23_ 



disturbance values (<0.5 cm) concentrated at the center of the mound (CTR, 200E, 200S; 

 Appendix A: Table 3- la). The primary cause of boundary roughness was biogenic activity 

 within surface sediments. 



The replicate-averaged mean camera penetration ranged from 12.86 cm to 18.91 cm 

 (Appendix A: Table 3-la). Dredged material was absent at three stations (400N, 600N, 

 600 W), and measured replicate-averaged dredged material thicknesses ranged from 3 cm at 

 600S to full penetration (20 cm) at many stations (Appendix A: Table 3-la). The apparent 

 absence of dredged material at stations 400N, 600N, and 600W may be attributed to 

 complete reworking of historical dredged material, to the extent that there are no 

 recognizable indicators. Redox rebound intervals, areas of intermittent or seasonal 

 oxidation below the oxidized surface layer, were noted at several stations, including two of 

 the three stations which had no measurable dredged material (400N, 600N). 



3.1.2.2 Benthic Community Assessment 



Three parameters were used to assess the benthic recolonization rate and overall 

 health of the project mounds relative to the CLIS reference areas. The apparent Redox 

 Potential Discontinuity (RPD) depth, infaunal successional status, and the Organism- 

 Sediment Index (OSI) were mapped on station location plots to outline the biological 

 conditions at each station. 



The apparent RPD depth is the depth of oxygenation in the upper sediment layers. 

 This value indicates dissolved oxygen conditions within sediment pore water as well as the 

 availability and consumption of molecular oxygen (0 2 ) in the surface sediments. Since 

 actual oxygen status in the sediment is not measured, the apparent RPD is estimated by 

 measuring the thickness of the layer of high reflectance in contrast to the usually gray to 

 black reduced sediments at depth (Rhoads and Germano 1982). 



Replicate-averaged RPD values over the NHAV 93 mound ranged from 0.91 cm at 

 600E to 4.23 cm at 400E, indicating improvement relative to the 1994 survey, especially at 

 the stations previously exhibiting slow benthic recovery (Figure 3-5; Appendix A: Tables 

 3-la and 3-lb). RPDs of < 2 cm were measured at the central, south, and east sections of 

 the sampling grid (CTR; 200E, W, and S; 400S; and 600S and E). Station 600E, 

 displaying a relatively shallow RPD depth, has probably been affected by the recent 

 deposition of CDM over the CLIS 94 mound reducing the level of oxidation in the surface 

 sediment layers. However, the mean RPD value for the entire project area was 2.14 cm, 

 indicating improving conditions relative to the 0.78 cm RPD value for July 1994. Neither 

 methane nor low dissolved oxygen was noted in any photograph. 



Monitoring Cruise at the Central Long Island Sound Disposal Site, September 1995 



