67 



The penetration depth of the camera serves as a measure of sediment density or 

 compaction. At the reference areas, the replicate-averaged mean camera penetration ranged 

 from 4.6 to 10.3 cm (7.3 cm average; Table 3-2). The recently deposited dredged material 

 at the Seawolf Mound was less consolidated than the reference area sediments, with deeper 

 penetration values at mound stations ranging from 5.4 to 17.0 cm (13.5 cm average; Table 

 3-1). Lower values in the range were detected on the apron of the mound, where thin layers 

 of dredged material overlaid ambient sediments. 



Boundary roughness values at the Seawolf Mound ranged from 0.7 to 1 .8 cm, with an 

 average of 1.1 cm, which was higher than the average value measured at the reference areas 

 (0.7 cm). Although there was no obvious spatial pattern of boundary roughness values, 

 several replicates from four stations, including 150E(a), 150S(c), 300N(a and b), and 

 450NW (a), were identified as having winnowed relief. Shell lag deposits predominated. 

 Boundary roughness at the surface of the Seawolf Mound was primarily attributed to 

 physical forces, as were those at the reference areas, although some surface disturbances 

 were indeterminate or caused by biogenic activity. Further discussion of the potential for 

 physical disturbance of the Seawolf material is provided in Section 4.0. 



The apparent redox potential discontinuity (RPD) is measured on each photograph to 

 determine the thickness of the aerobically mixed layer of sediment. The replicate-averaged 

 apparent RPD ranged from 0.47 to 5.2 cm (2.5 cm average; Table 3-1). Although the range 

 of RPD values measured at the Seawolf Mound was wider relative to the replicate-averaged 

 reference values (1.8 to 3.5 cm), the average RPD at Seawolf was close to the reference area 

 average (2.4 cm). A low dissolved oxygen (DO) condition (thin or non-existent apparent 

 RPD) was noted at the sediment surface in only one photograph, 150N(c). Some stations 

 had a visible redox rebound varying between 3 and 10 cm depth. 



The successional status was intermediate to advanced, showing healthy Stage n, 

 Stage II to HI, or Stage II on HI communities inhabiting the sediments of the Seawolf Mound 

 (Table 3-1). In 14 of the 86 replicate images, the infaunal successional stage could not be 

 determined clearly (indeterminate). Stage HI organisms were present in 31 replicates and at 

 21 of 29 stations. 



Replicate-averaged OSI values ranged from +3 to +1 1, with an overall average of 

 +7.1, consistent with the median OSI values (Table 3-1). Although the OSI values were 

 more variable than those at the reference areas (range +5 to +10), the average OSI value for 

 the Seawolf Mound was similar to the reference area average (+6.7; Table 3-2). All stations 

 within 75 m of the center station had average OSI values of >+6, except 75E (+5.5) and 

 75WSW (+5.5). Past mapping experience has shown that OSI values <+6 tend to be 

 associated with stressed environments or early successional populations. The OSI at 



Monitoring Cruise at the New London Disposal Site, Seawolf Mound 1995 - 1998 



