Do wind farms threaten marine life?
Green energy is good, but what are the effects on marine life of constructing the foundations for offshore wind farms?
Professor Han Lindeboom of the Imares Maritime Research Institute based on the Dutch island of Texel has been looking into the issue of wind farms and their impact.
The professor is worried by the 200 decibels of noise generated by hammering the foundations' 4-metre-diameter concrete piles into the seabed. Construction work is set to continue for decades even if wind farms end up providing just one-fifth of the Netherlands' energy needs.
Death by noise
Humans suffer permanent damage to their hearing when subjected to just 80 decibels. What does Professor Lindeboom think the effects of 200 decibels will be on marine animals such as seals and porpoises?
"We've measured the sound generated by the construction of the wind farm off the coast near Egmond aan Zee. Porpoises could die as a result of the noise experienced up to about one kilometre away."
The problem is worse in the sea than on land because sound travels further through water than through air. Companies are being advised to use ‘pingers', which produce noises that seals and porpoises find unpleasant.
The idea is to chase the animals away from the sites before construction begins. Professor Lindeboom says ‘pingers' are already used by the fishing industry to stop marine mammals being caught in nets:
"The ‘pinger' is started about four hours before work is due to begin. The porpoises swim off and have covered kilometres before the hammering starts."
Stop that noise!
Neither the researchers nor the construction companies appear to have realised quite how intelligent marine mammals are or how much they value their peace and quiet.
When the Imares researchers began to monitor the position of the animals, they were found to have disappeared long before construction work had even begun. They can still hear the hammering at a distance of 6 to 10 kilometres, but it no longer poses a danger to their hearing.
Research has already shown that birds do not fly into the windmills' blades. There has been no increase in the number of dead birds washed up on the shore near wind farms. The situation for fish is more complicated, with some species leaving the area covered by wind farms, while others appear to like the new habitat which protects them from shipping and fishing.
The construction of the foundations for marine wind farms only appears to pose a real problem for life on the seabed. Shrimp, and other deep-sea flora and fauna, are simply destroyed when subjected to 200 decibels.
However, Professor Lindeboom argues that this is a very short-term problem. When construction is complete, a relatively peaceful environment is created and deep-sea marine life is quick to return.
"I think that at the end of the day the positive effects of the lack of other human activity outweigh the negative effects of the noise.
We're carrying on measuring those effects and in around six months should know much more but, so far, there is absolutely no indication that it's a real problem for the animals that live there."
Professor Lindeboom says constructing foundations could be done in winter outside breeding seasons, and countries could co-ordinate building work to limit the areas of the North Sea affected at the same time.
There are also ways of driving the concrete piles into the seabed which are less disruptive than hammering although these are generally more expensive. He sums the situation up:
"The construction of wind farms doesn't have to pose insuperable problems for marine life, but you should keep an eye on the situation."
Thijs Westerbeek van Eerten