This is the second article in a series on the monitoring programme at Maasvlakte 2 in the Netherlands.
The first article appeared in Terra et Aqua, number 129, December 2012 and described the framework of the monitoring of Maasvlakte 2 following the Environmental Impact Assessment and discussed the juvenile fish survey and the possible mismatch between cockles and algal bloom.
This second article focuses on the monitoring aspects of silt (fines or SPM in the water column) resulting from the construction of Maasvlakte 2 and the possible effects on the benthic communities (mid and far field).
The aspects that will be described are:
– the silt in the water column along the Dutch coast;
– the monitoring strategy for silt;
– the effects on the food chain.
Silt in the water column is extremely variable in space and time. High concentrations of suspended silt as well as high concentrations in the seabed are found along the coast.
The highest concentrations are in the region south of Scheveningen, especially in the “Voordelta”, whereas low concentrations are found further offshore. Owing to the residual current along the Dutch coast, silt is mainly transported in north-north-eastern direction.
Because of the Coriolis force (the deflection of moving objects caused by the rotation of the Earth), the silt remains close to the shore.
A heavy storm has a large effect on the concentration of silt in the water column; the higher waves cause silt to be released from the seabed. Only after some time will such silt return into the seabed, for example as a result of the activity of benthic fauna, which is more active in summer than in winter.
An increased flow velocity (during ebb and flood) also brings silt in suspension from the thin fluffy layer on the seabed that is present during slack tide.
Because of the expected effects of enhanced silt concentrations on the food chain, a condition was included in the permit for the construction of Maasvlakte 2 that silt should be monitored.
Press Release, March 6, 2013