Abstract
INSPIRE Environmental conducted a pre-construction benthic survey at Empire Offshore Wind, LLC’s (Empire’s) planned offshore wind farm Empire Wind 1 (EW 1) located in the designated Renewable Energy Lease Area OCS-A 0512 (Lease Area) and along the planned EW 1 export cable route in federal waters. A total of 90 Sediment Profile and Plan View Imaging (SPI/PV) and 30 sediment grab stations were sampled at EW 1 and 96 SPI/PV stations were sampled along the EW 1 export cable route. These 2024 benthic data provide a description of baseline conditions that will be compared with post construction results following the development of the project as detailed in the Empire Wind Fisheries and Benthic Monitoring Plan (INSPIRE 2023). The survey design was a Before-After-Gradient (BAG) design, consisting of selected wind turbine generator and offshore substation foundation locations and a BAG design along the EW 1 export cable route stratified by two pre determined benthic habitat characterizations. SPI/PV and sediment grab stations were positioned with increasing distance from the location of the planned infrastructure (either a foundation location or the export cable centerline).
The results of this survey agreed with baseline observations synthesized in the Empire Wind Habitat Mapping Report to Support Construction Compliance (INSPIRE 2024a). The physical parameters including sediment type derived from SPI/PV and Coastal and Marine Ecological Classification Standard (CMECS) Substrate Subgroup at the West survey area were all Very Fine Sand, while the more heterogeneous East survey area contained mostly Fine Sand with some Medium Sand and occasional gravels. In general, there were no apparent spatial patterns observed in relation to any physical or biological parameters with the distance from the proposed foundation locations or the proposed EW 1 export cable. It is expected that following construction sediment types and CMECS Substrate Subgroups will vary with distance from the planned foundation locations at EW 1 and from the planned EW 1 export cable centerline, a factor that will be the focus of future monitoring reports.
The biological communities observed at EW 1 and along the EW 1 export cable route were characterized as CMECS Biotic Subclasses Soft Sediment Fauna, Inferred Fauna, and/or Attached Fauna. The CMECS Biotic Subclass corresponded with the CMECS Substrate Subgroup classifications; Attached Fauna such as northern star coral occurred more frequently at stations characterized as Boulder or Cobbly-Bouldery Sand, while Soft Sediment Fauna such as scallops, sand dollars, snails, and polychaetes occurred at stations with finer sediments.
The oxygen penetration into the sediments was assessed using the apparent redox potential discontinuity (aRPD) depths, and at EW 1 with sediment grab sample component analysis from grabs. Oxygen penetration and sediment oxygen demand are expected to change, particularly near the EW 1 foundation locations, following construction. The prevalent coarser sediments (i.e., substrates coarser than fine sand) had generally indeterminate aRPD depths, portraying a lack of optical contrast between oxidized and reduced particles, largely due to the low organic content in the substrate. This was corroborated by the total organic matter, total organic carbon and total nitrogen results from the sediment grab sample analysis. Benthic habitat types defined by finer sediments at EW 1 and in survey areas along the EW 1 export cable route were more likely to have distinguishable aRPD depths. More frequently discernable aRPD depths at finer sediment stations were expected given the higher inventory of organic material typical in these environments relative to coarser sediments. Sediment grab sample analysis at EW 1 stations revealed relatively low total organic matter, low total organic carbon, and low total nitrogen concentrations.
Similar to aRPD depths, advanced infaunal successional stage (Stage 3) taxa rely on environmental factors present typically in depositional and soft sediment environments (e.g., supply of organic matter, infrequent natural physical disturbances to the seabed). Successional stage classifications across the stations surveyed at EW 1 were typically Stage 2. Stage 2 and Stage 3 were typically observed along the EW 1 export cable route stations in the West survey area; at the East survey area the successional stage was most often Stage 2, with rare occurrences of Stage 2 on 3. More advanced successional stages observed at the West survey area are consistent with finer sediments with relatively low natural physical disturbance; less advanced successional stages were noted at the East survey area where there were coarser sediments.
No non-native taxa, sensitive taxa, or species of concern (sensu Guida et al. 2017) were observed at EW 1. Northern star coral, Astrangia poculata, a non-reef-building hard coral, was observed at the EW 1 export cable route in the East survey area at stations with boulder or cobble sized gravel. Atlantic sea scallop, Placopecten magellanicus, was noted at one station at the West survey area of the EW 1 export cable route in sandy habitat.