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Does offshore production of wind energy harm marine wildlife?
No matter how energy is produced, there is an environmental cost. In traditional means of generating power, human health, wildlife and the environment are adversely affected by carbon dioxide, sulfur dioxide and other harmful emissions caused by the burning of fossil-based fuels. When it comes to understanding effects of wind energy, there are few offshore wind energy generating sites from which we can gather information. In northern Europe, off the coast of Denmark and Scandanavia wind generating sites are small in size, with an average of less than 20 turbines per site. Most of these turbines are less than 300 feet in height. Most have not been in operation for any great length of time. While there is some indication that land-based sites have posed a hazard to some bird species, there is less information on the effects of offshore sites on birds. We know even less about possible effects on whales, seals, fish and marine turtles.
How could a wind farm harm marine life?
Questions exist about a number of possible adverse impacts on marine life. Sources of concern include electromagnetic fields generated by turbines, noise of installation and operation, fragmentation of habitat, and possible degradation of habitat.
Electromagnetic fields: The generation and transmission of electricity produces electromagnetic fields around the generators and cables. There are a number of possible effects of electromagnetic fields on marine wildlife. We know that turtles and some fish and mammals appear to use the earths magnetic field for navigating. If the electromagnetic field generated by an offshore wind facility is sufficient, it might disrupt navigation necessary for seasonal migration to breeding areas. Additionally some species of fish are either attracted to or repelled by magnetic fields, which may displace them from normal habitat.
Noise: It is necessary to anchor wind turbines deep in the sea bed. To do this there are a number of options for installation, all of which generate noise. The most detrimental of these is pile driving, which has been shown to displace marine mammals from their normal habitat. Vibrating pile drivers are estimated by their developers to be up to one third quieter, but still create disturbance over the course of the many months required to install a large scale offshore site. During operation of the turbines, a low frequency (25-400 hertz) hum occurs. This has been measured at 98-130 decibels, a level somewhat greater than the noise generated by an operational offshore oil platform. A study of seals near Danish sites indicates that the noise of operation doesnt seem to have a great effect on them. We do not know whether or not this sound would harass or displace dolphins, porpoises or large whales, some of which are more sensitive to low frequency sounds.
Fragmentation of habitat: The larger the area occupied by a wind generating facility, the greater the chance that it may have an effect on animals swimming in the area. Large farm sites, with 100-300 turbines occupy tens of square miles of ocean. While turbines are often spaced well apart (900 feet or so) this matrix of towers may present something of a maze to animals used to traveling or feeding unhindered through the ocean. If this effect is sufficiently disruptive to them, it may force them to use habitat that is less productive or more risky (near entangling fishing gear or in the path of commercial ship traffic).
Degradation of habitat: Each turbine receives routine maintenance approximately twice a year; this necessitates boats traveling through large wind farms on virtually a daily basis. This disruption may discourage normal activities of resident or migratory animals. Additionally, the installation and maintenance of cables causes sand and other sediment to be suspended in the water. Movement of cables, and changes in current brought about by the barrier created by the base of a turbine (which has a footprint of approximately 16 square feet) may cause scouring of the bottom in some parts and accumulation of sediment in others. This change in the bottom contour can affect suitability of habitat for small fish and invertebrates that are important in the food chain. Turbines are often supported with rip rap at their bottom, creating an artificial reef. This may attract species that were previously unable to find habitat in the area and thus change the diversity of species in the area and/or competition for available resources.
So does this mean that we shouldnt have wind energy generated offshore?
No. It is important to understand the potential risks before undertaking any new enterprise. Prior to siting a wind farm, it is important to understand what marine wildlife use the area and how they use it. Once we know what animals are resident in an area or rely on the area as a migratory corridor, we can better assess the overall risk to them. For example, different degrees of caution may be warranted depending on whether or not an area is used by endangered sea turtles, part of the migratory route of endangered right whales, or is in essential fish habitat. Where we have concerns, but insufficient information to assess relative risk, studies of the habitat use of the area should be conducted prior to construction of any offshore facility--whether it is a wind generating facility, offshore aquaculture or any other permanently anchored structure. After we have looked at the habitat use by various marine species, we can make an informed assessment of risks and benefits and choose the most appropriate locations these facilities.
For More Information:
Check out -- http://www.seascape-energy.co.uk/ The link to the Environmental Statement for this proposed wind farm in Great Britain provides a good summary of basic types of concerns that should be evaluated for any proposed offshore wind farm. |
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