HS Environment | A large artificial island will rise in front of Copenhagen, and it may not be the only one – researcher fears harm to the Baltic Sea

If The construction sites in Kalasatama or Jätkäsaari seem large, it is worth looking at Copenhagen.

A whole new artificial island, Lynetteholm, is being built in front of the city. Among other things, 15,000-20,000 residential buildings and a new subway line are planned for the 60-hectare island.

The decades-long construction project has started with the construction of the island’s shorelines. They are expected to be completed by 2026.

The completion of the entire island will take decades, probably into the 2050s. After that, a new residential area may be built on top of it for another twenty years.

Copenhagen the population is predicted to grow, so there is a need for new apartments.

However, the real reason for building Lynetteholm is the concern about sea level rise. If the estimates of sea level rise are correct, Copenhagen’s historic center threatens to be largely submerged by floods by the end of the century.

Tekosaari serves as a dam protecting the old town. It also allows for a sluice gate that can be used to close the port when storms threaten.

The city could have been protected by a dam alone, but the island has three advantages compared to that. First of all, it is a natural investment location for land that is constantly being created in other construction projects in Copenhagen and its surroundings.

Land acquisition is Lynetteholm’s key means of financing. The income from the apartments, on the other hand, could enable the development of the island into a district.

All are not unreservedly enthusiastic about the island. Professor of applied marine ecology and modeling at Aarhus University Jacob Carstensen is concerned about the effect of the island to the state of the sensitive Baltic Sea.

Lynetteholm will be built in the Juutinrauma strait between Copenhagen and Malmö. It is one of the three straits through which North Sea water enters the Baltic Sea. Juitrauma’s share of the total flow is more than a quarter.

At Lynetteholm, the strait is less than 27 kilometers wide. In addition to this, a part of the island extends to one of the strait’s depths.

“In my opinion, it is clear that the island will have an impact on the flow of water between the Baltic Sea and the North Sea. It is unclear what effect it will have on the Baltic Sea ecosystem. The matter would require an even better evaluation,” says Carstensen.

from Lynetteholm an environmental assessment has naturally been carried out.

According to modeling by the Danish Hydrological Institute, Lynetteholm reduces the water flow in the strait by an average of 0.25 percent. According to the most optimistic calculation, the flow will not decrease at all, according to the most pessimistic one, the change is in the order of 0.5 percent.

Later, the same result was confirmed by the Dutch consulting company Deltares. Carstensen does not suspect modeling as such.

“However, the question is what an average of 0.25 percent ultimately means for the biosystem of the bottom of the Baltic Sea and the amount of oxygen in the depths.”

by CarstenSEN the fear is related to the so-called salt pulses, They are masses of salt water that pass through the Danish straits in exceptional storm conditions.

The pulses repeat randomly, typically only a few times in decades. They are practically the only way in which the oxygen-free depths of the Baltic Sea get new oxygen-rich water.

“If the flow decreases by an average of 0.25 percent, how much does it cut from the exceptional flow like a salt pulse? In my opinion, modeling this is very difficult,” reflects Carstensen.

When the Juutinrauma bridge connecting Sweden and Denmark was built, efforts were made to compensate for the effects of the bridge on the currents by widening the flow channel. In Lynetteholm’s plans, something similar has not been taken into account.

Lynetteholmia will be built by the By og havn company jointly owned by the city of Copenhagen and the Danish state.

The project manager of the technical side of it Hans Vasehus knows environmental assessments well. According to them, the island’s effect on the salinity of the Baltic Sea is of the same order as the current, i.e. 0.25 percent.

“This has been assessed to be so small that no compensation was deemed necessary. But in the end, of course, it’s a political decision – if compensation is needed, it would technically be possible to do it.”

“Of course, excavations of the seabed or beaches always disturb the local ecosystem, so there is another side to the matter.”

The fact that the future rise in sea level has been estimated to compensate for the decrease in flow in about ten years is also weighing on the balance sheet.

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“Ecosystems are very complex and unpredictable.”

Lynetteholm is not Denmark’s only artificial island project. The country plans also two large energy islandsta, where the idea would be to produce carbon-neutral energy with wind turbines. Denmark produces energy organization IEAaccording to , already half of the electricity is in the wind.

The plan for the island planned for the North Sea side has been approved, and it is supposed to be completed in 2033. The island planned for the Baltic Sea side is only in the planning stage. On these islands, Carstensen sees no threats to the currents.

“In the planned location, the sea is so wide that I don’t think the island will create a bottleneck for the movement of water”.

Others however, there may be effects on the islands.

“For example, there may be animal species that currently cannot move across the sea, but a possible resting place in the middle would change the situation. Ecosystems are very complex and unpredictable.”

Although the professor understands the need for wind power and the protection of Copenhagen, the utilization of marine areas makes him thoughtful.

“We don’t have untouched nature in Denmark, everything is shaped by man. Personally, I would like a thorough discussion before the same thing is done to marine areas.”