Predicting the large-scale consequences of offshore wind turbine array development on a North Sea ecosystem

• We modeled the impact on waves, sound and biogeochemistry of an offshore wind-turbine array.
• All three models suggested relatively weak environmental changes.
• Most changes occurred within the turbine array, with small changes in tens of km outside the array.
• Combining, we found different combinations of changes within the array that may affect marine life.
• Further work is required, including additional mechanisms and different hydrographic settings.

Three models were applied to obtain a first assessment of some of the potential impacts of large-scale operational wind turbine arrays on the marine ecosystem in a well-mixed area in a shelf sea: a biogeochemical model, a wave propagation model and an acoustic energy flux model. The results of the models are discussed separately and together to elucidate the combined effects. Overall, all three models suggested relatively weak environmental changes for the mechanisms included in this study, however these are only a subset of all the potential impacts, and a number of assumptions had to be made. Further work is required to address these assumptions and additional mechanisms. All three models suggested most of the changes within the wind turbine array, and small changes up to several tens of km outside the array. Within the array, the acoustic model indicated the most concentrated, spatially repetitive changes to the environment, followed by the SWAN wave model, and the biogeochemical model being the most diffuse. Because of the different spatial scales of the response of the three models, the combined results suggested a spectrum of combinations of environmental changes within the wind turbine array that marine organisms might respond to. The SWAN wave model and the acoustic model suggested a reduction in changes with increasing distance between turbines. The SWAN wave model suggested that the biogeochemical model, because of the inability of its simple wave model to simulate wave propagation, over-estimated the biogeochemical changes by a factor of 2 or more. The biogeochemical model suggested that the benthic system was more sensitive to the environmental changes than the pelagic system.