Dahl, K., Hansen, J.L.S., Pedersen, I.K., Lønborg, C. & Göke, C. 2022. Videnskatalog. Potentielle natur og miljø virkemidler, forvaltningsprincipper og overvågning i vindmølleparkområder. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 54 s. - Videnskabelig rapport nr. 490. http://dce2.au.dk/pub/SR490.pdf

Summary

There are ambitions for a very large expansion of wind farms in the regional sea areas Denmark shares with our neighboring countries. In Danish waters alone, the plan is to expand by a further 10 GW by 2030. In order to address possible conflicts between development plans for offshore wind and nature conservation and the overall goal to achieve good environmental status in Danish seas, the Danish Energy Agency have asked DCE to provide a catalog of concrete measures to secure the marine biodiversity and good environmental status. This includes management principles and relevant monitoring activities that can be brought into play in connection with future development of offshore wind.

As for the rest of the world, Denmark faces a biodiversity crisis and a number of anthropogenic pressures affects the biodiversity and environmental condition of the regions of Danish seas. Establishment of offshore wind turbines causes a loss of original seabed area where the sedimentary substrates is typically replaced by hard substrates of the towers and scour protection. Consequently, the biological communities will change from soft bottom communities to hard bottom communities and due to reef effects, where mobile organisms are attracted to these reef-like structures, ecosystem changes are not confined to the wind farms. In areas where hard substrates do not naturally exist, which is particularly true in the central and southern North Sea, wind turbine foundations and associated scour protection can lead to increased immigration of non-indigenous fauna and macroalgae species. Wind farms have an effect on seabird species. Some species are displaced from food areas, other species might get longer flyways, and finally there is a risk of collisions.

The second part of the report consists of a literature review within the subject of environmental instruments in relation to offshore wind. There is overall knowledge, although limited, in topics such as turbine design, lighting principles, collision risk and protection against electromagnetic fields around cables. Other topics are mentioned in the literature but have not been studied in the field. These are the effects of surface structures, the location of the turbines, erosion protection and establishment of oyster banks.

The third part of the report consists of concrete nature and environmental instruments that can be implemented with varying degrees of experience:

• Restoration of boulder reef areas and eelgrass meadows. Those measures will be particularly relevant in cable corridors. In former time boulder reefs was extracted at water depth to approx. 10 m and eelgrass has is main distribution areas at relatively low water depths. The risk of implementing both instruments is very small, and they will both be in line with national efforts for restoring lost habitats. There is experience in Denmark regarding the restoration of both boulder reefs and eelgrass meadows.
• Establishment of artificial boulder reefs (i.e. reefs where there have been no reefs before). It is a useful tool if the goal is to promote hard bottom communities at the expense of soft bottom communities. The instrument is associated with risks of unintentional introduction of non-indigenous species (which is also a general risk on windmill foundations and scour protection). There may be implications in relation to three of the Marine Strategy Directive's descriptors “seabed integrity” and “biodiversity” and “non-indigenous species” that should be clarified. The level of experience creating reef sites is high in Denmark.
• Establishment of European oyster beds and release of lobsters around scour protection are two measures that can be considered. There is experience for breeding both species under laboratory conditions, but not for release in relation to wind farms. It is also uncertain whether there have been oyster beds in Danish waters years ago or just scattered individuals. It is also unknown if oysters will be able to thrive in the Danish part of the North Sea, Skagerrak and Kattegat. Release of lobster will promote a process assumed to take place any-way over years. There is very limited experience in the use of these measures in Denmark.
• For seabirds, three measures have been proposed. One is the design of wind farm designs in relation to prevailing flyways. The design should reduce the barrier effect. The second tool deals with the special vertical lighting in the wind farm at night, a lighting that can lead to the risk of collisions. An active demand-driven lighting strategy controlled by presence of airplanes in the area will reduce the risk. The last measure is a temporary closure of the park under conditions that are characteristic of major nocturnal bird migration and under invisible weather conditions. There are experience with these measures in Denmark.

The last part of the report deals with monitoring needs for a prober management of marine areas. There are so far no established guidelines how to monitor offshore wind farms in relation to the ecosystem-based management. It is important to have a monitoring program that is representative for the different seabed types and that the program fulfill the obligations set by the Marine Strategy Directive. In this context, it is also important to have a risk assessment made for unintentional introduction of non-indigenous species of the full implemented plan for wind parks in Danish as well as neighboring waters. Monitoring in the free water masses is also important as well as marine mammals. Setting up and servicing automatic measuring stations for in selected parameters in wind farms will generate important data for developing and calibrating hydrodynamic models for different water basins.