Ecological effects and opportunities of deep sand extraction

Abstract

For Maasvlakte 2 (MV2), a seaward harbour extension of the Port of Rotterdam, 220 million m3 of sand was extracted in a 15 km2 large area with water depths of 20 m and sand extraction depths up to 20 m. We studied the ecological effects and compared these with other sand extraction case-studies with intermediate and shallow extraction depths on the Dutch continental shelf (DCS). We observed significant short-term changes in faunal species composition and sediment characteristics in the 40 m deep MV2 borrow pit. Biomass of macrozoobenthos and demersal fish biomass increased on average 10 to 20-fold in the deep areas 2 years after extraction. Macrozoobenthos and demersal fish distribution 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 maximize the sand yield and decrease the surface area of direct impact. The EBD rules can be applicable in other regions than the DCS depending on the extraction depth, hydrodynamic regime, and the supply of suspended matter. For areas outside Europe, ecological data for comparable deep sand extraction sites may be necessary. In general, the EBD rules can help to even make large-scale and deep sand extraction sustainable by mitigating or preventing related processes with potential negative impacts.

Full text

Ecological effects and
opportunities of deep
sand extraction
Maarten de Jong (BwN)
Bas Borsje (Deltares, TU Twente)
Martin Baptist (Wageningen Marine Research)
Daan Rijks (Boskalis)

Sand extraction DCS
•Past: avg. y-1: 26 Mm3, nourishments: 12 Mm3
0
20
40
60
80
100
120
140
Volume sand (Mm3)
•Recent: MV2: 220 Mm3 + Sandmotor: 21.5 Mm3
•Future: Nourishments w.r.t. sea level rise → 40–85 Mm3 y-1?

Sand extraction on DCS and PhD research
4 “Case studies” on DCS:
1
1. 2 m ex. depth
2
2
2. 8 m deepened shipping lane
3
3
3. MV2 pit (20-24 m ex. depth)
MV2 (2), a large harbour
extension of the PoR: 220 Mm3
4
4. Ecological landscaping

Methods of research (2009-2012)
•Macrobenthos and sediment
(Box core)
•Macrobenthos on the seabed
(bottom dredge)
•Fish (Beam trawl)
•Multibeam images

Ecological effects sand extraction
•Shallow extraction  recovery 2-4 y. (van Dalfsen et al. 2000)
•Deep extraction  changes in species comp. white furrow
shell (
Abra alba
) and plaice (
Platessa platessa
)
and
peaks of
10-20 times > biomass (de Jong et al. 2014, 2015)
•and > fine sediment + > sedimentation rate (de Jong et
al. 2014, 2015)
•Ecological landscaping  changes in ecology (de Jong et
al. 2014, 2015)

Ecosystem-based design (EBD) rules
Ecology + bed shear stress ( 𝜏𝑏 2D)
𝜏𝑏 2D: Force exerted by flowing water on the seabed surface area

Conclusions
•> Ext. depth  > changes in species composition and
biomass + > recovery time but also < surface area of
disturbance (de Jong et al. 2014, 2015 a,b)
•Include sand extraction in the assessment of effects of
mega-nourishments such as the Sandmotor

Maarten de Jong | Marine Ecologist
+31 6 44598167 | mfdejong@hotmail.com
mfdejong4.wixsite.com/de-jong-consultancy
De Jong
EcoLogical Consultancy
Questions