), Bio-Environmental Research group and 
Chemical monitoring and Product Technology, Ankerstraat 1, B-8400 Oostende, Belgium 
E-mail: gert.vanhoey@ilvo.vlaanderen.be  
2 Management Unit of the North Sea Mathematical Models, Gulledelle 100, B-1200 Brussels, Belgium 
3 Maritime Access Division, Tavernierkaai 3, B-2000 Antwerpen, Belgium 
 
 
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 harbours throughout the year (ca. 10 million tonnes dry matter per 
year). This dredged material is disposed at 5 designated areas, in total 16 km² or 0.44% of the BPNS 
surface. The disposal of dredged material may have effects on the water surface, in the water 
column and on the seabed (MEMG, 2003). Several studies show that the fine sediment plumes that 
originate from dredge disposal have a noticeable effect outside of the disposal areas (Fettweis et al., 
2003; 2011). The sediment plumes influence the turbidity of the water column and results in an 
increase of the suspended sediment concentration near the bed suggesting the formation of fluid 
mud layers at the site and in its neighbourhood. The size of the seabed surface that is impacted by 
the disposal depends on the hydrodynamic conditions and the composition of the disposed material 
(Van Lancker et al., 2011). Chemical contaminants can be released in the water and sediment 
through disposal of dredged material, leading to changes in the chemical environment. For the 
BPNS, however, the concentrations of heavy metals, PCBs and pesticides only slightly differed 
between control and impact sites, with a small increase noted at 2 disposal sites (Van Hoey et al., 
2011). Also, the accumulation of pollutants in marine organisms at the disposal sites seems to be 
minimal. The disposal activity results further in habitat modifications at certain sites and 
smothering of the benthic life. This is most visible at the frequently used disposal site Br&W S1, 
where the extent of the Abra alba habitat is slightly reduced and the benthic diversity and 
abundance is lower than expected (Van Hoey et al., 2011). On the other hand, the disposal activity 
can invoke a slight increase in benthic diversity, as observed at the disposal site Br&W S2, but also 
in the far field of Br&W S1. The deposition of fine sediments (silt) in a naturally more sandy area 
(Vlakte van de Raan) seems to favour several ‘mud loving’ opportunistic species. 
The research at the dredge disposal sites indicates some local and neighbouring effects on the 
ecosystem (Lauwaert et al., 2011). 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. If this approach is applied 
to all human activities on the BPNS, we will have made a giant step towards sustainable 
management of our marine ecosystem. 
 
 
References  
Fettweis M. and D. Van den Eynde. 2003. The mud deposits and the high turbidity in the Belgian-
Dutch coastal zone, Southern Bight of the North Sea. Continental Shelf Research 23:669-691. 
Fettweis M., M. Baeye, F. Francken, B. Lauwaert, D. Van den Eynde, V. Van Lancker, C. Martens and 
T. Michielsen. 2011. Monitoring the effects of disposal of fine sediments from maintenance 
dredging on suspended particulate matter concentration in the Belgian nearshore area 
(southern North Sea). Marine Pollution Bulletin 62:258-269.  
Lauwaert B., R. Delgado, J. Derweduwen, L. Devriese-, M. Fettweis, K. Hostens, J. Janssens, 
C. Martens, J. Robbens, S. Timmermans, G. Van Hoey and T. Verwaest. 2011. Synthesis report 
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on the effects of dredged material disposal on the marine environment (licensing period 2010-
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and chemical effects of the disposal of dredged material in the Belgian Part of the North Sea 
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Van Lancker V., M. Baeye, I. Du Four, S. Degraer, M. Fettweis, F. Francken, J-S. Houziaux, P. Luyten, 
D. Van den Eynde, M. Devolder, K. De Cauwer, J. Monbaliu, E. Toorman, J. Portilla, A. Ullman, M. 
Liste Muñoz, L. Fernandez, H. Komijani, T. Verwaest, R. Delgado, J. De Schutter, J. Janssens, 
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Dredged material disposal: does it substantially affect the ecosystem?

Dredged material disposal: does it substantially affect the ecosystem?

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