The Ecology of Offshore Wind Farms A Focus on Europe

Research Assignment/Chapter Draft November 9, 2009 ENST 70: Senior Seminar The Ecology of Offshore Wind farms: a Focus on Europe I. Introduction It has long been acknowledged that humanity is constrained in its available resources; maximizing the profitability of such resources is essential to survival. While the burning of fossil fuels has existed as the main form of energy generation for a number of generations, there have been recent calls to encourage the switch to sustainable options. In particular, the past two decades have seen the use of wind power escalate by a significant amount, in order to minimize production costs and promote clean energy use. Wind is not only unlimited – it is entirely free. Land-based wind turbines have made invaluable contributions to the sustainable energy movement, but there has been a recent push to move offshore and put to use the largely untapped wind resource at sea. Europe stands ahead of the United States in offshore wind turbine construction – there are 28 offshore farms currently operating in European seas, and although the United States has several proposals in waiting, the United States has yet to open its first offshore farm (EWEA 2009). Although the cost of wind itself is zero, the construction, operation, and maintenance of wind turbines carry substantial ecological and economic implications. The aim of this section is to examine the ecological effects of offshore wind farms in selected areas throughout Europe, with a focus on Denmark and the United Kingdom. In order to prepare for a more successful offshore wind movement in the United States, it is valuable to analyze the ways in which the ecological community has been affected by the presence of offshore wind farms in Europe. 1 First, it is critical to investigate how the farms are constructed at sea, as it is easier to imagine the effects that the turbines have on marine and avian life with a mental image. When a suitable place for the farm has been found, piles (deep foundations) are driven into the seabed, usually complete with erosion protection to prevent damage to the sea floor. The top of the foundation is typically painted a bright color to make it visible to boaters and commercial ships. The turbine itself is comprised of three blades and a nacelle, a small cover housing that holds the blades in place – some nacelles are equipped with sensors to detect the direction of optimum wind speeds to maximize energy output (BWEA). Wind causes the blades to rotate, which, via gearbox, transfers energy to cables within the turbine’s shaft (structure held up by the piles), and then on to power a generator at the base. Subsea cables take the power to an offshore transformer, which converts the electricity to high voltage before running it back to a grid onshore (BWEA). II. Effects on Avian life As many turbines are constructed in a single wind farm, it is quite plausible that their presence would have some tangible consequences for the surrounding ecological community. Avian death and habitat displacement have been major concerns for the offshore wind movement. European evidence for the main effects on birds, which include collision, displacement due to disturbance, barrier effects, and habitat loss, has shed some light on the ecological cost of offshore wind farms (Drewitt and Langston, 2006). In order to be effective, wind farms must be sited in open, exposed areas with high wind speeds – typically areas that provide habitats for avian breeding, wintering, and migration. However, the effects of a wind farm on birds are highly variable and depend on a wide range of factors, which gives further reason to investigate 2 the specification of the development, the habitats affected, and the number and species of birds present (Drewitt and Langston, 2006). The first issue surrounding avian life and wind turbines is the possibility of collision mortality. According to Allan Drewitt, direct mortality or severe injury can result not only from collisions with rotors, but also with towers, nacelles and associated structures such as cables, power lines, and meteorological masts (Drewitt and Langston, 2006). In addition, there is a possibility for birds to be forced downward by the vortex created by the moving rotors (Winkelman, 1992). It is important to understand that although turbines pose a constant risk to birds, relatively low mortality levels have been recorded – this could be attributable to the fact that many records are solely based on located corpses, and do not account for bodies that are overlooked or removed by scavengers (Langston & Pullan, 2003). Assessing collision risk is also important in analyzing the threat that offshore turbines present for birds. First, the risk is amplified, as offshore turbines are typically taller and have longer rotor blades; simply put, the offshore turbines take up more space. Also influencing risk are the number and behavior of a particular bird species, weather conditions, and the specific nature of the wind farm itself (Drewitt and Langston, 2006). Risk is clearly increased if there are large numbers of birds feeding, roosting or mating in a particular area, or if the area of the wind farm is in the middle of a popular migratory flyway (Drewitt and Langston, 2006). Larger birds are also likely to have relatively poor maneuverability, while species that typically fly at dawn or dusk are probably less likely to successfully avoid turbines (Brown et al., 1992, Larsen & Clausen, 2002). Risk is also positively influenced by weather patterns, as areas with a tendency towards dense fog and heavy rain are likely to impair visibility of large structures (Drewitt and Langston, 2006, Erickson et al., 2001). Collision risk is also augmented because of the natural 3 noises that are generated from wind and waves at sea – the ability to hear while in flight is a vital detection mechanism for avian life. Although avian death statistics are somewhat limited for offshore wind farms, several coastal projects in Northwest Europe have yielded relevant information. Studies at these sites have shown varied results - for instance, in the Netherlands, the yearly average collision rate ranges from 0.01 to 1.2 birds killed per turbine; at Blyth, a famous wind farm in Northumberland, England, 6 birds are killed per turbine; and at three study sites in Flanders, Belgium, between 4 and 23 birds/turbine (Painter et al., 1999). At Blyth in particular, in Northern England, there was observed a greater level of bird death by the Common Eider (Somateria mollissima) by about 0.5 – 1.5%. The Eider, a large sea duck, is particularly common in coastal areas where it can regularly breed and dive for food. Due to their large colonies, (there are about 2 million Eiders in North America and Europe) it seems probable that simple space constraints while in flight could lead to a number of collisions. Also a possible influence of increased collision rate could be the Eider’s characteristic wide body, which also increases the probability of an accident. Observations at Nysted offshore wind farm in Denmark have introduced some information on flight paths that could influence the observed rate of collision. Radar and thermal imaging studies, for example, suggest that most birds begin to divert their flight paths up to three kilometers away in daytime and up to one kilometer at night, highlighting the willingness to avoid the turbines altogether (Desholm, 2005). In the light of day, birds can clearly see the turbines, although the chance of flying through the cluster is greater because they can more accurately judge the space between turbines. On the other hand, birds are more likely to fly around the clusters altogether at night to practice complete avoidance due to their impaired vision. It seems as though birds (the Eider, in particular) have the ability to adapt to the farms 4 almost completely when the turbines are visible, but experience a much greater risk as night falls due to their loss of spatial awareness. Another phenomenon that has stemmed from the presence of turbines in European waters is the barrier effect, or the result of birds altering their migration flyways or local flight paths to avoid a wind farm. Evidence from 2004 studies at Horns Rev and Nysted in Denmark suggested that Common Scoters on migratory fights avoided the wind farm and its immediate vicinity, although changes in their distribution were “likely not solely caused by the presence of the wind farm” (Exo et al., 2003). A major contributing factor is the distance between turbines; at Nysted, the Common Eider routinely flies in between turbines that are 480 meters apart (Christensen et al, 2004). It has also been observed that a wind farm in the German Exclusive Economic Zone (EEZ) has had a barrier effect on migrating birds, which forces them into energy consuming evasive action. These forced detours can lead either to direct loss of individuals, or reduce reproduction rates, and hence have a negative impact on the population or development of some species. (Koeller et al., 2006) Apart from collision risk and the barrier effect, avian life is also susceptible to long-term habitat loss and displacement. Habitat loss involves resident birds simply being pushed out of the areas in which they live due to the presence of wind turbines. Studies of two Danish wind farms at Tuno Knob and Horns Rev provide examples of such avian disturbance: at the two sites, a decrease in the number of Common Eiders and Common Scoters (species of large sea duck) was observed following turbine construction. This initial decrease was followed by a more than full recovery of Common Eiders, but only a partial increase of Common Scoters (Guillemette, et al. 1998). It may have been the case that Eiders were more suited to adapt to the changed landscape, and were better prepared to tolerate the increased noise disturbance. An alternate explanation 5 could be that the construction led to a dampened “reef effect” in which the base of the wind turbines became temporary habitats for mollusks; as Eiders prefer mussels as a source of food, it seems likely that an increase in the Eider population would follow as a result. Besides speciesspecific differences in disturbance avoidance, the degree to which birds are able to live in offshore wind farm locations also depends on several factors, which include the availability of alternative habitats (especially roosting and feeding areas), time of year, flock size, and the layout of the wind farm (Exo et al., 2003). Habitat loss of birds that exist in coastal waters is also linked to a number of other factors. During the construction phase, considerable acoustic emissions are common during foundation implantation – species of birds in the North and Baltic Sea are typically displaced, contingent on noise intensity and frequency range. In addition, the Baltic Sea remains one of the busiest transportation waterways in the world. According to the Helsinki Commission, around 2000 ships are normally at sea at any time on the Baltic, and cargo and container traffic is expected to triple and oil transportation is estimated to increase by 40% by 2017 (B.S. 2020). As the Baltic contains a large number of islands, narrow straits, and difficult-to-navigate routes that are ice covered in the winter, the Sea is an area of high risk for accidents. Collisions of ships with offshore turbines could occur, causing irreparable damage to the surrounding avian habitat. The degree to which a specific ecosystem is affected, however, is highly dependent on the layout of the wind farm and the biodiversity at that location. Essentially, birds such as the Common Eider have demonstrated the tendency to colonize in large numbers in centralized locations; the introduction of offshore wind turbines could potentially lead to a flurry of other issues, and leave the species without a reasonable or accessible alternative habitat. 6 To date, little is known of the effects of wind farms on bird populations because of a lack of pre- and post-construction studies that show change over a period of time. Thus far it is reasonable to conclude that birds have shown the ability to avoid wind turbines, but this response varies within and between species (Hotker et al., 2006). Birds such as the Common Eider were able to adjust their flight trajectories to avoid the wind farm area post-construction at Nysted, which shows a learned response to the presence of turbines. The additional distance that Common Eiders typically have to travel in order to avoid the farm is trivial in comparison to their migratory distance. However, studies have also indicated that the cumulative effect of many similar wind farms could impact a population; that is, if birds are constantly forced to avoid turbines, they will expend an amount of energy significantly greater than if the turbines did not exist (Masden et al., 2009). Avian concerns have played a significant role in the construction of offshore wind farms in Europe to date, although the extent to which avian populations will be affected over time by the construction of offshore wind turbines is largely unknown. At this juncture, it is apparent that the risk of avian death is heightened by factors that include, but are not limited to: a lack of light (that is, the birds cannot physically see the turbines), construction acoustics, natural noise of wind and water, turbines that are placed too close together so as to prevent birds from flying in between them, habitat-specific characteristics (such as human presence), and species-specific differences (i.e., a particular bird has a relatively larger body than other birds in the area, and may be less likely to maneuver its way through a row of turbines). It is obviously important to consider these factors in the selection of offshore locations, and scientists and designers are only able to use the limited, short-run information that they have about avian death to make long-term decisions about turbine placement. That said, current evidence is yet to show that any of the 7 aforementioned factors is certain to pose significant long term implications for the offshore wind industry. Still, by committing to maximizing the level of ecological protection, the American offshore wind campaign can learn a great deal about avian activity around offshore turbines in Europe. III. Effects on Marine Life Many similar issues affecting birds that arise from offshore turbine construction also adversely affect the marine community. According to Marcus C. Ohman, during the construction phase sedimentation and underwater noise could influence fish and other marine organisms; during the operation phase, the submerged part of the power plant locally changes the habitat causing a reef effect (the hard structure underwater may act as an artificial reef that provides a habitat for fish and sessile organisms, such as barnacles). Most importantly, the marine environment can be largely affected by the presence of subsea cables underwater that are used to carry electricity from the generator in the turbine to the offshore transformer before it is converted to high voltage. Marine animals can be influenced by the electromagnetic fields that the electric current induces, although there are marked differences in cross-species fish behavior when exposed to magnetic fields. Ecologically speaking, examining the three main consequences for marine life – the introduction of new habitats, increased noise, and exposure to electromagnetic fields – will shed some light on the insight Europe has gained from their experiences with offshore wind turbines. A bottom-up approach is necessary in analyzing the impact of turbines on the marine community. The collection of organisms that live on or in the sediment of the sea floor is known as the benthic community, or more simply benthos. The benthic community is typically 8 comprised of infauna, animals and bacteria of any size that live in bottom sediments, and epifauna, which refers to animals that are attached to or move on the bottom sediment, such as oysters, mussels, barnacles, snails, starfish, sponges, and sea squirts (Wind Energy Fact Sheet). Essentially, the introduction of the hard foundation of the wind turbine creates a new habitat for marine epifaunal organisms (Wind Energy Fact Sheet). As organisms such as mussels and barnacles attach themselves to the base of the turbine, small fish species may become attracted to the area, which can lead to an increase in the number of seabirds present. What is happening here is an ecosystem shift – as the prey move their location, the corresponding predators have no choice but to follow. The point is that the construction of offshore wind farms will modify the relationships of benthic communities, and therefore create new local ecosystems (Koeller et al., 2006). Specifically, evidence about marine ecosystems from Horns Rev wind farm in Denmark is particularly strong. Monitoring studies at the farm have indicated that indigenous infauna habitats have been effectively replaced by an epifauna community associated with hard bottom habitats, with an estimated 60-fold increase in availability of food for fish (Boesen and Kjaer, 2005). The most important news in relation to an increased level of diversity is the presence of two new species: the ross worm (Sabellaria spinulosa) and the white weed (Sertularia cupressina), and both are considered as threatened in the Horns Rev region of Denmark (Boesen and Kjaer, 2005). This information is valuable because it signifies that the introduction of offshore turbines has actually increased biodiversity and confirms the oft-discussed habitatcreation potential of these farms. The process of wind turbine construction is interesting in an ecological sense because it changes the way the surrounding ecosystem functions – predators, 9 such as the Common Eider and the Common Scoter, will inevitably move towards the new location of their epifaunal prey and the ecosystem will food chain a geographical shift. The construction of Horns Rev and Nysted wind farms has had a negligible impact on fish in terms of creating a new artificial habitat. While fish may have access to greater prey numbers caused by the wind turbines, species composition of fish in and around both Danish farms has remained relatively constant (Koeller et al., 2006). Only the population of sand eels has demonstrated a different pattern, with the population increasing by about 300 percent in Horns Rev and decreasing by 20 percent outside of it (DEA, 2006). However, it is difficult to measure such activity when the colonization process is immature – many European offshore wind farms have existed for less than a decade. There are studies that suggest that fish could be influenced by the magnetic fields induced by flowing electric current through cables on the ocean floor. First, small amounts of magnetic material actually exist within some species of fish, including the European eel (Anguilla Anguilla) and the yellowfin tuna (Thunnus albacores) (Hanson et al., 1984, Walker 1984). It is also important to note that migrating fish, such as the yellowfin tuna, are expected to use magnetic fields for orientation, that is, the sense of their surroundings (Walker, 1984). However, the human-introduced magnetic fields that occur due to turbine construction have had some negative effects. For instance, magnetic exposure was observed to modify hormone levels in brook trout, while it was also shown to have slowed down embryonic development (Lerchl et al., 1998). Krzemieniewski and his colleagues also noticed that in a laboratory experiment with the European catfish, biomass decreased and mortality increased when exposed to a constant magnetic field with an intensity ranging from 0.4 to 0.6 T (Krzemieniewski et al., 2004). 10 Thus far, studies are able to offer only indicators of potential environmental danger associated with the construction of offshore wind turbines. While the information available is limited, it can be argued that wind turbines may have the potential to increase habitat availability to some marine organisms, while at the same time hamper the physiology of some fish through magnetic field conduction. It would be valuable to be able to do longitudinal studies of marine populations both before and after the construction of turbines. 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