Multi-modal Approach for Benthic Impact Assessments in Moraine Habitats: a Case Study at the Block Island Wind Farm

Abstract

Benthic assessment techniques utilized in soft sediment areas are of limited utility in glacial moraine habitats that are structurally complex and largely composed of hard substrata. We present a multi-modal approach consisting of multibeam bathymetry, video, and still imagery that collectively provides the knowledge base necessary to perform impact assessments in these habitats. Baseline and post-construction surveys were conducted adjacent to the Block Island Wind Farm to develop and test these methodologies within the context of offshore wind development, specifically for detecting and documenting anchoring-related impacts to moraine habitats. Habitat data were evaluated using the substrate and biotic components of the national classification standard, the Coastal and Marine Ecological Classification Standard, recommended by federal regulators, with modifications to present results in terms of predicted vulnerability to disturbance. Habitats near the wind farm were diverse and patchy, ranging from rippled gravelly sand to continuous cobble/boulder fields with high biotic cover. Anchor furrows were detected in moderate value habitats in bathymetric and video data. The multi-modal survey approach tested at the Block Island Wind Farm and presented here is now specifically recommended by federal agencies and is being used to inform efforts currently underway to map and assess benthic habitats for a number of U.S. projects seeking federal permits.

Effects of the Block Island Wind Farm on Coastal Resources: Lessons Learned

“…Habitat data were evaluated using the Coastal and Marine Ecological Classification Standard (CMECS) recommended by federal regulators (FGDC, 2012), with modifications to reflect inferred physical stability (Guarinello and Carey, 2020). In addition to our study, a separate project recorded visual observations of construction activities during each phase of the project, and MBES monitoring was conducted on disturbance features from anchors and jackup barges in soft sediments at six-month intervals from May 2016 to May 2017 to document physical recovery (HDR, 2018).…”

“…Because HBH is present in several proposed US OSW areas, monitoring effects of construction within these habitats is important for potential mitigation of OSW development. Baseline, mid-, and post-construction surveys were designed to develop methodologies for assessing the abiotic and biotic features and distribution of HBH and OSW construction effects on these habitats (Guarinello and Carey, 2020) and to detect and evaluate disturbance and recovery from anchoring activity conducted proximal to these habitats (Guarinello et al, 2017).…”

“…However, biological recovery of HBH may be inversely related to seabed mobility (Wilhelmsson and Malm, 2008). Two studies evaluated recovery of the seafloor from physical disturbance that resulted in distinct furrows due to anchor drag (HDR, 2018;Guarinello and Carey, 2020). Some furrows (drag marks) were unchanged in MBES signature over time due to the presence of boulders lining the furrows (Figure 3).…”

“…Modification of CMECS to include physical habitat stability proved a useful tool for interpreting video data, and combining this approach with adaptive sampling could be an effective methodology for studies of hard bottom effects at other OSW projects that involve relocated boulders (Guarinello and Carey, 2020).…”

“…A timeline illustrates the overlap between construction events and each of the four studies ( Figure 2). Detailed results of these studies are presented in a series of technical reports and publications (Guarinello et al, 2017;Guarinello and Carey, 2020;Sabo et al, 2020;Wilber et al, 2020a,b), with more forthcoming. Here, we critically examine study designs to identify lessons learned from assessment of potential effects of the pilot-scale BIWF on multiple resources and stakeholders.…”