Impact of sound from offshore wind farms

Sounds from offshore wind farms are among the main contributors of anthropogenic noise to the marine environment. Despite 30 years of offshore wind farm operation in European waters, our understanding of their impacts on marine ecosystems during their operational lifetimes is limited. Eleven institutes from seven countries united their skills and expertise in the PURE WIND project, funded by the JPI Oceans initiative ‘Underwater noise in the marine environment’. Our goal is to expand our knowledge of the radiated noise and the biological consequences of these operations and to place them in appropriate regulatory contexts.

The sustainable blue economy provides an important contribution to the mitigation of the causes of climate change. In one implementation, there is growing interest in the rapid development of offshore turbines. Offshore wind farms (OWFs) can provide clean and renewable energy by exploiting the force of wind, which reaches a higher and more constant speed in the open sea than on land thanks to the absence of barriers.

It is important that this does not negatively impact marine biodiversity. Current technological development, however, has exceeded our ability to reliably assess environmental impacts. This makes it necessary to test for unwanted effects of the noise caused by the installation and operation of turbines in the marine ecosystem.

PURE WIND

PURE WIND aims to analyse in depth the impacts of OWFs on the marine ecosystem in the medium and long term, including on the lowest components of the food web, and in turn the top predators. To achieve this, researchers will analyse historic passive acoustic measurements and wind statistics available from OWFs in the offshore areas of Northern Europe as well as data acquired specifically within the project to analyse the impact of the construction and installation of floating parks in the Canary Islands as a test site.

The analysis of data obtained from operational wind farms allows for verification of the long-term patterns of traditional wind platforms (fixed turbines), while new data acquisition will make it possible to establish the impact of new technologies on local soundscapes. This data is fundamental for the development of a model based on wind intensity to predict the environmental noise generated by the turbines. In turn, this will enable us to establish the levels of sound pressure on the biota in the environment.

The analysis will be conducted in various marine areas, including the basins of Northern Europe and the Canary Islands, which are characterized by the presence of operational wind farms, and the Mediterranean Sea and Norway, where there are no wind turbines.

Acoustic impacts on the food web

The impact of underwater noise on the marine ecosystem has mainly been studied with regard to the effects on marine mammals and fish, which represent the apex of the trophic food chain. Arguably, studies focused on possible impacts on organisms lower in the food web, starting from zooplankton, are still in their infancy.

The researchers involved in PURE WIND will attempt to observe the impacts of marine environmental noise on the food webs that connect zooplankton to the top predators and fishing activities, both in areas not disturbed by industrial activities and in areas where wind farms are operational offshore, which can act as artificial reefs, providing new habitats and possibly impacting fisheries resources. Construction of wind farms in the open sea can affect local hydrographic regimes and it is not yet fully established how these changes influence upwelling/downwelling episodes and, therefore, phytoplankton blooms and zooplankton abundance.

PURE WIND researchers will analyse underwater environmental noise data acquired from hydrophones installed on subsurface moorings or other existing research infrastructure. This data will be acquired near the wind farms currently operating in Northern Europe and the prototypes being tested in the Canary Islands, as well as in areas where the environmental noise is mainly made up of natural sources (wind, rain, marine animals) and marine traffic, such as the Ligurian Sea and the Norwegian fjords.

The temporal evolution and statistical characteristics of environmental noise in both conditions (presence and absence of wind farms) will be compared with biomass data derived from acoustic backscatter observations to highlight the zooplankton behaviours corresponding to different wind regimes and sound level thresholds. Specifically, variations in the depth of the zooplankton, the daily migration cycle and abundance will be analysed.

Modelling

The study of the impact of underwater noise produced by OWFs requires the ability to predict the characteristic features of the anthropogenic sound spectrum and its pressure levels with regard to specific wind turbine type and local meteorological conditions, in particular the random variables wind speed and direction. To achieve this, we intend to build a model based on acoustic data acquired by the project partners using statistical learning techniques capable of predicting the acoustic impact as the wind regime varies.

The underwater noise generated by wind turbines during their operation is characterized by several components. The largest of these is the vibrations produced by movement of the mechanical parts and induced by the wind on the pylon or the mooring lines that keep them in place. However, noise is also produced by the blades when rotating close to the sea surface and by whistles created by wind against the superstructure.

The spectrum, which is the distribution of energy as a function of frequency for a particular sound source, has particularly meaningful contents concentrated at low frequencies, especially below 1kHz, composed of a continuous component (called broadband noise) to which tonal components positioned at the rotation frequencies of the various mechanical parts and their harmonics are added. This means that the shape of the spectrum is influenced by the size of the turbine, the wind speed, the type of pylon or mooring line and the foundations that support the entire generation plant, in the case of a fixed OWF.

In recent years, underwater noise generated by turbines has been measured and characterized on several occasions. Unfortunately, the different measurement conditions and the absence of common protocols have made it difficult to compare specific features of the turbines and to develop common models.

The increasing wide availability of acoustic measurements taken at sea for long periods, accompanied by the corresponding environmental data, allows the development of a black box model based on machine learning (ML) algorithms. ML techniques, thanks to their generalization and interpolation capabilities, have already been successfully used in similar problems, such as linking variables related to the behaviour of an energy transformation plant to its operating conditions.

Seal tagging

As OWF roll-out accelerates across the North Sea and beyond, we need a better understanding of how the operational phase of these infrastructures affects habitat use and the foraging success of small odontocetes, seals and other marine fauna. A variety of field efforts to address this question continues in the North Sea. In one, harbour and juvenile grey seals in the German North Sea will be tagged using GPS phone tags. These will be deployed on individual seals to determine spatial use of the North Sea over periods of up to four months, recording surfacing positions and foraging behaviour. In combination with previous tagging data, this will enable the calculation of the level of occupancy of OWF areas. Long-term passive acoustic monitoring of harbour porpoises will also continue, to evaluate their foraging behaviour within operational OWFs.

Mesocosm experiment

An in situ mesocosm experiment will be conducted in an open water environment without operational OWF noise at Trondheimsfjorden, Norway. Mesocosms are experimental, (semi-)enclosed systems that allow investigations on pelagic and benthic species and communities under near natural but controlled conditions. Biotic and abiotic conditions can be manipulated, thus allowing simulations of disturbance and impacts of external drivers on biological interactions and processes. Mesocosm approaches are considered an ideal tool to tackle ecological causes and consequences of global change, because external drivers such as temperature, dissolved carbon dioxide, nutrients, light or sound fields can be manipulated, and the responses of species and communities analysed over time. Playback experiments will be conducted to identify the response of the plankton community to operational wind farm noise.

Conclusions

PURE WIND intends to study the impacts of infrastructure for the exploitation of offshore wind energy on the marine ecosystem, with sometimes cumulative effects through: 1) analysis of the impacts of noise produced by wind farms on the behaviour of different taxa in the food web (from zooplankton to large predators); and 2) the simulation using mathematical models of the contributions of wind energy generation processes, which will be considered within the different marine reporting units that spatially define specific marine areas. These results will then be compared with in situ measurements.

The project also intends to contribute to the policy development process by producing recommendations based on past experiences and knowledge gained through this project to achieve an eco-sustainable development (green economic development).

Acknowledgments

The PURE WIND consortium acknowledges the principal investigators and the researchers of each involved institution: Ana Širović, Justine Sophie Emilie Courboules and Nicole Aberle-Malzahn (Norwegian University of Science and Technology); Sara Pensieri and Roberto Bozzano (Consiglio Nazionale delle Ricerche); Silvana Neves, Eric Delory and José Antonio Díaz (Oceanic Platform of the Canary Islands); Benedikt Niesterok, Carina Juretzek, Christian Krueger, Isabella Kratzer and Maria Boethling (Federal Maritime and Hydrographic Agency of Germany); Shauna Creane, Andrew Millar and David O’Sullivan (Gavin and Doherty Geosolutions); Alain Norro, Bob Rumes, Silvia Paoletti and Sofya Aoufi (Royal Belgian Institute of Natural Sciences); Patricia Caro Ruiz, Alonso Hernández Guerra and Ion Urtiaga Chasco (University of Las Palmas de Gran Canaria); Andrea Trucco (University of Genoa); Gerry Sutton and Jessica Giannoumis (University College Cork); Joseph Schnitzler, Tobias Schaffeld, Nina Maurer and Dominik André Nachtsheim (University of Veterinary Medicine Hannover, Foundation); Aliaksandr Lisimenka (Gdynia Maritime University).

PURE WIND is a project supported by the JPI Ocean Initiative ‘Underwater noise in the marine environment’ and by the national funding bodies of the consortium.

Further reading

https://www.ntnu.edu/web/biology/research/marine-sciences/pure-wind