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4.3 USCGA Mound 



The objective of the August 2000 REMOTS® sediment profile photography survey 

 was to document the status of benthic recolonization over the USCGA Mound, five years 

 after the development of this mound during the 1994-1995 disposal season. The previous 

 (August 1995) sediment profile photography survey had shown an advanced stage of 

 recolonization relatively soon after the creation of this mound, with the benthic community 

 dominated by Stage 11 and III taxa (Table 4-3). The average median OSI value of +6.4 

 calculated in August 1995 suggested only a moderate level of benthic disturbance related to 

 dredged material disposal; this is a relatively high value which reflected the apparent rapid 

 recolonization of the USCGA Mound by advanced successionaJ seres (Stages II and III). 



The August 2000 survey showed that the successional status of the benthic community 

 over the USCGA mound continued to be advanced, with Stages n and HI continuing to be 

 dominant. Evidence of head-down, deposit-feeding infauna (Stage III) was observed in the 

 photographs at 10 of the 13 stations, and amphipod tube mats (Stage II) were widespread 

 across the surface of the mound. Both larger adult and smaller juvenile amphipod tubes were 

 observed at the sediment surface, with the larger adult tubes appearing to be both active and in 

 various stages of decay. A layer of organic detritus was mixed with the amphipod tubes in 

 many images, suggesting that near-bottom energy levels in and around the USCGA mound 

 were relatively quiescent (depositional) in the weeks leading up to the survey. Larger tubes of 

 the Stage III polychaete Chaetopterus sp. were visible in several of the images on the USCGA 

 Mound, providing fiirther evidence of the advanced recolonization status. 



The average RPD depth of 3.8 cm observed at the USCGA Mound in August 2000 

 was notably deeper than that observed at the reference areas (2.8 cm) or in the previous 

 mound survey of August 1995 (2.7 cm). These deeper RPD depths are attributed to the 

 bioturbation activities of recolonizing Stage III organisms present across this mound since its 

 creation in 1995. The feeding and bioturbation activities of these larger-bodied infauna 

 apparently have acted to increase sediment aeration and decrease sediment levels of both 

 organic carbon and its associated, reduced breakdown products (e.g., sulfides and ammonia). 

 In contrast to the 1995 survey, there was no evidence of low dissolved oxygen (DO) 

 conditions or methane bubbles observed in the sediment profile photographs collected across 

 the USCGA Mound in August 2000. As levels of organic carbon and sulfides have 

 decreased due to consumption by benthic organisms and oxidation, surface sediments at the 

 USCGA Mound generally have become lighter in color (Figure 4-5). 



The relatively deep RPD depths and advanced successional status across the USCGA 

 Mound in August 2000 are reflected in relatively high OSI values. The overall average OSI 

 value of +8.8 is indicative of healthy or undisturbed benthic habitat quality, and was higher 

 than the average value of +6.9 at the NLDS reference areas and the average of +6.4 observed 

 in August 1995. These results suggest that the benthic community and overall benthic 



Monitoring Cruise at the New London Disposal Site, August 2000 



