25_ 



Physical REMOTS® parameters indicated the surface and near surface layers of the 

 mound were mainly composed of silts and clays with the major modal grain size 

 consistently reported at >4 phi. Mean camera penetration over the H mound showed no 

 distinct pattern, with the shallowest penetration (12.98 cm) at lOOW and the deepest 

 penetration (18.57 cm) at 50N (Appendix A, Table 3-1). Replicate-averaged surface 

 roughness values for the REMOTS® camera stations over the H mound ranged fi-om 0.64 

 cm at lOOE to 3.24 cm at lOOS. The surface dismrbances were classified as indeterminate 

 in the majority of replicates; however, several replicates displayed evidence of surface 

 roughness due to physical effects and biogenic activity. 



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 WLIS 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 a measure of the level 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 (Oj) in the surface 

 sediments. Since acmal oxygen status in the sediment is not measured, the apparent RPD 

 is estimated by measuring the thickness of the layer of high reflectance oxidized sediments 

 in contrast to the usually gray to black reduced material at depth (Rhoads and Germano 

 1982). 



The mapping of successional stages is based on the theory that organism-sediment 

 interactions follow a predictable sequence after a major seafloor disturbance (Rhoads and 

 Germano 1982). This sequence is defined by end-member assemblages of benthic 

 organisms. Stage I is made up of pioneering assemblages usually consisting of dense 

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

 infaunal deposit feeders such as shallow-dwelling bivalves or mbicolous 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-dismrbance regimes (Rhoads and Germano 

 1986). 



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

 depth, successional stage 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 



Monitoring Cruise ai the Western Long Island Sound Disposal Site, July 1996 



