35 



detected to varying depths at all project mound REMOTS® stations. The data acquired 

 from the project mounds were compared to data collected at the three reference areas 

 surrounding CLIS. Complete REMOTS® results for the NHAV 93 disposal mound are 

 available in Appendix B, Table 1. 



The relatively homogeneous cap of the NHAV 93 mound is composed of silts and 

 clays dredged from the outer New Haven Harbor. The major modal grain size for the 13 

 REMOTS® stations over the NHAV 93 mound was consistently greater than 4 phi, 

 indicating no significant coarsening of the surface layers by bedload transport of fine- 

 grained material. The replicate-averaged boundary roughness values, a measure of the 

 relative complexity of the sediment- water interface, ranged from 0.04 cm at 400E to 

 4.31 cm at 600S (Appendix A, Table 8). The type of surface roughness was classified as 

 physical disturbance in the majority of replicates. 



Dredged material was identified and measured at all 13 REMOTS® camera stations. 

 Replicate-averaged dredged material thickness ranged from 6.41 cm at 600S to full 

 penetration (20 cm) at 200E. The thickness of dredged material was greater than camera 

 penetration at all stations except 600S and one replicate at 400S. As expected with a 

 recent dredged material deposit, there were no indications of redox rebound intervals, 

 areas of intermittent or seasonal oxidation below the oxidized surface layer, in any 

 replicate. No methane gas was noted in the subsurface sediments; however, a layer of 

 reduced dredged material was seen in two replicates of 400S. 



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 stages, and the Organism- 

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

 conditions at each station (Figures 3-12 and 3-13). 



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

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

 availability and consumption of molecular oxygen (O2) in the surface sediments. Since the 

 actual oxygen statos 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). 



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 



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



