To protect the Dutch coast from rising sea levels, the coastline is strengthened and widened with sand. This is urgently needed, but also has negative consequences for the ecosystem in the North Sea. Wageningen University & Research (WUR) is investigating how the Netherlands can extract and replenish sand in an ecologically responsible manner.
On February 28, the International Panel on Climate Change (IPCC) published a new report on global warming and its effects. The effects of climate change are already noticeable and the risks of extreme droughts, forest fires and floods are increasing. It is therefore necessary to work on climate adaptation: adaptations to cope with the consequences of climate change. In the Netherlands, for example, this is done by using sand to protect the coast from rising sea levels. Every year, 12 to 15 million cubic meters of sand is extracted from the North Sea to be used for sand nourishments.
Impact on shellfish and sea ducks
These protective measures on the Dutch coast are urgently needed, but they do have ecological consequences. Sand extraction in the North Sea can kill a great deal of benthic life (life on the bottom of the sea), and when the sand is applied (sand nourishment), the benthic life is buried under a layer of sediment. This can be disastrous for shellfish, for example, but also for the (protected) common scoter that feeds on these shellfish. In addition, sand extraction has a great impact on the shape of the seabed. When a deep pit or trench is dug, the seabed will be changed permanently- and with it the habitat of animals.
WUR maps the state of the shellfish populations along the coast annually. This information is used to determine where sand nourishment is legally not permitted. Marine ecologist Martin Baptist: "We have a lot of knowledge of the coastal system, so the ecological damage of nourishments should be taken into account. More knowledge is needed about the ecological damage of sand extraction offshore.'
Where exactly should sand be extracted, and how deep? It's a tricky puzzle, Baptist explains. ‘The deeper you dig, the longer the underwater landscape is affected. During the construction of the Maasvlakte 2 at the Port of Rotterdam, a sand extraction pit was dug 20 meters deep. This slowed down the current, caused suspended material to sink to the bottom and made it very muddy. It might therefore be better to extract sand, in order to let the soil recover more quickly. On the other hand as most of the benthic life is found at the surface, extracting sand from the surface also kills of a large part of marine life.’
Furthermore, researchers must take into account not only the mining depth but also all kinds of other factors. For example, the discharge of freshwater from the Rhine, the shape of the seabed and other uses of the North Sea, such as cables, pipelines and wind farms. In time, the shortage of sand will also play a role.
Predicting and cooperating
The need for research into sand extraction and nourishment is indisputable: the sea level is going to rise in the coming decades, as the IPCC report once again confirmed. In response, WUR and many other parties have submitted a major research program as part of the National Science Agenda. Within this program, Baptist and his colleagues want to develop reliable predictions of the ecological consequences of sand extraction. In this research, they work together with fishermen, who know the underwater landscape in detail and know where they catch a lot of fish. Moreover, the commercial fisheries have an interest in knowing the effects of sand extraction and replenishment. Larvae of plaice and sole, for example, can get trapped in deep excavated trenches and thus fail to reach their nursery grounds.
The research program includes the design of a serious game in which the researchers predict and discuss future scenarios. In addition, the aim is to work much more intensively with Rijkswaterstaat, part of the Dutch Ministry of Infrastructure and Water Management, dredging companies, commercial fisheries and NGOs such as Stichting de Noordzee. Baptist: 'In preparing the research program, more parties have been brought together than before. We want to work together on a plan for future sand extractions, so that we can keep the Netherlands safe in an ecologically sustainable way.'