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Monitoring the Restoration of Benthic Habitats Impacted by Dredging at a Former Shoreside Landfill in Narragansett Bay, Middletown, RI

Benjamin T. Allen and Gregory A. Tracey

Science Applications International Corporation (SAIC), Newport, RI

Restoration of benthic habitats impacted by remedial dredging activities was monitored using a complement of survey tools that provided complete data coverage with high-resolution components. Baseline site-wide substrate characterization was accomplished with side-scan sonar and single beam bathymetry. Planview and Sediment Profile Imaging (SPI) cameras were used to obtain high-resolution characterization of habitats. The 35 mm planview camera was effective in capturing top-down images of 0.3 m2 of seafloor, which were analyzed and assigned epibenthic habitat classifications (e.g., eelgrass, rock, sand/silt, macroalgae). The digital SPI camera collected 20 cm x 15 cm vertical cross-section images of the seafloor, which were analyzed to determine infaunal habitat characteristics including apparent grain size and depth of sediment oxygenation, as well as stage of the benthic community. From these metrics, a summary of benthic habitat quality was calculated.

After dredging and subsequent restoration activities, monitoring was repeated to document post-dredging conditions. Side-scan analysis and bathymetry depth-differencing appeared to confirm as-built substrate characteristics. Planview photography results suggested that epibenthic habitats appeared to have been restored, except for eelgrass in some areas. SPI photography also indicated that infaunal habitat appeared to have been restored, as the benthic community had recolonized the substrate. The study exemplifies application of complementary techniques with different levels of resolution for monitoring benthic habitats.

Keywords: benthic habitat, dredging impacts, eelgrass, monitoring

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