P_Bataillard_et_al.mp4

Recording of presentations at the Suricates project closing conference

Title : Agronomic beneficial use of dredged sediments from the Rance estuary: desalination rate and fertility potential

Authors : Luca SITTONI*1 1 Societa’ Italiana Dragaggi (SIDRA – DEME Group), via Carlo Zucchi 25, 00165, Rome (Italy) * Corresponding author e-mail: sittoni.luca@deme-group.com

Summary :

In 2014, the Lyvet sediment trap was created on a former mudflat in an upstream part of the Rance estuary, to limit silting upstream of the estuary. The same year, the La Hisse transit site was created for disposal of the dredged sediment. The site is composed of seven lagoons with a total capacity of 100,000 m3, for draining the salt from the sediments. The Rance estuary sediments dredged from the Lyvet trap and stored on the La Hisse site are currently mostly used as amendment in agriculture. This solution is not optimal for operational reasons, as it takes several years for the sediment to desalinate and its massive, pasty structure makes it difficult to apply to the soil. In addition, it requires finding agricultural plots to receive the sediment as part of a spreading plan. To avoid these constraints, BRGM has explored the possibility of transforming the sediment into topsoil that could be made available to farmers, developers and landscapers.

Pilot plots were set up on the La Hisse site in April 2022. The aim is to carry out full-scale tests to assess the structure and fertility improvement of the Rance estuary sediment after mixing with organic matter and a fine clay fraction. The system comprises 4 flat plots, each 4 m square and separated by approximately 0.5 m (Figure 1a). In each plot, the soil on the site was replaced by the mixtures of sediment and amendments (Figure 1b) to a depth of 50 cm. The pilot plots were sown 4 months after their installation (Figure 1c)

The compaction of the mixtures was monitored thanks to a precise topographical record of the plots. After 8 months, the biomass produced on the plots was harvested and destructive coring was carried out in the plots. After observation of the cores, samples were collected for salinity measurement by leaching, analysis of agronomic parameters (grain size, cation exchange capacity, organic carbon, Olsen phosphorus), as well as quantification of aggregates and measurement of their stability. The results acquired so far show that the use of amendments significantly improves biomass production on the plots, as well as the bulk density of the constructed soil.

Acknowledgements: The SURICATES project is funded by the European Regional Development Fund (ERDF) as part of the Interreg NWE programme 2014-2020