26 



from zero replicates in September to one in March. In some replicates, the distinctions 

 among redox rebounds, multiple dredged material layers, and relict RPDs indicating dredged 

 material over ambient sediments were not clear. These distinctions are discussed further in 

 Section 4.1.3. 



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

 mound were mainly composed of silt and clay with the major modal grain size consistently 

 reported at >4 phi. Mean camera penetration over the I mound showed no distinct 

 pattern, with the shallowest penetration (7.28 cm) at CTR and the deepest penetration 

 (15.89 cm) at 150N. Replicate-averaged surface roughness values for the REMOTS® 

 camera stations over the I mound ranged generally from 0.52 to 3.16 cm. Although some 

 replicates were indeterminate, surface roughness was attributed primarily to physical 

 effects, with some replicates indeterminate or indicating biogenic activity. 



During the March 1998 survey, we detected dredged material at all five central 

 stations over the I mound. The replicates of the 5-station grid were characterized again by 

 a thin layer of oxidized, brown silt over black mud. Although the grain size was primarily 

 silt and clay, some rocks, sand, and large shell fragments were visible at Station 50N. In 

 September, the grain size varied from medium sand to clay. In March, the average 

 penetration depth at 50N (1.90 cm) was significantly less than the depth of 12.7 cm 

 observed in September. The difference in grain size may have affected the penetration 

 depths at 50N. The CTR station had a comparable mean penetration depth of 6.52 cm in 

 March relative to 7.28 cm in September. In contrast, the mean penetration depths 

 increased by about 3 cm for 50E, 50W, and 50S from September to March. The 

 penetration depth indicates the relative sediment water content at sites with similar grain 

 size because the camera acts as a static-load penetrometer (Revelas et al. 1987). In March, 

 surface roughness was attributed to physical effects for CTR, SON, and 50E, and was 

 indeterminate at 50S and SOW. 



3.2.2.2 Benthic Community Assessment 



Using three parameters, we determined the benthic recolonization rate and overall 

 health of the project mounds relative to the WLIS reference areas. We examined the 

 infaunal successional stams, the apparent Redox Potential Discontinuity (RPD) depth, and 

 the Organism-Sediment Index (OSI). The RPD and OSI values were mapped over the 

 target locations to show the distribution of biological conditions. The Rhoads and 

 Germane (1982, 1986) protocol for REMOTS® analysis was followed for measurements 

 and interpretation. In some replicates, wiper smears obstructed successional stage 

 identification and RPD measurements in both September and March surveys. 



Monitoring Cruise at the WLIS Disposal Site, September 1997 and March 1998 



