24 



and NL-85 REMOTS® grids (Figures 3-7 and 3-10). The frequency distributions for 

 boundary roughness values indicated that the majority of disposal site stations were in the 

 1-1.5 cm class interval, whereas stations in the reference areas were largely in the 0.5-1 cm 

 class interval (Figure 3-13). 



The mean apparent Redox Potential Discontinuity (RPD) depth on the disposal site 

 was 4.28 cm (s = 1.25 cm), which was greater than the mean RPD depth of the pooled 

 reference stations (3.50 cm, s = 1.19 cm). The difference between the two areas was 

 statistically significant (p = 0.027, Mann- Whitney U-test), although there was no clear 

 pattern of RPD depth distribution over either the NL-TR or NL-85 mounds (Figure 3-14). 

 The frequency distribution of RPD depths at the disposal site indicated that the majority of 

 values were evenly divided between the 3, 4, and 5 cm class intervals whereas reference 

 station RPD depths fell principally in the 3 to 4 cm categories (Figure 3-15). 



Stage II and Stage II on III taxa dominated the successional series present at the NL- 

 TR disposal mound (Figure 3-16). Likewise, the NL-85 mound also consisted of principally 

 Stage II and Stage II on III, although some Stage I and Stage I on III taxa were present in the 

 central region of the mound. Reference areas NE-REF and NL-REF were similar in 

 successional sere to the NL-TR mound, with most stations being either Stage II or Stage II 

 on III. The western reference area, W-REF, was largely indeterminate due to low camera 

 penetration. At the few stations with sufficient penetration, Stage III and Stage II on III were 

 the only series evident. These were observed in the central and western stations of W-REF. 



Based on results of past REMOTS® surveys, Organism-Sediment Index (OSI) values 

 of +6 or less are considered indicative of chronically stressed benthic habitats and/or those 

 which have experienced recent disturbance (e.g., erosion, dredged material disposal, 

 hypoxia, intense demersal predator foraging, etc.; Rhoads and Germano 1986). For the 

 present survey, median OSI values ranged from +6.5 to +11 on the disposal site mounds 

 and from +5 to +11 across the three reference areas (Figure 3-17). On the NL-TR and 

 NL-85 mounds, the most frequently occurring value was +11, but at the reference stations 

 +9 was the most frequent (Figure 3-18). However, there was no significant difference in 

 median OSI values between the disposal site and reference stations (p =0.865, Mann- 

 Whitney U-test). The lowest OSI values at the NL-TR mound were distributed unevenly but 

 tended to be found west and south of the center station. At the NL-85 mound, lower OSI 

 values generally were clustered in the center of the REMOTS® grid (Figure 3-17). 



3.3 CTD and Dissolved Oxygen Sampling 



On 3 July 1990, near-bottom (1 m above the bottom) oxygen concentrations were 

 uniformly 8.3 mg-1* 1 at both the disposal site mounds and the three reference areas (Table 

 3-1). Although temporal comparisons were not truly valid from single point- in-time 

 readings, these measurements were consistent with oxygen values of 5.3 to 8.3 mg-1" 1 



Monitoring Cruise at the New London Disposal Site, June- July 1990 



