comparatively deep RPD and showed no evidence of erosion such as shell 

 or sand lag deposits, suggesting that the mound apex is physically 

 stable. 



The distribution of infaunal successional assemblages showed 

 a patchy mosaic of Stage I, II, and III seres (Figure 3-74). Stage 

 I seres dominated (11 of 17 stations) , which could suggest an aberrant 

 rate of colonization or simply reflect the lack of replication. 

 Thepresence of Stage III seres at station Center, however, support the 

 interpretation of the mound apex being stable. Tubicolous amphipods 

 (probably Ampelisca sp.) were present in low abundance at station 

 400N. 



The frequency distribution of OSI values was skewed toward 

 lower values, with the major mode in the +5 class interval (Figure 3- 

 72). The mean OSI value was 5.86 ± 1.75. OSI values at this mound 

 were significantly lower than the new CLIS reference station (p < 

 0.001), and only the MQR mound had a lower mean value. OSI values 

 have not changed significantly at this mound since August 1985. The 

 spatial distribution of values was somewhat patchy, with stations 

 north and south of the mound center having higher OSI values than 

 stations on the eastern and western flanks (Figure 3-75) . 



3.3.9 CLIS-86 Mound 



Recently-disposed dredged material was apparent at all 

 stations except 400N, 600N, 200SW, and 600S (Figure 3-76) . The 

 boundary of the deposit could not be determined (i.e., contoured) 

 accurately because dredged material extended in several directions 

 beyond the area covered by the REMOTS® grid. Generally, the CLIS- 

 86 mound appeared to have an irregular, elliptical "footprint" with 

 a north-south radius of 350 to 400 meters and an east-west radius 

 greater than 600 meters (Figure 3-76) . 



The major modal grain-size at the CLIS-86 mound fell within 

 the silt-clay (> 4 phi) size class. Stations located within 200 to 

 400 meters of the center also had a very fine, fine, and medium sand 

 subordinate mode in the near-surface layers (Figure 3-76) . The 

 centers (topographic high) of many of the CLIS disposal mounds have 

 developed shell and sand "lag" deposits over time, related to the 

 washing of fines from the sediment as the tidal stream moves over the 

 mound. There was no evidence as yet of a lag deposit at the CLIS-86 

 station Center. 



The major mode for small-scale boundary roughness fell 

 within the 0.8 cm class interval (Figure 3-77), with a mean value of 

 0.86 cm ± 0.31 cm. The origin of this roughness appears to have been 

 a combination of biogenic and physically-produced microtopography. 



The histogram of the mean apparent RPD depths at this mound 

 showed the major mode shared between the 3 and 4 cm classes (Figure 



25 



