Press release 15 years of monitoring the ecological effects of Belgian offshore wind farms continues to yield new insights

30/01/2024 Source:
Cover of WinMON report

Fifteen years after its inception, monitoring of the ecological effects of Belgian offshore wind farms continues to provide new insights. That is an important conclusion from the latest WinMon.BE report, which summarizes findings on benthic invertebrates, fish, porpoises and birds. Only through sustained and adaptive monitoring can we ensure that offshore wind farms are designed and built in the most environmentally friendly way.

Eight offshore wind farms are currently operational in the Belgian part of the North Sea, with a total installed capacity of 2.26 Gigawatts (GW) and consisting of 399 offshore wind turbines. Together they cover an area of 238 km² along the border with Dutch waters and produce an average of 8 TWh annually. This accounts for about one-third of the gross electricity production from renewable energy sources in Belgium.

The impact on the marine ecosystem, both positive and negative, has been studied from the beginning of the construction of the first wind farm in 2008 through the WinMon.BE monitoring and research program. The scientific insights obtained have always informed the management and development of this first Belgian offshore wind farm area. In a new (Dutch-language) report scientists from the Institute of Natural Sciences, the Institute for Nature and Forest Research, Ghent University's Marine Biology Research Group and ILVO discuss the latest findings from 2022, summarize some trends from 15 years of monitoring and indicate where additional research and the development of additional mitigation measures are needed.

Macrobenthos

The long-term effects of offshore wind farms on the macrobenthic communities (roughly comprised of the organisms living on the seabed that are visible to the naked eye) inhabiting the surrounding natural soft sediments were studied over a 13-year period (2008-2020). In this context, the sediments around and between the wind turbines were also studied.

Because wind turbines affect water flow, fine sediments settle more easily there. Sediments in wind farms are also organically enriched by the feces of organisms that have colonized the turbines themselves (such as mussels, anemones and crustaceans), and by dead animals that fall off of the turbines. For the macrobenthos, higher numbers and species richness and diversity were found around the wind turbines. Moreover, higher numbers were also documented in the channels between the sandbars on which wind farms are typically built. The macrobenthos community continues to change, no steady state has yet been reached after 13 years of offshore wind farm operations.

Additionally, macrobenthos diversity, numbers and species richness were also correlated with climate-related parameters (sea surface temperature and its natural variability on a time scale of decades), demonstrating the importance of including such environmental variables in the study.

Bottom-dwelling fish

Changes in species distribution patterns were identified for fish living on and just above the seabed, as was illustrated for plaice Pleuronectes platessa. For this species, spatial distribution, diet and movement patterns were extensively studied in relation to offshore wind farms. A combination of visual dive transects (at turbine scale), arboreal samples (at wind farm scale), and tracking of tagged animals showed that erosion protection around the base of wind turbines and sand patches between turbines have become important feeding habitat for plaice.

The findings suggest that offshore wind farms act as a refuge for plaice, potentially reducing direct fishing mortality and likely enhancing production (reproduction). It was previously documented that fishing vessels caught more plaice for the same fishing effort just outside the wind farms than at the same sites before the wind farms were built. However, it remains to be investigated whether this is a true spillover effect that persists over the longer term, and will also hold up in the context of the expected large-scale expansion of offshore renewable energy zones in the broader North Sea.

Porpoise

Changed distribution patterns of species should not be interpreted solely in relation to the presence of offshore wind farms, but may also depend on other human activities, such as shipping, fishing and mariculture. This is particularly the case for highly mobile species such as marine mammals. Data from aerial censuses (2009-2022) allowed analysis of the distribution patterns of the harbor porpoise Phocoena phocoena as a function of both environmental and human-induced stressors.

The distribution of the harbor porpoise followed a consistent seasonal pattern, with the highest densities in spring. The species was shown to prefer the western part of the Belgian North Sea waters, with a strong overlap with the marine protected area 'Flemish Banks'. Distribution was also negatively correlated with the intensity of vessel traffic and with the distance to the nearest offshore wind farm. However, it is essential to be cautious about over-interpreting these correlations. Further monitoring and research is recommended to better understand the interaction between natural factors driving porpoise spatial distribution, such as prey availability and anthropogenic stressors.

Seabirds

The monitoring strategy for seabirds aims to document not only how they seek out different areas at sea than before the construction of the wind farms, but also from what distance they avoid (or are attracted to) wind farms and the effect of turbine density on seabird movement. The results presented at this stage (data from February 2021 to April 2023) should be considered indicative, as more data and advanced spatial models are needed to make stronger conclusions.

Nevertheless, based on currently available data, it is interesting to note that the observed responses are consistent with what has been found previously and elsewhere for various seabird species. The results indicate an attraction effect for great black-backed gull Larus marinus and cormorant Phalacrocorax carbo, and an avoidance effect for gannet Morus bassanus. On the other hand, avoidance of wind farms by guillemots Uria aalge was no longer observed and an increasing number of razorbills Alca torda were observed in wind farms.

Migratory birds

Since the southern North Sea lies on one of the main migratory routes in Europe, mitigating the impacts of offshore wind farms also entails measures to reduce collisions with wind turbines by migratory birds. The highest flight intensities at sea are recorded at night during spring and autumn migrations, mainly of migrating songbirds. Normally these migrate at higher altitudes, but some fly at rotor height of the wind turbines and are therefore at risk of collisions. Especially adverse weather conditions bring large numbers of songbirds into the range of the turbine engines.

Temporary shutdown of turbines during periods of high collision risk for songbirds is expected to substantially reduce mortality. This management measure is not yet regularly applied, but has already been tested in the Netherlands, among others. Site-specific monitoring remains necessary to assess the effectiveness of this measure and to refine the strategy. Moreover, a regional approach may be best suited to maximize the efficiency and ecological benefits of such a measure.

Long-term and adaptive monitoring

Most environmental monitoring programs for offshore wind farms are discontinued five years after installation. In contrast, WinMon.BE adopts a long-term research philosophy that covers the entire life cycle of offshore wind farms, from construction through the operational phase to final decommissioning. The program shows that 15 years after the first installation of offshore wind turbines in the Belgian part of the North Sea, changes in the marine ecosystem are still being observed, as was the case for macrobenthos communities. This underlines the importance of long-term research for responsible management of offshore wind farms.

The monitoring program must also be adaptive. Not only continued research, but adapted and new research is indispensable to increase understanding of how marine ecosystems respond to wind farms. This research should focus not only on attracting hard substrate species (where wind turbines represent artificial hard substrates), but also on species less obviously impacted by offshore wind farms, such as plaice and other bottom-dwelling fish.

Steven Degraer (Institute for Natural Sciences/MARECO), coordinator of the WinMon.BE consortium: "We must continue to think critically about the efficiency and effectiveness of the monitoring and research program to ensure that we collect the best data, as evidenced by the modified draft of the seabird monitoring program. As has been demonstrated for marine mammals, we need to answer the most pertinent questions and contextualize the effects of offshore wind farms. Advancing insights are needed to develop evidence-based, efficient and effective mitigation measures, and to design and build environmentally friendly offshore wind farms."

WinMon.BE continues to inform

In het marine spatial plan 2020-2026 an additional Belgian marine renewable energy zone was designated, the Princess Elisabeth Zone. An additional installed capacity between 3.15 and 3.5 GW is planned here on an area of 285 km². WinMon.BE's progressive insights are also being used to guide the design of this zone in an environmentally sensitive manner, and also during the construction and operation phases of future wind farms, WinMon.BE will document and learn to understand the effects on the marine environment. As the Princess Elisabeth Zone overlaps with the marine protected area 'Flemish Banks', additional knowledge on nature-inclusive wind farm design was gathered in the EDEN2000 study "Exploring options for a nature-proof development of offshore wind farms inside a Natura 2000 area" (2019-2023).

Moreover, Belgium is not the only country betting on wind farms in the southern North Sea. In the countries surrounding Belgium, many wind farms are either already operational, under construction or planned, and there is a statement of intention to install 300GW of wind energy in the North Sea by 2050. Therefore, cumulative ecological effects on a larger geographical scale than the Belgian part of the North Sea are also a concern. The results of WinMon.BE and EDEN2000 are also directly useful in the context of the Greater North Sea Basin Initiative, which strengthens cooperation on marine spatial planning among North Sea countries. An additional reason why it is important to continue monitoring the ecological effects of offshore wind farms!

"WinMon.BE still has a long future ahead of it. Encouragingly, the program is also serving as an example internationally for environmental monitoring in offshore wind farms. Discussions are ongoing with policy makers and scientists from different countries, who want to draw inspiration from the Belgian example.", Steven Degraer concludes.

About WinMon.BE

The WinMon.BE monitoring program is carried out on behalf of the Federal Government in the context of environmental permit conditions for offshore wind farms. The monitoring made use of the research vessel Belgica (sailing time on RV Belgica was made available by BELSPO and the Institute of Natural Sciences), the research vessel Simon Stevin (operated by the Flemish Institute of the Sea), several private vessels, the Belgian scientific diving team and the aerial surveillance aircraft of the Institute of Natural Sciences.

WinMon.BE is a collaboration between the Institute for Natural Sciences, the Institute for Nature and Forest Research (INBO), de Marine Biology research group of Ghent University and ILVO and is coordinated by the Institute of Natural Sciences' Marine Ecology and Management (MARECO) team. MARECO also coordinated the EDEN2000 study on the expected ecological effects of future offshore wind farms in the Princess Elisabeth Zone.

(ILVO, within the WinMon.BE consortium, is responsible for monitoring the effects on fish)

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