85_ 



photography stations that display accumulation of new material. Thin layers of material 

 were observed at two stations falling outside the predicted area of accumulation (Stations 

 300N and 100S). The presence of this material at these stations suggests a thin layer on 

 the margins of the new deposit spread 25 m to 50 m beyond the radius predicted by the 

 model. 



The replicate- averaged mean camera penetration at the NL-91 and D/S mound 

 complex ranged from 6.5 to 15.8 cm, with an overall average of 12.4 cm (Table 3-4). As 

 in previous surveys, fine to very fine sand characterized the surface sediments over the 

 mound. The major modal grain size was 4 to 3 phi (very fine sand) in most photographs. 

 Surface sand overlying fine-grained sediment (sand-over-mud stratigraphy) was noted over 

 the majority of the NL-91 and D/S mound complex. Sand, pebbles and hydrozoans were 

 noted once again at Station 200S, consistent with the findings of prior surveys 

 (Figure 3-31). 



The replicate-averaged boundary roughness values ranged from 1.0 to 3.2 cm, with 

 an average of 1.5 cm (Table 3-4). Boundary roughness was attributed to a combination of 

 physical and biogenic forces. Evidence of physical disturbance and possible winnowing of 

 the surface included abundant disturbed amphipod tube mats, surface scour, and shell lag 

 deposits. 



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

 to determine the depth of penetration of oxygen into the sediment (Figure 3-32; Table 3-4). 

 The replicate-averaged apparent RPD depths over the NL-91 and D/S mound complex 

 ranged from 1.2 to 6.1 cm (3.6 average). No stations over the mound displayed any visible 

 redox rebound layers. 



The successional status was advanced, showing healthy Stage II or Stage II on III 

 communities inhabiting the sediments of the disposal mound. Some stations showed a 

 slight decline in successional stage relative to data collected in 1997. The reference area 

 showed a similar decline in comparisons between the 1997 and 1998 dataset (Table 3-12). 

 Stage III organisms were present in 15 of the 39 replicates distributed among eight stations 

 (Figure 3-33). The remainder of the July 1998 photographs were classified as Stage I, or 

 Stage I to II if amphipod (Ampelisca) tube mats were present. 



Median OSI values ranged from +3.0 to +11.0, with an overall average of +7.5 

 for the NL-91 and D/S mound complex (Figure 3-32; Table 3-4). The only median OSI 

 values of < +6.0 (indicating continued disturbance) occurred at Stations 300E and 400E. 

 The low OSI values were due in part to shallow RPDs, disturbed amphipod tube mats and 



Monitoring Cruise at the New London Disposal Site, 1992 - 1998 



