Environmental Consequences of a Large Scale Coastal Engineering Project on Aspects of Mussel Cultivation in the Eastern Scheldt

Abstract

The rewatering location in the Eastern Scheldt at Yerseke has an important function for the Dutch mussel culture, safeguarding the keeping quality of the mussels. The mussels are relaid during 2–4 weeks on rewatering plots between production and marketing. It was feared that, after completion of the Storm-Surge Barrier in the Eastern Scheldt, the rewatering function would deteriorate as a consequence of accumulation of mussel-deposited mud (pseudo-faeces) and a decline of water quality during periods of low current velocity. A research program was drafted in order to make a prognostication of sedimentation and erosion and of the occurrence of adverse water quality and food shortage on the plots after the completion of the Storm-Surge Barrier. A study was made of erosion factors such as tidal currents, wave action and periodical dredging of mussels on the plots. Besides, food content and water quality parameters were measured. The measurements were carried out during 13-hours periods at half-hourly intervals. Periodic dredging of mussels on the plots appeared to be the most important among the erosion forces, while tidal currents and wave action have less impact. Sedimentation is almost entirely caused by the filtering activity and deposition of faeces by the mussels. It is expected that after the completion of the Storm-Surge Barrier the erosion forces will decrease slightly. Whether the erosion and sedimentation balance on the rewatering location, presently more or less in equilibrium, will change, will mainly depend on the future rate of faeces production. This, however, is difficult to predict.