Abstract
Wozep (the Wind Op Zee Ecologisch Programma) is an integrated research programme to reduce the knowledge gaps regarding the possible negative environmental effects of offshore wind farms (OWFs) on the North Sea.
In a first study published in 2021 it was shown that ecosystem effects of large-scale offshore wind farms can be profound (Van Duren et al. 2021). These effects are due to interactions of the wind turbines with the ambient flow, resulting in changed currents, stratification, changes in fine sediment dynamics and consequently changes in primary production. The 2021 study was the first project where the full range of the DCSM-FM model with fine sediment and water quality and ecology modelling were used in an applied project. The modelling suite showed its potential, but in this first exercise there were also a few teething problems highlighted. Many of these were solved in a follow-up study in 2022 (Van Kessel et al. 2022). The current report details further improvements in parameterisation of certain parameters, significantly improving model performance.
The first modelling study (Van Duren et al. 2021) had identified a potential decrease of fine sediment transport to the Wadden Sea. This was with the first version of the model that showed a significant bias in absolute suspended particulate matter (SPM) concentrations. This effect was now further investigated with the latest version of the model. The present study confirmed the decrease in mud fluxes towards the Wadden Sea. It appears that the changes in alongshore transports are a consequence of the larger scale changes in hydrodynamics of the Rhine region of freshwater influence (ROFI), affected by the combined presence of wind farms in the southern North Sea.
The main part of the current study comprises the results of two new scenarios. One is relatively close to the expectations of wind farm locations in the Dutch North Sea around 2040, the second one is a more extreme upscaling scenario, including wind farms that may not be developed due to user conflicts and a few areas that are currently not in the set of official wind search areas. The new scenarios did not give rise to significant changes in the way we currently think different parts of the North Sea will respond to the presence of wind farms. However, particularly the use of the now fully coupled model indicated a more severe effect of increased fine sediment concentrations in the top layers of the water, resulting in more areas showing a decrease in primary production due to limited light availability. The presence of mussels on the turbine monopiles had some effect on primary production, but limited effect on chlorophyll concentrations. The impact of mussels and other grazers needs further investigation before we can draw quantitative conclusions about their impact.
Finally, the report describes planned relevant follow-up research, particularly efforts on gaining insight in the knock-on effect of changes at the base of the food web on higher trophic levels.