They might produce renewable energy, but offshore wind farms are a scourge for porpoises. Researchers have found that construction noise at a turbine site off the German coast has scared away the marine mammals, who depend on their acute hearing. A "bubble curtain" could protect the sensitive cetaceans from future stress.
The offshore wind farm Alpha Ventus is a project of imposing dimensions. A total of 12 wind turbines rise from the North Sea in an area of about 4 square kilometers (1.5 square miles). Each one stands about 150 meters (490 feet) high and weighs 1,000 tons. The farm is designed to provide electricity for about 55,000 households.
Now the environmental impact of the massive project, which lies some 45 kilometers (28 miles) north of the German island of Borkum, is becoming clear. Germany's Federal Maritime and Hydrographic Agency (BSH) has completed its first study of the impact of the wind farm -- and found that the racket made by the construction of the site had scared off porpoises living in the area.
Speaking at a conference on the marine environment in Hamburg Wednesday, Klaus Lucke of the Büsum-based Research and Technology Centre Westcoast (FTZ) said that construction noise can damage the hearing of porpoises, which are "dependent on healthy hearing" for finding food, orientation and communication. Population counts carried out by plane over the southern North Sea showed that, during the construction phase, porpoises avoided an area with a radius of over 20 kilometers around the wind turbine site, the researcher said. It is unclear if the creatures will return to their former habitat now the site is up and running.
Protected by Bubbles
Lucke called for measures to protect the vulnerable mammals from the piercing noise of future underwater construction. "We must do everything possible to avoid such an impact," said Lucke. One feasible plan would be a so-called "bubble curtain," a kind of protective layer of artificially generated bubbles in the water which would reduce the propagation of sound waves.
Another side effect of the wind turbine construction site is likely to be the creation of artificial reefs, said BSH scientist Karoline Weber-Streidt, speaking at the same conference. She explained that the site of a research platform near the wind turbines was already coated with a dense growth of mussels, sea anemones and even oysters.
Researchers are studying the impact of Alpha Ventus on various aspects of the marine environment, including fish, marine mammals, seabed organisms and migratory birds. The wind farm officially went into operation in April, and around 70 other offshore wind farms have already been approved or are soon to get the green light.