Research project landscape mounds

Risks, ecological development prospects and management
of mounds made of brackish dredged silt

Period: 2000-2006

Aim of the project

The overarching objective of this research was the development of a practically feasible and scientifically well-founded concept for the construction and maintenance of dredged sediment mounds. The mounds must impound as much silt as possible (i.e. they must be as high as possible) and have an optimal buffering effect, be aesthetically pleasing, and be ecologically attractive.

Ecotoxicological aims

The ability to assess and control the ecotoxicological risks was an essential condition for all potential applications of dredged silt, including landscaping and nature development. Mounds of dredged material may only play a buffer role if they themselves are not a burden on their environment. This required a multidisciplinary approach in which constructional aspects, ecotoxicology, forestry and ecology all played an important role.

Sites

The possibilities to use contaminated dredged material for landscape construction were investigated on an experimental mound in the port of Antwerp. Additional data were gathered on several older disposal sites.

Ecotoxicological results

Ecotoxicological modelling revealed that the bulk quality of the dredged material from the Antwerp harbor docks does not pose human risks when dikes are used for recreation. Metal accumulating plant species like willow or poplar should be avoided because metals can be mobilized by leaf uptake and litter fall. Phytoextraction using trees was not possible; whereas phytostabilisation seemed a good option when appropriate species are chosen.

Ecological development

Spontaneous development and a cut/removal regime were also tested and proved to be valuable management alternatives to afforestation under certain conditions. It was concluded that sediment mounds can be used as a buffer area between zones with incompatible functions and can become a functional part of the ecological infrastructure in the port area.

Overall conclusion

If we now return to the central question of "Is it possible to assume that landscape development using dredged silt is a policy option”, we are able to say that during the course of the project no scientific arguments were found that excludes this form of re-use. Certain conditions must be met and a number of guidelines be complied with to guaranty the safety and satisfactory functioning of the landscape mounds in terms of buffering and ecology. The final report of this research project was finished in October, 2006. Further documents produced during the research can be found and downloaded on the download page.