To assess the situation prior to the large-scale and deep sand extraction for the construction of MV2, data were collected by NIOZ and IMARES in the framework of the baseline study for the Environmental Impact Assessment (EIA). The EIA was commissioned by the Port of Rotterdam (PoR) and investigates (ecological) effects of the Maasvlakte 2 project. A set of 470 boxcorer and bottom sledge samples from the baseline monitoring campaign of PoR was selected from data collected in April-June 2006 and 2008 at 235 locations in a 2500 km2 study area off Rotterdam (Fig. 9).
The boxcorer had a surface area of 0.084 m2 and a maximum penetration depth of 30 cm (Fig. 10). Samples were wet-sieved using a 1 mm mesh sieve and the residue was stored in jars with a seawater solution of 6% buffered formaldehyde (Perdon & Kaag 2006, Craeymaeersch & Escaravage 2010). The bottom sledge was equipped with a 5-mm mesh cage of 10 cm, penetrating up to 10 cm into the seabed (Fig. 10). On average, a surface area of 15 m2 was sampled during each sledge haul of around 150 m length. Specimens were identified up to species level when possible. Infaunal ash-free dry weight biomass (g AFDW m-2) was analysed by means of loss on ignition (2 days at 80°C followed by 2 hours at 580°C). Wet weight of epifauna without sampled fish (g m-2 WW) was directly measured. Biomass of razorblade Ensis spp. was determined by using regression equations based on previous IMARES field surveys (Craeymeersch & van der Land 1998).
Sediment samples from the upper 5 cm were collected from untreated boxcorer samples and kept frozen until analysis. Sediment samples were analysed with a Malvern Mastersizer 2000 particle size analyser. Percentile sediment grain size (D10, D50, D90) and sediment grain size distribution among the different classes; clay (< 4 μm), silt (4-64 μm), mud (<63 μm), very fine sand (63 μm-125 μm), fine sand (125 μm-250 μm), medium sand (250 μm-500 μm) and coarse sand (> 500 μm) were measured as percentage of total volume (vol%). Sediment sorting (D90/D10) was determined, sediment organic matter (SOM) was analysed by means of loss on ignition (freeze-dried sediment samples were placed for 2 hrs at 580°C) and values of SOM were calculated as percentage of sediment mass (mass%).
Figure 9: 235 Sampling locations of the Port of Rotterdam (PoR) baseline study in 2006 and 2008.