Abstract
The steadily rising concentration of Greenhouse Gases (GHG) in the Earth’s atmosphere is a consequence of the increased emission by anthropogenic activities. These emissions and the consequential climate change have caused and are continuously causing serious threats to ecosystems, single species as well as human health. To reduce these emissions and hence diminish the consequences of climate change, several international (e.g. UNEP) and national institutions have established programs and projects to mitigate, reduce, or integrate effects of climate change. Among others, the European Union has developed programs and targets to replace energy from fossil sources by energy from renewable sources. The renewable energy targets developed by the EU in 2008 and renewed in 2014, aim for
- a 40% cut in greenhouse gas emissions compared to 1990 levels
- at least a 27% share of renewable energy consumption by 2030
Energy generated from wind power is one of the most promising tools to reach this EU targets and make energy production more sustainable. Besides generating energy from wind with land-based turbines, the field of offshore windfarms located in the oceans is developing since more than 25 years and gains raising awareness. Windfarms located offshore benefit from favourable wind conditions for efficient energy production and seem to profit from almost “infinite” space. However, OWFs impact on the surrounding environment and the more OWFs are developed, the greater the competition for space with the environment and other anthropogenic activities is becoming.
Since 1991, when Denmark built the first OWF, 17 countries have constructed OWFs, most of them located in Northern Europe (GLOBAL WIND ENERGY COUNCIL 2018). In the Mediterranean there is no OWF present so far. Turbines of OWFs usually have greater dimensions compared to the turbines onshore, and reach higher efficiency and yielding more energy per installation. Across Europe there have been about 4000 turbines installed so far (WIND EUROPE 2018). The present turbines are designed for relatively shallow waters (±40 m), as can be found in the North Sea and the Baltic Sea. To ensure resistance to severe weather conditions the foundations of those turbines are piled 30 m and more into the sea bed. Recent projects and developments also take possible locations further offshore, in deeper waters or on ground not suitable for piling, into account. However, major constraints, like the efficient transmission of the produced energy to the shore, are still under research and development. Floating turbines have been developed, which do not require a solid foundation, but are instead anchored in the ground. Until now several test sites and pilot projects have been constructed (e.g. OWF ‘Hywind’ in Scotland). Nevertheless, there are several projects in the early or advanced planning phase, for instance in the Mediterranean, where this construction technique is seen as most promising for the prevailing conditions (e.g. ‘Les éoliennes flottantes du Golfe du Lion” in France) (4C OFFSHORE LTD 2018).
The construction, operation and decommissioning of OWF are impacting on the surrounding marine environment and also have consequences on a socio-economic level. It is proven that OWFs impact on the hydrographic conditions in their vicinity and that certain animal groups and habitats can severely be affected by an OWF. Potential impacts of OWF are investigated for instance for benthic communities, fishes, birds and marine mammals. Chemical pollutants, e.g. from sacrificial anodes can accumulate in the sediment with currently unknown consequences for the marine environment. Benthic communities can suffer from habitat loss due to the space the OWF requires and the seabed that is moved during construction of the turbines and associated constructions (e.g.cables) (HUDDLESTON 2010). The impact of electromagnetic fields emitted by the cables transporting the energy from the turbines to the shore on benthic animals and invertebrates in general is not very well known. On the other hand benthic communities can use the newly introduced structures as additional habitat and this way contribute to generating an artificial reef (LINLEY et al. 2007). Such an artificial reef may be attractive for mobile animals, such as fish or marine mammals, which may use the reef as a feeding ground or, in case fishing is prohibited in the OWF, as a refuge (DEGRAER et al. 2013). Whether these secondary impacts of an OWF are beneficial for an ecosystem depends on several factors, such as the native habitat structure or the organisms, mainly colonizing the artificial reef. As some fish species have excellent hearing capabilities fish may also be harmed by the noise introduced to the marine realm by the piling of the foundations into the ground or by the pressure associated with the piling events (MUELLER-BLENKLE et al. 2010).
Marine mammals are known to respond at large distances to noise levels generated during construction. The main concern is that the sensitive auditory systems can be seriously harmed by pulsed noise generated during piling activities (e.g., eliciting a temporary or permanent threshold shift (BRANDT et al. 2014)). Also temporary or permanent displacement (habitat loss) is seen as a major pressure on marine mammals, because it can be followed by negative effects on the individual as well as on the population level. For birds several negative impacts are known. The physical presence of the OWF can lead to habitat loss as some species tend to avoid the windfarm area (Garthe et al. 2018). Furthermore the OWF can act as a barrier on migration routes of migrating birds and force the birds to change their original route. Furthermore birds face a potential risk of mortality due to an elevated collision risk with the turbines (DEGRAER et al. 2013).
In order to minimize negative impacts of OWF on the marine environment, it is recommended to follow the principles of 1. Avoidance 2.Mitigation and 3.Compensation. Negative impacts should be generally avoided. If this is not possible, these impacts should be mitigated following best-practice strategies and, as the least preferred option, the impacts should be compensated adequately. Possible strategies for avoidance and mitigation of negative pressures of most concern are presented in this report, including case studies of OWF, where these methods have been applied. Furthermore monitoring methods and research projects are highlighted, focussing on Northern European countries and how those can be adapted to future projects in the Mediterranean Sea.
Rising anthropogenic activities by increasing offshore wind developments will also cause spatial competition with other economic sectors (e.g., fisheries or tourism) as well as ecologic interests and targets, such as existing/planned Marine Protected Areas (MPAs) or sites of special ecological value. Since the 1950 there has been consistent progress in establishing protected areas in the Mediterranean Sea and in 2016 there were 1231 sites designated as MPAs, which equals 7.14% of the area of the Mediterranean Sea (MedPAN et al. 2016) (Figure 1.1).