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The Port of Rotterdam Authority investigates marine life on the bottom of the North Sea

This spring, scientists are investigating which animal species and how many of them are living on the bottom of the North Sea.They are doing this at some 300 locations up to 50 kilometres from the coast between Schouwen and IJmuiden. The study is what is known as a 0-measurement By repeating the same study when sand is extracted for Maasvlakte 2 and comparing the two sets of results, any effects of sand extraction can be identified.

Some 325 million m³ of sand are needed for the construction of Maasvlakte 2. Most of this sand has to come from the North Sea in the vicinity of the area to be raised, so that dredging vessels carrying the sand have the shortest distance to travel. The Environmental Impact Assessment for the Construction of Maasvlakte 2 (Milieu Effect Rapportage Aanleg Maasvlakte 2, abbreviated to MER) describes what the expected effects on marine life will be as a result of the sand extraction. This is done based on current scientific knowledge and state-of-the-art computer models developed specially for this purpose. The report shows that the expected effects on marine life in the North Sea will be limited.

Permit under the Earth Removal Act
Before construction begins, a permit under the Earth Removal Act must first be obtained for sand extraction from the North Sea. This also involves measuring the effects of sand extraction in order to see whether these remain within the limits predicted in the MER.

Fore-delta
Sand extraction will take place far from the coast where the North Sea is deeper than 20 metres. This is in fact the edge of the fore-delta situated directly along the coast. The fore-delta has a richer, more varied and more vulnerable marine life than where the North Sea is deeper. Outside this 20-metre zone the EU Birds and Habitats Directives, which impose strict requirements on intervention in this area, do not apply. All existing sand extraction locations in the North Sea are outside the 20-metre boundary.

0-measurements
The Port of Rotterdam Authority, responsible for the construction of Maasvlakte 2, must and wants to manage the marine environment responsibly. For this reason, life on (epifauna) and in (infauna) the seabed is being analysed before the start of construction. In order to obtain the best possible picture of natural variations over the years, measurements will be taken in both years before the start of construction (spring 2008), i.e. in both 2006 and 2007. These two 0-measurements will together cost about € 800,000. There will be additional costs during construction too, for monitoring and studying whether the effects occur as predicted.

300 grab and slice samples
Two types of study will be carried out at some 300 precisely established locations. A grab sample will be taken from the seabed, 20 cm deep and 32 cm across, and the scientists will slice off a layer of the seabed 10 cm wide and 7 cm deep over a distance of 100 metres. The first sample focuses on the infauna; all animals living in the seabed such as shellfish and lugworms. The second study focuses not only on the infauna but also on the epifauna living on the seabed, such as crabs, starfish, hermit crabs and marine snails such as whelks. The slice will be taken along fairly long strips of 100 metres in various directions, because the seabed has dune and wave patterns which can produce marked local differences in marine life.

On board the research vessel the ‘grab' and ‘slice' samples will be analysed straight away. Scientists will record the species found and measure the weight of each species, while at the same time samples will be taken from the seabed for further laboratory analysis. The aim of this is to see whether there is a relationship between seabed composition (sand grain size, silt concentration) and marine life.

Science
Thanks to the development of sophisticated computer models and 0-measurement, followed by monitoring together with verification of the new computer models, we can obtain a vast quantity of new knowledge on the effects of sand extraction on marine life in the North Sea. In the Second Regional Earth Removal Plan for the North Sea (Tweede Regionaal Ontgrondingsplan Noordzee, abbreviated to RON2) of 2004, which describes national policy for sand extraction at sea, there are some gaps in our knowledge of the effects of large-scale, deep sand extraction. That is why RON2 wants to use the first project as a pilot project with a comprehensive monitoring programme in order to increase our knowledge in this area. The 0-measurements currently underway are the first steps in this direction, and the Port Authority aims in this way to make a genuine contribution to our knowledge of the North Sea.

Deep sand extraction pits
The contractor who will be awarded the contract for the construction of Maasvlakte 2 is responsible for the sand extraction. The Port Authority anticipates that this contractor will want to extract the sand in deep pits. The usual technique is to extract sand to a depth of 2 metres, but in view of the quantity of sand required, it would need to be extracted from an area of the North Sea measuring 11 by 30 km. That is why the Port Authority expects that the contractor will want to obtain the sand from much deeper pits with a much smaller surface area. Extraction to a depth of 10 to 15 metres in relation to the existing seabed would appear to be the most obvious solution here. Pits dug this deep will be refreshed with water during every tide, preventing the build-up of deoxygenated water, since the latter would make life on the seabed virtually impossible.

Silt particles in suspension
The effects that are predicted as a consequence of sand extraction are two-fold. On the one hand, marine life will disappear at the extraction location itself. Recolonisation will allow marine life to recover to its former levels within a few years. On the other hand, silt particles from the seabed will become suspended in the seawater. This occurs because the trailer suction hoppers pump not only sand but also water to the surface. This water flows back, over the edge of the dredging vessel, into the sea together with a small quantity of sand and silt particles. The sand settles quickly on the seabed again, but the lighter silt is transported by the sea currents for some distance before it settles. This silt makes the water turbid so that less light can penetrate to the seabed. Algae will grow more slowly, reducing primary production and making less food available for molluscs and shellfish, which in their turn are food for animals higher up the food chain. Too must silt in suspension in the water would therefore appear not to be beneficial.

Water turbidity can also have an impact on fish and birds that hunt by sight. At the same time, this may have positive benefits for those species that are prey to these hunters. It is also possible that primary production will be increased at those places where the silt settles, allowing the fauna to increase there too. However, it is highly doubtful whether these various theoretical possibilities will actually occur in real life, and moreover be actually measurable.

Natural phenomenon
The presence of silt in suspension in seawater is in fact a natural phenomenon. Rivers continually transport silt. It settles in still or slowly moving water and is dislodged again as water flow increases or by the waves in strong winds. For example, the water in the fore-delta contains much silt, particularly in what is known as the ‘coastal river', the continual current of water from south to north along the coast.

As the sand is used to raise the ground level of Maasvlakte 2, only a very small fanning out of silt in the North Sea is anticipated. Most silt will in fact remain in the sea as it overflows from the dredging vessel. The rest will be mostly ‘packed in' by the sand as the land is raised.

Expert meetings
In the preparations for the study, the Port Authority has held a number of expert meetings, during which the objectives and study methods have been discussed in detail with a group of some 20 experts in marine ecology and research. The study is to be carried out by Imares and the Netherlands Centre for Estuarine and Marine Ecology, using the Directorate-General of Public Works and Water Management's multi-purpose vessel Arca. The entire study will take about 4 to 5 weeks this spring.

Page updated at: 07-07-2009