Effects of offshore wind farms on suspended particulate matter derived from satellite remote sensing Version 3

The impacts of offshore wind farms on water quality remain to be quantified. This study examines the water quality in and around four offshore wind farms in the Dutch part of the North Sea using suspended particulate matter (SPM). Satellite-derived SPM was used in a Before-After-Control-Impact (BACI) analysis to assess changes in water quality caused by wind farm construction. In addition, relationships between satellite retrieved SPM and environmental variables from models (i.e., salinity, temperature and current velocity from the hydrodynamical GETM model, and wind speed from ERA-5 re-analysis meteorological data) were investigated to identify the drivers of SPM change in each of the four sites. Results show that SPM concentrations (as well as temperature and salinity) changed significantly when comparing a period of ca 6 years before and after wind farm construction, while no significant changes were observed when comparing control and impact treatment. The BACI analysis thus did not reveal a significant effect on SPM in response to construction of the wind farms. Scatterplots showed a complex interaction of hydrodynamic and meteorological variables on SPM changes, superimposed on a clear seasonal variation; when analysed by season, surface water temperature correlated most with SPM variations. Our results suggest that the combination of BACI and the visualization of satellite-derived and model derived data provide insight in the potential impact of wind farms. Satellite imagery was crucial in providing SPM data at relevant spatio-temporal scales; however, the satellite data may be biased by sampling under clear sky and low wind speed conditions, while the environmental variables were retrieved disregarding the wind farms in the hydrodynamical model. Despite these drawbacks, such information provides an understanding of the possible environmental impacts of offshore wind farms that can be used in policy making, and in general terms, these results may aid the planning of new wind farms.