The ecological effects of deep sand extraction on the Dutch continental shelf. Implications for future extraction

On the Dutch continental shelf, approximately 26 million m3 of marine sand is extracted each year which may increase up to 40 to 85 million m3 to counteract sea-level rise. For Maasvlakte 2 (MV2), a seaward harbour extension of the Port of Rotterdam 220 million m3 of sand was used. The Dutch authorities permitted 20 m deep sand extraction depth instead of the common 2 m to decrease the surface area of direct impact.

We studied the effects of deep sand extraction (20 m) and compared these with Dutch sand extraction case studies with intermediate and shallow extraction depths. We observed significant changes in faunal species composition and sediment characteristics in the deep areas of the MV2 borrow pit. Biomass of macrozoobenthos increased 7-12 fold and demersal fish biomass increased 20-fold in the deep areas. Macrozoobenthos and demersal fish correlated with sediment and hydrographic characteristics and time after cessation of sand extraction.

Ecological and bed shear stress data were combined and transformed into Ecosystem-based design (EBD) rules which can be used in the design phases of future borrow pits in order to simultaneously maximise the sand yield and decrease the surface area of direct impact.