bathymetric volume calculation and barge log volume estimates. 



The predisposal bathymetry revealed the western portion of an historic 

 mound in the northeast region of the survey grid (Figure 3-1). The postdisposal 

 survey was extended an additional 300 m east in order to delineate the boundaries 

 of this mound more clearly (Figure 3-2). The contour plot indicated that the 

 postdisposal bathymetric survey was extended far enough to include the eastern 

 boundary of this mound; however, REMOTS® sediment-profile analyses indicated 

 that dredged material extended beyond the mound area detectable with bathymetry. 

 It is important to note that the eastern-most REMOTS® station (350E) extended 

 approximately 100 m beyond the postdisposal bathymetric survey area (Figure 2-2). 

 Dredged material was therefore apparent up to at least 350 m east of the center of 

 the mound. 



Although mapping of dredged material was possible, clearly-defined layers of 

 dredged material were not apparent in the REMOTS® photographs. This was not 

 unexpected, because approximately 10 years had passed since the last significant 

 volume of dredged material was disposed at this site, during which time the layers 

 of dredged material could become incorporated into or made indistinct from each 

 other or the ambient sediment. Despite the lack of clearly-defined layers, mapping of 

 the dredged material was possible based on the changes in sand content and 

 sediment grain size. 



Ambient sediment characteristics were observed at the two western-most 

 stations of the REMOTS® transect, 350W and 300W. Camera penetration was 

 deepest here (11.8 and 14.0 cm, respectively). Sediment was well sorted, with a 

 grain size typical of fine-clay and silt (> 4 phi). OSI values (+11) and mean apparent 

 RPD depths (greater than 6 cm) showed a lack of disturbance. Stage III taxa were 

 evident in all replicate photographs at these two stations. 



At stations nearer the center of the mound, marked changes in all these 

 parameters were noted, indicating the presence of dredged material. RPD depths 

 decreased, ranging from 2.8 cm to 3.5 cm at stations 250W and 250E to < 1 cm and 

 indeterminant at the center of the mound. RPD could not be measured at the center 

 of the mound (stations 50W and CTR) where the sediment was loosely consolidated. 

 Given the time since last disposal, 4 years, it would be expected that recolonization 

 would have reached Stage III on the mound. Limited camera prism penetrations (>4 

 cm), resulting from the increase in sediment grain size and shell content, precluded 

 an accurate determination of successional stage at six stations near the apex of the 

 mound. Shallow RPDs and increased grain size at these apex stations, evidence of 

 erosion or winnowing, may indicate a lack of Stage III taxa due to impact on the 

 benthos by scour or erosion. However, these taxa may have been present below the 

 depth of penetration. Several stations had shell lag (Figure 3-10). Presumably only 

 one component of the dredged material, this shell lag, remained after the finer 

 silt/sand components of the dredged material had been washed away. The height of 



Monitoring Cruise at the Cape Cod Canal Disposal Site and Springhill Beach Site 



