Benthic Recolonization of a Capped Dredged Material Mound at an Open Water Disposal Site in Long Island Sound

In 1995–96, an estimated 305,000 m³ of unacceptably-contaminated dredged material (UDM) was placed on the open seafloor at the New London Disposal Site (NLDS) in eastern Long Island Sound and subsequently capped with approximately 556,000 m³ of clean capping dredged material (CDM) to form the Seawolf Mound. As one component of a comprehensive environmental monitoring program, multiple surveys have been conducted to assess recolonization of the Seawolf Mound by benthic macroinvertebrates. Sediment grab samples for benthic taxonomic analysis were collected at six stations across the capped mound in September 1997 (1.5 years following completion of the capping operation) and June 2001 (5 years postcap). REMOTS sediment-profile images were collected simultaneously at the six stations in both years, as well as in July 1998 and August 2000. Both monitoring techniques indicated progressive recolonization of the mound over the five-year postcap period, consistent with expectations. By September 1997, the mound had become colonized by a benthic assemblage dominated by moderate numbers of surface-dwelling organisms indicative of early-to-intermediate successional stages (Stages I and II). Numbers of species and individuals both increased with distance from the center of the mound, reflecting a gradient in the degree of physical disturbance associated with the cap material placement. The subsequent surveys of July 1998, August 2000, and June 2001 indicated further increases in numbers of species, organism abundance, and diversity, with significantly higher numbers of advanced Stage III taxa collected in June 2001. Benthic recolonization over the surface of the mound was at an advanced, "equilibrium" stage five years following completion of the capping operation, consistent with predictions based on established successional models for Long Island Sound.