27_ 



material targets, the plan view photographs revealed areas of cobble and larger sharp- 

 edged rocks (Figure 3-11). The sharp angularity of the rocks, and their presence at a 

 known disposal site, suggest that they may be construction debris. More solid evidence 

 that transect C4 contained construction debris was found while sieving one of the grab 

 samples. A small rounded piece of concrete with two planar sides was found in the grab 

 sample from Station C4-5. This small piece probably was bored from a larger slab either 

 for blasting or attachment of lifting cables. 



4.3 Benthic Recolonization 



The identification of a dredged material signature on side-scan records, and the 

 further investigation of the dredged material by REMOTS® sediment-profile photography, 

 were necessary to determine if remediation was needed. The primary step in determining 

 if remediation was required at BLDS was to examine the status of benthic recolonization 

 and compare the dredged material with apparent ambient sediments within the disposal 

 area. There was no preexisting reference area for BLDS; however, the ambient sediment 

 at Station C6 should provide a good basis for comparing the effects of dredged material 

 disposal on the benthic habitat. Information derived from sediment structures was 

 compiled into the multiparameter REMOTS® Organism-Sediment Index. At BLDS the 

 OSI value was primarily a function of the successional stage of the populating infauna and 

 the depth of biogenically enhanced oxygen penetration (RPD). 



The most striking evidence for a healthy benthic habitat at BLDS was the abundant 

 and diverse benthic community The subsurface sediments were populated by burrowing 

 polychaetes both large and small as well as other Stage III genera including caudate 

 holothurians (Figures 3-2, B; 3-3; and 3-8). The surface sediments were dominated by 

 sedentary, tube-dwelling Stage III polychaetes and by Stage II stick-building amphipods 

 (Family Podoceridae) (Figure 3-6, A). The presence of Stage II organisms in the surface 

 sediments is probably from secondary colonization, and not indicative of a recovery from a 

 recent disturbance. Following disposal activity and the progression of recolonization to a 

 Stage III community, the Stage III organisms began to feed in deeper sediments. The 

 movement of the Stage III group out of the upper sediment cleared space for reoccupation 

 by surface-dwelling Stage II infauna. 



In addition to the abundant benthic community, several pieces of information from 

 the sedimentary structure suggested a healthy benthic habitat has persisted for some time. 

 Numerous water-filled voids were observed in subsurface sediments (Figures 3-2 and 3-7). 

 These voids were created by the feeding activity of head-down deposit feeding Stage III 

 organisms. A halo of oxidized sediments, which surrounded the voids, suggested recent 



Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994 



