The impacts of burning fossil fuels for energy generation on the environment, specifically increasing the rate of climate change, is well documented and studied. In recent years there has been a shift to renewable energy sources, with solar and wind farms growing in popularity. This global adoption of renewable energy also includes the large-scale development of offshore wind farms. Advances in technology are allowing higher capacity wind turbines to be installed in deeper water. Although the switch to renewable energy sources has an overall positive effect on our environment, the construction of these large developments can have local negative impacts both on land and offshore.
Offshore Wind Farms
Offshore wind farms (OWFs) are quite a sight – large turbines slowly churning away on the horizon. Despite the clean energy benefits that these large developments have, their construction and long-term operation is impacting the marine life living beneath the rotating blades. Different types of OWFs will have varying impacts on their surrounding environment, as the base or anchor of the turbine will influence the level of disturbance. There are also competing uses for the marine environment, such as commercial fisheries, which will undoubtedly be impacted by the construction of an OWF in areas targeted for commercial fishing.
One of the earliest impacts that OWFs have on their environment is during the construction phase, due to physical damage caused to the seafloor. Not only is seafloor habitat destroyed to install the piles that anchor the turbines, but sediment is also suspended in the water column due to this disturbance. It is expected that this suspension of sediments has a negative impact on marine life, as it increases the turbidity in the water, mobilizing contaminants buried in the sand, and also smothering filter-feeding animals like corals, sponges and anemones. The increased turbidity and decrease in visibility may also impact algae that depend on sunlight filtering through the water for photosynthesis.
Marine noise pollution, such as noise from vessels, can affect the behaviour of marine animals, especially those that depend on vocalizations for communication, or echolocation for navigation. During the construction of OWFs, a lot of noise is involved due to pile-driving. During operation, the turbines generate noise above water, however, some noise still transmits through the tower and radiates into the ocean. This noise can have a negative impact on social interactions of porpoises, as well as other migratory species.
Prior to the construction of OWFs, seismic surveys are conducted to map the seabed. Studies have shown that certain whale species, such as humpback whales, avoid areas where seismic surveys are being conducted. Although the noise of a seismic survey is of short duration, it is still worth noting the impacts it may have on animal behavior.
Electromagnetic fields are created by the transportation of the generated energy through the electric cables that are placed on the seabed. It is possible that these electromagnetic fields have an effect on animals that depend on electroreception for detecting prey, such as sharks and rays.
Studies have shown that the introduction of artificial structures into the marine environment (such as OWFs, oil rigs and ports) promotes the spread of non-indigenous species. These invasive species disrupt natural food webs, causing changes in populations of endemic species, which in turn has a knock-on effect on the entire ecosystem. Known invasive species found on OWFs include barnacles, oysters, amphipods, midges and limpets.
Similar to construction impacts, the decommissioning of wind farms at the end of their lifetime will again disturb the surrounding environment. Even if the larger structures and piles are left behind, removal of infrastructure and cables will result in disturbances to the environment, and again may result in a short-term increase in turbidity and sediment suspension, as well as noise pollution.
Despite all the negative and harmful impacts listed above, it is not all doom and gloom, as OWFs also contribute to positive impacts in their surrounding ecosystems.
The construction of OWFs introduces a new three-dimensional hard substrate, which can act as an artificial reef on a previously flat seabed. It has been argued that the initial disturbance caused by OWFs during construction is only short-term, and that long-term they can create up to 2.5 times more habitat. This habitat can then be used by sessile organisms, intertidal organisms, and also fish species.
The benefit of a new habitat created by the tower is the increase in biodiversity – a key indicator of ecosystem health. Observations at an OWF in the Baltic Sea found that biological activity was increased on a portion of the turbine where blue mussels were abundant. These mussels modify their habitat by filtering organic matter from the surrounding water, and also act as a secondary hard substratum for other creatures to colonize, promoting biodiversity. Other OWFs reported similar findings, with an increase in diversity and abundance of benthic organisms and fish.
OWFs can also act as a refuge for commercially exploited species. These species are attracted to OWFs due to the increase in biodiversity – and subsequently food – and fishermen avoid OWFs due to fear of entanglement or collisions. As such, fish living among the turbines are less likely to be commercially harvested. In the future, it may be possible to combine OWFs with Marine Protected Areas to further protect commercial fish species, and to bolster marine ecosystems.
Although current research suggests that OWFs have a predominantly negative impact on their surrounding marine environments, due to damaging impacts of construction and ongoing noise pollution, it must still be noted that some of these negative impacts are counteracted by positive effects. For example, although the construction of an OWF destroys the seabed habitat, in the long term it creates a new habitat that may be colonized by different species. Similarly, OWFs are introducing foreign species, however they are also increasing local biodiversity. More research is needed to determine to what extent the negative impacts of OWFs are offset by the positive impacts.
We also cannot consider the impacts of OWFs alone, as they contribute to cumulative human impacts in the marine environment, including fishing, dredging, and drilling. Further studies into the impacts of OWFs – both construction and operational impacts – will enable renewable energy companies to decide whether they should focus on alternative sources of renewable energy, such as solar power, to mitigate climate change, especially if the protection of the marine environment remains a priority.