As is with other relatively new industries, the environmental effects of offshore wind energy have not been fully examined. In their comprehensive review, Wilson et al. (2010) find that although many gaps in knowledge exist, overall, offshore wind generation does result in adverse ecosystem effects. These effects were generally minor, but their magnitudes are dependent on the sensitivity, migration patterns, mating and feeding habits of the specific fish, benthic invertebrates, birds, marine mammals, and other creatures which inhabit potential wind energy sites. Negative environmental effects during the exploration, installation, operation and decommissioning of wind farms result from increased noise, the presence of electromagnetic fields, habitat loss and degradation, and the potential for collision with turbines. There is also evidence that environmental benefits may result from offshore wind energy generation. For instance, the towers and foundations of offshore wind turbines have been found to act as artificial reefs which may increase fish and benthic populations. Furthermore, wind farms may deter commercial fishing, especially the use of beam-trawling, creating, in effect, wildlife protection areas. The authors caution that the magnitude and direction of environmental consequences, especially long term, are not well examined and thus additional research is needed.—Juliet Archer
Wilson, J., Elliott, M., Cutts, N., Mander, L., Mendão, V., Perez-Dominguez, R., Phelps, A., 2010. Coastal and offshore wind energy generation: Is it environmentally benign? Energies 3, 1383–1422.
Wilson and colleagues at the Institute of Estuarine and Costal Studies at University of Hull (Hull, United Kingdom) determined the potential environmental effects of an offshore wind farm using a conceptual model or “horrendogram” and then analyzed these effects relative to an undeveloped offshore site. The authors separately analyzed environmental effects during the different phases of a project, such as exploration, construction, operation and decommissioning. They further classified their findings based on whether the impact was likely to have a major, moderate, minor, negligible, nonexistent or beneficial interaction. Wilson et al. also considered the persistence (days, weeks, months, etc.) and spatial extent (nearfield, far-field) of an impact. The classification of impacts was based on historic data, recent studies, reports, and expert judgment.
In regards to the seabed, Wilson et al. determined that when utilizing current monopile foundations, disturbance and possible alteration of the sediment structure is unavoidable. The alteration of sediment structures occurs when fine particles are released from the drilling of monopiles into hard chalk or other bedrock. Drill cuttings may also smother benthic and other creatures. The installation can also cause scour or erosion of the seabed around the base of the new turbine as the flow of currents in the immediate area changes. To minimize current, wake, and habitat changes, turbines can be spaced further apart so that the affected area is small compared to the size of the entire wind farm. To minimize erosion of the seabed, scour protection can be installed. Depending on the type of material and design used, such as rocky substratum adjoining to sandy substrata, scour protection can also increase the surface area available for colonization.
The authors noted that habitat increases can be especially beneficial for juvenile benthic creatures, such as crabs. This impact would therefore be beneficial to both the benthic ecosystem and commercial fisheries as populations are protected within a certain area yet increase overall. Fish populations have also been shown to increase when wind farms are located in nursery areas, as juvenile mortality decreases and spawning biomass increases. Furthermore, scour protection design considerations that increase complexity, like holes and artificial seagrass beds, can increase the number of fish in an area. Again, increased fish populations would benefit commercial fisheries as larger populations spill out into fishing grounds. However, it is unclear whether habitat creation would offset habitat loss for native organisms and so the overall direction of the impact is unknown. Also, the magnitude of the impact may be dependent on the location of the wind farm and the specific aquatic populations with which it interacts.
Wind farms also have negative impacts on fish communities. For instance, electromagnetic (EM) fields, created by export cable routes and connecting cables, may cause a significant moderate impact, especially on sensitive species like elasmobranchs, and teleosts, and on other demersal, and benthic organisms. Potential EM field impacts include decreased hunting performance and incomplete migrations. The significance of these EM field effects is dependent on the type and magnitude of current, insulation type, conductor core geometry, particulars of the seabed, and the depth of the cable (if buried). In addition, noise and increased turbidity during the construction phases may have moderate to minor impacts on hearing specialists and visual predators, respectively. Noise pollution can also occur during operation and may lead to sublethal effects like disturbances in fishes’ gathering of information about other fish (prey, predators, competitors, and mates) and locations (migration routes and feeding grounds). Overall the many potential feedback loops make it difficult to predict precisely how wind farms will impact fish and benthic organisms.
The effect on mammals and coastal and sea birds is, on the other hand, overwhelmingly negative. For instance, the probability of collision with turbine blades is especially high if species pass through often. This impact can be mitigated by proper placement of wind farms in regards to wind currents and birds’ foraging and breeding areas. However, the probability of collision for large birds, which cannot easily maneuver may be unavoidable. Times of low visibility and/or high winds are likely to exacerbate the problem. Bats are also especially susceptible to collisions because of their curiosity and attraction to the turbines’ artificial lighting and high insect populations. In the long run, habituation to wind farms has been shown to decrease avian mortalities as birds learn to recognize the wind turbines as dangerous. Improving turbine technology, by using larger blades that rotate more slowly, for instance, may also decrease the collision rates of birds and bats.
Another potential impact on avian creatures is habitat loss and resulting displacement as birds avoid the turbine structures. If the required diversions, and thus extra energy expenditures, are large enough, then the wind farm can become a barrier and may reduce the breeding and survival rates of the population. As with fish populations, the impact of habitat loss on bird populations is dependent on location. For example, if the farm is located near an estuary or on a coast, then it may decrease the area available for feeding or roosting. Furthermore, if a wind farm is poorly located in regards to adjacent developments then cumulative effects may be detrimental to bird populations. Cumulative effects may occur if a chain of wind farms is located in a flyway corridor for a rare species. More information via improved predictive and observational models is needed in order to determine the significance of the above impacts on birds and mammals.
Marine mammals like cetaceans (dolphins, whales, and porpoises) and pinnipeds (seals and sealions) may be significantly impacted by the noise produced by wind farms. These marine mammals are extremely vocal and some also use echolocation to communicate, navigate, avoid predators, forage, and locate other individuals. The noise interference with these activities would be greatest during exploration and construction. Noise interference would also occur, at minimal levels, during operation. The results of this interference may include displacement (temporary or permanent), changes to feeding and social behaviors, reductions in breeding success, stress, and death. The magnitude of these effects is dependent on the mammals’ habituation to noise, low-frequency hearing abilities of specific species, sound-propagation conditions, and ambient noise levels. To decrease the cumulative effects of a proposed wind farm, location decisions should give consideration to the breeding and migration patterns of marine mammals in relation to existing offshore activities.
Wilson et al. recommend a number of improvements to the technologies and processes of determining and measuring the environmental effects of proposed offshore wind farm sites. The technologies recommended are very specific to each affected organism, while some of the processes are in the form of general guidelines. For example, the authors recommend that future research distinguish between real and perceived impacts of offshore wind farms. Additionally, they advise that monitoring be in proportion to the actual effects and not to the publics’ perceived effects. They also advise monitoring programs for endangered, protected, and ecosystem key organisms. Lastly, the authors emphasize the many gaps in knowledge and the need for studies focusing on long term effects. Wilson and colleagues conclude by acknowledging that offshore wind farms are not entirely environmentally benign. Yet the authors remind readers to weigh the costs with the environmental benefits, including the creation of renewable energy.