Near-field Spatial and Temporal Benthic Monitoring at the Block Island Wind Farm, USA

Anwar A Khan, HDR, Inc., Athens, AL, United States, Monique LaFrance Bartley, University of Rhode Island Narragansett Bay - Graduate School of Oceanography, Oceanography, Narragansett, RI, United States, Paul English, Fugro GB Marine Limited, Portsmouth, United Kingdom, John W King, Univ Rhode Island, Narragansett, RI, United States and Zoe Hutchison, University of Rhode Island Narragansett Bay, Graduate School of Oceanography, Narragansett, United States
The Block Island Wind Farm (BIWF) is the first offshore wind facility in the United States. The third of a four-year benthic monitoring study has been completed. Grab sample and imagery data were collected at three of the five turbines and three control areas. The data are being used to assess near-field temporal and spatial alterations in benthic macrofaunal communities, sediment composition, and sediment organic enrichment caused by the BIWF structures.

In Year 1, samples were collected 20-80m from the perimeter of the turbine jacket foundation structures. The results indicated macrofaunal communities and sediment characteristics remained comparable within turbine and control areas, dominated by polychaetes and nematodes within medium and coarse sand. Sampling was expanded in Year 2 to include the area under the foundation structures (i.e. the footprint). There continued to be no significant changes, with the exception of the Turbine 1 footprint. This area exhibited dense blue mussels (Mytilus edulis) colonizing the entire seafloor, elevated organic content, and increased fine sediment. The Year 3 sampling followed that of Year 2. Preliminary results suggest sediment characteristics within the 20-80m sample sites continue to be comparable to the control samples. Macrofaunal communities, however, show signs of change, with increased presence of mussels and mobile epifauna, such as crabs and snails. Within the footprints, Turbines 3 and 5 are comparable to Turbine 1 from Year 2. The Turbine 1 footprint is transitioning into a mussel reef, having an elevation of 40cm above the seafloor.

Overall, this study suggests minimal impact has occurred over the short term (<3 years) for the area surrounding the turbines (>20m). Whereas the footprint areas have transitioned to habitats with entirely different characteristics than previously existed. Monitoring efforts should continue to further understand the longer-term benthic ecological impacts of offshore wind facilities.