38 



aggregations of near-surface, tube-dwelling polychaetes. If left undisturbed, Stage II 

 infaunal deposit feeders such as shallow-dwelling bivalves or tubicolous amphipods then 

 colonize the recovering seafloor. Stage III organisms are generally head down-deposit 

 feeding invertebrates whose presence results in distinctive subsurface feeding voids. Stage 

 III taxa are associated with relatively low-disturbance regimes (Rhoads and Germano 

 1986). 



Organism-sediment index values are calculated by summarizing the apparent RPD 

 depth, successional stams, and indicators of methane or low oxygen. OSIs can range from 

 -10 (azoic with methane gas present in sediment) to 11 (aerobic bottom with deep apparent 

 RPD, evidence of mature macrofaunal assemblage, and no apparent methane). OSI values 

 are useful in mapping disturbances and quantifying ecosystem recovery (Rhoads and 

 Germano 1982). 



The NHAV 93 mound is showing the beginning stages of recovery four months 

 after completion of disposal activity. The replicate-averaged RPD values for the 13 

 stations in the NHAV 93 project area ranged from 0.35 cm at Stations 400S and 400W to 

 2.04 cm at Station 200S (Appendix A, Table 8; Figure 3-12). The mean RPD value for 

 the entire NHAV 93 project area was 0.94 cm. The successional stage was predominantly 

 Stage I organisms with occasional Stage II and Stage III assemblages present at peripheral 

 stations (Figure 3-13). As a result, median OSI values for the NHAV 93 project area also 

 indicated the beginning stages of ecosystem recovery, ranging from 2.0 at 200E and 400S 

 to 6.0 at 600N (Appendix A, Table 8; Figure 3-12). 



As the REMOTS® analysis progressed, three areas of concern were discovered on 

 the NHAV 93 project mound. Several of the REMOTS® photographs obtained at Stations 

 CTR, 200N, and 400S indicated limited recolonization, possibly caused by sediment 

 toxicity or high labile organic content (Figures 3-12 and 3-13). The REMOTS® 

 photographs were taken approximately four months post disposal, revealing shallow or 

 discontinuous layers of oxidized sediment over black reduced cap material, with patchy 

 Stage I benthic infaunal communities (Figure 3-14A). An example of healthy recovery 

 was the conditions existing at Station 200S with an average RPD depth of 1.50 cm and a 

 solid Stage I community (Figure 3-14B). 



3.1.4 Sediment Toxicity Testing 



As part of the DAMOS tiered monitoring protocol, two of the three stations 

 exhibiting anomalous REMOTS® results were revisited in late September 1994 (Germano 

 et al. 1994). Due to the apparent unhealthy benthic conditions, comprehensive sediment 

 toxicity testing was performed on the surface sediment layers of Stations CTR and 40QS 

 Monitoring Cruise at the Central Long Island Sound Disposal Site, July 1994 



