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Nachrichten, Termine, Experten
Nachrichten, Termine, Experten
Through sand extraction and the disposal of dredged harbor silt, around 200 million tons of sediment are relocated every year in the coastal waters of the North Sea. The Wadden Sea is particularly strongly affected. This is the result of a new study by the Helmholtz Centre Hereon, which for the first time evaluated comprehensive data on dredging activities along the North Sea coasts. At the same time, dredged material could potentially be used in the future to help raise the seabed in areas that do not naturally accumulate enough sediment to compensate for rising sea levels. The study was recently published in the scientific journal Nature Communications.
Every year, specialized vessels extract large quantities of sand from the North Sea, which is used to build new port facilities or for coastal protection. Off the islands of Sylt and Wangerooge, for example, sand is regularly deposited because winter storms and wave action erode parts of the beach. Harbor basins and river shipping channels have to be dredged annually, otherwise they would silt up. This silt is “dumped,” that is, redeposited at other locations off the coast.
Researchers at the Hereon Institute of Coastal Systems – Analysis and Modeling have now calculated for the first time how much sand, gravel, and silt are transported back and forth in the Wadden Sea of the North Sea through dredging and dumping. The scale is enormous: a total of 200 million tons of material per year — about the same amount as is naturally transported by North Sea currents and all surrounding rivers combined. “For our study, we compiled and analyzed data on dredging activities from 30 years,” says Dr. Lucas Porz, an expert in sediment transport at Hereon.
Environmental burden or opportunity for coastal protection?
Dumped sand and harbor silt do not remain where they are deposited but are gradually carried away by water currents. Often, the material accumulates again in ports or shipping channels, which then have to be dredged once more. The simulations conducted in the Hereon study make it clear that a large portion of the dumped material also settles in the Wadden Sea in the long term.
In a previous study, a research group led by Porz’s colleague and Hereon scientist Dr. Wenyan Zhang found that the Wadden Sea is not keeping pace with rising sea levels. The reason is that most tidal flats are no longer accumulating enough sediment naturally. Relocated sand and silt could counteract this. “If dredged material were strategically relocated, it could reach the affected areas and allow the tidal flats to grow again,” says Porz. He is currently working with his colleagues to determine in detail which areas would be suitable for this. However, since harbor silt in particular can be chemically contaminated, the impacts on the marine environment would have to be carefully assessed in advance, and any targeted relocation of the material could only take place in harmony with nature conservation.
Carbon is released
However, dredging and extracting sand from the sea also has a significant drawback: it releases large amounts of carbon that have accumulated in the seabed along with the remains of algae and other marine organisms. In the current study, Porz therefore also determined the amount of carbon released each year by offshore dredging. Globally, the amount of carbon stirred up in this way is estimated at up to 500 million tons annually - significantly more than is released by activities such as pipeline construction or offshore wind farm installation. If this carbon reacts with oxygen in the water, the greenhouse gas carbon dioxide is produced. “These data are important for better estimating in the future how much carbon dioxide is released overall in coastal regions,” he says. “So far, these human activities have not been taken into account at all in carbon budgets.”
Cutting-edge research for a changing world
Helmholtz-Zentrum Hereon`s scientific research aims at preserving a world worth living in. To this end, around 1000 employees generate knowledge and research new technologies for greater resilience and sustainability - for the benefit of the climate, the coast and people. The path from idea to innovation leads through a continuous interplay between experimental studies, modeling and AI to digital twins that map the diverse parameters of climate and coast or human biology in the computer. This is an interdisciplinary approach that spans from the fundamental scientific understanding of complex systems to scenarios and practical applications. As an active member of national and international research networks and the Helmholtz Association, Hereon supports politics, business and society in shaping a sustainable future by transferring the expertise it has gained.
Dr. Lucas Porz
Scientist
Hereon Institute of Coastal Systems – Analysis and Modeling
Mail: lucas.porz@hereon.de
https://www.nature.com/articles/s41467-025-68105-5
https://www.hereon.de/institutes/coastal_systems_analysis_modeling/index.php.en
https://www.hereon.de/communication_media/news/119358/index.php.en
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